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Motional Feedback Disk Recording System Design Special Ef­fects Plugins
Old 4 weeks ago
  #1
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Motional Feedback Disk Recording System Design



My recent publication in in the Journal of the Audio Engineering Society, titled "An Investigation of Motional Feedback Disk Recording System Design", discusses the design problems of motional feedback cutter head transducers and my development of a cutting amplifier system of a very high performance.

Motional Feedback Disk Recording System Design – Agnew Analog Blog

AES E-Library >> An Investigation of Motional Feedback Disk Recording System Design

If you are interested in the technical details regarding how records are cut, this may be of interest.
Old 4 weeks ago
  #2
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Nice tour of the history of cutting systems. The medium, with its diameter loss / ...of fidelity and surface noise and the playback tracing and scanning issues effectively render the best cutting systems of the late '70s, 'over-engineered'.

Not cutting high frequencies loud for more than a fraction of a second seems best to the ear/wax. In the era of digital precision, I sometimes view the sound of the slower land as merciful. We really only need the Attack of a high treble note in vinyl... The restriction imposed by cutting only 'playable' grooves is rather a 'feature'. Sean Davies went back to the Ortofon / Lyrec all-tube advance repro tape-to-disk system for his mastering of Kogan's Beethoven sides. His results are clearly stunning.

Where you write, 'The 6 dB/oct rising slope, starting at 2.12 kHz...', while it's certainly close enough for Jazz, I noticed that one might have added another '2' after the second one (and an infinite string of numbers to the right of the missing 'decimal place' of the frequency);. So, this frequently-cited frequency (2,120 Hz) is a little low, compared to that which is technically defined by 75 µs. The reason for this is that the formula for determining the time constant of a frequency is often cited as '159 / F (in kHz) = Tau'. However, the constant, '159', is severely truncated from its actual value in order to result in a(n) (fake) integer. It comes from the well-known formula, '1/2π' (x 1,000, so that the frequency will be in kHz). With more numbers to the right of the 'decimal', the constant reads, 159.1549... (for ever and ever not repeating, just like π). So, the 6 dB /octave rising slope, technically, starts much closer to 2.122,xxx... kHz. A small difference, perhaps, but, if you used 75 µs as math code for a street address, you'd end up at the wrong house if you went to # 2120, instead of #2122 ... (;

(Indeed, if one were specifying a time constant to equate to 50 Hz (as in RIAA / NAB), 3183 µs looks much closer to that than only 3180 µs. 500 Hz, could be 318,300 nanoseconds. But maybe they really wanted 3180 µs? So, it's not quite 50 Hz?)

It's surprising to read 30 dB feedback being used to get flat response. Existing drive packages from the '70s have flat frequency and phase response and low cross-talk, all when using no more than 13 dB feedback at 5 kHz.

http://www.discolathe.com/attachment...n_response.jpg

The feedback circuit in the GO741 amp works up to about 150 kHz (though it has twisted positive soon above the audio band). It also has an impedance matching passive network that makes a mirror image of the reactance presented by the cutting tool using capacitors and air core inductors. Also, there is no torque tube in the Ortofon cutting head, since it has the rocking bridge design, once tried by Neumann. It was ultimately 'knocked off' by JVC who improved on the helium channels (CH90 http://www.discolathe.com/download/file.php?id=181) and added more power (CA90), but this was to serve the interests of the Loudness Wars, rather than making better sounding records.

A square wave without overshoot or ringing is a noble goal, but it must be cut as a triangle wave. By the time it's picked up by the reproducing stylus, it will have departed much further. Also dann, even DSD can't get square waves quite right!
Old 4 weeks ago
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disk cutting

Quote:
Originally Posted by S_mask View Post
It's surprising to read 30 dB feedback being used to get flat response. Existing drive packages from the '70s have flat frequency and phase response and low cross-talk, all when using no more than 13 dB feedback at 5 kHz.
Your point is appreciated,
but lets not slight the performance of Westrex and Haeco cutters (Otto Hepp designs) which employed approximately 30 dB of feedback @ 1000 Hz.
They cut impressive lacquers in the 70's and continue to do so.
Quote:
Originally Posted by S_mask View Post
. Also, there is no torque tube in the Ortofon cutting head, since it has the rocking bridge design, once tried by Neumann. It was ultimately 'knocked off' by JVC who improved on the helium channels (CH90 http://www.discolathe.com/download/file.php?id=181) and added more power (CA90), but this was to serve the interests of the Loudness Wars, rather than making better sounding records.
The "JVC" head was still an Ortofon, when it blew up (unfortunately quite often), it was returned to Ortofon for rebuild.

The cutting amplifier at the JVC mastering facility in Hollywood was actually a Threshold, a zero internal global feedback unit, with a fancy front panel to disguise it's maker.
Old 4 weeks ago
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Quote:
Originally Posted by S_mask View Post
Nice tour of the history of cutting systems. The medium, with its diameter loss / ...of fidelity and surface noise and the playback tracing and scanning issues effectively render the best cutting systems of the late '70s, 'over-engineered'.
[...]!
S_mask, many thanks for taking the time to read my article and compose such a detailed response.

A) I agree, regarding what sounds more pleasing to the ear. However, I was not referring to this as an aesthetic consideration, nor as a restriction due to "playability" concerns. In fact, my only mention of repro cartridge tracking ability was in relation to cutter head excursion limits, beyond which mechanical damage may occur, which may be an issue at low frequencies but certainly not at high frequencies. Excursion at HF is nowhere near the limits of any cutter head and nowhere near the trackable excursion figures of any repro cartridge. The "playability" issue at HF has to do with stylus groove geometry and acceleration of the moving mass of the cartridge and is therefore not related to the duration of the HF passage.

The issue here is the thermal overload of the cutter head at HF, which is the most common way to destroy a head. I am describing the exact mechanism behind this phenomenon and point this out as a reliability issue. I have not proposed a concrete solution to this problem in this article, other than offering some food for thought on sensitivity/efficiency as related to cutter head transducer and loudspeaker driver design.

While I am working on overcoming this issue to the extent possible, for the new cutter head I am developing (Lab Report: The Agnew Analog Stereophonic Cutter Head – Agnew Analog Blog), this is simply to make a cutter head that is more reliable/durable, rather than to suggest that we should all start boosting the HF content on disk.

I do work mostly with tape and most of the masters I cut are transferred directly from 1/4" tape, entirely in the analog domain. Most of my circuit design work uses vacuum tubes and I absolutely love them as devices. I am slowly but steadily also working on a vacuum tube cutting amplifier system of high performance, but indeed, the size, weight, heat, and cost of it will most probably limit the scope of this project to a few hand-crafted prototypes for a few people intense enough to want to have one. I build a lot of gear this way and totally enjoy it. Not everything has to have mass-market potential.

B) Yes, indeed, I did not see the need for a third digit there, considering that I am addressing an audience who either already know the time constants, or can easily look them up if they need to. This shall not be construed as a proposal for change from 2122 Hz to 2120... I am still keeping to the long-established tradition. However, I am briefly discussing the issue of the missing final time constants, which could have a more dramatic effect, especially on the phase response.

C) I am not. This was to test the stability of the system under much more feedback than required for the linear operation of the transducer. Linear operation of that particular head can be achieved with 24 dB of feedback at main resonance, which is around 1 kHz. It is important to understand that as you deviate from the primary resonance, the feedback amount is not the same. Neumann introduced the concept of adjusting feedback at 5 kHz to prevent accidents, considering what a 600 W power oscillator can to to the poor drive coils if the operator should become momentarily distracted....!
To make a meaningful comparison, though, it is best to specify the amount of feedback at the main resonance. There is no way to compare 13 dB at 5 kHz on one head with 24 dB at 1 kHz on another head, when they are of entirely different design with different primary resonance frequency. But what I can say from experience is that there is no significant differences in the amount of feedback required by these two heads for linear operation. The amount at 5 khz is always a lot lower than the amount at primary resonance.

The JVC heads were actually just rebranded Ortofon heads with a lot of marketing talk on top. Just compare the two.

The feedback circuit could easily work up to 150 kHz. Whether this is a good idea or not is a different story though, as discussed along with measurements in my article. As the transducer will NOT play along to 150 kHz, the phase errors can significantly affect the square wave response.

Regarding crosstalk, this is a very complicated subject, but I will just point out that regardless of how well a cutting system measures on its own, crosstalk upon reproduction of the resulting disk is mostly limited by the repro cartridge, its own crosstalk characteristics, and its ability to geometrically "follow" what the cutter head did. Which is where the crosstalk problem really starts with rocking bridge heads... How many repro cartridges were designed to "follow" rocking bridge motion, which is quite different to the motion of the cutting stylus on 45/45 type heads?
Which is exactly why I have insisted on many occasions that what we really need is better communication between the people designing cutter heads (or other disk recording equipment) and the people designing repro cartridges (or other disk reproducing equipment), especially nowadays. You can't design one without a thorough understanding of the other.

D) The electrical signal reaching the drive coils of the cutter head is exactly what you see in the final scope pic of my article. A pretty good square wave. The electrical output of the repro cartridge (assuming a properly set up repro system of decent performance) is also a pretty good square wave. However, if you look at the shape of the groove modulation on the disk under the microscope, it looks like a triangle, which is a mathematically accurate velocity representation of a square wave. Nothing wrong with that. It is not cut as a triangle wave. It is cut as a square wave, but the actual groove shape ends up looking like a triangle. There is a big difference between the two.

An article on the square wave performance of different sound recording technologies is under way. It also includes DSD. More on this soon...
Old 4 weeks ago
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Quote:
Originally Posted by magneticfidelity View Post
S_mask, many thanks for taking the time to read my article and compose such a detailed response.

A) I agree, regarding what sounds more pleasing to the ear. However, I was not referring to this as an aesthetic consideration, nor as a restriction due to "playability" concerns. In fact, my only mention of repro cartridge tracking ability was in relation to cutter head excursion limits, beyond which mechanical damage may occur, which may be an issue at low frequencies but certainly not at high frequencies. Excursion at HF is nowhere near the limits of any cutter head and nowhere near the trackable excursion figures of any repro cartridge. The "playability" issue at HF has to do with stylus groove geometry and acceleration of the moving mass of the cartridge and is therefore not related...
It sounds better not to stress cutters with unnatural musical content, and there's no actual benefit to cutting hot enough to hurt the tool - just a run-away War of Loudness.


Quote:
The issue here is the thermal overload of the cutter head at HF, which is the most common way to destroy a head. I am describing the exact mechanism behind this phenomenon and point this out as a reliability issue. I have not proposed a concrete solution to this problem in this article, other than offering some food for thought on sensitivity/efficiency as related to cutter head transducer and loudspeaker driver design.

The thermal sensitivity of the drive coil glue is well documented, so, it makes the engineer more mindful of the peril and, fortunately, it's aesthetically advantageous to mind the peril and limit excessive sibilance.



Quote:
While I am working on overcoming this issue to the extent possible, for the new cutter head I am developing (Lab Report: The Agnew Analog Stereophonic Cutter Head – Agnew Analog Blog), this is simply to make a cutter head that is more reliable/durable, rather than to suggest that we should all start boosting the HF content on disk.
The existing designs are already over-engineered for best sound and reliability. However, if they had refrained from cutting hotter than +0, there would have been a lot less down time and a lot fewer rejects.


Quote:
I do work mostly with tape and most of the masters I cut are transferred directly from 1/4" tape, entirely in the analog domain. Most of my circuit design work uses vacuum tubes and I absolutely love them as devices. I am slowly but steadily also working on a vacuum tube cutting amplifier system of high performance, but indeed, the size, weight, heat, and cost of it will most probably limit the scope of this project to a few hand-crafted prototypes for a few people intense enough to want to have one. I build a lot of gear this way and totally enjoy it. Not everything has to have mass-market potential.
Tape is a bad pair for vinyl because the tape recording has odd harmonics and the groove playback adds even...

Stan Ricker told me his best sound was with the Ortofon solid state amps and an SX-74. He tried using the DSS with tube amps, too.

Quote:
B) Yes, indeed, I did not see the need for a third digit there, considering that I am addressing an audience who either already know the time constants, or can easily look them up if they need to.
The RIAA time constants should be 3183 µs for 50 Hz, 318.3 µs for 500 Hz, and 75 µs should be for 2,122 Hz, but nowhere does it read this way. Even the Ortofon manual says 2,120 Hz, but they use the formula with the truncated constant, '159', resulting in, '2.12' on calculator.


edit:

{I just noticed that Ampex agreed with this notion that one should use a more complete constant (i.e., 159.1549...) in the numerator of the quotient (for Tau), as evidenced in the manual for the ATR-100 tape machine where (p. 5-18) it gives time constants for the high frequency transition frequencies' -3dB values for the various tape equalization standards selected when using an otherwise unequalized flux loop on the heads (Table 5-5):

http://www.discolathe.com/Control_C/3183.jpg

Note that '50 µs' is said to equal '3183 Hz'. This is equivalent to saying that 50 Hz = 3183 µs, since one can put either the time constant, or the frequency (in kHz) in the denominator. So, 159.1549... / 50 µs = 3183 Hz, and 159.1549.../3183 µs = 0.050 kHz. So, we should revise the NAB and RIAA standards similarly so that we use 3183 µs = 50 Hz, 318300 nanoseconds = 500 Hz, and 75 µs = 2.122 kHz.}


Quote:
This shall not be construed as a proposal for change from 2122 Hz to 2120... I am still keeping to the long-established tradition. However, I am briefly discussing the issue of the missing final time constants, which could have a more dramatic effect, especially on the phase response.
The phase response of the best Neumann and Ortofon drive packages is already excellent. Abandoning the use of silicone fluid for resonance control in favor of negative motional feedback was inspired, according to Burgess Macneal, who used to have to tune the viscosity of his Grampian's head fluid from time to time before he got an Ortofon.

Quote:
C) I am not. This was to test the stability of the system under much more feedback than required for the linear operation of the transducer. Linear operation of that particular head can be achieved with 24 dB of feedback at main resonance, which is around 1 kHz. It is important to understand that as you deviate from the primary resonance, the feedback amount is not the same. Neumann introduced the concept of adjusting feedback at 5 kHz to prevent accidents, considering what a 600 W power oscillator can to to the poor drive coils if the operator should become momentarily distracted....!
To make a meaningful comparison, though, it is best to specify the amount of feedback at the main resonance. There is no way to compare 13 dB at 5 kHz on one head with 24 dB at 1 kHz on another head, when they are of entirely different design with different primary resonance frequency. But what I can say from experience is that there is no significant differences in the amount of feedback required by these two heads for linear operation. The amount at 5 khz is always a lot lower than the amount at primary resonance.

Yes there's a difference, so, I'm glad you're not attenuating 5 kHz by 30 dB with feedback. However, the Ortofon primary resonance is above 2 kHz, so, while the 5 kHz feedback adjustment of -10 dB makes the peak at ~ 2.2 kHz drop by an apparent 31.5 dB at full chat, when make-up gain is applied to restore 10 dB, the flat line brings the resonant peak frequency back to a normalized - 21.5 dB, as shown in the graph, attached. It puils down the hump no further than 'the bar', but the bar moves, so the measurement should, with it. Of course I realize the difference between the resonance and the feedback level-setting frequency (dampening at 5 kHz, or phasing, at 1 kHz), as I've dialed in the feedback without playing 5 kHz and just watched the hump, itself, go down (adjusting both channels' feedback simultaneously) on the FFT spectrum analyzer, since the resonant hump is there (on both channels) singing in the circuit without any outside signal added.


Quote:
The JVC heads were actually just rebranded Ortofon heads with a lot of marketing talk on top. Just compare the two.
It's definitely similar, but surely is not a DSS821 with a different coat of paint and new badge. The Phonotech head looks similar to the Ortofon, though it had significant design changes, too, more like the CH-90, including increased max. displacement and enhanced gas flow.

Quote:
The feedback circuit could easily work up to 150 kHz. Whether this is a good idea or not is a different story though, as discussed along with measurements in my article. As the transducer will NOT play along to 150 kHz, the phase errors can significantly affect the square wave response.
The high feedback bandwidth is necessary to give the cutting head flat phase and frequency response in band, and it works with stability, so, it's a great idea.

Quote:
Regarding crosstalk, this is a very complicated subject, but I will just point out that regardless of how well a cutting system measures on its own, crosstalk upon reproduction of the resulting disk is mostly limited by the repro cartridge, its own crosstalk characteristics, and its ability to geometrically "follow" what the cutter head did. Which is where the crosstalk problem really starts with rocking bridge heads... How many repro cartridges were designed to "follow" rocking bridge motion, which is quite different to the motion of the cutting stylus on 45/45 type heads?
The rocking bridge looks very different, but it makes 45/45 diagonal 'solo' cuts and, when the channels are summing at equal intensity in phase, or out, cuts perfectly laterally or vertically. My Stanton cart follows cuts by Ortofon or Neumann cutting heads equally well, but it sounds as if it prefers the Ortofons - how does it know? (;

Quote:
Which is exactly why I have insisted on many occasions that what we really need is better communication between the people designing cutter heads (or other disk recording equipment) and the people designing repro cartridges (or other disk reproducing equipment), especially nowadays. You can't design one without a thorough understanding of the other.
Ortofon have been manufacturing moving coil pickup cartridges since '48. The cutting systems were designed with complete knowledge of the playback technology.

Quote:
D) The electrical signal reaching the drive coils of the cutter head is exactly what you see in the final scope pic of my article. A pretty good square wave. The electrical output of the repro cartridge (assuming a properly set up repro system of decent performance) is also a pretty good square wave. However, if you look at the shape of the groove modulation on the disk under the microscope, it looks like a triangle, which is a mathematically accurate velocity representation of a square wave. Nothing wrong with that. It is not cut as a triangle wave. It is cut as a square wave, but the actual groove shape ends up looking like a triangle. There is a big difference between the two.
That's what I'm saying. The problems of recording are swamped by those of repro, same as with tape.


Quote:
An article on the square wave performance of different sound recording technologies is under way. It also includes DSD. More on this soon...
Thanks
Attached Thumbnails
Motional Feedback Disk Recording System Design-ortofon_response.jpg  

Last edited by S_mask; 1 week ago at 09:46 AM.. Reason: new corroboration found
Old 3 weeks ago
  #6
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Quote:
Originally Posted by cathode View Post
Your point is appreciated,
but lets not slight the performance of Westrex and Haeco cutters (Otto Hepp designs) which employed approximately 30 dB of feedback @ 1000 Hz.
They cut impressive lacquers in the 70's and continue to do so.
I agree. These heads have indeed cut impressive masters, with a cutting amplifier "only" capable of delivering 75 W, at very decent levels.

Quote:
Originally Posted by cathode View Post
The "JVC" head was still an Ortofon, when it blew up (unfortunately quite often), it was returned to Ortofon for rebuild.
Exactly.

Quote:
Originally Posted by cathode View Post
The cutting amplifier at the JVC mastering facility in Hollywood was actually a Threshold, a zero internal global feedback unit, with a fancy front panel to disguise it's maker.
Which they called "CA-90 cutter drive package". JVC openly stated in their advertising literature of the time that the cutting amplifier is a Threshold Stasis 2 (reference 11 of my article). So, you are correct on this as well.

Quote:
Originally Posted by S_mask View Post
It sounds better not to stress cutters with unnatural musical content, and there's no actual benefit to cutting hot enough to hurt the tool - just a run-away War of Loudness.
Indeed. However, even natural musical content at conservative level can prove "hot enough to hurt the tool" sometimes. Not to mention trying to cut a test record.... Which is quite necessary for the development, testing and calibration of all the equipment needed for the reproduction of natural music cut at very reasonable levels.

Quote:
The thermal sensitivity of the drive coil glue is well documented, so, it makes the engineer more mindful of the peril and, fortunately, it's aesthetically advantageous to mind the peril and limit excessive sibilance.
Sibilance is a whole new discussion...But yes, nobody likes to hear excessive sibilance. I wish it were only the glue we had to worry about.


Quote:
The existing designs are already over-engineered for best sound and reliability. However, if they had refrained from cutting hotter than +0, there would have been a lot less down time and a lot fewer rejects.
The existing designs are the culmination of the collective body of thought, knowledge, understanding available materials, resources, research and development, as it was in the 1970's. That was 49 years ago. Time for an update.
As for cutting hotter than +0 or not.... I suspect you are referring to average level, or VU meter indication. But, how about the peaks? How much higher than +0 dB are the peaks allowed to reach? Isn't it good engineering practice to allow a generous margin there? If so, then how long in duration are these peaks allowed to last? How frequently are they allowed to recur? Now think again about the heating power of each peak and the thermal time constant of the transducer and the ability to cut a decent, unbutchered, dynamic range to disk. Without needing protective signal processing. This is where we may be able to improve upon the current situation.


Quote:
Tape is a bad pair for vinyl because the tape recording has odd harmonics and the groove playback adds even...
Which is a bit of an oversimplification, but in any case, you have stated yourself that you found the results of Sean Davis' tape-to-disk transfers "stunning", so it obviously CAN sound good if done properly.


Quote:
The RIAA time constants should be 3183 µs for 50 Hz, 318.3 µs for 500 Hz, and 75 µs should be for 2,122 Hz, but nowhere does it read this way. Even the Ortofon manual says 2,120 Hz, but they use the formula with the truncated constant, '159', resulting in, '2.12' on calculator.
The other way around: It is customary to specify time constants rather than frequencies. So, it is 3180, 318 and 75 μs, plus the missing ones at the top. This translates to 50.04872424 Hz, 500.4872424 Hz, 2122.065908 Hz etc... Which is often rounded t 50.05 Hz, 500.5 Hz and so on...


Quote:
The phase response of the best Neumann and Ortofon drive packages is already excellent. Abandoning the use of silicone fluid for resonance control in favor of negative motional feedback was inspired, according to Burgess Macneal, who used to have to tune the viscosity of his Grampian's head fluid from time to time before he got an Ortofon.
Regarding phase response, let us first consider the cutting system on its own. Looking at the comparative square wave response figures in my article, it becomes quite obvious that my system outperforms the Neumann SAL74 in this respect.
Now let us consider the entire cutting and subsequent reproducing chain.
What happens above 75 μs?
The Ortofon and Neumann systems took different approaches to this. Reproducing phono stages most often do not take this into account in their implementation of the RIAA de-emphasis. The few that do, chooser either the Neumann, or the Ortofon approach (or neither of the two!). As such, phase response suffers unless the pre-emphasis matches the de-emphasis in a practically achievable manner.
To further complicate matters, cutter heads are the real limiting factor and their thermal overload problems render both the Neumann and the Ortofon final time constant approaches questionable at best. This is a topic for yet another article.. Perhaps the time is ripe for the standardization of the final time constants to reasonable values. Then we can ensure decent phase response throughout.
As for silicone damper oil, it wasn't just a matter of convenience. The frequency and phase response of a Grampian head is far from impressive. It was monophonic. It needed loads of power to drive it. It leaked... on the platter...!


Quote:
Yes there's a difference, so, I'm glad you're not attenuating 5 kHz by 30 dB with feedback. However, the Ortofon primary resonance is above 2 kHz, so, while the 5 kHz feedback adjustment of -10 dB makes the peak at ~ 2.2 kHz drop by an apparent 31.5 dB at full chat, when make-up gain is applied to restore 10 dB, the flat line brings the resonant peak frequency back to a normalized - 21.5 dB, as shown in the graph, attached. It puils down the hump no further than 'the bar', but the bar moves, so the measurement should, with it. Of course I realize the difference between the resonance and the feedback level-setting frequency (dampening at 5 kHz, or phasing, at 1 kHz), as I've dialed in the feedback without playing 5 kHz and just watched the hump, itself, go down (adjusting both channels' feedback simultaneously) on the FFT spectrum analyzer, since the resonant hump is there (on both channels) singing in the circuit without any outside signal added.
If you are seeing a hump on a spectrum analyzer with no signal applied, then there is something really wrong with your system!



Quote:
The high feedback bandwidth is necessary to give the cutting head flat phase and frequency response in band, and it works with stability, so, it's a great idea.
The JVC CH-90 published specs state that the active feedback range of the transducer shall be limited to 16 kHz (there is a change of sign from negative to positive feedback at 18 kHz). Which means that there is no correction past 16 kHz. The practical implication of this:

A report from Mr Boden and Mr Lewter of the JVC cutting center in Hollywood, to Mr Kageyama and Mr Niimi of JVC in Japan, dated March 24, 1982, on the performance of the CH-90/CA-90 package, states that the frequency response of CH-90 NR-805 is measured to be +- 1 dB 30 Hz-16 kHz, driven by the CA-90, accurately calibrated. They also mention an early failure of the CH-90 (highlighting my reliability concern). How good can the phase response be in view of the above?

A discussion of feedback range, adjustment procedures and change of sign, also appears in the book "Physical Processes of Cutting Gramophone Records" by Frits Nygaard of Ortofon, written in 1979 (reference 31 of my article).

Further, the stability margin for the CH-90/CA-90 combination in 6 dB. Not exactly a stellar figure.

Quote:
The rocking bridge looks very different, but it makes 45/45 diagonal 'solo' cuts and, when the channels are summing at equal intensity in phase, or out, cuts perfectly laterally or vertically. My Stanton cart follows cuts by Ortofon or Neumann cutting heads equally well, but it sounds as if it prefers the Ortofons - how does it know? (;
The rocking bridge system does not follow the same path/arc vertically, laterally or diagonally, as a 45/45 head. The geometric differences in each plane of motion between cutting and reproducing are the main limiting factor for maintaining channel separation. They also introduce distortion. Your Stanton cart (or any other cart) will play back both, of course. Which combination will give you better channel separation is another story though.


Quote:
Ortofon have been manufacturing moving coil pickup cartridges since '48. The cutting systems were designed with complete knowledge of the playback technology.
Sadly, they discontinued their cutting system a very long time ago.
I still wonder which ones (if any) of their reproduction cartridges were specifically designed/optimized for rocking bridge heads, such as their own cutter heads.

Quote:
That's what I'm saying. The problems of recording are swamped by those of repro, same as with tape.
With the difference that you can record test tones at operating level for as long as you like on tape without blowing the head. You cannot do that on disk. But you can play back both test tapes and disks all day long without damaging anything.


Quote:
Thanks
My pleasure!
Old 3 weeks ago
  #7
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Quote:
Which they called "CA-90 cutter drive package". JVC openly stated in their advertising literature of the time that the cutting amplifier is a Threshold Stasis 2 (reference 11 of my article). So, you are correct on this as well.

...modified in order to be able to work with a cutting head, so, not Uncle Norman's Threshold.


Quote:
Indeed. However, even natural musical content at conservative level can prove "hot enough to hurt the tool" sometimes. Not to mention trying to cut a test record.... Which is quite necessary for the development, testing and calibration of all the equipment needed for the reproduction of natural music cut at very reasonable levels.
Natural music will have a high crest, which means the average persistent level will be low, though sharp transients may carve modulations with pathological radii.

Rather, it's unnaturally compressed, unnaturally mic'd (i.e., close-mic'd cymbals and cabs) pop and rock, especially cut as hot singles, that lead to so many failures (and changing the stylus of the Ortofon without learning how not to break the coil wires under the bridge).


Quote:
Sibilance is a whole new discussion...But yes, nobody likes to hear excessive sibilance. I wish it were only the glue we had to worry about.
Sibilance's relevance here is that it's where the power demand is highest. Excessive sibilance is mostly that which lasts too long.

Quote:
The existing designs are the culmination of the collective body of thought, knowledge, understanding available materials, resources, research and development, as it was in the 1970's. That was 49 years ago. Time for an update.
The existing art is higher than necessary. We simply need more cutter and amp repair techs.

Sean Davies writes in AES Convention Paper 5751 on the development of disc cutting heads (00033.pdf) '...The last generation of cutterheads ( it is unlikely that there will be significant new departures at this stage of the discipline ) are extremely high precision products in which special materials allow a very high performance...'



Quote:
As for cutting hotter than +0 or not.... I suspect you are referring to average level, or VU meter indication. But, how about the peaks? How much higher than +0 dB are the peaks allowed to reach? Isn't it good engineering practice to allow a generous margin there? If so, then how long in duration are these peaks allowed to last? How frequently are they allowed to recur? Now think again about the heating power of each peak and the thermal time constant of the transducer and the ability to cut a decent, unbutchered, dynamic range to disk. Without needing protective signal processing. This is where we may be able to improve upon the current situation.

By reference to O VU ref:7 cm/sec peak lateral velocity, I mean that the pickup signal should be peaking at 0 VU (with a properly damped VU meter's ballistics). This is plenty hot for a full length, 'hit' LP and , if the sustained fortes can rest down at - 8 to - 6 VU, the cutting head is relatively safe and it will be engraving modulation that can be played by most decks. There may be a fortissimo that surpasses 0 VU. But it will be quite rare.



Quote:
Which is a bit of an oversimplification, but in any case, you have stated yourself that you found the results of Sean Davis' tape-to-disk transfers "stunning", so it obviously CAN sound good if done properly.

Dynamic music has lots of quiet passages which buys time in the thermal budget imposed by a given 'side'.



Quote:
The other way around: It is customary to specify time constants rather than frequencies. So, it is 3180, 318 and 75 μs, plus the missing ones at the top. This translates to 50.04872424 Hz, 500.4872424 Hz, 2122.065908 Hz etc... Which is often rounded t 50.05 Hz, 500.5 Hz and so on...
That which is customary is what is being called into question. There's no JEDIC value of a 3180 xF cap, after all, so, since the time constant isn't the value of a part, why not enshrine the time constant, 3183 µs, which makes dead nuts 50.00 Hz? Instead, someone settled on 3180 µs, but it was because he used a truncated constant, '159', in the formula for Tau, instead of the more exact replica, 159.1549, which I recommend all use - just four more numbers for a lot more precision.

Sengpiel's website, and that of Dr. Jordan, agree: RIAA Filtering



Quote:
Regarding phase response, let us first consider the cutting system on its own. Looking at the comparative square wave response figures in my article, it becomes quite obvious that my system outperforms the Neumann SAL74 in this respect.
...however, your modified loudspeaker amp does not outperform the Ortofon drive package in this respect.

behold:

http://www.discolathe.com/Control_C/1kHz_sq_731.jpg

{The Tek 465M (100 kHz bandwidth dual-trace 'scope) is displaying the monitor output of the left chassis of a vintage GO741 amp set with audio transformer inputs (not bypassed) driving the DSS731 (actual) cutting head, 'in air', with a 1 kHz square wave from a Krohn-Hite oscillator going through only the final level and driver stages of the mastering console.

The dumbie load (DL791) works for testing the safety circuit's automatic heat-estimating mute relay, and it's possible to adjust the feedback with it, since it has four (stationary) coils, but its response is not as good as the actual cutting head - especially with the square wave. So, the actual cutting head can be referenced at low signal levels with the 75 µs RIAA filtering bypassed (on record and monitor) and the power limited (using the front panel switches of the GO741 chassis, Power Limit and Test).}



Quote:
Now let us consider the entire cutting and subsequent reproducing chain.
What happens above 75 μs?
The Ortofon and Neumann systems took different approaches to this. Reproducing phono stages most often do not take this into account in their implementation of the RIAA de-emphasis. The few that do, chooser either the Neumann, or the Ortofon approach (or neither of the two!). As such, phase response suffers unless the pre-emphasis matches the de-emphasis in a practically achievable manner.

Neumann supposedly use 3.18 µs, which is around 50 kHz. Ortofon may use 3.5 µs, down at 45.5 kHz. Of course, these are proprietary deviations from the RIAA standard which doesn't include a time constant above 75 µs.

Quote:
...To further complicate matters, cutter heads are the real limiting factor and their thermal overload problems render both the Neumann and the Ortofon final time constant approaches questionable at best. This is a topic for yet another article.. Perhaps the time is ripe for the standardization of the final time constants to reasonable values. Then we can ensure decent phase response throughout.
Of course, it's the pickup stylus which is the limiting factor as cutting heads can easily carve untraceably chaotic modulation that would require a laser to decipher. Cutting heads overloading thermally is mostly pilot error.

Quote:
If you are seeing a hump on a spectrum analyzer with no signal applied, then there is something really wrong with your system!
Well, clearly not. Have you heard of people yelling at the cutting head during silence and making audible modulation? These hi fi cutting systems are very sensitive needing the slightest trepidation to excite a small response. The amps are fine. The resonant hump on screen completely disappears with the addition of negative feedback, and, by the way, when I can see it before feedback is summed, and with no signal applied, it's way down at the bottom of the spectrum analyzer of Spectra Foo (using a Lavry AD122MKIII for digitization, so the A/D self noise is maximally low). I'm just looking that deeply into the signal.




Quote:
...Further, the stability margin for the CH-90/CA-90 combination in 6 dB. Not exactly a stellar figure.
It's quite acceptable, actually. The stability margin for a given system depends on the feedback to program ratio. The (green) DSS821 can be used with only 3 dB stability margin from feedback presence for hi fi acoustic music, but the 6 dB-margin feedback ratio is better for rock and Disco and -8, perhaps, for hardstep, and/or electronic ('unnatural') music.

I don't know about the JVC products - just that our Larry said the cutting head he was using then was a knock-off of the Ortofon.

Of course, people abuse systems to make records louder than other cutting engineers since that's how jobs were awarded - by trial. Bob Ludwig explained in one of his YouTube interviews how he lost the Led Zep II gig by cutting loud enough to cause Ahmet Ertegun's daughter's record player to skip, but he cut it that loud in an attempt to win the gig, not because it needed to be like that for Art's sake, but because people making the calls are at least temporarily impressed with loud records, so, normally, it would have won.

A veteran Hollywood engineer told me about his exploits He claims to have vari-sped a major celebrity musician's master tape a little to subtract from the program duration just enough to require just enough less land at the starting level in order to get the sides a little hotter, taking up the saved space - and they approved it without commenting about the pitch bump. This was a major crooner of serious Pop.

Quote:
The rocking bridge system does not follow the same path/arc vertically, laterally or diagonally, as a 45/45 head.
Sorry, that's not correct. Despite appearances, the rocking bridge is just a different way to achieve the same cuts. The stylus doesn't know it's not being pushed diagonally from a torque tube linkage. However, for the geometry of the orthogonal rocking bridge to work correctly and for the groove modulation to have the best channel separation, the stylus protrusion from the bridge must be exactly 2.50 mm. To confirm this, the Ortofon stylus inspection microscope has a reticle with lines showing 0.1 mm intervals. One needs to use tweezers in order partially to lift the inner edge of the rubber diaphragm that covers the bridge hole area around the stylus aperture puncture, in order to view the top of the bridge in the microscope. Otherwise, the measurement is easy. It helps one be sure that the shank is correctly seated in the bridge hole, and a sight line on the cutting head helps indicate correct orientation of the major facets.


Quote:
The geometric differences in each plane of motion between cutting and reproducing are the main limiting factor for maintaining channel separation. They also introduce distortion. Your Stanton cart (or any other cart) will play back both, of course. Which combination will give you better channel separation is another story though.
When correctly used, the rocking bridge stylus motion is not making an appreciably different groove geometry. There's no difficulty tracing and scanning Ortofon cuts or seeing very good signal response and channel isolation. As mentioned, the necessary cutting geometry of the right angle, made 45 degrees, is dependent on the exact protrusion of the synthetic ruby jewel from the bridge and the intrinsic (included) angle forming the vertex. There is a .1 mm tolerance +/- for best results. Is your tip rake at 88.2 degrees while making a 30 degree impression force angle to compensate for 5 degrees of lacquer spring back and 5 more degrees of stylus holder flexion so as to recoil to an effective 20 degree cutting v.a.? (l; Yes, Ortofon knows grooves, from the company's first MC cart of 1948 and their first lateral cutting head with feedback from 1949, cited in the Sean Davies paper. For a better understanding of how Ortofon helped to invent the modern gramophone system, visit: Ortofon true Mono cartridges range



Quote:
Sadly, they discontinued their cutting system a very long time ago.
I still wonder which ones (if any) of their reproduction cartridges were specifically designed/optimized for rocking bridge heads, such as their own cutter heads.
They didn't have to be designed for rocking bridge cuts since this isn't an issue.

Ortofon discontinued making cutting systems only in the early '80s. The amps are out there, waiting to be recalibrated. However, you must have the factory instructions in order to achieve the specified tight electrical handshake between each card of a circuit in a given chassis, since the values of the auxiliary capacitors and resistors on each board are not known until you assemble each chassis with its specific cards and do the procedures for each circuit. After that, you will not be able to swap just any card from channel A into channel B and have it perform the same, if at all. Like Dunlavy cross-overs, a matched set will likely have slightly uniquely-valued components in each channel. Hr. Rønne, of etec, who made much of the Ortofon cutting gear (and who hosts the Nygaard paper on his website) has the know-how and test equipment for working on the amps and repairing the DSS cutting head models.


Quote:
With the difference that you can record test tones at operating level for as long as you like on tape without blowing the head. You cannot do that on disk. But you can play back both test tapes and disks all day long without damaging anything.


No worries, I don't want to listen to test tones, even quietly. (;


Speaking of test tones, here's the lateral 1 kHz square wave cut on the CBS STR 112 test record:
http://www.discolathe.com/Control_C/..._1kHz_sq_L.jpg

...and the vertical:
http://www.discolathe.com/Control_C/..._1kHz_sq_V.jpg


...as the cover text explains, if you play a square wave cut back with a ceramic (piezoelectric / quartz) type pickup, due to being amplitude-responding, rather than velocity-..., the output signal will be a triangle wave. But, also, if you use a velocity-responding pickup to play back the square wave cut with the default RIAA and RF filtering, you'll (still) get a triangle wave, as from the phono pre of the NAD 7100:

http://www.discolathe.com/Control_C/NAD_triangle.jpg

If you probe the phono cart's output directly, bypassing any forced filtering, the 'scope shows a good approximation of the square wave, although it has some Myan pyramiding going on, not unlike the bedways of the Scully lathe:

http://www.discolathe.com/Control_C/Cart_2_Tek.jpg
Old 3 weeks ago
  #8
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JVC cutting amplifier

Quote:
Originally Posted by S_mask View Post
...modified in order to be able to work with a cutting head, so, not Uncle Norman's Threshold.
Actually, Uncle Norman (his real name is starts with D) installed a stock front panel and has been using it on loudspeakers for the past 30 years.
Otherwise modified, not.
Do not confuse external RIAA emphasis network with an otherwise standard power amplifier.
You are aware of the many rooms that employed McIntosh MI-200 amplfiers with Grampian and Westrex heads ?
Old 3 weeks ago
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Quote:
Originally Posted by cathode View Post
Actually, Uncle Norman (his real name is starts with D) installed a stock front panel and has been using it on loudspeakers for the past 30 years.
Otherwise modified, not.
Do not confuse external RIAA emphasis network with an otherwise standard power amplifier.
You are aware of the many rooms that employed McIntosh MI-200 amplfiers with Grampian and Westrex heads ?
Uncle Norman is a reference to the character on the Courtship of Eddy's Father. (;

As our Larry's compendium of vinyl record gear brochures shows, the JVC CA-90 was built 'around' an unmodified Threshold no-feedback amp for drive, but it had to have custom peak meters added in addition to the creation of the RIAA encoding network and safety circuit, which included more than heat-estimation via DC resistance. I should expect some kind of impedance-matching network similar to the Ortofon amps, which presents a mirror-image of the reactance of the tool, using air core inductors, caps, and power resistors, since this helps fine tune the successful application of motional feedback to tackle the large mid-band resonance. The front panel of the CA-90 is not that of the Threshold, although the name appears on one side, while JVC appears on the other.



Speaking of Threshold DC amps, I love Nelson Pass's designs and just recently repacked a 24-device channel of one of his SuperSymmetry, no-fb, DC-to-100 kHz amps with hyper-matched NOS Hexfets. His loudspeaker amps are not plug and play disk cutting amps, to be sure, but they could be used for tack welding if pressed.
Old 3 weeks ago
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To attenuate further confusion about the cutting geometry of the rocking bridge design used in the Ortofon and JVC and early Neumann stereo cutting heads, please refer to this corrected drawing from our Larry's compendium, Basic Disc Mastering (p. AE-8): http://www.discolathe.com/Control_C/...ing_Bridge.jpg

{Please note that the drawings as they appear in the compendium, Basic Disc Mastering (p. AE-8), have distorted dimensions for the Neumann stylus silhouettes in the deflected positions of diagonal, lateral, and vertical cutting (and the lateral had missing the vertex reference line). The distorted silhouettes may have been so in an attempt to illustrate perspective caused by the modern inclined plane for cutting when the new angle is applied from behind the stylus (as the torque tube drive entails) with respect to the workpiece, as is the case with the Westrex/Neumann cutting heads, since, once inclined, the driving forces are no longer in the same plane as the stylus tip. However, the stylus width would not change from this vantage, yet, in the drawings, it does. Whereas, the Ortofon stylus silhouettes do not change size in the deflected positions of the drawings on this page.

So, using a ruler against the computer screen while the scan was magnified to 1000%, jeg corrected the Neumann stylus drawings so that its stylus silhouettes don't change size, either, when in the deflected positions. I used the original drawings' rotating points, on the left corner of the Neumann stylus silhouette, adding the correct amount of hangover to the right corner so that the width of the sapphire depicted doesn't change and thereby provide clearer comparison of the two ways of achieving the same 45/45 cuts..

It can be seen, therefore, that the correctly applied stylus motion of these systems of cutting are effectively identical, though the rocking bridge design works better with modern inclined plane cutting (and playback) since its moving elements remain connected as if in the same plane as the stylus tip, since they still push and pull right on top of the bridge when in the inclined orientation.

When cutting diagonally and laterally, there is some 'banking' of the curves engraved by both systems, since this is required by the undriven coil's hinge or linkage, neither of which can let go of the tube or bridge when the opposite side, alone is active. This effect is evidenced by the vertex which tilts with any lateral or diagonal displacement. Banking of curves is actually a 'feature', since it stabilizes the head shell during direction changes, whereas purely level curves would encourage skating at extreme displacements. Skiers will understand this choreography intuitively. Old highways have this problem for cars.

Also, a curve line was erased from the drawing of Figure 4 d because its radius was too small, suggesting that the Ortofon stylus tip loses more depth than Neumann as lateral deflection increases, but this is exaggerated in the drawing, and the tip has not become significantly more shallow than that of the Neumann at the moment where the deflection is depicted, as measurement of the vertices proves.}
Old 3 weeks ago
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Here's a quote about torque tube versus rocking bridge grooves and how cartridge behavior would differ with respect to crosstalk, from 1979, by JVC in their paper, 'Record and Record Player':


"Although crosstalk will be different, if you calculate crosstalk due only to the difference between them, it is less than -30 dB, so there is no harm in the beginning."

The difference results from the late use of an inclined plane for the vertical cutting angle of 15 - 20 effective degrees (rather than pushing down from 90 degrees into the workpiece), alluded to, above.

Please see the attached photo from the Japanese Analog Audio website of vinyl standards which provided the quote from JVC and also the photo of text excerpted from the Ortofon stereo cutting head manual explaining that the rocking bridge is, indeed, a 45/45 cutting system.
Attached Thumbnails
Motional Feedback Disk Recording System Design-dss_manual_excerpts.jpg   Motional Feedback Disk Recording System Design-jvc_cu5.jpeg  
Old 3 weeks ago
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Quote:
Originally Posted by S_mask View Post
.
Sibilance's relevance here is that it's where the power demand is highest. Excessive sibilance is mostly that which lasts too long.
Not exactly. We do not usually refer to a 20 kHz sine wave as sibilance.


Quote:
The existing art is higher than necessary. We simply need more cutter and amp repair techs.
I wholeheartedly disagree. Not to mention the extreme scarcity of the "existing art", taking in into the realm of "unobtainable art". At least for those who are trying to just enter the field now.
How would more techs help the situation?

Quote:
Sean Davies writes in AES Convention Paper 5751 on the development of disc cutting heads (00033.pdf) '...The last generation of cutterheads ( it is unlikely that there will be significant new departures at this stage of the discipline ) are extremely high precision products in which special materials allow a very high performance...'
Yes, exactly, reference number 1 of my paper. But this was 16 years ago already! Yes, I agree with him. Back then it was indeed "unlikely" (but not impossible) "that there will be significant new departures", given that at that time, in the UK at least, people were literally giving away lathes, record players and entire record collections. Many academic institutions threw out their entire libraries of music on vinyl records, "since they had access to the same music on mp3", around that time. There was simply no market at the time.
I also agree that the heads he is referring to "are extremely high precision products... high performance". But I still believe in meaningful evolution.

Quote:
By reference to O VU ref:7 cm/sec peak lateral velocity, I mean that the pickup signal should be peaking at 0 VU (with a properly damped VU meter's ballistics). This is plenty hot for a full length, 'hit' LP and , if the sustained fortes can rest down at - 8 to - 6 VU, the cutting head is relatively safe and it will be engraving modulation that can be played by most decks. There may be a fortissimo that surpasses 0 VU. But it will be quite rare.
Assuming the reference of OVU resulting in a peak lateral velocity of 7 cm/s (at 1 kHz), true peaks on natural music would actually be allowed to reach +20 dB over this, which is what is considered good engineering practice in most other audio systems:

a) + 4 dBu nominal electrical signal level: Well designed equipment should be able to handle minimum +24 dBu peaks.

b) -20 dBFS for a + 4 dBu signal implies a 20 dB margin of safety, and an ability to cope with +24 dBu signals on the analog side.

c) 185 nWb/m for a +4 dBu signal in magnetic tape recording: SM900 saturation flux is given as 2320 nWb/m (approximately + 22 dB) while ATR Master Tape works out to a saturation flux of 2800 nWb/m, implying a signal handling ability of almost +28 dBu, or elevated operating levels plus 20 dB of margin.

As such, a well engineered disk recording system should also offer a minimum of 20 dB safety headroom over the nominal operating level without blowing up, and a well engineered reproducer should be able to actually reproduce this.

Quote:
That which is customary is what is being called into question. There's no JEDIC value of a 3180 xF cap, after all, so, since the time constant isn't the value of a part, why not enshrine the time constant, 3183 µs, which makes dead nuts 50.00 Hz? Instead, someone settled on 3180 µs, but it was because he used a truncated constant, '159', in the formula for Tau, instead of the more exact replica, 159.1549, which I recommend all use - just four more numbers for a lot more precision.

Sengpiel's website, and that of Dr. Jordan, agree: RIAA Filtering
Interesting point. Is there a 3183xF cap?
We could change it to something seemingly practical, such as 3300 μs, 330 μs, etc... This works out to a very memorable 48.22877063 Hz, but at least the capacitors are easily available.
However, in the real world, there are things like stray capacitance, source impedance component tolerances, and interaction from bundling together more than one time constant in a complex network. So we might as well just stay with 3180 μs and take all aspects into consideration when designing a circuit. As an example: Lab Report: Type 710 Pre-Emphasis Module Prototype – Agnew Analog Blog

Quote:
The dumbie load (DL791) works for testing the safety circuit's automatic heat-estimating mute relay, and it's possible to adjust the feedback with it, since it has four (stationary) coils, but its response is not as good as the actual cutting head - especially with the square wave. So, the actual cutting head can be referenced at low signal levels with the 75 µs RIAA filtering bypassed (on record and monitor) and the power limited (using the front panel switches of the GO741 chassis, Power Limit and Test).}
Exactly. So, not much difference in the end at the feedback monitor. The question is how does it put that to disk?

Quote:
Neumann supposedly use 3.18 µs, which is around 50 kHz. Ortofon may use 3.5 µs, down at 45.5 kHz. Of course, these are proprietary deviations from the RIAA standard which doesn't include a time constant above 75 µs.
Exactly, time to have a well defined and standardized approach.

Quote:
Of course, it's the pickup stylus which is the limiting factor as cutting heads can easily carve untraceably chaotic modulation that would require a laser to decipher. Cutting heads overloading thermally is mostly pilot error.
Not really. Just recently I was testing a few decent cartridges with the FloKaSon test record (Absolute Polarity for Disk Records – Agnew Analog Blog) and some can easily follow the sweep to 50 kHz. Do you know of any cutter head that can do a continuous accurate sweep to 50 kHz without tricks?
Thermal overload is indeed pilot error. The "aircraft" in question could benefit from some further development though, to decrease the likelihood of error under conditions which are generally accepted as common in all other sound recording disciplines.

Quote:
Well, clearly not. Have you heard of people yelling at the cutting head during silence and making audible modulation? These hi fi cutting systems are very sensitive needing the slightest trepidation to excite a small response. The amps are fine. The resonant hump on screen completely disappears with the addition of negative feedback, and, by the way, when I can see it before feedback is summed, and with no signal applied, it's way down at the bottom of the spectrum analyzer of Spectra Foo (using a Lavry AD122MKIII for digitization, so the A/D self noise is maximally low). I'm just looking that deeply into the signal.
But you do realize that of course in the absence of signal, what you are measuring is noise? Considering that it has a hump at main resonance, without feedback, this can only be due to the mechanical resonance of the moving system, since the feedback coil /error amplifier noise would not be humped. So it can only be amplifier noise exciting the moving system, therefore generating a signal according to the system transfer function (uncorrected) at the feedback coils.
As for yelling at the cutter head, with feedback applied, the feedback controlled moving system would resist external disturbances. So, what is actually happening there is that you are "modulating" the (large) portion of the moving system, which lies outside feedback control.

Quote:
It's quite acceptable, actually. The stability margin for a given system depends on the feedback to program ratio. The (green) DSS821 can be used with only 3 dB stability margin from feedback presence for hi fi acoustic music, but the 6 dB-margin feedback ratio is better for rock and Disco and -8, perhaps, for hardstep, and/or electronic ('unnatural') music.

I don't know about the JVC products - just that our Larry said the cutting head he was using then was a knock-off of the Ortofon.

Of course, people abuse systems to make records louder than other cutting engineers since that's how jobs were awarded - by trial. Bob Ludwig explained in one of his YouTube interviews how he lost the Led Zep II gig by cutting loud enough to cause Ahmet Ertegun's daughter's record player to skip, but he cut it that loud in an attempt to win the gig, not because it needed to be like that for Art's sake, but because people making the calls are at least temporarily impressed with loud records, so, normally, it would have won.

A veteran Hollywood engineer told me about his exploits He claims to have vari-sped a major celebrity musician's master tape a little to subtract from the program duration just enough to require just enough less land at the starting level in order to get the sides a little hotter, taking up the saved space - and they approved it without commenting about the pitch bump. This was a major crooner of serious Pop.
Theory dictates otherwise. But in any case, this is not about how loud you can make the apparent loudness of a record. It is about how stable and reliable you can make the feedback control system, while taking into consideration musical peaks and thermal overload, as well as bandwidth.

Quote:
Sorry, that's not correct. Despite appearances, the rocking bridge is just a different way to achieve the same cuts. The stylus doesn't know it's not being pushed diagonally from a torque tube linkage. However, for the geometry of the orthogonal rocking bridge to work correctly and for the groove modulation to have the best channel separation, the stylus protrusion from the bridge must be exactly 2.50 mm. To confirm this, the Ortofon stylus inspection microscope has a reticle with lines showing 0.1 mm intervals. One needs to use tweezers in order partially to lift the inner edge of the rubber diaphragm that covers the bridge hole area around the stylus aperture puncture, in order to view the top of the bridge in the microscope. Otherwise, the measurement is easy. It helps one be sure that the shank is correctly seated in the bridge hole, and a sight line on the cutting head helps indicate correct orientation of the major facets.
This is not what I am referring to.

Quote:
When correctly used, the rocking bridge stylus motion is not making an appreciably different groove geometry. There's no difficulty tracing and scanning Ortofon cuts or seeing very good signal response and channel isolation. As mentioned, the necessary cutting geometry of the right angle, made 45 degrees, is dependent on the exact protrusion of the synthetic ruby jewel from the bridge and the intrinsic (included) angle forming the vertex. There is a .1 mm tolerance +/- for best results. Is your tip rake at 88.2 degrees while making a 30 degree impression force angle to compensate for 5 degrees of lacquer spring back and 5 more degrees of stylus holder flexion so as to recoil to an effective 20 degree cutting v.a.? (l; Yes, Ortofon knows grooves, from the company's first MC cart of 1948 and their first lateral cutting head with feedback from 1949, cited in the Sean Davies paper. For a better understanding of how Ortofon helped to invent the modern gramophone system, visit: Ortofon true Mono cartridges range
Let us start with the "tip rake", or better worded, the cutting stylus rake angle. To keep to traditional machining terminology, you are talking about a rake angle of 1.8 degrees. This in itself should match the reproducing stylus rake angle, especially if elliptical or line contact. A typical Neumann system cutting rake angle was nominally 1 degree, but other less than that. So here we already have a difference of 1 degree between the two systems. But then there is the Westrex 3D, 0 degrees cutting stylus rake angle without a wedge to tilt the head, and 15 degrees or more with a wedge. A 15 degree error in rake is quite severe!
Vertical Modulation Angle errors should similarly be avoided. You can avoid one OR the other, but there is a fixed relationship between SRA and VMS for each cutter head and likewise between SRA and VTA for each reproducing cartridge.

Quote:
They didn't have to be designed for rocking bridge cuts since this isn't an issue.
See above, and also later on.

Quote:
No worries, I don't want to listen to test tones, even quietly. (;
I tend to deal with tones quite a lot, since accurate audio equipment cannot just be designed by ear. So I take this quite seriously. I often need to cut test records, and play them back.

Quote:
Speaking of test tones, here's the lateral 1 kHz square wave cut on the CBS STR 112 test record:
http://www.discolathe.com/Control_C/..._1kHz_sq_L.jpg

...and the vertical:
http://www.discolathe.com/Control_C/..._1kHz_sq_V.jpg
Yes, how is that different to what I was saying?

Quote:
...as the cover text explains, if you play a square wave cut back with a ceramic (piezoelectric / quartz) type pickup, due to being amplitude-responding, rather than velocity-..., the output signal will be a triangle wave. But, also, if you use a velocity-responding pickup to play back the square wave cut with the default RIAA and RF filtering, you'll (still) get a triangle wave, as from the phono pre of the NAD 7100:

http://www.discolathe.com/Control_C/NAD_triangle.jpg
This is unbelievably wrong! Any decent MM or MC cartridge, hooked up to a properly functioning preamplifier with the correct de-emphasis (the inverse of what was used in recording as pre-emphasis) is capable of reproducing exceptionally accurate square waves. What you are showing here is absolutely not what should be happening.

Quote:
If you probe the phono cart's output directly, bypassing any forced filtering, the 'scope shows a good approximation of the square wave, although it has some Myan pyramiding going on, not unlike the bedways of the Scully lathe:

http://www.discolathe.com/Control_C/Cart_2_Tek.jpg
This is also wrong, unless the square wave was recorded without any pre-emphasis. If it had the 3180/318 μs at least, you should be seeing a peaking leading edge on the cartridge output, to be properly displayed as a square wave only upon application of the 3180 μs and 318 μs time constants as de-emphasis.

Quote:
Originally Posted by cathode View Post
Actually, Uncle Norman (his real name is starts with D) installed a stock front panel and has been using it on loudspeakers for the past 30 years.
Otherwise modified, not.
Do not confuse external RIAA emphasis network with an otherwise standard power amplifier.
You are aware of the many rooms that employed McIntosh MI-200 amplfiers with Grampian and Westrex heads ?
Indeed, even the "patented circuit" mentioned in JVC's sales literature actually refers to the threshold patent with Nelson S. Pass as the inventor.

Quote:
Originally Posted by S_mask View Post

Speaking of Threshold DC amps, I love Nelson Pass's designs and just recently repacked a 24-device channel of one of his SuperSymmetry, no-fb, DC-to-100 kHz amps with hyper-matched NOS Hexfets. His loudspeaker amps are not plug and play disk cutting amps, to be sure, but they could be used for tack welding if pressed.
Yeah, and if you also purchase the wire feeder retrofit kit along with an Argon gas bottle and regulator, you can turn it into a MIG welder! With a bit of additional investment, Nelson Pass himself will send you a TIG conversion kit along with a hand-written and illustrated booklet on how to weld thin aluminum sheet using just the noise floor of a suitably biased amplifier for the ultimate seam fidelity....

Quote:
Originally Posted by S_mask View Post
To attenuate further confusion about the cutting geometry of the rocking bridge design used in the Ortofon and JVC and early Neumann stereo cutting heads, please refer to this corrected drawing from our Larry's compendium, Basic Disc [.....].}
Quote:
Originally Posted by S_mask View Post
Here's a quote about torque tube versus rocking bridge grooves and how cartridge behavior would differ with respect to crosstalk, from 1979, by JVC in their paper, 'Record and Record Player':
[....].
This is exactly what I'm talking about. Notice how the Neumann head scribes an arc vertically while the Ortofon moves linearly?
In lateral (both channels operating) modulation, do you see how the Neumman movement is linear (no vertical component), while in the Ortofon system there is a small vertical component? Figure 3d and 4d.
So, which Ortofon (or other) cartridge can produce linear vertical motion or lateral with a small vertical component?
A small vertical component will be registered as such, thereby inducing crosstalk, among other things. To avoid such side-effects, the cartridge must be designed to move exactly along the same plane in every direction, as the cutter head did. Each cartridge can only mimic one cutter head's motion.
One size doesn't fit all.
Old 2 weeks ago
  #13
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Originally Posted by magneticfidelity View Post
Not exactly. We do not usually refer to a 20 kHz sine wave as sibilance.
My point was that, though transitory, the harmonics of sibilance are high frequency. 20 kHz is high duty, since it's a sine.

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I wholeheartedly disagree. Not to mention the extreme scarcity of the "existing art", taking in into the realm of "unobtainable art". At least for those who are trying to just enter the field now. How would more techs help the situation?
Seems as if there are always systems coming up for sale. The hard part is getting them to work given their usual condition. So, it would be nice if there were more head and amp techs to help studios keep their vintage systems on the air since the performance that the existing, best gear delivers, when functioning properly and used well, is sufficient to portray any material favorably (in stereo). Furthermore, the practical considerations for the technical limitations also encourage aesthetic signal conditioning.

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Assuming the reference of O VU resulting in a peak lateral velocity of 7 cm/s (at 1 kHz), true peaks on natural music would actually be allowed to reach +20 dB over this, which is what is considered good engineering practice in most other audio systems...
But we won't see it on the slow VU meter. They're damped against very brief transients and have ballistics which tend to match the voice to our auditory perceptions. Most VU meters show only 3 dB above 0 - some 6.

A reference cutting velocity is used so that we can make sure we have the input sensitivity for the cutting amp correctly set. But we must also adjust the specific signaling power of the master to the amps, from the console, so we can cut it more quietly, if needed, and simply add a minus sign to the number of dB for the peaks in our cutting log to indicate the program intensity of a given master/ref.


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Interesting point. Is there a 3183xF cap?
My point here was that the time constant used in the RIAA/NAB standard is not based on a standard capacitor value, nor does it point to an integer frequency, so there's no good reason to make it that number of microseconds (3180) and not the one (3183) that more closely makes 50.00 Hz. We know they want the bass corner to be at 50 and the midrange to be at 500 cycles per second, since it's almost there, as it is, and it's an audio filter - not a capacitance analyzer, so Hz is where it's meaningful. {Time constant standardization for the various audio filters was employed because the specified curves required the use of RC filters, having resistors and capacitors, and capacitance is easily measured with microFarads, and they fill up with charge in a finite amount of time (whence, seconds).} But the time constant that was enshrined for each corner frequency was obtained by using a formula with a rather truncated constant in the numerator (even though the first number to the right of the decimal place is only a 1). The constant to which I refer is based on Pi, so, it, too, will be irrational (i.e., of never-ending exactitude), so some truncation is wanted for practicality's sake. But if they had used a few extra digits to the right of the decimal (instead of none), they'd have been able to enshrine time constants that name the integer frequency of the first two corners to the curve much more closely (e.g., 50.00... Hz = 3183 µs), and they'd have made 2,122 Hz the frequency-namesake of 75 µs (or settled on 79 µs for '2 kHz').


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We could change it to something seemingly practical, such as 3300 μs, 330 μs, etc... This works out to a very memorable 48.22877063 Hz, but at least the capacitors are easily available.
However, in the real world, there are things like stray capacitance, source impedance component tolerances, and interaction from bundling together more than one time constant in a complex network...
Real capacitors and resistors get to have error (as their tolerances allow), but standards may be arbitrarily accurate. If we improve on the truncated constant in the numerator of the formula for Tau, we find that 500 Hz is much closer to 318.3 µs than it is to 318.0 µs. If you don't want decimal places in time constants, we can call it 318 k ns.


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Exactly. So, not much difference in the end at the feedback monitor. The question is how does it put that to disk?
I only saw your dumbie load tests and resistive load tests. So, comparing my actual cutter's response (in air) to that of Flo's and your dumbie loads, the Ortofon drive package's square wave performance is not improved on.



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Not really. Just recently I was testing a few decent cartridges with the FloKaSon test record (Absolute Polarity for Disk Records – Agnew Analog Blog) and some can easily follow the sweep to 50 kHz. Do you know of any cutter head that can do a continuous accurate sweep to 50 kHz without tricks?

I can give you a flat sweep up to 52 kHz if I may cut at 16+2/3 rpm for 33+1/3 playback. DSS731 is a CD-4 cutting head, so it's flat (+0 /- 1 dB) from 10 Hz to 26 kHz.

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Thermal overload is indeed pilot error. The "aircraft" in question could benefit from some further development though, to decrease the likelihood of error under conditions which are generally accepted as common in all other sound recording disciplines.
Safety measures are already in place, and we have the great body of long playing records that were successfully cut with the same technology in the 20th century which have reasonable cutting levels that we can safely match.


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But you do realize that of course in the absence of signal, what you are measuring is noise? Considering that it has a hump at main resonance, without feedback, this can only be due to the mechanical resonance of the moving system, since the feedback coil /error amplifier noise would not be humped. So it can only be amplifier noise exciting the moving system, therefore generating a signal according to the system transfer function (uncorrected) at the feedback coils.
Yes, the humps are the resonances, and I mentioned that I was looking deeply into the noise floor. I also explained that the hump on each channel completely disappears once feedback is applied. The system has a very low noise floor which allows quiet passages to be cut with a holographic 'filigree and lace of reverb tails', as Doug Sax put it.

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As for yelling at the cutter head, with feedback applied, the feedback controlled moving system would resist external disturbances. So, what is actually happening there is that you are "modulating" the (large) portion of the moving system, which lies outside feedback control.
It demonstrates how easy it is to move the system at telephone frequencies, with or without feedback.

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Theory dictates otherwise. But in any case, this is not about how loud you can make the apparent loudness of a record. It is about how stable and reliable you can make the feedback control system, while taking into consideration musical peaks and thermal overload, as well as bandwidth.
Praxis supersedes theory. Even at these margins, the feedback stability of pro cutting heads is not what's been wrong with vinyl all these decades. If one wanted to help the industry, s/he might figure out how to improve the flow of vinyl across the stampers or how to spray nickel on the lacquer, instead of silver, so that it wouldn't need to be removed for 2-step stamper manufacturing.



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This is not what I am referring to.

Let us start with the "tip rake", or better worded, the cutting stylus rake angle. To keep to traditional machining terminology, you are talking about a rake angle of 1.8 degrees.
We're actually comparing the SRA to 90 degrees, so, 88.2 makes sense, here, since it's slightly acute and is used by the Ortofon technical engineers. Numbers higher than 90 degrees are used for SRA by pickup techs who aren't thinking of the cutting head-to-stylus 90 degrees but the back of the pickup stylus (seen from the front of the turntable)-to-the-tone-arm-pivot angle.


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This in itself should match the reproducing stylus rake angle, especially if elliptical or line contact...
...and it will, if the cartridge provides the customary '91 to 95' -degree pickup SRA, which is actually saying 89, down to 85, -degree cutting SRA. Also, there's slight variability among the cartridges of the same model. Ortofon's 88.2 degrees is, therefore, compatible with the range of tolerances of pickup SRA seen in the field, being situated close to the middle of this range of angles.

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...Vertical Modulation Angle errors should similarly be avoided. You can avoid one OR the other, but there is a fixed relationship between SRA and VMS for each cutter head and likewise between SRA and VTA for each reproducing cartridge.
SRA seems to matter more than VTA according to Micheal Fremer and the guys at Discwasher Laboratories:

http://www.analogplanet.com/images/512MFVTA_article.pdf


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I tend to deal with tones quite a lot, since accurate audio equipment cannot just be designed by ear. So I take this quite seriously. I often need to cut test records, and play them back.
I also shoot tones every day, but I never audition them. That's what oscilloscopes and spectrum analyzers are for.


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Yes, how is that different to what I was saying?
It shows the triangle (shaped) modulation I was talking about.

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This is unbelievably wrong! Any decent MM or MC cartridge, hooked up to a properly functioning preamplifier with the correct de-emphasis (the inverse of what was used in recording as pre-emphasis) is capable of reproducing exceptionally accurate square waves. What you are showing here is absolutely not what should be happening.
Yet I used a Stanton stereohedron stylus cartridge and then a Shure conical stylus cartridge (on the lathe tone arm) with the same triangular wave results from my NAD phono pre. Both are velocity-responding carts.. That NAD has exceptionally flat RIAA de-eqing, so the square wave cut I was playing from vinyl must have been cut with the 75 µs corner bypassed, though this was not mentioned...

[edit: Apparently, at least two RC networks were applied in the NAD that were not applied during cutting the square wave (as triangular modulation), as explained, here:

How to Build a Square Wave to Triangle Wave Converter Circuit

...as shown on the 'scope. ]

...In any event, the oscilloscope pictures show that if one uses a velocity-responding pickup (rather than amplitude-responding) and has a way to bypass the RIAA playback equalization (such as by scoping the cart directly), the square wave can be made on playback of the triangular-shaped groove modulation, albeit with 'effects'.

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...Indeed, even the "patented circuit" mentioned in JVC's sales literature actually refers to the threshold patent with Nelson S. Pass as the inventor

Yeah, and if you also purchase the wire feeder retrofit kit along with an Argon gas bottle and regulator, you can turn it into a MIG welder! With a bit of additional investment, Nelson Pass himself will send you a TIG conversion kit along with a hand-written and illustrated booklet on how to weld thin aluminum sheet using just the noise floor of a suitably biased amplifier for the ultimate seam fidelity....
I'll pass. <duck>

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This is exactly what I'm talking about. Notice how the Neumann head scribes an arc vertically while the Ortofon moves linearly?
In lateral (both channels operating) modulation, do you see how the Neumman movement is linear (no vertical component), while in the Ortofon system there is a small vertical component? Figure 3d and 4d.
The Neumann stylus silhouettes from that set of cutting head modulation pattern drawings are distorted. The stylus dimensions are not consistent between the depictions of the starting and ending positions to a degree that must be beyond what would be caused by perspective. The width should not be seen to change. For lateral, the height should not change, even though there's a tilt at the excursions.

Nygaard states that the torque tube system of stylus motion also results in an arc:
http://www.discolathe.com/Control_C/Torque_Tube_arc.jpg

...yet states that the Ortfon stylus's lateral motion is essentially rectilinear:
http://www.discolathe.com/Control_C/...bridge_arc.jpg


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So, which Ortofon (or other) cartridge can produce linear vertical motion or lateral with a small vertical component?
All cartridges I've used have had no noticeable problem with either cutting head design used on disk, the difference in cross talk between systems is less than -30 dB (according to the JVC paper), and the stylus movements appear to be very similar schematically. As for the vertical difference, a ball can roll down a flume or slide with ease.

Although not correctly shown in the distorted images of the Neumann torque tube stylus modulation in Basic Disc Mastering, in order to achieve lateral and diagonal modulation, the moving elements (drive coils and links) apparently twist the torque tube (which is why it's called a 'torque tube'), as shown on this large-scale model:

http://www.discolathe.com/EM_enginee...Tube_Drive.jpg


In his stereo recording, reproducing, and broadcasting patent application of 1931, Blumlein suggests use of the rocking bridge model for the ideal groove pickup design after stating that the torque tube stylus holder (i.e., 'short, circular reed') and rocking bridge stylus holder (i.e., 'T member') will both cause their stylus's tip to produce the required 45-degree per channel, single-groove, stereo modulation necessary.

http://www.discolathe.com/Control_C/...A_excerpts.jpg

The torque tube model was probably appealing to Neumann's investors because of the market's familiarity with the Westrex stereo cutting head, leading Neumann to abandon their rocking bridge cutter. However, the torque tube stylus holder is somewhat inefficient because of the vertical arc that causes each impression and return to travel faster than necessary for the realized displacement, whereas the rocking bridge design's linear vertical modulations produce a groove geometry that's truer to the Blumlein patent's strictly vertical prescription, with no wasted 'mileage' through lacquer.

Nevertheless, at least some of the arc of the torque tube's vertical impressions is partially 'hidden' from the realized groove modulation because the workpiece was moving under the stylus, normalizing the vagaries of the arced impressions and retreats.

Added to this is the rarity of deliberately out-of-polarity stereo signals in music. Most elements of a mix are either in phase and shared by both channels, resulting in purely lateral modulation, or are panned elements that cause a diagonal component to be added to the lateral. I only see 180-degree Lissajous patterns when cutting 200 Hz out-of-phase (in order to test the lathe automation's L/V expansions (and depth increases)). Whereas, elliptically-equalized music program rarely shows more than 45 degrees of phase difference on the 'scope - like a right-tilted vesica piscis (or American football shape).

Last edited by S_mask; 1 week ago at 02:45 AM.. Reason: corroborative links added, with comment
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