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please help identify unwanted distortion, transistor amp
Old 1 week ago
  #31
Gear Maniac
 

Quote:
Originally Posted by forestcreature View Post
This distortion is new in the signal. Cool, thanks: this amp is getting well documented
Interesting. I did re-listen to your files, and I can clearly hear exactly what you're talking about in the "magnified" file . . . but it doesn't sound out-of-context in the full-chord recording for what I'd expect from such a simple circuit.

But I understand if it's an issue of a new artifact cropping up that wasn't audible before. From your original post I don't get the impression that you've really changed anything in the power-amp section, except perhaps the speaker-kill switch . . . and poor connections in the speaker circuit can very definitely cause a dramatic increase in second-harmonic distortion. This power-amp design is VERY susceptible to component tolerances . . . so even production differences between parts that are nominally "good" will produce different behavior. D61 and D62 are a great example of this . . . i.e. a Fairchild part from fifteen years ago versus a Diodes, Inc. part manufactured recently can be different enough to where the value of R67 might have to be changed to get the same bias point across the output transistors. Same goes for the outputs and drivers themselves. I'd imagine that different production samples of this amp would have pretty wide tolerances in their measureable distortion signature, and in many cases it'd be clearly audible.

But it's not forgone that the issue is in the power-amp. The difference you notice between the headphone and speaker may be from the impedance loading (which would point to the power-amp section), or it may simply be a difference in audibility . . . maybe try with/without the speaker load as you listen through headphones (i.e. putting the amp in another room so you can clearly hear through the 'phones only). Also, if any of your mods have introduced any DC on the power-amp input (base of Q61) then this will shift the operating point of the whole circuit, and change its distortion behavior.

But if you get to tearing your hair out over this . . . I'd say the possibility remains that you're expecting more consistency and a cleaner tone than is realistic from such a simple, cheap circuit . . . at least based on my impressions from the sound files.
Old 1 week ago
  #32
Gear Head
 

Thread Starter
Yep, that's reasonable. It's all because I wanted to try out the pickups that I'd hand wound (in the literal sense), and I was surprised that this old practice amp sounded better than I thought it would. And then all this palaver :D
Old 1 week ago
  #33
Quote:
Originally Posted by kirkus View Post
It would be nice if "commercially supplied" was synonymous with a lack of "egregious errors" . . . but I assure you that that's not the case, and certainly not here. The PNP transistors in the schematic tINY provided are indeed reversed emitter-to-collector.

But I agree that there's no clear audible indication in the OP's sound files that point to this amplifier being "broken". The circuit design wins points on both on the minimal number of parts required, as well as the cost of those parts it uses . . . but certainly not on having low distortion! Output stage crossover distortion is a given, but the input stage is teeming with distortion mechanisms as well. The voltage-amp stage uses simple resistive loading, and there's no buffering from the nonlinear loading of the quasi output stage.

If this amp doesn't give you a "clean" enough sound . . . then the only solution is to use a different amp.
Well, I was referring to the PDF file uploaded by the OP, but comparing it to Tiny's it does appear to be the same.

Yes, I didn't hear anything in the sound files significantly different from the sound quality of many really cheap SS amps I've herd, which is why I asked the OP about levels, as crossover distortion becomes greater as the level of the signal decreases opposite of typical harmonic distortion. So if he just noticed it while playing the amp low but recorded the files at a higher level the distortion would be less obvious in the files. I'm wondering if the OP actually got what I was saying when I mentioned that, as I'm suspecting that English is probably his second language, given that this is a German amp, not likely to be commonly found outside that country.
Old 1 week ago
  #34
Gear Maniac
Quote:
Originally Posted by forestcreature View Post
I have read that decoupling caps should be located as close to their voltage regulators. The capacitor pads are some 5cm of trace away from 10cm wire breakouts to the voltage regulators, which are screwed to the chassis. I uprated the caps from 2200uF to 4700uF, and in terms of life parameters (V, temp.), so they didn't fit on the board. These are also on 10cm breakout wires (of some non-thin gauge). Can that have anything to do with it?
It could. Regulators are sensitive to having the main caps at their input connected via long traces, which basically creates a resonant LC circuit, which is why if the distance is more than a couple of inches, a small decoupling film cap at the regulator input and right next to it is required. The caps are there (C3/C4, 100n, hopefully right next to the regs) but they don't have the usual value (depends on the manufacturer but the two most common options I've seen are 330n for both or 330n for the positive reg and 2.2u for the negative one) and you have changed both the capacitance and layout (if I understood you correctly) of the main filtering, so I wouldn't be surprised if one or both regulators had become unstable. Quick test: do they get noticeable hot to the touch after the amp has been switched on for a few minutes? Another quick test: put back the old caps and see if the distortion disappears.
Old 1 week ago
  #35
Gear Head
 

Thread Starter
Ooh yes worth a shot!

John: you have correctly guessed that I am an incomplete AI re-implementation of certain parts of John Denver. As such, I am still learning how to English properly, but I did get what you were saying about the IM distortion amplitude vs. signal. I just figured there was enough agreement from the verbal description alone that recording more audio would be moot and a waste of everyone's time
Old 1 week ago
  #36
Quote:
Originally Posted by forestcreature View Post
Ooh yes worth a shot!

John: you have correctly guessed that I am an incomplete AI re-implementation of certain parts of John Denver. As such, I am still learning how to English properly, but I did get what you were saying about the IM distortion amplitude vs. signal. I just figured there was enough agreement from the verbal description alone that recording more audio would be moot and a waste of everyone's time
John Denver? I would strongly advise you not pilot your own airplane, especially over mountains.....
Old 1 week ago
  #37
Gear Head
 

Thread Starter
Haha! That advice is strangely appropriate after this whole amp situation.
Old 1 week ago
  #38
Gear Head
 

Thread Starter
Epitaph: while poking around inside the amp it developed an odour and certain strong opinions. So I guess it's time to build something better!
Old 1 week ago
  #39
Gear Maniac
 

Quote:
Originally Posted by John Eppstein View Post
. . . as crossover distortion becomes greater as the level of the signal decreases opposite of typical harmonic distortion.
You are of course factually correct here . . . but if I may I'd like to point out a couple of conceptual errors that I frequently see extrapolated from this supposition.

To be precise . . . with crossover distortion, it's the THD ratio that increases as the signal level decreases, but the THD level stays constant. That is, the amplitude of the distortion components themselves tend to appear as soon as there is any significant signal at all, but don't follow the signal's dynamic envelope. It's still mainly a form of harmonic distortion . . . though amps with crossover distortion issues tend to have intermodulation issues as well, and the standard IM tests reveal a certain degree of harmonic distortion components.

But when we measure "THD" . . . the overwhelming majority of the time we're actually measuring THD+N, or the total of harmonic distortion AND noise. This means that if you look at a graph of an amplifier's THD+N ratio versus signal level (a common test procedure), the amp's noise floor will ALSO cause cause "THD" to appear to increase as the signal level is reduced, even if there is virtually no distortion at all. Put another way . . . the standard way of measuring the relationship between signal level and distortion performance is unable to differentiate crossover distortion from the equipment's noise floor.

As far as audibility goes . . . when I have investigated circuits on the test bench that have virtually no distortion except for crossover (i.e. some preamp-level CMOS- and FET-based signal switching), I can clearly hear it with a test tone at a VERY low level, less than 0.1%. I think it sounds a lot like a "more precise" version of a mechanical rattle like you'd hear from a loose speaker voice-coil winding . . . but similar in the sense that the basic presence of a signal causes it to get going, and increasing the signal level just tends to mask it more. It's definitely one of those "once you hear it, you can't un-hear it" nagging little sounds . . . and I can't imagine it ever being desirable from a tone standpoint except for perhaps the most specialized of situations.

All of this applies to typical solid-state circuits, NOT to the crossover distortion found in a push-pull tube power amp. In the latter, the distortion mechanism is completely different, occurring in the output transformer rather than as a result of the tubes' own transfer function. Hence, it's spectral characteristics those related to the transformer's hysteresis distortion, and occur more dramatically at higher signal output voltages and lighter impedance loadings . . . the opposite of a direct-coupled push-pull transistor circuit.

Quote:
Originally Posted by forestcreature View Post
Epitaph: while poking around inside the amp it developed an odour and certain strong opinions. So I guess it's time to build something better!
This, sir, is a capital idea.
Old 1 week ago
  #40
Quote:
Originally Posted by kirkus View Post
You are of course factually correct here . . . but if I may I'd like to point out a couple of conceptual errors that I frequently see extrapolated from this supposition.

To be precise . . . with crossover distortion, it's the THD ratio that increases as the signal level decreases, but the THD level stays constant. That is, the amplitude of the distortion components themselves tend to appear as soon as there is any significant signal at all, but don't follow the signal's dynamic envelope. It's still mainly a form of harmonic distortion . . . though amps with crossover distortion issues tend to have intermodulation issues as well, and the standard IM tests reveal a certain degree of harmonic distortion components.

But when we measure "THD" . . . the overwhelming majority of the time we're actually measuring THD+N, or the total of harmonic distortion AND noise. This means that if you look at a graph of an amplifier's THD+N ratio versus signal level (a common test procedure), the amp's noise floor will ALSO cause cause "THD" to appear to increase as the signal level is reduced, even if there is virtually no distortion at all. Put another way . . . the standard way of measuring the relationship between signal level and distortion performance is unable to differentiate crossover distortion from the equipment's noise floor.

As far as audibility goes . . . when I have investigated circuits on the test bench that have virtually no distortion except for crossover (i.e. some preamp-level CMOS- and FET-based signal switching), I can clearly hear it with a test tone at a VERY low level, less than 0.1%. I think it sounds a lot like a "more precise" version of a mechanical rattle like you'd hear from a loose speaker voice-coil winding . . . but similar in the sense that the basic presence of a signal causes it to get going, and increasing the signal level just tends to mask it more. It's definitely one of those "once you hear it, you can't un-hear it" nagging little sounds . . . and I can't imagine it ever being desirable from a tone standpoint except for perhaps the most specialized of situations.

All of this applies to typical solid-state circuits, NOT to the crossover distortion found in a push-pull tube power amp. In the latter, the distortion mechanism is completely different, occurring in the output transformer rather than as a result of the tubes' own transfer function. Hence, it's spectral characteristics those related to the transformer's hysteresis distortion, and occur more dramatically at higher signal output voltages and lighter impedance loadings . . . the opposite of a direct-coupled push-pull transistor circuit.

This, sir, is a capital idea.
It's not a form of harmonic distortion because the distortion products are not harmonically related to the signal. It's a form of IM, like the output of a ring modulator. I coined the term "Nonharmonic distortion" to describe it but it hasn't really caught on. And yes, it's audible at very, very low levels. At higher (signal) levels it adds a hard, grainy quality to the signal that most people don't immediately recognize as "distortion", they just think the amp sounds bad.

Yes, it will register on a THD meter (any frequency content that doesn't belong will register) but that doesn't mean it's "HD". That's why they call the measurement "THD+N" - in this case the IM adds to the "N" component. It's really a measurement that doesn't tell you much about what's actually going on, anyway, it's a blunt implement mostly useful for sales spec sheets.
Old 1 week ago
  #41
Quote:
Originally Posted by John Eppstein View Post
It's not a form of harmonic distortion because the distortion products are not harmonically related to the signal. It's a form of IM, like the output of a ring modulator. I coined the term "Nonharmonic distortion" to describe it but it hasn't really caught on. And yes, it's audible at very, very low levels. At higher (signal) levels it adds a hard, grainy quality to the signal that most people don't immediately recognize as "distortion", they just think the amp sounds bad.

Yes, it will register on a THD meter (any frequency content that doesn't belong will register) but that doesn't mean it's "HD". That's why they call the measurement "THD+N" - in this case the IM adds to the "N" component. It's really a measurement that doesn't tell you much about what's actually going on, anyway, it's a blunt implement mostly useful for sales spec sheets.
What is Crossover Distortion?


Actually, XOD is a type of harmonic distortion.



-tINY

Old 1 week ago
  #42
Quote:
Originally Posted by tINY View Post
What is Crossover Distortion?


Actually, XOD is a type of harmonic distortion.



-tINY

If you read that article you'll see that it's about crossover distortion in TUBE amps. As was noted earlier (not by me) that really isn't the same thing as crossover distortion in a solid state amp, although both are referred to by the same name - because they're somewhat similar - they're not the same thing. Now, in a class B tube amp* it's pretty much the same thing, because both tubes are off at crossover, but not in a Class AB tube amp.

I guess you haven't done much work on SS power amps from the early to mid '60s, or you'd be aware of the difference.
In such amps the distortion products are not harmonically related to the signal, they're determined by the time constant of the notch, which does not change with signal frequency.


* - which you don't usually run into in audio. The exception, so I'm told by a factory tech, is some of the old McIntosh tube amps which allegedly were biased Class B but overcame the distortion by some sort of proprietary winding trick in the output transformer - this was told me by a factory tech at one of the Mac clinics they used to hold back in the old days. At any rate, having a transformer in there changes the nature of the distortion significantly.
Old 1 week ago
  #43

I can see where there is some upper-harmonic IM that may come from the slew-rate of the signal. But, I don't see how it's fundamentally different between transformer-coupled homogeneous devices and direct-coupled complementary devices...

In the OP's case, it's a direct-coupled homogeneous pair. So, all bets are off as to the actual effect of changing the bias.

Care to school me on the en-harmonic distortion that's generated from the direct coupled or complementary pair?



-tINY

Old 1 week ago
  #44
Gear Maniac
 

Quote:
Originally Posted by John Eppstein View Post
It's not a form of harmonic distortion because the distortion products are not harmonically related to the signal. It's a form of IM, like the output of a ring modulator. I coined the term "Nonharmonic distortion" to describe it but it hasn't really caught on.
No. A ring modulator produces inharmonic distortion products as a result of the presence of the carrier . . . that is, the time relationship between the baseband signal and the distortion glitches from the diodes is uncorrelated as a result of being modulated by a second signal. The inharmonic relationship between the baseband signal and its distortion is exactly defined by a corresponding inharmonic relationship between the baseband signal and the carrier.

Crossover distortion on the other hand can be purely defined as a deviation from linearity of the system's transfer function, that occurs at the zero-crossing point of a given waveform. Given that the periodicity is wholly determined by the waveform's frequency content, the resulting distortion MUST be harmonically correlated. It's easily verified on the test bench with an FFT analysis of the distortion residual.

No offense, but I don't consider this to be a matter of argument or opinion . . . the mathematical basis for these conclusions has been extremely well-vetted for more than 150 years.

Quote:
Originally Posted by John Eppstein View Post
Yes, it will register on a THD meter (any frequency content that doesn't belong will register) but that doesn't mean it's "HD". That's why they call the measurement "THD+N" - in this case the IM adds to the "N" component. It's really a measurement that doesn't tell you much about what's actually going on, anyway, it's a blunt implement mostly useful for sales spec sheets.
The thing that makes for a THD+N measurement isn't the meter, it's the entire test, including the stimulus . . . that is, the results are a measurement of total harmonic distortion plus noise, as a result of applying a sinusoidal stimulus and measuring the output of the DUT with the stimulus filtered out. The standard IM distortion tests are likewise designed to measure the artifacts of intermodulation between the two stimulus signals applied.

Just because these terms are abused in marketing material does NOT mean that the testing methodology is "a blunt implement" . . . rather, it's both very precise and extremely useful for understanding what's going on in an amplifier circuit. In fact, the most reliable way of detecting the presence of crossover distortion is with the traditional THD+N test setup, and visually comparing phase relationship between artifacts in the distortion residual to the full, unfiltered output signal.

Quote:
Originally Posted by John Eppstein View Post
I guess you haven't done much work on SS power amps from the early to mid '60s, or you'd be aware of the difference.
In such amps the distortion products are not harmonically related to the signal, they're determined by the time constant of the notch, which does not change with signal frequency.
The notch has no "time constant" in and of itself, as its spectral content is well below the semiconductors' transition frequency. Its dimension on the horizontal axis of an oscilloscope is merely a result of the signal slewing across the discontinuity in the circuit's transfer function. It can also be easily and precisely represented by a graph of gain versus input voltage, such that time isn't even one of the factors. Doing so gives great insight into the foibles of many early semiconductor output stages, including the "quasi-complementary" design in the OP's amp.

Quote:
Originally Posted by John Eppstein View Post
If you read that article you'll see that it's about crossover distortion in TUBE amps. As was noted earlier (not by me) that really isn't the same thing as crossover distortion in a solid state amp, although both are referred to by the same name - because they're somewhat similar - they're not the same thing. Now, in a class B tube amp* it's pretty much the same thing, because both tubes are off at crossover, but not in a Class AB tube amp.
The mechanisms may be different, but it's STILL a deviation from linearity of the system's transfer function, that occurs at the zero-crossing point.

In a push-pull tube amp, the change of transconductance of the tubes themselves in the crossover region is a negligible contributor to nonlinearity. Rather, crossover distortion is the result of the supply current switching between each half of the output transformer's primary, combined with the increase in plate resistance from the tube that's entering cutoff. Imperfect coupling between the two halves of the primary cause the transformer's core to momentarily snap from being magnetized by one (half-)winding to the other.

In this situation we do indeed have some time-constants present, as defined by the leakage reactances of the transformer. But if there's no sustained oscillation, then there's no additional signal to modulate the baseband signal and create inharmonic distortion products - rather, these reactances are functioning merely to "apply EQ" to affect the relative levels of the harmonic distortion resulting from the amplifier's non-linear transfer function. And if we do end up with bursts of oscillation at every zero-crossing . . . then the phenomenon is something entirely different from crossover distortion.

Quote:
Originally Posted by John Eppstein View Post
The exception, so I'm told by a factory tech, is some of the old McIntosh tube amps which allegedly were biased Class B but overcame the distortion by some sort of proprietary winding trick in the output transformer
The proprietary part of a McIntosh amplifier is the "unity coupled" circuit, which all grew from the desire to increase the output transformer's performance by reducing its turns ratio. To achieve this, they split the primary winding in two parts, placing half in the cathode circuit, and half in the plate. This also had the side-benefits of being able to conveniently linearize the output tubes by modulating the screen bias, and applying local feedback to the cathodes. They manufactured their output transformers in-house, and used bifilar/trifilar/quadfilar winding techniques to achieve consistently high Q factors.

The main detractions of this design are that the output stage has extremely low voltage gain, and it subjects the transformer to some very high voltages between adjacent windings. On the larger amps, they also operated the output tubes in AB2, requiring DC-coupled cathode-follower to drive them. The result was a complex amplifier with lots of driver stages, and occasional problems with insulation breakdown in the output transformers . . . but overall they've been able to mitigate these drawbacks and produce some excellent products. The original winding machine that they built is still used to make their output transformers and autoformers in-house.

Quote:
Originally Posted by John Eppstein View Post
And yes, it's audible at very, very low levels. At higher (signal) levels it adds a hard, grainy quality to the signal that most people don't immediately recognize as "distortion", they just think the amp sounds bad.
I'm in absolute agreement with this description of the sound . . . and while I think of it as "distortion", I can see that in the context of instrument amplifiers this terminology can be ambiguous . . . and you're much better versed than I am in the matter of how guitarists describe their tone. I'd definitely think of it as being in the "distortion you don't want" category.
Old 1 week ago
  #45
Quote:
Originally Posted by kirkus View Post
Crossover distortion on the other hand can be purely defined as a deviation from linearity of the system's transfer function, that occurs at the zero-crossing point of a given waveform. Given that the periodicity is wholly determined by the waveform's frequency content, the resulting distortion MUST be harmonically correlated. It's easily verified on the test bench with an FFT analysis of the distortion residual.
In a solid state amp crossover distortion takes the form of a period in the waveform during which the output devices are not conducting, unlike a tube amp where hysteresis in the output transformer keeps conduction continuing. This can be plainly observed with an oscilloscope. This makes the nature of the distortion significantly different between the two types of amplifier. In the solid state amp since conduction is not occurring during a period defined by the switching constant of the circuit it is NOT harmonically related to signal, whereas in the tube amp partial conduction is occurring which supplies your harmonic correlation.

Quote:
Just because these terms are abused in marketing material does NOT mean that the testing methodology is "a blunt implement" . . . rather, it's both very precise and extremely useful for understanding what's going on in an amplifier circuit. In fact, the most reliable way of detecting the presence of crossover distortion is with the traditional THD+N test setup, and visually comparing phase relationship between artifacts in the distortion residual to the full, unfiltered output signal.
A meaningful measurement of harmonic distortion supplies the percentages of each harmonic. It's possible to have two amplifiers rated at e.g. 5% THD that sound markedly different depending of the ration of specific harmonics to each other. Therefore, for audio purposes, a simple THD+N figure is, indeed, a "blunt instrument" since it tells you little about the actual sonic properties of the amp. That's why tube amps with relatively large amounts of distortion (by modern standards) are often judged to be as clean (and sometimes more "musical" for whatever that's worth) than solid state amps rated at much lower distortion. The difference is the distortion spectrum. However that's a bit complicated and technical for the typical member of the public.

Quote:

The notch has no "time constant" in and of itself, as its spectral content is well below the semiconductors' transition frequency. Its dimension on the horizontal axis of an oscilloscope is merely a result of the signal slewing across the discontinuity in the circuit's transfer function. It can also be easily and precisely represented by a graph of gain versus input voltage, such that time isn't even one of the factors. Doing so gives great insight into the foibles of many early semiconductor output stages, including the "quasi-complementary" design in the OP's amp.
If you observe the waveform of a solid state amp with crossover distortion on a scope, the "off" period between the + and - portions of the waveform has exactly the same time period regardless of frequency or amplitude of the signal. If that isn't a "time constant" then what is? I used to run into this all the time working on early SS Hi-fi amps back in the early '70s.

Quote:
The mechanisms may be different, but it's STILL a deviation from linearity of the system's transfer function, that occurs at the zero-crossing point.
Yes, but the type of deviation is somewhat different.

Quote:
I'm in absolute agreement with this description of the sound . . . and while I think of it as "distortion", I can see that in the context of instrument amplifiers this terminology can be ambiguous . . . and you're much better versed than I am in the matter of how guitarists describe their tone. I'd definitely think of it as being in the "distortion you don't want" category.
Yes, quite!
Old 1 week ago
  #46
Quote:
Originally Posted by John Eppstein View Post

If you observe the waveform of a solid state amp with crossover distortion on a scope, the "off" period between the + and - portions of the waveform has exactly the same time period regardless of frequency or amplitude of the signal. If that isn't a "time constant" then what is? I used to run into this all the time working on early SS Hi-fi amps back in the early '70s.

Wrong. Crossover distortion is a gating function where the off-time is determined by the slew-rate near quiescent voltage and the period is determined by the fundamental frequency of the signal.

So, it generates only multiples of the test tone and the amount of each overtone varies by the amplitude of the signal applied.

It's Harmonic Distortion.

However, I imagine that significant XOD will increase IMD - but you'd have to apply two signals to the amp to see this. Our test toolbox is pretty limited when it comes to broadband systems.




-tINY

Old 1 week ago
  #47
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enorbet2's Avatar
As Sonny Boy (The Goat) Williamson once recorded in regards to the name of a song

"It's a little village muthaf***er! Look, you name it what you wanna. Name it your mammy if you wanna... Just name it when I get through with it!"

Part of it is admittedly because I find SS amps as boring as watching paint dry, but I frankly don't give a ratzass how you name the quality of crossover distortion as there's only two important issues. 1) Is that what OP hears? and 2) Can he get rid of it w/o scrapping the amp since getting rid of it is likely essential since crossover distortion is seriously obnoxious, less obnoxious on tube amps but crappy nonetheless.

I still think it is highly worthwhile to install a jack between the preamp and power amp for both comparison with known good for troubleshooting and if, as many of us suspect, it truly is in the power section just gut that bad boy out and use the preamp (likely where most of the character and color is anyway in a SS amp) into any power amp you choose. Problem solved.
Old 1 week ago
  #48
Quote:
Originally Posted by enorbet2 View Post
As Sonny Boy (The Goat) Williamson once recorded in regards to the name of a song

"It's a little village muthaf***er! Look, you name it what you wanna. Name it your mammy if you wanna... Just name it when I get through with it!"

Part of it is admittedly because I find SS amps as boring as watching paint dry, but I frankly don't give a ratzass how you name the quality of crossover distortion as there's only two important issues. 1) Is that what OP hears? and 2) Can he get rid of it w/o scrapping the amp since getting rid of it is likely essential since crossover distortion is seriously obnoxious, less obnoxious on tube amps but crappy nonetheless.

I still think it is highly worthwhile to install a jack between the preamp and power amp for both comparison with known good for troubleshooting and if, as many of us suspect, it truly is in the power section just gut that bad boy out and use the preamp (likely where most of the character and color is anyway in a SS amp) into any power amp you choose. Problem solved.
Well, he says it started emitting smells, so I think the problem is moot.
Old 1 week ago
  #49
Quote:
Originally Posted by tINY View Post

Wrong. Crossover distortion is a gating function where the off-time is determined by the slew-rate near quiescent voltage and the period is determined by the fundamental frequency of the signal.

So, it generates only multiples of the test tone and the amount of each overtone varies by the amplitude of the signal applied.

It's Harmonic Distortion.

However, I imagine that significant XOD will increase IMD - but you'd have to apply two signals to the amp to see this. Our test toolbox is pretty limited when it comes to broadband systems.




-tINY

I'm going to have to shelve this for now - I'm a bit distracted trying to keep informed of the latest news about the humongous wildfire that's about 5 miles or less from my house/studio. And thanks to a dickheaded accountant in the middle of my cash flow I currently have no insurance.

Not fun.
Old 1 week ago
  #50
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enorbet2's Avatar
Quote:
Originally Posted by John Eppstein View Post
Well, he says it started emitting smells, so I think the problem is moot.
Since that is often followed by "letting the smoke out" you are correct, Sir.
Old 1 week ago
  #51
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Mikhael's Avatar
 

Quote:
Originally Posted by John Eppstein View Post
I'm going to have to shelve this for now - I'm a bit distracted trying to keep informed of the latest news about the humongous wildfire that's about 5 miles or less from my house/studio. And thanks to a dickheaded accountant in the middle of my cash flow I currently have no insurance.

Not fun.
Good luck, John. I sincerely hope it misses you.
Old 1 week ago
  #52
Gear Maniac
 

Quote:
Originally Posted by John Eppstein View Post
And thanks to a dickheaded accountant in the middle of my cash flow I currently have no insurance.
I've been in this situation myself with a small business (a random car crashed into the front of the shop), and feel your pain. My sincerest best wishes.
Old 1 week ago
  #53
Quote:
Originally Posted by John Eppstein View Post
I'm going to have to shelve this for now - I'm a bit distracted trying to keep informed of the latest news about the humongous wildfire that's about 5 miles or less from my house/studio. And thanks to a dickheaded accountant in the middle of my cash flow I currently have no insurance.

Not fun.

Yikes. Gotta love Cali...



-tINY

Old 1 week ago
  #54
Quote:
Originally Posted by Mikhael View Post
Good luck, John. I sincerely hope it misses you.
Thanks! Things are looking up today, but that can change with the wind. At least the sky is mostly blueish today and the sun doesn't look like a burnt out ember.

The Fairfield PD just sent out a status update to inform me that nothing has changed since their earlier alert that nothing had changed - I guess that's good.
Old 1 week ago
  #55
Quote:
Originally Posted by kirkus View Post
I've been in this situation myself with a small business (a random car crashed into the front of the shop), and feel your pain. My sincerest best wishes.
Thanks!
Old 1 week ago
  #56
Quote:
Originally Posted by tINY View Post

Yikes. Gotta love Cali...



-tINY

Oh, yeah!
Old 1 week ago
  #57
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Mikhael's Avatar
 

Quote:
Originally Posted by John Eppstein View Post
Thanks! Things are looking up today, but that can change with the wind. At least the sky is mostly blueish today and the sun doesn't look like a burnt out ember.

The Fairfield PD just sent out a status update to inform me that nothing has changed since their earlier alert that nothing had changed - I guess that's good.
Yeah, I just know how quick Mother Nature can change her mind. My daughter lives in Houston...
Old 6 days ago
  #58
Lives for gear
 
enorbet2's Avatar
Since I consider all here a quantum closer than mere acquaintances, in fact Brothers In Arms, I wish us all Good Fortune in the vagaries of Life and Mother Nature. I certainly hope none are currently stuck in Peurto Rico.

One day many years ago I stepped out of Washington Music Center, stopped to light a smoke and looked up and saw the weirdest thing in the sky and, though diffuse, it seemed to be moving closer. Then I saw leaves swirling around once they got to a distance where I could make them out and soon learned a small tornado had occurred nearby. I was shocked one could even form there where it's a bit hilly. Mother Nature, she can be a crazy nasty ol' bat who changes her mind in a heartbeat..

The most constructive thing i can say is no matter where you live, if you don;'t already have one, put together an Emergency Kit. Here's one good example -- Red Cross DIY Emergency Kit ---
Old 5 days ago
  #59
Gear Head
 

Thread Starter
Good luck John!

Thank you enorbet---I took that suggestion on board but there was so much going on in the thread that I didn't get around to responding. I had planned to put in an effects loop anyway, which would have achieved the same aim. I also had a chance to play around with LED clipping. I agree, it is a pleasant sound!

Emergency kit *thumbs up*. Go on, say bug-out bag. You want to say it, and I want you to say it! I said it! Does anyone here know about Cresson Kearny?

Now my amp situation is reduced to a Marshall MS2 mini amp + the 8" Jensen. No expense spared, here!
Old 3 days ago
  #60
Well, it looks like the fires around here are pretty much over. I'm still OK, although the fires did get within maybe 3 or 4 miles.Thanks to everyone for the good thoughts!
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