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Schoeps cmc5 vs cmc6
Old 26th November 2013
  #31
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Quote:
Originally Posted by king2070lplaya View Post
It's at the very beginning of this thread that we're writing on.


Old 26th November 2013
  #32
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opsss i havent read the word "this" !!!
Old 12th February 2015
  #33
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I wish I'd seen this thread sooner. First of all the CMC 6-- amplifier is not "12 to 48 Volt phantom", for which no standard exists; it is for standard 12-Volt phantom powering OR standard 48-Volt phantom powering (as someone did post correctly).

Second, there have been two versions of the CMC 6--, which differ in some details of construction; the more recent version has better defenses built in against RFI. This version can be identified by looking into the XLR connector well--if you see a gold-colored plate at the far (inside) end of the well, it's the newer version. The changeover happened just a few years after the CMC 6-- was introduced, so the great majority of CMC 6-- amplifiers are of the latter type. For each of these versions there are other axes of variation, e.g. the "xt"/"+5 dB"/"lin." options.

The reason Schoeps suggests not mixing CMC 5-- with CMC 6-- in a stereo main microphone pair, if you use that recording approach, is simply that the low-cut filters are different: The CMC 5-- (default version) has a single-pole filter while the CMC 6-- (default version) has a two-pole filter at a somewhat lower frequency. That difference can throw off your stereo imaging if there is strong, very low-frequency content. Other than that, however, there's no problem; plenty of studios have both kinds of amplifier and use them together all the time.

The former chief engineer (actually his title was "Entwicklungsleiter") of Schoeps is Dipl.-Ing. Jörg Wuttke. The present head of engineering, who was recently promoted to something like general manager or managing director of the company, is Dr. Helmut Wittek. The names may be a bit similar and Mr. Wuttke is who brought Mr. Wittek into the company, but let's please not confuse them.

If you measure lower noise from the "+5 dB" version of a CMC amplifier, either you are measuring incorrectly or your preamp is broken. The "+5 dB" amplifier setting actually has slightly higher equivalent noise (around 1/2 dB relative to sound pressure levels). But the residual output noise voltage of either version is distinctly greater than the input noise voltage of any modern, professional microphone preamp, as with most studio condenser microphones (please note!). Thus the "+5 dB" version can help to overcome preamp noise only if you are recording very soft program material and/or are using remarkably insensitive preamp inputs (some users of Nagra III recorders used to connect T-powered microphones to the line inputs of their recorders, for example). Of course the "+5 dB" setting also reduces the maximum SPL by 5 dB, to around 125 dB SPL depending on the capsule type, so it's not something that should be chosen unless you're sure that you need it.

--This thread is the first I've ever heard anyone claim that the CMC 5-- is quieter than the CMC 6--. I question this, but will try to measure it for myself at least approximately (I have both types of amplifier, a pair of the MEC test heads referred to, and a DIN/IEC frequency weighting filter from Dolby Labs--unfortunately I lack the proper device for DIN quasi-peak weighting of the noise over time).

Best regards,
David Satz
Old 12th February 2015
  #34
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Quote:
Originally Posted by dseetoo View Post
…...I never heard back from Mr. Wuttek or Schoeps since that meeting…….

Who did he mean Wuttke or Wittek?
Old 2nd March 2015
  #35
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That was Mr. Wuttek, the gentleman who has been long retired.
Old 2nd March 2015
  #36
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Quote:
Originally Posted by dseetoo View Post
That was Mr. Wuttek, the gentleman who has been long retired.
There was never a Mr. Wuttek working at Schoeps, there is a Mr. Wittek though at Schoeps, but you meant Mr. Wuttke. I just found it funny you combined both Schoeps' staf members names to one new name.
Old 21st May 2015
  #37
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Hello again. A few messages up the thread, I promised to make a careful noise comparison of CMC 5 and CMC 6 amplifiers in response to a claim that the CMC 5 is audibly and measurably quieter.

All that I can say is that I didn't find that to be the case at all. On an unweighted basis my two CMC 6 amplifiers are in fact a few dB quieter than the two CMC 5 amplifiers that I measured, which I chose at random from the four that I own.

I believe that this difference is because my CMC 5 amplifiers are almost 40 years old by now, and in the years since then, the quality of the available parts has improved. So if I were to have these CMC 5 amplifiers rebuilt with new parts (especially the very high-value resistor and the FET), I think that their noise floor should essentially match that of my CMC 6 amplifiers.

--To make my measurements, I used a pair of Schoeps MEC "test heads," which each contain a capacitor equal in value to a capsule, built into a shielded enclosure with an input connector that allows either a shorting plug or a signal generator to be connected.

What also proved to be very important: isolation transformers (mine are by Jensen) between the signal generator and the inputs to the test heads. Initially I made a series of measurements without these transformers; those measurements seemed OK and there was no audible hum pickup, but the numbers that I got with the transformers in place differed from the initial set by several dB, and were also far more consistent as I then went on to measure and compare other Schoeps Colette-series amplifiers (e.g. an RCY Colette stereo extension tube connected to a VST 62 stereo amplifier).

So if someone thinks that he finds more noise in the CMC 6 than the CMC 5, I wonder whether he has perhaps been comparing a CMC 6 that is bridged for +5 dB gain vs. a CMC 5 that is not, or is failing to use isolation transformers at the inputs of the test heads. Only misleading results can be obtained without them.

--After I measured everything last night, I sent a note to the head of quality control at the Schoeps factory and was told that the noise performance of CMC 5 and CMC 6 amplifiers is essentially the same, i.e. with just a few tenths of a dB variation, such as normally occurs among the samples in any batch of either individual model.

--best regards
Old 21st May 2015
  #38
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Nice work DSatz
Old 21st May 2015
  #39
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yes, thank you very much DSatz!

In this context I remember a posting by Da-Hong Seetoo regarding the Mendelssohn Octet back in 2004 with Emerson String Quartet. Here is what he writes:

"The microphones used were Schoeps MK2H heads with modified bodies. The modification gave me a bit more than 10dBs of signal to noise ratio improvment over the original body and much wider frequency response, reaching down to 0.1Hz and up to couple of MHz."

And here is the thread:
https://www.gearslutz.com/board/remo...ml#post5855635

I am very surprised, that the Schoepses can be modified with such an improvement. Any thoughts?


All the best


bojan
Old 21st May 2015
  #40
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Quote:
Originally Posted by bojan_1 View Post
yes, thank you very much DSatz!

In this context I remember a posting by Da-Hong Seetoo regarding the Mendelssohn Octet back in 2004 with Emerson String Quartet. Here is what he writes:

"The microphones used were Schoeps MK2H heads with modified bodies. The modification gave me a bit more than 10dBs of signal to noise ratio improvment over the original body and much wider frequency response, reaching down to 0.1Hz and up to couple of MHz."

And here is the thread:
https://www.gearslutz.com/board/remo...ml#post5855635

I am very surprised, that the Schoepses can be modified with such an improvement. Any thoughts?


All the best


bojan
I don't know how the measurements were taken, but I highly doubt that the signal to noise ratio of entire microphone could be improved nearly as much. There is a built in HPF, so you can certainly extend low end if you remove it. AFAIK Schoeps can do that for you if you want.
I don't know why would anyone need a mic amplifier which works in MHz region, although I know situations where this could cause problems.
Old 21st May 2015
  #41
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Any thoughts about the two pole vs. single pole HPF? IME, I prefer single pole at a higher frequency. Any thoughts about why they switched to two pole at lower? How easy would it be to remove one of the poles?
Old 22nd May 2015
  #42
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Originally Posted by Piedpiper View Post
Any thoughts about the two pole vs. single pole HPF? IME, I prefer single pole at a higher frequency. Any thoughts about why they switched to two pole at lower? How easy would it be to remove one of the poles?
I don't know by heart how the HPF is implemented in the CMC preamps, but it shouldn't be difficult to change two pole filter to a single pole one.
The only reason for using a higher order filter at a lower frequency that I can think of is that the frequency response remains linear to a lower frequency while the subsonic noise still gets attenuated.
Old 22nd May 2015
  #43
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Figured, but the phase is effected more. I am often looking for a bit of ultra low roll off anyway and prefer a higher frequency softer angle.
Old 26th May 2015
  #44
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It's my understanding (please don't hold me to this since I've never had it done myself) that Schoeps can set the inflection point of a CMC amplifier's high-pass filter to almost any frequency that a customer wants. There's a standard option (called "lin") to set it at 0.5 Hz "for test and measurement purposes"; I'd be curious to know whether anyone ever actually requests that, though.

With pressure gradient (directional) capsules there will normally be some output at 20 Hz and below--but unless the microphones are very carefully suspended, much/most of that output will be due to solid-borne vibration and air currents rather than sound. Still, if there's actual sound energy at those frequencies, then (depending on your application) you might well want to preserve it along with the garbage. For that matter, the unwanted noise could psychologically enhance the sensation of the real sound energy (= vinyl effect). And for an audio purist who uses pressure transducers, or for someone who's doing acoustical measurement rather than sound recording, it's completely understandable to want 20 Hz audio response and below.

--Whether someone can achieve a 10 dB increase in "signal-to-noise" or not depends mainly, I think, on how they measure. The standard way to measure microphone signal-to-noise is to shunt the amplifier's input with a capacitance equal to that of the capsule, and to use 1 Pascal SPL (ca. 94 dB SPL) as the reference level--which is far below the overload point of any professional microphone. So the usual s/n measurement is simply an expression of the microphone's noise floor, not the total dynamic range.

I don't think most people use that specification very much; especially if you come from a hi-fi background where a $200 power amp could have a 100+ dB signal-to-noise spec (based on its 0.5% THD point), while the spec for a $2,000 microphone might be only 80 dB, and that tends to look just wrong. Plus, equivalent noise level specifications are generally available directly.

If you're going to make responsible noise measurements, you have to make responsible choices about bandwidth, frequency weighting, and integration (averaging) over time. Especially when a wide-band audio circuit is being compared with a deliberately band-limited circuit, those factors will all have a major influence on the results of the measurement. Even the top-tier manufacturers don't all handle these things in quite the same way, so published specs from responsible companies might differ by (say) 3 to 4 dB for microphones having the same noise performance. All in all, without a lot of details being known, one can't assume that noise (or signal-to-noise) specifications from different sources have been made on precisely the same basis, or on a basis that one would accept as meaningful and relevant.

The thing about condenser microphones is that the capsule's electrical impedance is a major noise source, which (because it's a capacitor) has a 1/f characteristic. In other words, it rises 6 dB/octave as you go down in frequency, and even a theoretically perfect amplifier can do nothing about this noise. At some point in the frequency range it "crosses over" with the noise of the first stage of the amplifier (the FET or tube), and then above that point the FET or tube noise takes over. (A third noise source is the very high-value resistor through which the capsule is polarized.) With small-diaphragm microphones the range of this crossover frequency tends to be a little higher than it is with large-diaphragm microphones, so a somewhat greater proportion of the noise floor is determined by the capsule's capacitance, leaving a bit less room for improvement in the amplifier.

All in all, I suppose I might find it credible if someone claimed to make an amplifier one or two or even three dB quieter than the stock Schoeps CMC amplifier, although I'd want to know exactly how that was measured. I might also find it credible if they extended the dynamic range upward (especially with specialized powering), and some people might count that as part of signal-to-noise while others would not (and officially, as I said, it doesn't count where microphones are concerned).

So yeah, 1 or 2 or even 3 dB at the bottom and 4 or 5 at the top, and several more dB due to differing measurement approaches and/or the phase of the moon--it could all add up to 10 dB with everybody still behaving in a perfectly honorable way. But whether that difference would ever be audible in any recording that I might make in the real world, I doubt very much.

--best regards
Old 26th May 2015
  #45
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Quote:
Originally Posted by DSatz View Post
It's my understanding (please don't hold me to this since I've never had it done myself) that Schoeps can set the inflection point of a CMC amplifier's high-pass filter to almost any frequency that a customer wants. There's a standard option (called "lin") to set it at 0.5 Hz "for test and measurement purposes"; I'd be curious to know whether anyone ever actually requests that, though.
I have a couple of pairs of 'lin' CMCs.
Old 26th May 2015
  #46
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Quote:
Originally Posted by 0VU View Post
I have a couple of pairs of 'lin' CMCs.

Can you hear differences?
Old 1 week ago
  #47
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Interesting thread which I’ve just discovered five years late to the party!

Quote:
Originally Posted by DSatz View Post
If you're going to make responsible noise measurements, you have to make responsible choices about bandwidth, frequency weighting, and integration (averaging) over time. Especially when a wide-band audio circuit is being compared with a deliberately band-limited circuit, those factors will all have a major influence on the results of the measurement. Even the top-tier manufacturers don't all handle these things in quite the same way, so published specs from responsible companies might differ by (say) 3 to 4 dB for microphones having the same noise performance. All in all, without a lot of details being known, one can't assume that noise (or signal-to-noise) specifications from different sources have been made on precisely the same basis, or on a basis that one would accept as meaningful and relevant.
This quote in particular is fascinating and I assume applies to preamp and converter measurements too?

Is there as much potential variation between two manufacturers publishing, say, A-weighted SNR figures?

(With the caveat that modern preamps are significantly quieter than most mics these days...)
Old 1 week ago
  #48
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Quote:
Originally Posted by Myles Eastwood View Post
Is there as much potential variation between two manufacturers publishing, say, A-weighted SNR figures?
Yes. For starters some manufacturers specify typical figures while some specify will not exceed values. This one of the reasons DPA mics spec noisier.

Second the bandwidth filter may vary (from Metzler)
Quote:
A measurement of random noise is not useful unless the measurement bandwidth is stated, due to the spectrally-spread nature of noise. It is not possible to accurately compare an actual noise measurement to a noise specification unless the noise meter uses the bandwidth (and possibly weighting filter) called out in the specification. For “white” noise (equal power per unit bandwidth), the measured power doubles (+3.01 dB) each time the measurement bandwidth is doubled.

Flexible noise-measurement instruments therefore normally include a selection of bandwidth-limiting filters. These may be available as actual bandpass filters, or as separately-selectable high-pass and low-pass filters. The most common bandwidth for noise measurements in professional audio, broadcasting, and consumer audio applications is 20 Hz–20 kHz, or the nearly-equivalent 22 Hz–22 kHz specified in CCIR 468. Communications applications are likely to specify a much narrower range consistent with the more limited bandwidth of communications-quality voice; 300 Hz–3.5 kHz is a frequent specification. Still other values of band-limiting filters may be offered for specific reasons. For example, some audio measurement instruments include a 400 Hz high-pass filter in order to provide much greater rejection of ac mains-related hum at 50 Hz or 60 Hz and the low-order harmonics of these frequencies. Some specifications refer to a “hum-to-hiss ratio,” where the “hum” is a full 20 Hz–20 kHz bandwidth measurement and the “hiss” is a 400 Hz–20 kHz measurement which rejects the hum components. Other values of low-pass filters which are often provided include 30 kHz and 80 kHz; these selections are included in audio analyzers principally for distortion measurements rather than noise measurements, and will be discussed later.
Third what resistance was used for the impedance?
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