Hi group,

I was tracking some drums a couple of days ago. I had a Schoeps MK21/CMC6U
on the snare, maybe 2 feet from it. On several of the loud strikes, the
mic actually mutes for a couple of milliseconds.

I was able to recreate the situation by just talking at the mic loudly
while very close to it. I could understand it distorting but the sound
actually drops out for about 1/10 second when I overdrive it which seems
like a pretty poor overload characteristic.

I'm using a preamp I built. It has a Jensen 1:3 transformer feeding a
AD275 op-amp. Even with no pad its nowhere near clipping. It looks like
the mic is putting out maybe -20dBV peaks, the preamp is set for 10dB gain
so its putting out -10 peaks. These preamps have good overload
characteristics and a regular dynamic mic doesn't do anything like this.

Phantom power is 48V through 6800 Ohm resistors to pin 2 and 3. With the
mic plugged in I measure 32.5 Volts at the mic after the dropping
resistors. That equates to 4.5ma of current which is exactly what Schoeps
specs. The CMC6 is supposed to operate on 12-48V.

I have 2 of these mics, both do exactly the same thing. I don't have a way
to measure the actual SPL but I'm surprised at what I'm seeing because the
general consensus is that these mics will take very high sound levels. I
guess I could buy the exorbitantly priced pad from Schoeps but that's a
*very* expensive capacitor!

Anyone else seen this? Bring on the drummer jokes :-)

--
Bill

Hi group,

I was tracking some drums a couple of days ago. I had a Schoeps MK21/CMC6U
on the snare, maybe 2 feet from it. On several of the loud strikes, the
mic actually mutes for a couple of milliseconds.

I was able to recreate the situation by just talking at the mic loudly
while very close to it. I could understand it distorting but the sound
actually drops out for about 1/10 second when I overdrive it which seems
like a pretty poor overload characteristic.

I'm using a preamp I built. It has a Jensen 1:3 transformer feeding a
AD275 op-amp. Even with no pad its nowhere near clipping. It looks like
the mic is putting out maybe -20dBV peaks, the preamp is set for 10dB gain
so its putting out -10 peaks. These preamps have good overload
characteristics and a regular dynamic mic doesn't do anything like this.

Phantom power is 48V through 6800 Ohm resistors to pin 2 and 3. With the
mic plugged in I measure 32.5 Volts at the mic after the dropping
resistors. That equates to 4.5ma of current which is exactly what Schoeps
specs. The CMC6 is supposed to operate on 12-48V.

I have 2 of these mics, both do exactly the same thing. I don't have a way
to measure the actual SPL but I'm surprised at what I'm seeing because the
general consensus is that these mics will take very high sound levels. I
guess I could buy the exorbitantly priced pad from Schoeps but that's a
*very* expensive capacitor!

Anyone else seen this? Bring on the drummer jokes :-)

--
Bill


They can take some pretty high SPL's but they have limits 132dB for theMK21 and
134 dBfor the Mk21h

You are smashing the diaphragm into the back plate, shorting out the microphone
and requiring the microphone to repolarize which is why it mutes.

Not designed for such use.
Richard H. Kuschel
"I canna change the law of physics."-----Scotty

It sounds like you're picking up subsonic blasts, from the snare or maybe even
from the drummer's arm waving through the air. Likewise from talking -- breath
blasts.

Try putting a foam pop filter on the Schoeps.

Peace,
Paul

Bill Thompson wrote:

I was tracking some drums a couple of days ago. I had a Schoeps MK21/CMC6U
on the snare, maybe 2 feet from it. On several of the loud strikes, the
mic actually mutes for a couple of milliseconds.

I was able to recreate the situation by just talking at the mic loudly
while very close to it. I could understand it distorting but the sound
actually drops out for about 1/10 second when I overdrive it which seems
like a pretty poor overload characteristic.

That should absolutely never occur. The overload level specified for the
CMC 621 is 132 dB SPL--and that is just the 0.5% THD point, not disastrous
clipping or wild misbehavior such as muting. I have never encountered
muting in any Schoeps CMC microphone, and have used them for all kinds of
live recording (including percussion ensembles) for nearly as long as the
"Colette" series has existed.

The microphones use class A circuitry, so their current consumption isn't
affected by the signal levels they are delivering. In addition, their
capsules are polarized from DC/DC converters which have a certain ramp up/
ramp down time to them. So the idea of losing capsule polarization at the
exact instant of a strong transient makes no sense at all. This has to be
something that's occurring farther "downstream."


I'm using a preamp I built. It has a Jensen 1:3 transformer feeding a
AD275 op-amp. Even with no pad its nowhere near clipping. It looks like
the mic is putting out maybe -20dBV peaks,

Again, these microphones can put out 0 dBu on peaks; you're nowhere near
overloading them.


Phantom power is 48V through 6800 Ohm resistors to pin 2 and 3. With the
mic plugged in I measure 32.5 Volts at the mic after the dropping
resistors. That equates to 4.5ma of current which is exactly what Schoeps
specs. The CMC6 is supposed to operate on 12-48V.

All that information is exactly correct.


I have 2 of these mics, both do exactly the same thing. I don't have a way
to measure the actual SPL but I'm surprised at what I'm seeing because the
general consensus is that these mics will take very high sound levels. I
guess I could buy the exorbitantly priced pad from Schoeps but that's a
*very* expensive capacitor!

The best test would be to use the much less expensive resistive in-line
type of pad--then you'd find out clearly whether the problem is in the
microphones or in some piece of equipment further down the signal path.
Try borrowing a Shure A15A attenuator. Or since you designed and built
your own mike preamp (good on you!), you can build a quick and dirty
balanced H pad with, say, 12 dB attenuation and repeat the experiment.

I don't know what is causing this problem but I strongly doubt that the
microphones are the cause of it, especially since two of them produce the
same result. Unless you are the world's champion hog caller and you're
using the microphone as a dental probe without a wind screen, you can't
overload a Schoeps CMC microphone by "just talking at the mic loudly."

Hmm, that reminds me to ask: What's the situation at low frequencies?
Even a Jensen transformer runs out of headroom much more rapidly at 30
Hz than it does at 60 or 100 Hz. The MK 21 capsule isn't terribly wind
sensitive, but it does pick up naturally-occurring sound with nearly flat
response down to the lowest audio frequencies.

On the other hand, if I recall correctly the symptom of input transformer
saturation isn't a total loss of signal, but more like a limiter being
hit way too hard with its attack time set way too fast. If you're getting
steady digital 0 or anything close to it, that must be happening somewhere
close to your A/D converters, no?

Please, please be sure to let us know what else you find out. And try
injecting tones into your mike preamps at -20 dBV at various frequencies
with the gains set exactly as you had them, just to make sure that they
behave as you expect, OK?

--best regards

Richard Kuschel wrote:

You are smashing the diaphragm into the back plate, shorting out the
microphone and requiring the microphone to repolarize which is why it
mutes.

?? A Colette capsule has a tensilized polyester (Mylar) membrane with the
gold layer on the _opposite_ side from the backplate. The membrane itself
is an insulator. So nothing shorts if you bottom out the capsule--and the
polarized membrane won't cling to the backplate, either as it can in
certain other microphones (necessitating a "reboot").

It's quite possible that some blast of air is causing this problem, but
that would cause the microphones to put out huge low-frequency audio
signals; they wouldn't mute. If only! Then, Schoeps could sell that
behavior as a feature (built-in protection for your P.A. system--or your
mix--from morons who blow into a microphone to see whether it's on).

--best regards

Bill Thompson wrote in message

I'm using a preamp I built.

These preamps have good overload
characteristics and a regular dynamic mic doesn't do anything like this.

Did you try it on another preamp yet? Dynamic mics don't have high
output and would not be expected to anything similar.

Mike

Bill Thompson wrote in message

I'm using a preamp I built.

These preamps have good overload
characteristics and a regular dynamic mic doesn't do anything like this.

Good lord! The output of a dynamic and the output of many condensers (the
Schoeps definitely included) are vastly different. I think you have you answer
now.

Garth~


"I think the fact that music can come up a wire is a miracle."
Ed Cherney

Richard Kuschel wrote:

You are smashing the diaphragm into the back plate, shorting out the
microphone and requiring the microphone to repolarize which is why it
mutes.

?? A Colette capsule has a tensilized polyester (Mylar) membrane with the
gold layer on the _opposite_ side from the backplate. The membrane itself
is an insulator. So nothing shorts if you bottom out the capsule--and the
polarized membrane won't cling to the backplate, either as it can in
certain other microphones (necessitating a "reboot").

It's quite possible that some blast of air is causing this problem, but
that would cause the microphones to put out huge low-frequency audio
signals; they wouldn't mute. If only! Then, Schoeps could sell that
behavior as a feature (built-in protection for your P.A. system--or your
mix--from morons who blow into a microphone to see whether it's on).

--best regards



You're right!

I tested a CMC6/41 yesterday by blowing into it.
I could not get it to mute. The speakers jumped about 3/4" though.

It's not the mic, must be the phantom or something else in the chain crapping
out.

I have had condensors mute due to excess humidity from singing /talking, but
that doesn't apply to snare drums.
Richard H. Kuschel
"I canna change the law of physics."-----Scotty

A few updates:

First, thanks all, particularly David for the thoughts and input. I've
checked the preamps over pretty carefully. They're very simple and it
would be hard for them to do anything much beyond simple clipping when
overdriven. Indeed I can apply a +20dBu signal to them and all they do is
make a nice square wave.

Maybe there's a future for me as a hog caller :-) What I'm doing to
overload the mic is to have my lips actually touching the mic with no
windscreen and talking loudly. That causes the mic to mute and then
recover. I hope I'm not hurting it but it seems like a mylar diaphragm is
tough enough to take a little of that. The mics sound as good as ever with
reasonable sound levels so I'm not too worried. By the way, my preamp has
a switchable passive 20dB pad ahead of the transformer and with that
switched in the mic acts exactly the same.

I have a pair of cheap Audio Technica 3031 mics which are pretty similar
to the Schoeps in form. I tried overdriving them the same way. They make
some nasty sounds when I do that but they don't mute and they put out a
few dB more level than the Schoeps before they misbehave.

I looked at the snare drum track I recorded carefully. Even when mic
muting isn't occurring I do notice clipping on many peaks. The converter
isn't overloading. The highest peak is -7.1dB below full scale. I'm
recording on a MOTU 2048-II which is fed from my preamp. MOTU says that
full scale is +4dBu but I haven't checked that. If that's true, the preamp
is putting out -3.1 on the hottest peak and the mic is putting out -13.1
because the preamp is set at 10dB gain. I'm beginning to suspect that the
MOTU hits full scale at a higher input than they say. I'll measure that today.

I'm also planning to hook the CMC6U mic body directly to a scope and
inject signals into it through a capacitor to see how the mic amplifier
itself acts. This eliminates the capsule, the preamp, and the converters.
I'll let you know what I find out. I'm really beginning to think I'm
seeing some very high peak SPL (maybe 140dB) a couple of feet from that
snare drum. (I keep telling the drummer he's too loud :-) )

Hopefully another update with better science in a couple of days.

--
Bill

In article writes:

Maybe there's a future for me as a hog caller :-) What I'm doing to
overload the mic is to have my lips actually touching the mic with no
windscreen and talking loudly. That causes the mic to mute and then
recover.

Is it worse when you say "Peter Piper picked a peck of pickled
peppers" than when you say "SOOOOOOEEEEEEEE"? Plosives can cause many
times the diaphragm displacement of even loud non-plosive speech.
That's why we have wind screens and blast filters.


--
I'm really Mike Rivers )
However, until the spam goes away or Hell freezes over,
lots of IP addresses are blocked from this system. If
you e-mail me and it bounces, use your secret decoder ring
and reach me he double-m-eleven-double-zero at yahoo

Mike Rivers wrote:

Is it worse when you say "Peter Piper picked a peck of pickled
peppers" than when you say "SOOOOOOEEEEEEEE"? Plosives can cause many
times the diaphragm displacement of even loud non-plosive speech.
That's why we have wind screens and blast filters.

I don't know because I didn't want to subject the diaphram to plosives up
close like that. So I just say "HELLO...O...O...O" in my most musical
voice, increasing the volume until the mic mutes and then quiet down and
listen to the audio reappear. I've now tried this on 3 different preamps
with 4 individual Schoeps mics, 2 MK21's and 2 MK4's all with CMC6U
amplifier bodies. I'm pretty sure anyone with these mics can re-create
what I'm doing. I haven't tried "SOOOOOOEEEEEEEE" :-)

I'll be interested in what I can do by just injecting a test signal into
the mic body. I'll post results when I get that done.

--
Bill

Bill Thompson wrote:

What I'm doing to overload the mic is to have my lips actually
touching the mic with no windscreen and talking loudly. That causes
the mic to mute and then recover.

Again I question whether the microphone is the piece that's muting. One
moment--let me try something here ...

OK, first of all, with even the simplest of pop screens (Schoeps B 5, $10)
on a CMC 64, I _can't_ drive it into overload with the sound of my voice
alone even at extremely close range. That doesn't surprise me, since I
often record trained opera singers who sometimes exceed 120 dB SPL during
certain concentrated exercises--at that point they're still 10+ dB below
the limit of the microphones--but I'm certainly not as loud as they are.

I came up with a guttural sound with which I could overload the microphone
by a few dB *if* I removed the windscreen. I'm not sure what my upstairs
neighbors thought was going on and my throat is sore now, but I don't mind
an occasional yelling and growling spree for the sake of Science. And I
was able to capture the waveform in Sound Forge. The overload syndrome is
a bit peculiar--I'm not sure how to describe it--but it is decidedly not
"lie down and play dead" at any point whatsoever.

So while you may be overloading the microphone with breath noise, I still
believe that any actual muting probably has some other cause.


I hope I'm not hurting it but it seems like a mylar diaphragm is tough
enough to take a little of that.

You're almost certainly right about not damaging a Mylar capsule from the
volume level alone. But protection against spit and smoke is always in
order when close-miking a voice, because long-term, deposits left on the
membrane can lead to leakage currents.

In addition, a capsule simply can't tell whether its membrane is moving
because of sound energy that you want to pick up or because of other air
motion. Similarly, a microphone can't distinguish between sound you want
to pick up and solid-borne vibrations. Both of these problems tend to be
acute in pressure gradient (directional) transducers. Thus the only
engineers who might not need shock mounts and wind / pop screens are those
who work exclusively with pure pressure (omnidirectional) microphones.


I'm also planning to hook the CMC6U mic body directly to a scope and
inject signals into it through a capacitor to see how the mic amplifier
itself acts. This eliminates the capsule, the preamp, and the converters.
I'll let you know what I find out. I'm really beginning to think I'm
seeing some very high peak SPL (maybe 140dB) a couple of feet from that
snare drum. (I keep telling the drummer he's too loud :-) )

Please let us know how this goes. The capsule capacitance is generally
around 35 pF if I remember correctly. But the impedance at the gate of
the FET is so high that shielding and stray capacitance become major issues
when injecting signals--I know that you're looking mainly at overload
behavior, but be prepared for lots o' hum and RFI. Also, if I recall
correctly, it is not advisable to feed much signal into an amplifier
until/unless phantom powering is already being supplied to it.

If you decide that you want to make more detailed measurements in this
way, you may want to obtain a Schoeps MEC test head. This is a special
Colette series accessory that is not listed in the catalog any more, since
it's not really of general interest, but I believe it is still available
on special order. I have one here and if there's anything you'd like me
to measure through it, please let me know; I'll do what I can.


By the way, my preamp has a switchable passive 20dB pad ahead of the
transformer and with that switched in the mic acts exactly the same.

That's very interesting, and I must admit that I wouldn't have expected
that result at all. It does tend to lend more credence to the guess that
you've actually got super-high SPLs in the picture--but even that still
wouldn't explain anything that resembles muting in the microphones!


Hopefully another update with better science in a couple of days.

If you have any kind of wind or pop screen available, please include it
in your experimental plan the next time you see your drummer friend, OK?

BTW, I should clarify that I'm not a representative of Schoeps, but I do
work for them as a translator/editorial consultant/"hairsplitter" from
time to time, and I use their microphones for most of the live recording
that I still do (which is less than I used to, unfortunately).