Looking for CM87 SE microphone schematics (Advanced Audio)

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rafafredd

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Jun 3, 2004
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So... A friend of mine came with a mic that has gone through a hard accident.

Head was destroyed and, upon inspection, so was the capsule.

We contacted Advanced Audio and brought a new head with grill. As I had a few chinese capsules on hand we didn't got a new capsule. The idea was to try a cheaper chinese variety and see how it sounds.

So, the head arrived and I've changed the capsule with one of the chinese ones I had. But the mic wouldn't work as it should. So we contacted AA and asked for a schematic so I could check for any problems on the circuit. In fact, this exact schematic was made available publicly in this forum by AA before, so I didn't think that would be a problem for them to provide it.

We've sent them pictures of the opened mic so AA could know the exact version of the mic and send us the right schematic. But the guy there, owner I think, didn't like the fact that we replaced the capsule with a chinese one, and stoped responding to our emails after asking why we changed the capsule.

I really didn't expect it to be a problem. You see, I've even sent them photo of the mic with the new capsule. My frient replyed back saying his tech just used what he had on hand. I actually have a few more chinese capsules in stock I've collected over the years and I've sold him a capsule for a much better price to help my friend, cause I brought it when the dollar wasn't that high.

We are in Brazil and the dollar exchange price is 1:5 nowadays, so I don't see why we would be forced to buy their capsule to replace in the mic, or send the mic to USA to be refurbished. The cost of mailing it and getting it back would be too much anyway.

Now they simply completely ignore all our subsequent emails trying to explain the situation and get some info to fix the mic.

So, if anyone can help with schematics for this mic, you will save a ton of time I would have to put into reversing a complete schematic just to fix a $500 mic.

I really don't see why would they do this. With so many classic schematics around, why would someone want or need to copy a CM87 SE schematic for DIY or even commmercial purposes? Their own mics are based on the classics everyone clones and sells.

I understand their need to protect their intellectual property, but specially coming from a company that was built on products based on U47, U47fet, U87, C414, C12, ELAM-251, etc, from Neumann and AKG, it's a shame they are denying the right of their customer to easily fix the microphone overseas, and replacing the capsule with whatever he has on hand, even after buying the replacement head and grill from them, and it wasn't exactly cheap.

Really doesn't make sense to me.

We just want to have this mic up and running again. The owner is my friend and isn't exactly rich, so he really needs it in his studio, to work and make a living on it. We are going through hard times in Brazil, and nowadays everything is so expensive to import, like 5 times more then the price you pay for gear in USA.

I am not trying to make any harm to their company with this post. Just openly presenting what has happened, and trying to get necessary info to fix the microphone. Yes, I think they do have the right to deny sending me the schematics, but I also do have the right to look for it in order to have the microphone fixed.

If the company will reevaluate their position and send me necessary schematics, I will gladly pull this post off.

I want to reiterate that I'll not share any info I get from the company, or use it for any other purpose then fixing my friend's microphone.

Thanks for any help.
 

Gus

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Pictures will help guess what the circuit is.

what wrong with it?

JFET to PNP  to transformer circuit?
 

analogguru

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Mar 25, 2007
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Vienna, Austria, Europe
rafafredd said:
Now they simply completely ignore all our subsequent emails trying to explain the situation and get some info to fix the mic.
Now, the followiing infos should do the trick.

rafafredd said:
.... I really don't see why would they do this. With so many classic schematics around, why would someone want or need to copy a CM87 SE schematic for DIY or even commmercial purposes? Their own mics are based on the classics everyone clones and sells.
And exactly this is the reason.  People should not know that they pay $ 500,-- for a china made microphone they can get elsewhere for $ 50,--:

"Advanced Audio Microphones is the imprint of Dave Thomas, well-known mic modder from British Columbia. The company imports a handful of tube and FET mic models from one of the higher-end factories in China,.....(Alctron).... "
http://recordinghacks.com/microphones/Advanced-Audio-Microphones

rafafredd said:
..... I understand their need to protect their intellectual property,....
Their ?  What ?  I think you are talking about chinese clone property.

Now let's have a look at the relabelled chinese microphone:

"The CM-87 is a large diaphragm, multipattern condenser microphone based on the Neumann U87. It is manufactured in China, initially by Feilo (through late 2008).

The CM-87 utilizes a dual-diaphragm 6-micron capsule and class A amplifier design. The FET is a 2SK170, known for low noise and high gain.

.....Also available is the CM87SE, which is intended to handle the fast and loud transients of close-mic drums. This is accomplished by employing a “more complex output transformer with dual windings and bi-metal laminations.”...."

http://recordinghacks.com/microphones/Advanced-Audio-Microphones/CM-87

So any of the following schematics which can be found on the web probably should do the trick:
Apex 420
Apex 430
CAD GXL3000
MXL 2001
MXL V67
t.bone SC-450

and others.....
 

RuudNL

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Apr 26, 2009
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Haule / The Netherlands
Here is a schematic I found years ago.
I am sure it is not 100% correct. (Gate resistor is missing, tot start with.)
 

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  • CM87_HandDrawn_sch.pdf
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dbelousov

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Jun 30, 2019
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Moscow, Russia
I have a couple of mics and a couple of separate capsules from Advanced Audio. Both are excellent stereo pairs, so I believe they are not just "repack" Chinese staff. Or I'm a very lucky person. The quality of components was higher than "average" as well, but I doubt it is still the case nowadays. I bought a mic from Thomann (Alctron with the T-Bone brand on it) recently because I liked its body and was VERY impressed with its guts and sound quality.

It's very possible the CM87 shares the circuit with CAD GXL3000. There are some pictures and schematics.

http://recordinghacks.com/microphones/CAD/GXL3000
 

rafafredd

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Jun 3, 2004
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Rio, Brazil
Thanks, it really helps!

Looks like the circuit is almost exact the same, with minor changes in the FET bias values.

I have enough now to sort it out.
 
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