output stage of condenser mca sp1 mic

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freespace377

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Apr 26, 2006
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The schematic of the SP-1 is the same as the mxl 603s with an exception.

In front of the 2n5401 transistors there has been added a cap (I forget the value and I'm at work, schemo at home) to shunt the highs to ground. Since no caps works for other mic's I figure I'm safe taking them out, but this is my first forray into mic's so I ask: aside from oscillations, is there a down side (assuming I want the added bandwidth)?

What do the diodes bridging the output do except provide severe clipping if the value exceeds +/- 0.7 V? Again, I'm new to mic's but I don't like diode clipping in guitar amps.

When doing the 1/2Pi RC calculation to reckon the effect of the .022uf caps shunting the out put, should I use the 150 ohm impedance the mic, or 600 ohms, or what? Any way I look at it, they seem like big caps to work against, if you want bandwidth. I notice Nueman uses smaller caps. Any comments?

Thanks

Dan
 
The diodes are actually zener diodes rated at 6.2 volts (usually).
They protect the 2 output transistors from accidents such as "hot plugging" a mic. with phantom power already turned on.
Other details about this type of microphone circuit, including those caps, have been discussed recently at the Yahoo Group MICBUILDERS.

ZAP
 
I immediately thought zeners, as well, but....

The old schemo that zebra (former Microphone Meta Moderator) posted showed them as 1n4148:

Schematic

Note that they are not shunted, but connected from collector to emitter, so not diode clipping like guitar effect.
 
http://www.omnipressor.com/MicSchLib/Schoeps.pdf


http://www.schoepsclassics.de/1964_cmt20.htm


http://www.schoepsclassics.de/1953.htm
 

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