MICROPHONE PREAMP HELP

Your description makes very little sense to me. How does the gain drop when you move the mic closer or further from a speaker? That is unclear gibberish that makes no sense. Reading between the lines and looking at the schematic in the url, I'm guessing that your problem has to do with DC offsets in the system. That is, DC from the mic or from you circuit is driving the amps into or near saturation under certain conditions. When this happens, there can be no signal output. Furthermore it will probably go through a region of severe clipping and high distortion.

For openers, the pre-amp must be AC coupled with capacitors blocking possible DC voltages that can exist. There is no sound signal in the DC, and therefore, no point in amplifying it. Secondly, get rid of the 741's, they are totally inappropriate amplifiers for audio purposes. Use a 5532 or something similar for low level audio. Thirdly, a differential instrumentation connected amplifier can work but is probably unnecessary. A simple, single ended gain of 20 to gain of 40 stage should suffice. Bob

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Try these guys

BTW my mic preamp for my AKG condensers is set to 46 dB gain which is

200. PC sound cards have very little headroom so external level control and metering would be needed for setting the actual gain in your installation. 741 'opamps' are OK for somethings. Audio isn't one of them. I use them as multi legged thumbtacks. GG

Hello Karthik,

we use some sennheiser mic's with .. .humm.. I think condenser-capsules with an integrated FET... aside of the phantom-power we plugged them directly into the PC and use the 20db Boost option nearly all AC97 (or better ) compliant soundcards offer. I have not much experience with electret-capsules, but AFAIK their output after the phantom-power is more or les similar to the one of condenser-capsules. Try plugging it directly into the PeeCee and swip on all boost-options in the computer.

Just my 2 Euro-Cent of thoughts

snipped-for-privacy@gmail.com wrote:

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Hochachtungsvoll

Rüdiger

1) what is the DC on the amp output? 2) is it AC coupled, input and output? 3) do you have resistors to ground on the inputs, say 10K 4) do you have a scope? 5)what are the voltage rails 6) why do "they" still make the 741? 7)is the mic balanced out? 8) how long is the mic cable?

have a look at TI's INA217, or use NE5532/4's

martin

"Facts are stupid things.." -- Reagan, '88

Oh I forgot, what value of R have you selected?

martin

"Facts are stupid things.." -- Reagan, '88

martin

"Facts are stupid things.." -- Reagan, '88

Thanx all for replyin....I was too stupid and dint put a capacitor in the input and also dint usse a couplin capacitor....thanx to grifftith....thank u all thank u