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Analog Line Level Preamplifiers , Passive Pre-amps, Crossovers, etc.

Preamp has unwanted delay (and hum)
Preamp has unwanted delay (and hum)
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Old 23rd January 2013, 04:14 PM   #11
EpicFail is offline EpicFail  England
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Location: Bristol
OK fair enough. Thanks for everyone's help with this.
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Old 23rd January 2013, 06:49 PM   #12
Osvaldo de Banfield is offline Osvaldo de Banfield  Argentina
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Join Date: Dec 2011
Location: Barrio Garay,Almirante Brown, Buenos Aires, Argentina
In the resistor divider to bias the opamps input, use two r's shunted both with caps, this way you are creating a compensated voltage divider as used in oscilloscope proves. I used that configuration several times, and the secondary advantage is that the input is bypassed to both rails. Also, you can use one more OP to decouple voltage divider from ICs's input, but not too necessary in this case.

In the schema you posted, the cap is charging to reach exponentially the value of VCC/2, on time the minimum voltage to the opamps can work in class A, in this moment the audio is getting from the output. And, also, when shut down the circuit, this cap continues charged although the opapms are not, and this is very dangerous to the input stage of the opamps.

Best regards.

Good luck!.
Osvaldo F. Zappacosta. Electronic Engineer UTN FRA from 2001.
Argentine Ham Radio LW1DSE since 1987.

Last edited by Osvaldo de Banfield; 23rd January 2013 at 06:54 PM.
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