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gmphadte 31st January 2013 09:45 AM

Trimming DC Offset on Nico's preamp
I have assembled this preamp(link below) with the intention of capacitor-less coupling. One of the channels is having -6mV and the other shows -16mVdc approx. The complementary matching of these BD139-16 n BD140-16 from the twenty each I purchased was impossible and I want the offset to be as low as possible. Is there any changes in resistors/or addition of preset I can incorporate so that I can trim the offset.

Help needed

Gajanan Phadte

lineup 31st January 2013 10:00 AM

6 and 16 mV is very good.
No need to have less DC-offset

jerluwoo 31st January 2013 11:56 AM

You can replace R5 or R6 with a trim pot.

gmphadte 1st February 2013 03:20 AM

I tried to trim one of R3/R4, but I did not like the way it(DC offset) drifts.

My worry is that if I connect this directly to my power amp, it will have big DC at the output.

Gajanan Phadte

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