[sdiy] DC offset removal help

[Magnus Danielson]

cs e wrote:
> I've got an ADSR envelope here, which has a TL072 as output buffer.
> Unfortunately, there's around a 200mV DC offset on its output, with no
> gate applied. (This won't allow my VCA to shut off properly - I know
> the VCA is OK, because I have other envelopes.)  Of note is that the
> 200mV reduces (over a long time) to around 100 mV or so.
> How can I easily and quickly remove this offset...I don't mind if 200
> mV is chopped off of the output.
> 
> Thanks for any ideas.

You can run the TL072 as a gain-stage with the unbuffered signal at the 
positive input (as I suspect you already have) and run a 1 k resistor 
from the output to the negative input and from there a 100k trim pot to 
the -15 V rail. You can now trim the offset. This gives a tiny bit of 
gain about +1,3% but it should be alright.

Not too complex and should be a small modification for you.

Cheers,
Magnus