2.5.2.0BC DC offset

[dasbin]

I built some of Fabio's 2.5.2.0BC PCB's (non-current-source version) and they sound fantastic - sweeter sounding than the OPA604 IC's I had in for testing. Strangely I noticed they will work even if the power supply is made to be single-ended! Not that I would run them like this, but that was interesting to find out.

Anyway I was wondering what I need to do to use the DC trim control. I'm getting about 1.5mv right now, not much, but I'd rather not slowly cook my output trafo. Obviously I need to put a trim pot at the point of R4-R5 but what does the other end connect to? Ground? And what value and range of resistance is required here?

Also, for those so inclined, have a question about the DI input of Fabio's 3.1.2 board which I posted here: http://www.groupdiy.com/index.php?topic=981&start=195

Thank ye thank ye.

 

[deveng]

The a*p*i data sheet says to use a 100k trimmer from the trim pin (point between the split collector resistance on the inside differential transistor) to +V. Connect +V to pin 1 and the trim pin to pin 2, leave pin 3 open.

Regards,
Jeff