Just finished 2 A12s...some questions/tips etc.

[bradb]

Overall a pretty easy build. The only hassle is getting the chassis/molex connector stuff together, PCBs are way easier that dealing with wire. After a weekend of 1 show, 1 rehersal (both on bass guitar), building mic cable and the Molex connector, my fingers are killing me.

After adjusting R25 and R29 to set the rail voltage (I used +/- 20VDC, but I think i'll drop it to +/-18VDC) do you need to go back and tweak these or are they generally heat/time stable?

I found it was convenient to pop off the SC25 and loop some wire around the pins to conveninetly measure and adjust R19 while the op amp was running and hot.

Also, It helps to read the N72 build instructions first for little hints like where to place the stop pin for the gain pot.

Using an oscilloscope to calibrate these things what is the procedure/goal?
Zeroing the DC with R19? Making sure you have enough headroom with the rail voltages?

thanks all,
Brad

[tpryan]

No need to tweak the power supply rails, they'll stay quite stable. No need to use a scope with the A12 either, unless you have an unusual problem. Eliminating any output offset voltage minimizes the standing current in the op-amp and primary of the output transformer.