I'm going to do more investigation myself on this, but I'm just wondering if anyone had any good pointers for where to look first:
My PPAS has been pretty darn cranky from the start. First, I had a huge DC offset issue which I found out was somehow related to the fact that I'd lifted one of its pins.
Now that got fixed for the night, but a couple of days later I started getting something like 100-200mV on both channels. I was debugging everything with the meter, and managed to short out two pins of the TLE for a moment (I think it's ground and one of the rails) Guess what? The offset disappeared, and it suddenly started working again. I suspected it was some bad solder joint, so I reflowed everything. Still working a couple of days after that.
I haven't been using the amp for a while, and today, just to retest it, I discovered that there was about 40something/30somethingmV offset on both channels. Actually, now that I check again, it's at 38mV/28mV. It's just within the range in which I'd call the offset unreasonably dangerous for 64ohm headphones. I'm most worried that this might be some weird intermittent/drifting problem. Any ideas on where this problem might be? I've already un-glue-gunned this thing and desoldered the jacks like ten times, and I'd rather not do it again unless I have a good idea of what to look out for.
My configuration is the one recommended in the first post, LMH6321 buffers, OPA2107 OPAR/L, and LM6171 in the ground channel. The isolation JFETs are in there, the CRDs are installed; pretty much everything's maxed out. The main nonstandard features in my PPAS are a homemade SOIC->DIP adapter, since I don't have any SOIC OPA2107's on hand, 12V TREAD power supply (no batteries), trimpots for volume adjustment, RCA outputs + 1/8" inputs. Weird, I know, but these are just a couple of needed modifications for a little project I'm working on.
**EDIT:
this is really weird now. I just plugged it in and tested again, and it measures 11mv/22mv offset. Bad component? weird solder joint? I'm really not sure what kind of problem this might be.
**EDIT AGAIN:
I just remembered, I bumped the voltage of my TREAD to 13V from 12.5V. Maybe the opamps just need voltage? I heard the OPA2107 likes lots of voltage. But then again, this looks a lot like something weird going on with the ground channel, and the OPA2107 is in L/R. I'll play around with the supply voltage a bit more. . .
--> It seems that it is a LR channel problem; all the offset in the L/R channels also appears as offset from input to output. Is this just a problem with the OPA2107 wanting more voltage, or is it a more serious problem? Anyone with experience with this confgiuration?