Hey there!
EDIT: Whooops, i found out i had a tiny lil' short between pins 1 and 3, mea culpa. I'm glad i didn't burn anything, now it works more less as it should.
I'm leaving the rest here for archival purpose, if anyone runs into the same kind of problems.
Well, the solution is to just check your board.
I'm in process of building my first 9k, and ran into a problem with running it.
The IC 23 gets hot (depending on the gain pot pos. very hot (up to untouchable) very fast, or slower).
A shallow introduction on my build:
I'm running all of +-18V, replacing the tl052 with opa2604, and the mat02 with carefully matched by hfe BC550C's. (All in all, it's just a close matched dual npn so it shouldn't be a problem as long as they're matched.) And i'm using a 2k log pot instead of rev. log, which also shouldn't pose any problems, given it's wired backwards, and labeled attentuation instead of gain (I think i accidentaly wired it not the right way, as a normal log, but it also shouldn't matter, just render gain setting impossible).
As a back end i have two switches, one for chosing bal XLR or unbal TS out, the second one responsible for activating the hipass (220nf cap in series).
Now, of things i already checked, and found inproper, or worth mentioning:
There's voltage on the gain pot. Of course it depends on pot setting, but for example (fixed position for all measurments) i got nearly 9V on gain A and slightly over 9v on gain B.
There's DC on the output -8V, what the...
Potentials on the problematic IC23 (tried swapping out different NEs, all work in the same manner):
pin 1 10V 12V pin 8
pin 2 9V 18.18 pin7
pin 3 10V -11,5V pin6
pin 4 -18.25V -17.6 pin5
I checked all the resistor values at least 5 times by now and cap values at least 2, and all are right (excluding small changes like 51k instead of 50k, and 4.3 instead of 4.22, just standard series values).
Oh, Ra is 28R, but i belive it doesn't matter that much.
The gain pot is also working strangely - statring on far left position up to 90% rotated (CW) pot not much happens, both with a mic and with a guitar connected (no DI, just ballanced connection of unbal source) it changes slightly the hum (it is present, just like it had a shortage, or a extreme case of ground loop) level, but not much. Right at some position aroud the 90% it goes quiet with the mike, with the guitar behaving like this: on a small part of the pot it actually amplified something. Well, extremely overdriving it, and not producing any high output level (it never does actually, no mater the gain pot position), but it was recognisable. Also, the hum level changed as i touched the strings. For the little rest of the pot scale nothing interesting happened, 'twas pretty quiet, maybe with a trace of hum.
I have absolutely no idea what might be the problem atm...
Should i check/swap the BC550s?
Resolder everything onboard?
Unplug the board from anything other and test it with no peripheral circuits? (Front end nor back end nor balancer)
It oscillates (i belive that might be the problem) equally plugged to backend, and unplugged.
I also unplugged the opa2604 to check if it's what causes the problem, but nope.
With the ic23 unplugged nothing strange happens, nothing's heating, nor the voltage on gain pot exists iirc (forgot to write it down before i started writing the post
).
I haven't build the second channel yet, so i have no comparison...
