Hairball Audio said:Try inserting a signal at TP15 and testing the output at output tx brown first, before removing the input tx. That'll bypass the input and test to see if the line amp and your test setup is working.
First thing I decided to do this morning was look through my signal generator setup. I've mentioned this a few times, but I'm using the OSC XLR out on the back of my SSL console and routing it to a signal tracer, where I'm clipping the black probe to D4 and putting the probe on whichever point I'm injecting signal at.
The mnats calibration guide is very adamant about not sending signal to ground and Mike, your description of a signal generator was a little different from my set up so I decided to get into my signal tracer and make sure everything was going where it was supposed to and found that the signal on one pin was markedly weaker than the other so I rebuilt it for this application and now my testing is going a little better.
I went back and tried injecting a 400mVAC signal at TP1 (I wanted to do 100mVAC but was having trouble getting my voltage reading low enough and I thought it would work well enough to see what I could see)
That now gives me 6VAC at TP15 and 225mVAC on either side of R5
Injecting 2VAC at TP15 gives me about 9VAC at the Brown wire of the Output TX.
It seems like the later stages are acting as expected to me !
Still, with one probe clipped to pin 2 of the input xlr and the other to pin 3 a .775VAC signal drops to 12mVAC unless the unit is in Full Bypass. (In Full bypass out put XLR pins 2&3 read .775VAC). I tried this with both the signal from the onboard OSC and from a DAW just to make sure there's not something weird going on with my test setup