5v333
Well-known member
Ok, i dont understand it really but it looks like its becoming a bit high impedance to meet a rather low impedance at the sec opamp...
Didnt think about caps...
Didnt think about caps...
Schematic Review SSL Type Preamp
- Thread starter sr1200
- Start date
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5v333
Well-known member
There is no shunt resistor before the that amp. Could it be a potential problem?
would R8 not account for this or would the bottom end of R8 have to be connected to pin 2 ?
5v333
Well-known member
I meant after c16
i used the the circuit diagram from THAT for that section of the schematic. It didn't seem to have or require a shunt on the input. @abbey road d enfer had suggested to not have any resistor between the two stages.
5v333
Well-known member
Abbey has the final word in my world.
I think R20 is left from the version with -dc introduced att the output of first opamp. But that resistor was in parallell with one of two 220uf, which you have Exchanged with one 100uf cap.
The resistor should be omitted aswell i think...
Another thought was that the dc might have biased the output of the opamp in class a.. . But the resistance to vee is a much too high i guess.
The gain pot seems to be both in parallell with first opamps feedback R and in series with the sec opamps input R. It varies the gain of both stages in the same direction.
With the 100k R, the pot seems to loose its roll.
I think R20 is left from the version with -dc introduced att the output of first opamp. But that resistor was in parallell with one of two 220uf, which you have Exchanged with one 100uf cap.
The resistor should be omitted aswell i think...
Another thought was that the dc might have biased the output of the opamp in class a.. . But the resistance to vee is a much too high i guess.
The gain pot seems to be both in parallell with first opamps feedback R and in series with the sec opamps input R. It varies the gain of both stages in the same direction.
With the 100k R, the pot seems to loose its roll.
Could certainly jump R20 to test its effect.
So i accidentally ordered way too many boards. When i put the order for 5 of them in i didn't realize that it was 5 PACKS of boards... so this weekend I'm going to try and put a couple of channels together and see if they work. IF they do (not holding my breath after my initial tests) if anyone is interested in trying one out. The only mistake ive found so far is the "cinemag" footprint for the input transformer, the holes are slightly too small (typo on the pad/hole size). the Lundahl footprint is perfect though.
