I can't adjust the bias correctly
Posted: Fri Jun 05, 2009 12:34 am
I have a J 99 Rev 3.3 with AD 797 OP Amps and I can't adjust the bias correctly.
This is the way I do it, let me know if I do something wrong:
Step 34. I short CONN1 pin 2 and 3. I turn R28 and R32 counter-clockwise until I hear a soft click and when I measure U1 and U2 between pin4 and pin3 it is ok I find 14V, when I measure between pin4 and pin5 the voltage is -14V.
After that, (the jumpers J6 and J8 are at ADJ position) I measure U1 and U2 at pin 6 and 4, with SW2 clockwise and after counter-clockwise and it's impossible to make the 2 measurements close. I tried to adjust R45 and R50 in every way and the measurements are very far from each other.
When I plug a microphone, the sound is very loud and with distorsion, and when if I turn the GAIN a big noise appears.
Thank you for your help.
This is the way I do it, let me know if I do something wrong:
Step 34. I short CONN1 pin 2 and 3. I turn R28 and R32 counter-clockwise until I hear a soft click and when I measure U1 and U2 between pin4 and pin3 it is ok I find 14V, when I measure between pin4 and pin5 the voltage is -14V.
After that, (the jumpers J6 and J8 are at ADJ position) I measure U1 and U2 at pin 6 and 4, with SW2 clockwise and after counter-clockwise and it's impossible to make the 2 measurements close. I tried to adjust R45 and R50 in every way and the measurements are very far from each other.
When I plug a microphone, the sound is very loud and with distorsion, and when if I turn the GAIN a big noise appears.
Thank you for your help.