asr still not working, need help
2006-03-01 by keith sterling
I've been staring at this asr for a few days now and I can't figure out
its problem. I get very small (on the order of millivolts)
fluctuations in all outputs relative to the counter state. I replaced
the 10uF caps with 100uF. Power supply is ample and stable. Resistors
are all hand precision matched. The other symptom is that the scale
factor is compressed- when driven by a keyboard the outputs are
slightly less than 1V/oct.
Because the error is the same in all outputs the obvious place to look
is the TL074 input buffer stage. But all the resistances and
connections verify in circuit with my ohmmeter. The next possibility
is a bad 4052. I replaced these. The power rails are stable and clean
when scoped and metered. I don't think the LF356 buffers could cause
these effects.
I'm tearing my hair out on this one, and it's getting hard because I'm
already almost bald. I would appreciate any ideas to steer my efforts
in a positive direction.
Keith
its problem. I get very small (on the order of millivolts)
fluctuations in all outputs relative to the counter state. I replaced
the 10uF caps with 100uF. Power supply is ample and stable. Resistors
are all hand precision matched. The other symptom is that the scale
factor is compressed- when driven by a keyboard the outputs are
slightly less than 1V/oct.
Because the error is the same in all outputs the obvious place to look
is the TL074 input buffer stage. But all the resistances and
connections verify in circuit with my ohmmeter. The next possibility
is a bad 4052. I replaced these. The power rails are stable and clean
when scoped and metered. I don't think the LF356 buffers could cause
these effects.
I'm tearing my hair out on this one, and it's getting hard because I'm
already almost bald. I would appreciate any ideas to steer my efforts
in a positive direction.
Keith