I have a subwoofer amp I built from an Electronics Now (remember that?) magazine article around 1992 or so. Recently it started making whoosh/thunder noises, now it just howls. I have the schematic and can trace down the parts, but was wondering if I should focus on a bad cap or something or do I have to check everything (IF I want to keep it)? Thanks for any help.
October -1995 Waldtraut , pretty simple circuit even the old IC,s could be updated .
Check you have low ripple -
+/- 35 V DC
+- 15 V DC
Then the feedback capacitors + output capacitor from IC1a
then C6.
As the output from the push-pull BJT,s is DC connected check for offset .
Have you got a ,scope ,its a lot quicker that way .
If the output BJT,s are blown you will get a very large offset up to one rail.
You didn't build the mosfet power amp in the same issue did you .
I know its a lot of work but have you seen the spec ?
Maybe 0.05% THD -20Hz to 20Khz isn't up to top spec. now but
2Hz to 300Khz -1db is pretty good as is the slew rate of 200V/us and 300W into 8 ohms doubling up for halving the impedance shows its not too bad a design for its day.
I downloaded the circuit to add to my archive.
Check you have low ripple -
+/- 35 V DC
+- 15 V DC
Then the feedback capacitors + output capacitor from IC1a
then C6.
As the output from the push-pull BJT,s is DC connected check for offset .
Have you got a ,scope ,its a lot quicker that way .
If the output BJT,s are blown you will get a very large offset up to one rail.
You didn't build the mosfet power amp in the same issue did you .
I know its a lot of work but have you seen the spec ?
Maybe 0.05% THD -20Hz to 20Khz isn't up to top spec. now but
2Hz to 300Khz -1db is pretty good as is the slew rate of 200V/us and 300W into 8 ohms doubling up for halving the impedance shows its not too bad a design for its day.
I downloaded the circuit to add to my archive.
Yep, that's it, the Little Earthquake sub. Nope, didn't build mosfet amp. Thanks for the quick response!