Just getting back into this amp after a few weeks off (beginning of the spring semester and getting adjusted to new students, etc. has kept me busy).
The amp occasionally makes a whining noise which slowly increases in frequency and then goes quiet. While testing various points in the power amp yesterday I accidentally touched something that didn't appreciate the attention. There was a loud POP from the speaker but fortunately didn't damage anything... but all the noise went away! It eventually came back but the whole thing brings to mind something charging and then discharging. So I'm going to throw the dice and replace the main filter caps. They're cheap enough.
On another note: I found an big error in the official schematic diagram. (Nothing that affects my particular problem, unfortunately.) The clean/overdrive channel switching circuit couldn't possibly work as shown. So I followed the traces on the circuit board and found out the real deal. Here's my corrected schematic:
Also: The Frontman 65R is virtually identical to the 1990's "Princeton 65" solid-state amp. The only difference I can find is that the overdrive channel on the Frontman has midrange controls as well as treble and bass.
The amp occasionally makes a whining noise which slowly increases in frequency and then goes quiet. While testing various points in the power amp yesterday I accidentally touched something that didn't appreciate the attention. There was a loud POP from the speaker but fortunately didn't damage anything... but all the noise went away! It eventually came back but the whole thing brings to mind something charging and then discharging. So I'm going to throw the dice and replace the main filter caps. They're cheap enough.
On another note: I found an big error in the official schematic diagram. (Nothing that affects my particular problem, unfortunately.) The clean/overdrive channel switching circuit couldn't possibly work as shown. So I followed the traces on the circuit board and found out the real deal. Here's my corrected schematic:
Also: The Frontman 65R is virtually identical to the 1990's "Princeton 65" solid-state amp. The only difference I can find is that the overdrive channel on the Frontman has midrange controls as well as treble and bass.