Hi All, Some time ago I posted about fixing the hum on my QED amp. It turned out to be the bias setting, and I'm convinced the hum went away. Most of the caps have been replaced during this episode, except the large cans which I'm going to have a problem sourcing alternatives, however they did check out on my tester OK, I think, I'm not an expert. A/the hum is back, it's annoying, but not intrusive as it's really quite low level, but there. Here is a trace of the +/- 33v power rails, scope set to AC:
Upper plot is R channel, lower L channel. P-P volts varies up to 500mV (Setting the bias slightly alters this level), so I reckon smoothing caps not doing their job? This is with the amp idle, no input or load, a perceptible hum is heard with headphones and speakers up close. Maybe this is normal for this amp? Maybe I should just ignore it? The reason I like this amp is because is sounds better (better overall sonic separation) than the Technics amp I am using, and it has a MC pre-amp built in for my turntable (cartridge), which I want to get back in action!
Sorry to blather, any advice most welcome.
Upper plot is R channel, lower L channel. P-P volts varies up to 500mV (Setting the bias slightly alters this level), so I reckon smoothing caps not doing their job? This is with the amp idle, no input or load, a perceptible hum is heard with headphones and speakers up close. Maybe this is normal for this amp? Maybe I should just ignore it? The reason I like this amp is because is sounds better (better overall sonic separation) than the Technics amp I am using, and it has a MC pre-amp built in for my turntable (cartridge), which I want to get back in action!
Sorry to blather, any advice most welcome.
