Bizarre left channel failures on amps

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This is quiet bizarre, but over the years I've had 4 or 5 amps where Left channel failed. Not completely, it just gets weaker, less punch or even about 2db less in volume. Amps are all vintage Pioneer and Yamaha.
Few days ago it happened again, this time to Yamaha A-550. So far it's intermittent but it can drive me crazy, thinking my hearing is going :)
Normally I would think recaping, but why always a Left channel? I never had a Right one to fail. Can anyone have a guess what can cause this, perhaps the way amps are build? I use various speakers so it's not caused by speakers.
Or could it just be an amazing coincidence?
Bad volume potentiometer? Poti seldom have very consistent track resistance, unless premium parts or stepped with fixed resistors is used. Could easily develop imbalance between channels during many years of use since there is two tracks, one for each channel.

Is the imbalance on all volume levels or just with the regular listening level?
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Joined 2003
Paid Member
Put your right ear near the left speaker.

I had a similar observation on two systems. I heard background hiss in right, not in left. But when I put my right ear to the left speaker, it hissed fine.

I was going deaf. Faster in left than right (odd but not unusual). See image of my hearing in 2011 (over-laid on my Dad's curve, suggesting I am my father's son).

Mine was progressively but consistently worse over several years. There are other ear conditions where hearing fluctuates day by day. Minor colds and clogs; also Meniere's.

In most lands, an initial hearing test is free or cheap.


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No it's not the posts, cables, etc. I tested all that. it's not my ears because everyone in my family can also hear the difference. it's more obvious when I hook it up to NS-10 speakers, it's almost like there is some phasing going on weakening the signal at certain frequencies making it sound like less volume. But I can't do this by ear, I need to measure the channels and get to the bottom of it.
Is there some software that could measure minute differences in each channel?
I tried some VST plugins but nothing was sensitive enough to show any difference. The only thing I achieved was using EQ duplication VST which showed my that EQ curve in each channel is slightly different. But that still doesn't tell me if there is distortion or something going on there and I don't have a hardware scope.
Joined 2011
Try swapping the entire speaker wire between channels. Maybe there's an internal defect in one of them.

Are you sure it's not room acoustics? Can you get the speaker on the other side of the room to sound
that way by swapping just one end of the speaker wires?
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I'm now sure it's the amps. I remembered I had old software called Soundcard Oscilloscope so I used that. I measured the A550 and left channel shows 1db lower but the whole waveform of both channels is also moving around slowly like a seesaw so definitively something wrong there. That would explain why it seems to be intermittent to the ear.
While at it, I also measured another two failed amps, both were 2db lower on the left.
So I guess it's nice to have old amps but the parts just eventually deteriorate, no way out of it.
Still don't know why LEFT channels only but maybe just a very bad luck or because I'm in Australia which is upside down so maybe that has some effect on electronics :)
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