CA-2010 lazy right channel

belgianbrain

Super Member
A year or so ago I posted a question about this unit - at very low volumes, the left channel kicks in but no right channel. Even the meter indicates no output from the right. I can flip the 20db attenuator and turn up the volume to avoid this. No one seemed to have any suggestions.

Today I've been messing with it. Opened it up to fix a cracked plastic switch on the front. Also deoxit'ed the coupler switch on the rear since I'd never done this. I also checked the voltage bias in Class A/AB and all is right on.

Was playing an audiophile tester CD tonight that outputs sounds of constant volume from alternating speakers and, as I always suspected, even at normal volumes the right channel is a tad weaker.

I can balance it out using the balance control if I put it around the 18-16 mark.

This unit has been completely restored by me - recapped entirely, new relays, new transistor grease, etc.

Any ideas?

I attach a pic just for fun.
 

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Does the problem remain in the same channel if you swap the source inputs around?
 
Do you mean switch R for L input cables?

Yes. It's always the R channel that's quieter. Even when you use the selector switch to REV R and L channels, etc. R is always quieter.

Same result with all inputs.

It's not a big volume difference, but enough to make you think the singer is closer to the left side of the stage when listening.
 
Balance control may be buggered up. Throw a scope on it to see where your signal is getting attenuated.
 
Balance control may be buggered up. Throw a scope on it to see where your signal is getting attenuated.

Maybe you're onto something, Avionic.

I just tried decoupling the preamp from the power-amp and using jumper cables. Problem remains, but follows the reversing of the cables, which eliminates the power-amp section as a problem.

When I balance the sound out with balance control, the problem with one channel kicking in only at higher volumes also disappears - both channels increase proportionally with volume control - to an extent.

BUT, the problem only seems prevalent at lower volumes (e.g., 5w and less). At lower volumes (e.g., at 1W) I can listen to the two channels, watch the meters, and balance it out by rotating the balance knob to the right a bit, but when I crank it up and shake the house (e.g., 5-10W), then suddenly the right channel is stronger and I need to center the balance knob again. This one has me scratching my head.

The variable nature of this problem would point away from balance control, would it not?
 
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Is this and audible issue or visual power meter issue ?
 
You need to put the amplifier on a dummy load and troubleshoot it at the input level that exihibits the worst case imbalance. Possibly out of tolerance resistors.
 
Worse case imbalance is at VERY low volume where left channel kicks in and right channel is still silent.

What section do you believe problem would exist at?

Any reason a dummy load is needed as opposed to troubleshooting while it's playing music? I assume you're suggesting following the signal path with a scope?
 
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BUT, the problem only seems prevalent at lower volumes (e.g., 5w and less). At lower volumes (e.g., at 1W) I can listen to the two channels

If it were me.I'd be looking very closely at the volume control..Sounds like its still dirty.Or possibly a cold solder connection.
 
If it were me.I'd be looking very closely at the volume control..Sounds like its still dirty.Or possibly a cold solder connection.

Will do....thanks for the suggestion.

You've mentioned before it can be disassembled and cleaned. This is one thing I did not do when restoring the unit 2.5 years ago.

Got a short plan for doing so, including any things to watch out for? Do you recommend using Deoxit in there - there does appear to be a hole in the front giving you access?

I notice it looks like you would desolder it from the circuit board and then take two long screws out to take it apart.
 
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I notice it looks like you would desolder it from the circuit board and then take two long screws out to take it apart.

Remove the two long screws and you should be able to seperate the segments a couple millimeters--enough to get the deoxit where it will do the most good.
 
Just finished doing a thorough deoxit of volume and balance control.

Spent quite a lot of time spraying it thoroughly into every section.

No difference!

One thing I did notice when testing with older source equipment with low output levels is that the problem is virtually unnoticeable.

It's with my newer DACS and such that have output levels around 2-3 V peak to peak that the problem becomes prevalent with right channel only kicking in at higher volumes and some unbalance existing at lower volumes after that.

With older equipment likely putting out 1V or so, this problem is virtually undetectable.

Wondering if the hot output of my DACS is overdriving the preamp in the CA-2010. Thinking of buying some Harrison 12dB RCA inline attenuators to try out. It seems the 20dB attenuator built into the 2010 is too late in the path to correct the problem entirely.

Thoughts?
 
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This seems to be what I'm seeing and hearing now...except reversed. It's my left channel that's 'lazy'.
 
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