Bottlehead Kits > Crack-a-two-a

Lost sound in the right channel [resolved]

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TheRedMantra:
My amp is the stock circuit (no stepped attenuator). It’s been working flawlessly for many months. Today I rolled in a new 6AS7G tube and after about an hr the right channel started to buzz. Then it cut out completely. I put in a known good tube and the right channel was still silent. No buzz, no hum, no noise.

All LEDs glow. I checked resistances and voltages and all are to spec. I cleaned the contacts in the headphone jack. I use a 1/4” to 3.5mm adapter and checked it in another amp (it works). I tried a second set of headphones and the issue seems to be the amp.

I tugged on the solder joints and checked for cracked cables. Nothing. What else can I check?

TheRedMantra:
After sleeping on the problem I warmed up the amp and tried something different. I rocked the knob for the Balance pot forward and backward and started hearing the sound in the right channel come and go. I found a “balance point” where it seems to be back to working but if I breathe on it wrong I have issues. I have a 2 Quiet upgrade waiting to be installed but I wanted to use the stock amp for 6 months and roll tubes to get a really good feel for it before upgrading.

Is it more likely that I have a wonky balance pot or maybe a bad solder joint? I’ve visually inspected them and they’re clean looking with no damaged wires.

Also, unrelated, I’ve noticed when changing to an unused input to test for noise floor in new tubes that sound can bleed through the selector switch sources; only at dangerously high, unlistenable volumes. Nothing I can perceive when listening, but I’m thinking of upgrading the switch down the road. Any recommendations?

Paul Birkeland:

--- Quote from: TheRedMantra on December 10, 2023, 05:06:09 AM --- maybe a bad solder joint? I’ve visually inspected them and they’re clean looking with no damaged wires.

--- End quote ---
This is very likely the issue.

--- Quote from: TheRedMantra on December 10, 2023, 05:06:09 AM ---Also, unrelated, I’ve noticed when changing to an unused input to test for noise floor in new tubes that sound can bleed through the selector switch sources; only at dangerously high, unlistenable volumes. Nothing I can perceive when listening, but I’m thinking of upgrading the switch down the road. Any recommendations?

--- End quote ---
You can certainly replace the selector switch, but I would not expect improvement from doing this.  If you have no source plugged into a set of jacks, it will be very receptive to picking up the neighboring source.  If you have multiple sources plugged into your amp, having the source actually plugged into the set of input jacks is going to mitigate this effect substantially, so in essence you are only likely to experience this problem with unused inputs at unrealistic listening levels.  As soon as you hook up a source, that input isn't likely to pick up signal from its neighbor.

TheRedMantra:
Okay. I’ll remove and re-solder all the connections to the balance pot. Unexpected bit of fun for today. The practice is making me better at this though. Thanks Paul.

Paul Birkeland:

--- Quote from: TheRedMantra on December 10, 2023, 06:24:44 AM ---Okay. I’ll remove and re-solder all the connections to the balance pot.

--- End quote ---
I would not do that.  Plug a cheap pair of headphones into the C2A and run some music into it, then poke around the balance pot with a wooden chopstick to see if you can figure out what you need to poke to get the issue to occur.

Keep in mind that it might be a wire that connects to a balance pot that's the issue, but it could be the end of that wire that doesn't connect to the balance pot. 

If you desolder, remove, then reinstall all of these connections, you may end up making more issues than you have now.

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