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Old 5th May 2013, 02:30 AM   #1
Lamber is offline Lamber  United States
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Default K-12g one channel louder than the other

Hello all,

I recently completed the kit and I'm having some trouble. Everything works fine, but the left channel is much louder than the right channel. Any ideas? All of the tubes glow with about the same brightness.

thanks!
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Old 5th May 2013, 01:19 PM   #2
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Check your build one more time.
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Old 5th May 2013, 01:30 PM   #3
GoatGuy is offline GoatGuy  United States
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Well... if its an amplifier that is symmetric (i.e. same tubes on left and right channels), then swap tubes one at a time between the channels, and see which if any have substantially more or less gain. Easy, trivial, informative - even if nothing shows up.

There will only be 2 outcomes: a tube is indicted, or, nothing will change. If a tube is indicted, then just order another one from the SAME manufacturer, or TWO from a different manufacturer. Substitute it/them in. The problem should go away. But though it is more likely that the replacement tube(s) will have higher and correct gain, there's always a chance that the real problem was a tube with TOO high gain! Rare, but possible.

IF NOTHING changes when you swap the tubes initially, then ... follow SoonerOrLater's advice, and check your wiring and hookup carefully. You might have substituted a wrong resistor value someplace that is cutting the weak channel's gain.

There you go.

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Old 5th May 2013, 02:02 PM   #4
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If there is cathode caps of preampl. and power tubes, check wires.
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Old 5th May 2013, 04:25 PM   #5
Lamber is offline Lamber  United States
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Thanks for the input. I've swapped the tubes around and haven't noticed a change. I'll go through it and check resistor values later today. Is there anything else I should check? It's consistent in that the sound level on the right channel is always the same amount softer than the left channel.

Could there be a problem in the volume pot? I've read that the volume pot in the K12g kit is low-quality and can cause problems. How would I check if it's bad, though?
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Old 5th May 2013, 04:31 PM   #6
Mooly is offline Mooly  United Kingdom
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Just transfer the wiper (middle pin) connections from the pot over, one channel to the other. Is there any possibility of confusion over tappings on the OP tranny.
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Old 5th May 2013, 06:38 PM   #7
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IIRC the pot is soldered directly into the pcb so not so easy to check out a faulty pot, might be easier to swap inputs to the dc blocking caps at the start of the signal paths to see if the fault moves channel. Before that try swapping source RCA plugs to eliminate them. If no change then eliminate speakers again by swapping. Only then can we assume the fault is in the amplifier. This might seem very basic but it has to be done. Fault finding has to proceed logically from a firm foundation.

The output transformer primary and secondary leads are also ( IIRC ) soldered onto the pcb so I can't think what could go wrong there that wouldn't be far more catastophic


Ps Welcome Lamber to the forum

pps do you have access to a meter that you could use to check the resistances either side of the wipers on your dual gang pot.
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Last edited by Soonerorlater; 5th May 2013 at 07:00 PM.
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Old 5th May 2013, 07:23 PM   #8
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swap output transformers. if the problem moves to the other channel, its the OT



swap c1 and c4 . to see if the caps are ok.


replace volume control, or sub it with a resistor and a jumper.
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Old 5th May 2013, 10:41 PM   #9
Lamber is offline Lamber  United States
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Alright, sounds like I have a good foundation to start checking from

I have swapped the speakers and the problem is the same (except it's the left channel that's quieter, as expected).

I don't have access to a meter today, but I'm bringing it in to the lab tomorrow to work on it (this is an independent project for electronics lab).

By the way, I just figured out something weird. I'm not sure if this helps or not, but when I turn down the input volume and max out the amplifier volume, the problem is less pronounced. The lower the volume of the amplifier, the greater the difference in channel output (as far as I can tell by listening). Does this point to the volume pot as the problem?

I'll check things out with a meter tomorrow and see what I can come up with.

Thanks for the help! I'm pretty new to amps so I don't know much yet, but I'm learning.
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Old 6th May 2013, 06:34 AM   #10
Mooly is offline Mooly  United Kingdom
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That does point to a problem with the pot but if that were the sole cause then the volume would be equal with it on maximum.

The definitive test for all this is to use a scope and just check the absolute levels at the key points in the circuit. Its literally a minutes work.
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