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Uneven volume output level (Read 904 times)
bateo102
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Uneven volume output level
03/07/19 at 20:09:40
 
The output level on my Rachel are not even.  I can confirm this with the dual volume controls.  The left knob has to be at 1 o’clock position while right knob is at 10 to have even sounds.  Is there anything wrong with my amp?
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Lon
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Re: Uneven volume output level
Reply #1 - 03/07/19 at 21:02:15
 
Doesn't necessarily mean that your amp has anything wrong with it. Your input and/or output tubes could be "not matching."
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bateo102
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Re: Uneven volume output level
Reply #2 - 03/08/19 at 13:59:37
 
Thanks
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Steve Deckert
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Re: Uneven volume output level
Reply #3 - 03/09/19 at 02:30:29
 
Yes, with matching tubes the most the volume controls would differ is one hour.

Steve
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bateo102
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Re: Uneven volume output level
Reply #4 - 03/09/19 at 03:38:38
 
Steve - These are stock tubes so I assume they were matched. I swapped the output tubes, then the input tubes, then the speakers and the imbalance stayed unchanged. When I swapped the speaker cables on the amp, the imbalance changed sides.  I think there’s nothing wrong with the tubes, speakers or cables.  I tried to use a sound meter app on my phone and it measured the difference between the channels at 12 o’clock is 10-15dB.  What should be the next step to troubleshoot?
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Steve Deckert
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Re: Uneven volume output level
Reply #5 - 03/09/19 at 05:58:18
 
I think you answered you own question!

You swapped tubes left for right and no change.  Problem not the tubes.

You swapped speakers left for right and no change.  Problem not the speakers.

You swapped speaker cables left for right and problem went to the other side...  bingo.  Problem is the speaker cables, more specifically one of the speaker speaker cables.

Steve
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bateo102
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Re: Uneven volume output level
Reply #6 - 03/09/19 at 06:10:54
 
No, I just swapped the speaker cable connections on the amp, ie left posts went to right speaker and right posts went to left speaker...then the problem went to the other side.
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Steve Deckert
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Re: Uneven volume output level
Reply #7 - 03/10/19 at 04:01:19
 
OK, I see...

Since the tubes are not the problem or the speaker wires, it would have to be the amplifier.   Most likely scenario is an output tube that partially or fully shorted causing the screen to plate resistor to become partially fried.  This would result in reduced output and probably pretty poor sound as well.

It could also be a bad volume control, but that would have symptoms leading up to this result which you never mentioned.

Sometimes when an output tube shorts, we swap the tubes left for right to troubleshoot the amp and in so doing, begin to piss off the resistor in the other channel as well.

This resistor protects the amplifier from any serious damage. Alternately the same thing could be done with a replaceable fuse, as you will see in many amplifiers, but that would destroy the sound quality : (

This is just a hypothesis of course.

Steve


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bateo102
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Re: Uneven volume output level
Reply #8 - 03/10/19 at 19:18:07
 
Thanks Steve for the explanation. I think you’re right about the reduced output and poor sound quality. I will replace to output tubes. If that still doesn’t help, should I send my Rachel back for diagnosis/repair?
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Steve Deckert
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Re: Uneven volume output level
Reply #9 - 04/10/19 at 20:38:23
 

Yes, if you have replaced the output tubes with no luck, then send it in and we'll repair it.  Just print out a copy the RA form and fill it out so that you can include it with your amp when you ship.  Turn around is 10 business days.

Thanks,

Steve

RA FORM:  http://www.decware.com/newsite/service.html
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