Blues King 12 help - volume loss with effects loop

rockymtnguitar

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Two years ago I bought a Supro Blues King 12 on Sweetwater's closeout. Fun amp.

Anyway... jamming with buddies Monday night and my volume was really low. We've played together for a couple of years, so we're used to our sounds. Mine was roughly half what it usually is. I've got a pedal board (bunch of the usual pedals) - some going through the effects loop and some on the main line in. No changes have been made to the amp or board in months.

I did a bit of reading and just tested the amp with and without the effects loop and it seems to be the culprit.

Guitar > amp (no pedals), but with the effects loop plugged in and the board powered = low volume
Guitar> amp (no pedals) and effects loop unplugged = full volume.

Can anyone point me toward the next steps?
 

jaxjaxon

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Look and see if you have a selector switch for the FX loop parallel is where the preamp is bypassed so you get a volume drop and series is where the FX loop uses the preamp and no volume loss. So if it has no switch and your FX loop is a parallel type you will need a boost for the signal some use a preamp pedal some use a EQ with a volume slider set high for the extra decibel boost and some use a dirt pedal for the boost you need to get up to volume continuity.
 

naneek

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I was really confused until I remembered that the supro name had been revived. I was thinking "I never heard of an old valco amp with an effects loop..."

carry on lol.
 

wabashslim

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Spray contact cleaner into the FX jacks (power OFF). Work a plug back & forth in the wet jacks. The bypass switch on the jacks isn't in direct contact with the plug so you have to let the cleaner kind of slop itself around in there, but I betcha that's the problem.
 

rockymtnguitar

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Update. I *think* the contact cleaner solution resolved it. I'll need a few hours of testing before my trust level comes back up.

There's no selector switch for the effects loop, so it's certainly not something there. It's weird - worked great for 2 years, then - nothing.
 

rockymtnguitar

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And... the problem is back. So above jaxjaxson did a great job explaining the parallel and series differences. My amp has no switch. However, mine quit working all the sudden, with no changes to pedal configuration, etc. One night it was great, the next it was really quiet.

I'm at a loss - could this be tubes? I don't know how tubes fail - are they all or nothing? or do they fade?
 




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