FDP Forum / DRRI - bass control not working reverb channel/ 6 messages in thread.

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Aftermidnight



Australia

Aftermidnight
Oct 27th, 2016 03:57 PM        

I purchased a used DRRI and now after sometime the bass control on the reverb channel has stopped working and volume on that channel is way down on what it should be - other channel is fine. Can I get a bit of guidance - what to check - what to eliminate - all the valves seen fine. Thanks.<br /> <br /> Brad



willie

Contributing Member
*******

Too Near Atlanta GA

Amp Tech Emeritus
Oct 28th, 2016 04:06 PM        

Could theoretically be caused by a number of things...first always check V2 or swap it with a known good tube; possible component value or solder connection failures or flaws in C8, C9, C11 or R-21 (midrange resistor to ground off of the bass control). Those are good places to start.<br /> <br /> w



reverendrob

FDP Data Goon
Moderator

When I sin

I sin real good
Oct 29th, 2016 01:21 AM        

Also, check that the fuse is correct.<br /> <br /> All too often they're not on used amps!<br /> <br /> It won't cause the problems you're describing, but....



Aftermidnight



Australia

Aftermidnight
Oct 29th, 2016 08:33 PM        

Thanks for those suggestions. I dismantled the amp and found that C8,C9,C11 or R21 had no disconnection visable. I'm not a tech so i didn't measure anything with a multimetter or anything like that, I just had a look to see if I could see any obvious breaks. I can't tell if all the valves are ok - but I pulled them all out and they looked ok. I reassembled the amp. Here's what it's doing. Normal channel - no problem. Vibrato channel - (vibrato and reverb not engaged - foot switch not inserted) loss of volume and bass control not working - when the treble control is turned up the volume increases - its like the volume and the treble control are linked and interactive - if the volume is turned up not much increase - when the treble is increased the volume increases dramatically. Connecting the foot switch and selecting reverb / vibrato works - but the volume is still choked. Can anyone advise if this could be the V2 or is it something else?? Thanks - much appreciated



willie

Contributing Member
*******

Too Near Atlanta GA

Amp Tech Emeritus
Oct 30th, 2016 07:09 AM        

Sounds very much like you have a tone stack ground issue...<br /> <br /> w



Aftermidnight



Australia

Aftermidnight
Oct 30th, 2016 02:13 PM        

Thanks Willie,<br /> <br /> Could you expand on that diagnosis - what exactly is "a tone stack ground issue" and how do i repair it - Thanks <br /> <br /> Brad <br /> <br />



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