RM20 Volume Fluctuations

[chas_w]

Hello,

I have searched forum and found similar threads, but no conclusive answer. Perhaps there is none. :shock:

I fired up the RM20 today and the volume seemed lower than normal, then not, then low, then not, etc. I changed modules and same thing. I search forum and start reading.....

I checked power tube bias and good at 17, play again, up, down, up down. Read forum some more with no conclusions amp idling the whole time. Played again no issues, problem gone. Turned amp off.

One hour later I plug in my new JF Trilogy (that kicks *** BTW) and no issues with volume up/down.

Any ideas? The only thing that changed from the time I turned on the amp with the problem until it was gone was the position of the sun in the sky or roughly 35 minutes and one hour after it was fine it was fine from a cold start.

Head scratcher for sure. I have not yet pulled tested and cleaned any of the pre or power tubes. If it was digital I may consider it a 04/16 coding bug. :lol: I say that because I had a raid card that would clock errors every Saint Patricks day and be solid until the next.

Regards,
Charlie

 

[warlok]

After it worked fine with the Trilogy, did you re-try the module(s) you started with earlier when it was fluctuating?

 

[chas_w]

No I did not try any mods after the Trilogy. Next time I will start out with the Trilogy and if fine I will put in those other 2 mods that I was getting swells with.

 

[speed2dirt]

I get the same thing with my RM4. I don't touch the volume knob, but the mod gets super quiet & muffled and then normal again. I've noticed with mine that it starts out fine, but after 10 minutes or so, it starts to do it. I can change the channel to a different mod, which fixes it for 30 seconds or so and then it does it again. I've run the same mods in my RM20 with no issue at all. I've cleaned the FX jacks as well as the volume & FX knobs on the RM4 with no success. Very frustrating!

 

[audiomidijace]

Sounds like a bad master volume pot. Try to wiggle and tap the knob to see if the sound changes. This was the case with one of my RM4s and a new volume pot solved the problem.
Good luck.

 

[speed2dirt]

Sounds like a bad master volume pot. Try to wiggle and tap the knob to see if the sound changes. This was the case with one of my RM4s and a new volume pot solved the problem.
Good luck.

That's kind of what I was thinking. If so, that'd be a relatively easy fix since I can just remove the small volume/FX board and send it to Rob. Or if I knew the value of the pot, could do the repair myself. I really don't want to ship an RM4 across country needlessly. I was fearing it could be the midi board or opto-couplers going out, which would be a big, expensive fix. Hopefully Rob can chime in on this topic.

That said, that wouldn't explain the OP's issue since the RM20 doesn't have a master volume. Hmmm...

 

[Jaded Faith]

If you are only having an issue when certain modules are involved and not others, that turns attention to the modules themselves and not your amp.

Read the info in this post: http://mtsforum.grailtone.com/viewtopic.php?t=19525

Look at the tubes in the offending modules. I often see donors here where one tube was damaged by using it in V2 and it not being able to handle the CF circuit. It's not a complete failure and all that that needs to be done is a simple swap of V1 and V2. As a matter of fact, I saw 2 modules this week with this very issue.

Hope this helps. If you still have problems, please email for a prompt response.

 

[chas_w]

Thanks all the input. I will investigate further when it happens again.

Yesterday there were no issues and it didn't matter what module. The problem was gone. It for sure was not imagined the day prior as it obvious to hear and the line out into my DAW showed roughly 5db swing.