trinityamps.com

I have had the VRM module in my sIII for a while now and I really use it a lot on the normal channel. However when I have the VRM control down near its lowest,it only works properly on the normal channel. The TMB channel is a LOT quieter on the TMB master vol when the VRM is turned down low . In other words, each channel reacts dramatically different to the VRM control position, I can't AB switch between the channels when the VRM is cranked down low, does that make sense?

Are you controlling the voltage on all tubes or just the power tubes?
Stew

It is just the B+ reduction so I guess power tubes only....It is only really noticable when I have both channels dimed and the VRM cranked down low.

Hmm!?! I think you are actually controlling all tubes if the VRM is on the B+. I'm thinking the tube layout of the TMB channel doesn't respond well to the extremely low voltages particularly the triode feeding the tone stack. But then again I don't have VRM on my plexi 18.
On my bastardized Traynor I have "power scaling" on the o/p tubes AND the PI but not on the preamp. Then there is a master volume to deal with too.
Perhaps Coco will have a better explanation.
Stew

Thats what I was thinking actually . The TMB preamp section seems "starved" when the voltage is low. It is really hard to explain in words, but maybe the TMB preamp just needs a little more juice than the normal channel,because it seems fine near higher VRM settings.Just trying to get my head around whether there was an issue or not.. Thanks Stoo!

In my own work I have found that preamps sound best and give best definition when their rail voltage is kept reasonably high. On 18watt.com after a lot of people trying VVR/VRM modules in different ways, the over-riding consensus was that it works best just to scale the power amp and PI, but not the preamp. There are schematics in 18watt.com's Downloads section, showing how to do this.

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