Unpleasent Distortion when Boosting Blackface

[Tube Head]

I have been using a visual sound visual volume pedal in front of my RM100. Just recently I noticed some very high frequency distortion when I have the pedal up full on the blackface module.

The pedal has some clean boost when it is at maximum though im not sure what the numbers are it seems like alot. The problem is only with the blackface module, my other ultra modules is set for midgain and the 1086 for high gain.

I am suspecting the pre amp tubes of the blackface module or could it be the input?

 

[joey_truelove]

The Fenderesque modules are a bit tricky to master from a design point of view. The clean channel of a Fender of such type should basically have one input triode, then volume control and EQ, followed by a phase inverter. These modules, if I understand it correctly, let the signal go through at least four gain-stage triodes (with the input valve V1 included).

My advice would be replacing the valves on the module with AT7s or similar or, with a bit of soldering, even AU7s. If that shouldn't work or if I wanted to try something else I'd but any boost or overdrive post the pre-amp section (the module included). No, it won't sound the same but that's the problem taken care of.

 

[Rich G.]

I had the same problem with my Blackface module. Doing THIS mod fixed it.

 

[Tube Head]

Thats it. I checked it out and I have the old resistor. Thanks!

 

[seeker]

I did the same mod to my Brown. I tried the 150 ohm resistor but it killed the sound. If you do the mod, pickup some other resistors as well , like a 330 just in case the 150 doesn't work for you. They're inexspensive , and it's fun to experiment.


H