Background (you can skip and jump strait to my question of you want):
The amp had an EQ bypass switch, which I recently had changed out to a jack that can be used with an external foot switch (when nothing is plugged into it, the EQ is allowed to go to ground and enabled, when a pedal is plunged in, it can either allow the EQ to go to ground or breaks the ground bypassing the EQ). I love the sound of the EQ bypassed! Obviously, when bypassed the volume level also goes up. If I was alternating between lead and rhythm, this might be ideal. However, I typically just play rhythm and often play without a band (so a more constant volume level would be desired. The ideal usage for me would be a miens by which I can enable the EQ when I want a clean sound, then bypass the EQ to get something a little more open that breaks up a little, but without having too significant a change in volume.
Question:
My amp has a master volume control. Would it be possible, without significant modification to the amp, to either have an expression pedal that would just drop the "master volume" a little or to have an external expression pedal that could be used instead of the master volume knob (So, the master volume knob is enabled when nothing plugged in. When Something is plugged in, the expression pedal sets volume and the master volume knob on the amp is bypassed). The two ideas I had were as follows:
1. Expression pedal (first idea): Put a stereo 1/4" jack in the amp that has a little built in switch. The master volume (from what I understand) essentially acts as a variable potentiometer between the preamp stage and the output stage. So, I would have an expression pedal with a potentiometer that matches the one in the master volume of the amp and essentially run everything through a shielded TRS cable as shown in the picture bellow.
Concerns: Running the signal through a 10 ft cable could drain the tone. In fact, I think this is a bad idea for just that reason...
2: Foot-switch (second idea): On the signal going to the master volume, solder a resistor (not sure what volume) to the ring of the already existing jack that handles EQ Bypass. Replace the current mono cable on the foot-switch that I have with a shielded TRS cable, and have the switch alternate between grounding/enabling the EQ and grounding the resistor connected to the signal going into the master volume (which should attenuate it without making lots of smoke and fire I hope?). See picture bellow.
Concern: Adding a resistor to ground may cause unforeseen consequences.
3. Combination of 1 and 2 (not pictured): Solder a resistor to one end of the master volume to a 1/4" jack. Use an expression pedal with a potentiometer, one end soldered to ground and the middle lug soldered to a foot switch going to the wire leading to the resistor soldered to the master volume pot. The resistor will prevent the master volume from going completely to ground, the potentiometer would allow to vary how much the signal level is dropped, and the bypass switch would enable full volume.
Concern: Same as second idea
Thank you for taking the time to read this and I look forward to hearing from you.
PS: I know some basics, but I am NOT someone who is qualified to just go messing around inside a tube amp. I am NOT planing on doing any of these modifications on my own without first speaking to the person who designed and built this amp. I just want to know if these ideas seem like they could work and if anyone has a different idea.
