Relays and switchable MV

[Smokebreak]

Where is the unused triode? I have a crazy idea if it is towards the backend of the preamp.

Well it's in the middle. 2nd tube, inbetween 2nd and 3rd stage. I'm all ears. Watcha got?

[JazzGuitarGimp]

I'd use the extra triod as a cathode follower. Place it between the output of the tone stack and the two MV pots. No load on the tone stack....

[Jana]

Lou is reading my mind.

[Smokebreak]

Ok very interesting. So I'm assuming the voltage divider sets unity gain for the CF, as a gain stage, and then the MVs don't load the tone stack. I hadn't even considered the MVs in a rheostat setup. I like that.

So, being that since the 70s the normal master setup has loaded the tone stack, what sort of sonic differences could I expect?

[Jana]

The cathode follower is going to be unity gain already (actually a hair less). You want to set the divider of R1 and R2 so that you don't push this CF stage into clipping with a max overdrive signal (unless you want to do that).

The rationale behind the rheostat setup is this: there will never be a time when the input to the PI is disconnected from one source and connected to another. It should be very quiet when switching. You are simply changing the resistance value to ground.

It's a lot simpler too. Otherwise you have all those connections between the two pots to connect and disconnect.

Yes, they have been "loading" the tone stack with the master volume for a long time and some have complained about it. I honestly don't think it is the 1M load that people are hearing but instead it is the increased and widely varying grid stopper that is now present at the PI input (because of the 1M pot).

[Smokebreak]

Thanks Jana, I'm gonna go with that smart MV setup. I'm scared to put the CF stage in because I'll be zigzaggin signal with the location of the unused triode. I'm gonna get the relays in first.
I've just ordered the relays from Colossal, and I already recommend his boards to others. Here's a picture of the amp, as it stands today, because I'd like to find the best locations for these boards. I've got plenty of room underneath all those wires
For kicks, I played out some youthful dreams and recorded this amp with Maiden. Dave Murray got me hooked on electric guitar sounds, so I figured why not. The interlude still gets me every time.
https://soundcloud.com/jeremyslemenda/p ... plexus-50w

[LeftyStrat]

Um, I hate to be the one to point this out, but it seems to me that you are going to have an unused triode!

Nooooooooooooo!

[10thTx]

There are numerous schematics, layouts, photos on how to do relay switching and hook up foot switching relays here:

http://el34world.com/Forum/index.php?topic=14348.0

With respect, 10thtx