25k Mid Pot Slope Resistor Switch?

[JohnnyCrash]

I got a 25k DPDT push/pull switch pot combo...

I’m considering using it to change the slope resistor. It’ll be in my Micro Bassman, so it’s going to put an 82k resistor in parallel with the existing 56k slope resistor when turned on — giving me the stock 56k or a 33k (56k + 82k = 33k) “Marshall” shift to the tonestack.

Does this sound crazy? Any issues you can think of?

 

[ThermionicScott]

Should work. When I've had this thought in the past (long list of unimplemented ideas!), I thought it would be cool to start with a 91k or 100k slope resistor for more of a BF cut in the low mids, then parallel it with a 56k to get in that 33k Marshall zone.

 

[NTC]

I know the choice has been made, but how about a pot in series with a resistor? You could turn it up to 100k for blackface territory.

 

[Lowerleftcoast]

Rob's site shows 76 VDC on the resistor. It might bother the switch. Maybe only switch when the amp is *off*?

Possibly you could put a .022uF coupling cap followed by a 1M resistor to ground (RC filter) in between the cathode and the tone stack, then the tone stack would not have DC on it.

 

[JohnnyCrash]

I had not considered the voltages there. It just never occurred to me.

I was thinking a DPDT would suffice to parallel in a resistor on one switch/side and parallel in another 250pF... but it’s not looking so simple after all.

 

[JohnnyCrash]

I’m exhausted, so I may be foraying into voltage territory, but maybe I could use the 25k DPDT to swap caps in the Presence control for different sounds (Resonance?)...?

 

[JohnnyCrash]

I’m going to go with Rob’s 25k Presence pot, but with the DPDT pull switch turning off the Negative Feedback/Presence circuit.

Might as well find a way to use this weirdass 25k switch pot that I ordered

 

[NTC]

In the early Brown Fenders there is a 0.5uF cap between the first gain stage and the tone stack. That would fix the DC problem (which is also a problem for the pot). One could use a 0.1uF or even a 0.22uF to be sure you didn't loose low end due to the caps being in series .