rock/jazz switch

[phsyconoodler]

Now being lazy by nature,I want to add a rock/jazz switch to an amp without rewiring the whole tone stack.
  Does anyone know what the rock/jazz switch on a Dumble style amp actually does?

[bobmegantz]

If I remember correctly, the rock switch just lifts the bottom of the tone stack from ground, so the gain goes up and the tone controls are mostly ineffective.  I think there's a large resistor there instead of the usual smaller value.

[VMS]

Merlinb explains this at the Amp Garage with pictures in thread called 'Dumble tone stack explained (in 60 seconds)'.

Rock mode is basically fendery type tone stack and the Jazz is James type stack with mid control.

[Tone Junkie]

Cool I will have to go over and read that , thanks for the heads up I have to say i really like that switch in my Tweed bluesmiester  I was going to add to to another build but didnt really quite understand it. Good question phyconoodler.
Thanks Bill

[jojokeo]

IMHO it can be what YOU want it to be. I make many of my amps w/ something like this to vary gain in various stages...call it what you want. It could be a switch called rhythm/lead or jazz/rock or talk/scream as long as fits the description of what you are doing/making. Obviously calling something a "jazz" setting should fit the description and be a clean sounding & playing setting that would be appropriate for playing jazz. How you do it is using your own creativity and building knowledge to get the job done. I've seen guys getting good money for their amps w/ this control (besides others) being simply a bypass cap on a gain stage. Incorporating two different tone stacks or using a ground lift are other ways. I've usually seen the ground lift technique called a "Tweed" setting not a "Rock" setting and supports what I've said earlier.