Preamp Switcher

[negativefx]

Hi everyone,

I posted this on FSB as well but haven't received a response.  I'm trying to build a looper of sorts but instead of having independently selectable loops, I want to toggle between them, one or the other always on.

I have a Super Bassman head and a Meatsmoke Preamp pedal. I want to run the Meatsmoke directly into the Bassman poweramp, bypassing the Bassman pre, but I'd like to be able to switch between the two. So basically my chain is:

Guitar > bunch of pedals > BassmanPre-or-Meatsmoke > bunch of pedals > Power Amp In

I don't need parallel/blending, nor do I *think* I need a buffer. I'd prefer if the pedal doesn't use power so an LED indicator is a nice to have but not a requirement... if I do have one, I'll have to feed it 18V because I'm out of 9V jacks on my power brick. The LED would only need to be on when I'm using the Meatsmoke, off with the Fender or vice versa. I don't need to alternate two LEDs. I don't plan on switching between the two during songs, so dropping the LED and pushbutton in favor of a toggle switch would be fine too as that would remove the need for a power source, correct?

I drew up the attached design but I'm not sure if it's correct, and what to do with the grounds.  I know I need to eliminate hum somehow so I may need a 4PDT instead of 3PDT but I'm not sure.

http://imgur.com/RY3RRNM

Any help would be greatly appreaciated.  Thank you!

[mth5044]

It would be helpful if you drew the wires in instead of writing down where each goes as it's initially very hard to follow. Also why all the J's?

But if I'm seeing what you are trying to do correctly, it looks like it should work. You can consider the preamp of the Bassman to just be like another pedal in this instance. It's basically an A/B pedal without a Y. I'd imagine you have a lot of cables going back and forth with that kind of set up. Without an LED you can just use a DPDT toggle.

[negativefx]

Thanks for the feedback.  The Js are a result of digikeys sketcher requiring the J prefix and the lack of wires are because I couldn't figure out how to get them to connect in the sketcher. 

Should I just have the in/out sleeves always connected to the loop out sleeve or do those need to toggle as well?

I plan on having the switcher sit up on my amp to reduce cabling but I'm also using low impedance (~20pf/ft) cables.

[negativefx]

Also to your point about it basically being an A/B switcher, I agree, but in this case I think it's more like two A/B switchers controlled from a single switch, right?

A/B branches to the two preamp ins, then another A/B that 'joins' the two preamp outs.

[dwmorrin]

and what to do with the grounds.  I know I need to eliminate hum somehow so I may need a 4PDT instead of 3PDT but I'm not sure.

Are you getting a hum problem?  There's no obvious reason why it would hum.  Don't over-think that element.  I see no need for a 4PDT here.
If you're using metal jacks, metal nuts, on a metal box, then you won't even need to connect any of the ground lugs on the jacks.  They will already be connected.  Check with your multimeter.
If they are isolated (plastic nuts/barrels/washers, etc) then just connect them together... and don't worry about it so much unless you actually create a ground loop.

[mth5044]

Unless you are going to use insulated jacks, the sleeves are most likely already grounded together by touching the enclosure. I wouldn't worry about switching the grounds. You only need 6 jacks, a toggle and an enclosure to give it a try. If you get hum we can debug it then.

I have always called the boxes that switch between 'this or that' A/B boxes. I guess most do not have a return setup like yours, but you only have two functions, A or B, you can't have A and B and you can't have neither. Thus the A/B!

[negativefx]

OK, I'll start drilling.  Thanks for the help!

[negativefx]

http://imgur.com/rDSX8ki

Made a better layout for future reference.

[mth5044]

That is how I would initially attemp it as well!