Help: AB selectable input pedal

[burningman]

Can anyone provide recommendations on building an AB box that would me to switch between two inputs (one for guitar and the other for mandolin). I'd have one output and a tuner out as well. I'd imagine a buffer on each input might be a good idea. Is an isolation transformer a good idea and should I follow the example of the Keen's Humfree ABY?
Thanks. BM

[iaresee]

If you're going to run the output into pedals (especially if the pedals have buffers) you can probably stick to doing this as a passive box. Although, if you went with buffers you could add gain knobs that would let you do level matching between the two instruments so when you switched from one to the other the output from the box was consistently loud.

You could use one buffer but toggle between two gain setting sections: one for the A input, one for the B. That's a lot of switching. You might be able to take care of it with a 4PDT switch: two poles to switch between A and B, one pole to switch between the A/B LED(s), one pole to switch between two different gain pots. Not sure how reliable or prolific 4PDT stomp switches are. If they're hard to come by you could do unbuffered relay based switching with ICs and a momentary which would also make the number of things you could switch with a single stomp fairly high.

If I could draw worth a damn I'd put a block diagram together for you...but here's a summary: A/B switch the inputs with a 3PDT (two poles for tip, ring of the inputs, one pole for LED indicators); feed output from A/B switch into a second 3PDT that switches between the tuner output and the input to a buffer (2 poles for tip, ring switching, one pole for LED indicator for the tuner mute). Output from the buffer goes to single output from the box.

[theundeadelvis]

I have built a couple of these using the GGG mini mixer and making each channel switchable. Then you have switchable inputs and you can adjust the levels before your effects.

[iaresee]

Visio to the rescue! This is what I was trying to describe:



If you made the first switch 4PDT you could also toggle between two gain pots on the buffer.

[burningman]

Thanks for the suggestions guys. I was wondering a couple of things

...if you went with buffers you could add gain knobs that would let you do level matching between the two instruments...

by gain knobs do you mean just a log volume pot or a booster circuit?

Do you think that I should isolate the tuner output from the regular output using a coupling transformer? What type and how should I wire one if applicable?
Thanks, BM.

[iaresee]

...if you went with buffers you could add gain knobs that would let you do level matching between the two instruments...

by gain knobs do you mean just a log volume pot or a booster circuit?

If you use something like Jack Orman's MOSFET Booster to do the buffer section you could switch between two different R6 5k gain controls. This would let you boost and buffer both signals.

Do you think that I should isolate the tuner output from the regular output using a coupling transformer?

I don't think you'd need to isolate the tuner output. None of those true bypass looper strips that seem to sell by the boat load do and people seem to get along fine with them.

What type and how should I wire one if applicable?

What type of wire? I recently asked the same question for a junction box build. Answer: solid core hook up wire is great. I think I used 22 AWG solid core.

[arizonabay]

Hi, not wanting to highjack this thread but its so close to what i want to build.

Would this work in reverse, with single guitar plugged into the 'out' and A and B going to separate channels on say a Fender Deluxe?

Thanks very much for the sketch!
Matt

[jkokura]

You don't need to go quite so complex for what you're talking about - you just need a simple AB box for that. There are many, easy layouts for that. You just need one switch. Check out the Layouts Link at the top of the page and search for AB box.

Jacob

[arizonabay]

Hi Jacob,

Thanks for the reply, I've had a look everywhere and can't find one that, like the above, has:

one input
A & B output
LEDs for A & B
additional 'tuner' output
tuner out mute switch

Would iaresee's schematic work for me if I plugged the guitar into the output and used it in reverse?

Thanks,
Matt

[jkokura]

What you're looking for is an ABC box really. Check out the Lehle Dual. If that is similar to what you want, start saving!

http://www.lehle.com/frameset.php?country=ca&lang=en

Either that, or you can build an analog version that essentially works the same. The Lehle gives you lots and lots of options. The 1 at 3 might be pretty cool for you as well, especially if you use effects loop also.

Jacob