A/B/Y question

[scotsman]

A friend of mine asked me I could find/build him an A/B/Y box - I said "no problem"  there are a few great layouts that are pretty easy and quick.  Here is the catch - that stumped me.  He would like 3 seperate footswitches for each selection.  One for amp A, a 2nd for amp B and a 3rd for both.  Anyone know how/if this works or is possible?  My search has brought of nothing so far.

[TheBigMan]

Presumably he means pressing one switch would cancel the other selection.  That would require some work with switching logic if I'm not much mistaken.  Pretty complex considering how simple a "standard" ABY is.

[scotsman]

Presumably he means pressing one switch would cancel the other selection.  That would require some work with switching logic if I'm not much mistaken.  Pretty complex considering how simple a "standard" ABY is.

Actually no - they do not need to cancel the other selection.  As dumb as it sounds he just wants an "A", "B" and a "Y" switch - even though the "Y" is redundant.  I was checking out http://generalguitargadgets.com/pdf/ggg_amp_aby.pdf as a possibility.  But is it possible to re-wire it to make it do what I want?

[pjwhite]

Here's a simple solution:
http://www.electrongate.com/projects/aby1a.jpg

How it works:
The relays are a special latching type (DigiKey 255-1043-ND).  Pressing button A energizes the SET coil on relay 1 and the RESET coil on relay 2.  This connects input A to the output and disconnects input B, and turns on LED A.  Pressing button B does the opposite, and pressing button Y energizes the SET coils on both relays, connecting both inputs to the output and turning on both LEDs.  A 9 volt battery powers the circuit.  If the LEDs are included, you should add a power switch to prevent the LEDs from running the battery down.  If the LEDs are omitted, the battery should last for years under normal use, so a power switch is not needed.

[scotsman]

It appears to me that that was for switching inputs - where I need to be switching outputs.

Then again - I cant read a schematic!

[zpyder]

This should be doable without using any relays.  Relays can be spendy and there's really no reason to use them.

The decision I think that needs to be made is does he want this pedal to be passive or active?  The pro of passive is it uses no battery (unless you add LED's) but the con is that when it's in "Y" mode (or "A" AND "B" - same thing) the signal to each of the outs will not be as strong since it's not buffered or anything-you'll loose juice.  Pro of active is that "A", "B", and "Y" will all have the same output levels, ie there will be no volume loss on A when B is also activated (which would probably happen if it's passive), the con is that you'll have to put together a circuit, pretty simple one mind you.  The TL072 opamp works perfectly for this and a circuit to do this is the ROG Splitter-Blend.  You will only use the "Splitter" half of the circuit though... You can find it at http://www.runoffgroove.com/splitter-blend.html

Whether or not you want to use the splitter is up to you... the rest can be done the same way no matter what.  I would do it with two SPST on/off latching switches, and one DPST on/off latching switch.

If you're interested I can tell you more, but I'm hungry gonna go get some lunch.

zpyder

[pjwhite]

It appears to me that that was for switching inputs - where I need to be switching outputs.

Then again - I cant read a schematic!

Since the inputs and outputs are connected via relay switch contacts and nothing else, they could easily be reversed.  Just change the labels from input A to output A, input B to output B and output Y to input Y.

[pjwhite]

Oh, and I forgot to mention, in case it's not clear from the schematic, that all three switches (A, B and Y) are momentary pushbuttons.