2 loop pedal

[aron]

Just want to be sure on this. This is what I want to do:

Make a pedal that chooses between 2 loops with a single foot switch. Ideally, I'd like to ground the input of the switched out loop and have LED indicators. I don't think I can do this with a 3PDT - I think I only have enough poles to either ground the inputs or have an LED.

I suppose I could use a Millenium bypass - but it's been so long since I used one (although it worked fine for me).

Other than using a Millenium bypass or relay, I believe I'm correct in that I cannot do the above with a single 3PDT right?

[aron]

I guess that's why I need this:

http://www.smallbearelec.com/Detail.bok?no=670

[widdly]

Could you put a buffer on each send, leave them always connected and just switch the returns?  Then you could use a DPDT.

[Processaurus]

Grounding the input is a very good idea, I have one I made (two loop, one switch) that doesn't do that, and high gain stuff will feed back on itself with the input floating.  Also it will do that in the loop its in, I think because of my messy wiring.

A simple and slightly inferior solution is to ground only one of the loop's inputs, make that the high gain loop.  With the 3rd pole of the switch with ground on the common, the LED - on one throw, and then with the other throw you are free to ground the input of one of the loops.

If you wanted, you could ground the other loop (the loop that is on when the LED is on) in bypass by an arrangement with a NPN transistor with the base attached to the same throw as the LED (-), and the collector connected to the loop input, and the emitter to ground.  When the LED is on, it will connect the base to ground, turning the transistor off.  When the LED is off (cathode not connected to ground), it will tie the base high, turning the transistor on, into a conductive state, making a clintonian ground connection that should be more than adequate for the task of stopping oscillation in the unused loop.  Off it should be in a high impedance state and not load the instrument down at all.  A FET would work too, if it were an enhancement mode JFET.

I'd reccomend using the middle pole of the 3pdt for this, to keep the ins and outs as isolated as possible.  Shielded input wire wouldn't hurt.  I'll have to do this modification to mine, now that I think of it, mine has been a problem in certain high impedance + high gain situations (and its like, AAAGH, how hard is it to make a stupid switcher!!??).

[Toney]

 

  This should do the trick...

[Toney]

Or, if you want to keep the grounds seperate and use milleniums.

[Processaurus]

  This should do the trick...

regarding the first diagram, unfortunately the led is always connected to the input, it will mess with the audio and make it pop like crazy.  The loop that is on will have ~7.6v DC on it, then you switch to other loop, which is being held at ground, and there'll be a 7.6v transient.  POP!

[Toney]

   My understanding of diagram one, is that the chance of popping comes from the sudden ramp up of the opposite LED as the switching occurs as signal ground and power ground are shared. When you say "the led is always connected to the input" you mean via the ground pathway, right?
Other than the chance of a pop, how would it interfere with the audio pathway?

Darn simple loopers!!

Anyhow, diagram two, the millenium solution is the safest bet for this.

[Processaurus]

Hi, a better way to explain the flaw of the first diagram is that the input that is being heard is tied to the +, through the floating LED, giving it a 7.6v (9v - the LED drop, 1.4v for red) DC bias.  Then you switch to the input that was being held at ground.  People get pops from little DC differences in their bypass switches (hence the universal 1M pulldown resistors to drain any DC leaking through in/out capacitors).  This is a giant DC difference, relatively.

The millenium version may have problems too, the millenium control line is meant to be totally floating when the LED is on, and to a light load to turn it off, with it always connected to the input of the first effect in the loop, that may load it enough to turn the LED off always.

[Processaurus]

Toney, I used your drawing sort of, this was what I was thinking, a transistor used as a switch to ground one of the inputs.  Comments welcome for sure.  I think you could use an enhancement mode JFET in a similar way.

[Paul Marossy]

This is how I did my looper: http://www.diyguitarist.com/PDF_Files/LooperSchem.pdf

[aron]

>A simple and slightly inferior solution is to ground only one of the loop's inputs, make that the high gain loop.  With the 3rd pole of the switch with ground on the common, the LED - on one throw, and then with the other throw you are free to ground the input of one of the loops.

I never even thought of this. This would work for the hi-gain loop.

And that NPN transistor idea is great! I'm going to try it. Yes, I'd like to ground the inputs for sure. I did order that 4PDT, but I am going to try that transistor idea as well.

Thanks everyone!

Aron

[Processaurus]

I totally got the transistor thing backwards so I took the picture down, the way its drawn it will short out (turn on the transistor) the loop  you're trying to play through, I'll get back to y'all on that when I have some time later.  I can think of a way to do it with 2 transistors and hooking the + to the common on the 3rd pole, then you could use a bi color LED, like Paul did, might be hot...

[r.mckillop]

This is how I did my looper: http://www.diyguitarist.com/PDF_Files/LooperSchem.pdf

I made something along these lines last night to switch between the preamp in my Bivalve and an external Mesa Boogie V-Twin preamp, signal goes through one or the other preamps, then to pedals and then back to the Bivalve's power amp.  I'm getting a bit of a pop when I switch preamp loops though, did any of you end up implementing the transistor/millennium bypass designs?  I'd love to be able to use my V-Twin for distorted sounds and the bivalve for clean while playing live, but the pop has to go.  Any suggestions?