Stereo Loop Pedal

[Sleipnir]

Hi everyone,

I want to build a stereo loop pedal that will take a stereo input and route it to a stereo output when bypassed but then send it to another stereo pedal via stereo send and returns when switched on. I could not find any schematics or layouts when searching online, but I think I came up with a design which will work using a 4PDT switch. When bypassed, the two inputs (L & R) will get routed directly to the two outputs (L & R) while the two sends are grounded. When in the ON position, the two inputs get routed to the L & R sends which would go to stereo effects pedal(s) and then routed back via the stereo L & R returns and ultimately to the L & R outputs.

The only downside I see is the lack of an LED. I assume there is no way around that for such a stereo setup, but please let me know if I am missing something. I have read a little about the millenium bypass circuit and although it could potentially work here, I don't think I would have the space.

Also, is it absolutely necessary to ground the sends for a loop pedal? What is the downside of not grounding the sends? Loud pops, perhaps?

[Cozybuilder]

The only thing I would add to this is capacitor coupling for the send and return lines. 100nF between the switch and jack for each of these will assure no DC mismatch of whatever is in the loop from your input and downstream of this looper. Grounding the sends is a nice touch.

[samhay]

If you have a stereo signal, then I'm guessing that this has been through at least on stompbox/effect, so is effectively buffered?

If so, making a true bypass looper doesn't make much sense to me as the switch is going to be expensive, difficult to get hold of (I assume you want a foot swtich?) and not terribly reliable.

How would you feel about a non-true bypass option?

[Cozybuilder]

One reasonable priced option, there are others:

http://www.mammothelectronics.com/4SFS4PDT-LS-p/800-1004.htm

[samhay]

Wow - the last time I looked they cost closer to $20.
Concerns about reliability, the lack of LED indicators and the general rationale for using true bypass still stand.

[Sleipnir]

Thanks guys. I actually plan on having this after a Fulltone True-path ABY pedal which has switchable buffers. I like the option to go through no buffers as well as I like playing my amps with no pedals looped in. In the loop of this pedal will be a Rotosphere pedal. The outputs of this pedal will go to two different amps (a Super Reverb and a Tweed Bassman). The Rotosphere sounds great in stereo, but sometimes I like it coming through only one amp with the other amp completely bypassing the Rotosphere (it makes the effect more subtle). I will add a switch to the stereo loop pedal which will allow me to operate it in full stereo or in mono. I looked at the schematic of the Rotosphere, and both its inputs and outputs use regular jacks for the mono (R) jacks, but shorting jacks for the stereo (L) jacks. Thus, it appears possible to switch between mono and stereo with cables plugged in by simply shorting the L & R jacks together for mono operation. In mono mode, one output from the Fulltone ABY pedal would be going to the Rotosphere in mono and out to only one amp, then the other output from the ABY would go directly to the other amp, bypassing the Rotosphere. In stereo, the outs from the Fulltone would each go through one side of the Rotosphere and then to separate amps.

Anyway, I am curious about the 100nf capacitor suggestion. Are you saying to put these inline with the wires from the send and return jacks to the switch (i.e. 4 in total)? Would the capacitors not add some sort of filtering to the sound, or is 100nF big enough that all audio is bypassed? If there is a DC mismatch, is the result loud pops when switching or something else altogether?

Regarding the grounding of the sends, I am not sure if it is really necessary, but even if I don't ground them, I don't see how I could add an LED, so I might as well ground them?

[joelo]

Hello!

I am resurrecting this thread because I am looking into making the same box. Did you end up making one yourself?