Loop station considerations and questions

[Fancy Lime]

Hi there,

I am a bit fed up with putting footswitches in each and every pedal. They take up room, are tedious and error-prone and relatively time consuming to build compared to the actual meat of the circuit. So I was thinking I could save me some tedium in the long run by simply building a loop station and putting switchless "pedals" in the loops. For my purposes, something on the order of 5 or 6 loops should be plenty. In the end, certain pedals are almost always used in combination, so thay can stay in the same loop and be switched on by a single stomp.

One question that haunts me is, how to implement the switches. It is not going to be hardware 3PDT, that's for sure (for a lot of reasons, reliability being chief among them). The original idea was Boss-style JFET switches. The whole thing is definitely going to have a buffer in the very front and one at the very end. But with, let's say 6 loops, there are a lot of parallel resistors from the signal path to virtual ground (V+/2), meaning we probably want some additional buffers. Would a buffer between each loop be a good idea? Or is there a less noisy alternative? Buffer after every other loop, maybe? I was considering TL072 in non-inverting buffer operation.

Or would I be better off implementing the whole thing with relays? What are the catches and pitfalls of relays that someone who has never worked with them might fail to consider? How about switching noise?

The other question that is on my mind is about the activator circuits. After extensive research and some experimentation, I am at the point of being almost decided to go with the tried and true Boss-style activators. Can be made to reliably turn on in off-state upon power-up. Can easily be remote controlled. Is cheap, easy, reliable and not picky about supply voltages, part tolerances or anything of the sort. BUT: I have yet to figure out how to make it so that I can change the foot-switch operation from latching to momentary with the least amount of extra switching around of components in the circuit. Ideally, this should only require a single on/off switch, because then I could use one switch from a DIP multi-switch, which I will be using for setting other options anyway. So far, the simplest version I can think of that I think should work (not tested), needs a SPDT switch. Has anyone else done this and come op with something easy and functional?

Thanks and cheers,
Andy

[SPoT_D]

So you are saying that you want a foot switchable pedal, without a standard hardware switch?
There are some options that avoid popping noise or tone suck, but all of them still use some sort of hardware footswich.
muzique.com has a true-bypass version that uses a microcontroller and relay https://www.muzique.com/schem/bypass.htm (i think i've seen one from coda-effects as well)

[Fancy Lime]

So you are saying that you want a foot switchable pedal, without a standard hardware switch?
There are some options that avoid popping noise or tone suck, but all of them still use some sort of hardware footswich.
muzique.com has a true-bypass version that uses a microcontroller and relay https://www.muzique.com/schem/bypass.htm (i think i've seen one from coda-effects as well)

Hi SPoT_D,
well yes, since I have yet to figure out the whole psychokinetic switch activation business and Uri Geller won't return my crystal-ball video calls, there is going to be some kind of hardware activator for me to interact with the actual switching circuit. My point was just that it wasn't going to be true bypass, hence the sentence "It is not going to be hardware 3PDT...". In fact it could even be a non-mechanical switch, like a capacitive or photoelectric trigger circuit, but I find those a bit overly complicated for my purposes and they tend to have reliability issues under adverse conditions (aka "live on stage"). So it is going to be a momentary single pole, normally open hardware footswitch. My question was related to the pros and cons of the many different methods to utilize those things for activating an internal JFET or relay based switching circuit and the potential cons of relays as such.

Cheers,
Andy

[patrick398]

I recently (blindly) ventured into the world of relay switching. Preliminary results are promising. I stumbled across the 'Incandenza Bypass' designed by Steve Demedash and had some PCBs made up. I opted for his because it avoided the need for PICs and only required an inexpensive non-latching DPDT relay, 555 chip and momentary SPST footswitch.
With most circuits it seems to be virtually popless, thought with higher gain circuits there's a very small click/pop. Totally inaudible if your switching whilst playing though. 

It's the small board in this picture. I'm more than happy to send you the files if you want.
https://postimg.cc/rRSHP6xj

Schematic:
https://www.instagram.com/p/Bpse3QZnTVI/

Layouts:
http://effectslayouts.blogspot.com/2018/11/demedash-effects-incandenza-bypass.html

Hopefully he doesn't mind this all being posted. He uploaded the schem on instagram so i assume it's fair game

[Ripthorn]

I've been building a lot of microcontroller enabled projects lately. A little bit of a learning curve, but it opens up a world of possibilities. I built a midi controllable 5 loop switcher. I have full documentation and a video here: https://scientificguitarist.wixsite.com/home/mls-5

[SPoT_D]

Hi SPoT_D,
well yes, since I have yet to figure out the whole psychokinetic switch activation business and Uri Geller won't return my crystal-ball video calls, there is going to be some kind of hardware activator for me to interact with the actual switching circuit. My point was just that it wasn't going to be true bypass, hence the sentence "It is not going to be hardware 3PDT...". In fact it could even be a non-mechanical switch, like a capacitive or photoelectric trigger circuit, but I find those a bit overly complicated for my purposes and they tend to have reliability issues under adverse conditions (aka "live on stage"). So it is going to be a momentary single pole, normally open hardware footswitch. My question was related to the pros and cons of the many different methods to utilize those things for activating an internal JFET or relay based switching circuit and the potential cons of relays as such.

Cheers,
Andy

You joke, but the psychokinetic switch activation thing is in the realm of possibilities
https://www.engineersgarage.com/contribution/appliance-control

micro controllers will make both JFET and relay switching work using a momentary switch. JFETs will need buffers with a chance of coloring the tone a bit. Relays work well as true bypass switches with a chance of some switching noise, especially when you use a couple of them in one path. nothing near the noise of a 3pdt tough. Unfortunately I had some noise from micro controllers bleed into my signal a bit at one point.. probably due to bad layout.