A few switching/routing questions...wanna help me out?

[lwatford]

So, I'm in need of some help making a switcher for a band I work with.

I need to switch two inputs (mando & guitar) to two outputs (two separate channels). I need a tuner out, and an effects loop between the two a/b's. I know I could do this with a couple of 3pdts (one on the input, and one on the output), but I would love to have it rigged up so that one switch changed both the input and output selection (keeping it simple onstage). I want to use LEDs for the selection also. Am I over thinking this, or is there a good way of doing it.

[R.G.]

I need to switch two inputs (mando & guitar) to two outputs (two separate channels). I need a tuner out, and an effects loop between the two a/b's. I know I could do this with a couple of 3pdts (one on the input, and one on the output), but I would love to have it rigged up so that one switch changed both the input and output selection (keeping it simple onstage). I want to use LEDs for the selection also. Am I over thinking this, or is there a good way of doing it.

Switching can get very convoluted. It is very difficult in general to start with the devices (3PDTs for example) then fit them to the task, at least for any application that's nonstandard. What does work in all cases is to break it down to the simplest possible cases of as many SPDTs as you need to do the switching, then to group the SPDTs back together to get the N-pole-DT that you actually need. Once you know what "N" is, then you can pick actual switching devices.

In your case, you can probably do it with a number of DPDT relays, all controlled by one footswitch.

Or N footswitches. 

[lwatford]

I need to switch two inputs (mando & guitar) to two outputs (two separate channels). I need a tuner out, and an effects loop between the two a/b's. I know I could do this with a couple of 3pdts (one on the input, and one on the output), but I would love to have it rigged up so that one switch changed both the input and output selection (keeping it simple onstage). I want to use LEDs for the selection also. Am I over thinking this, or is there a good way of doing it.

Switching can get very convoluted. It is very difficult in general to start with the devices (3PDTs for example) then fit them to the task, at least for any application that's nonstandard. What does work in all cases is to break it down to the simplest possible cases of as many SPDTs as you need to do the switching, then to group the SPDTs back together to get the N-pole-DT that you actually need. Once you know what "N" is, then you can pick actual switching devices.

In your case, you can probably do it with a number of DPDT relays, all controlled by one footswitch.

Or N footswitches. 

Thanks! I like the relay idea...back to your website I guess to re-read the relay articles!

[R.G.]

To a first order, non-latching relays are just electrically-operated momentary switches. The simple concept is that the incremental SPDT has a common ("C") or pole, a normally open (NO) throw and a normally closed (NC) throw/contact. With the coil not energized, the C is connected to the NC. When you put enough current through the coil, the C connects to the normally open (NO) contact.

You can get relays with no NC contact, which are open/closed switches. You can also get relays with combinations of one, two, three, or up to eight (!) SPDT sections. All sections are electrically insulated, and they all change together with coil energized or not.

The best-compromise relays for use in most pedal-oriented musical equipment are DPDT types with a 9V coil. This is primarily because there is 9V power there most of the time. Mouser carries these now, for about $3.00 each. So you can use one, two, three... relays to get two, four, six, etc. SPDT sections. It's OK and convenient to use the simplest-compromise relay and ignore one section if you want, and also OK to use only the C and NO or NC section for a single switch.

It's this last consideration that leads to the short cut I told you - figure out your switching in SPDT sections, then use as many as you need; finally, case up the SPDT sections in "N" relays as needed.