Tonefiend Forum

It's been almost two years since I got a wild hair to make a looper switcher for use with 2 amps. I have not prototyped this... still on the drawling [sic] board. I just found the schematic I'd drawn and so bear with me while I trace through it to see what I had in mind!

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OK starting at the bottom left, there is a DC power supply input J5.

Above that is J1, the guitar input, which goes to a JFET source follower (just think of it as a high-input-impedance unity gain buffer). The output of that follower goes to a tuner output J4 and to the loop send J2. When there's nothing plugged into the loop send, it is connected directly to the loop return. The loop return also goes to a JFET source follower.

So then what (right now, I'm as lost as you are)?

Here's a table showing what happens when various switches are in different positions. As I recall, S1 through S4 are "preset" switches and S5 is the footswitch that you'd hit to select what's going on.

S3 S4 S5 Amp out 1
down down down Guitar
down down up Guitar
down up down Guitar
down up up Loop return

up down down Loop return
up down up Guitar
up up down Loop return
up up up Loop return
==================================
Let's simplify this a little.

If S5 is UP, it picks off Return if S4 is up and Guitar if S4 is down. S3 does not matter.
If S5 is DOWN, it picks off Return if S3 is up and Guitar if S3 is down. S4 does not matter.

In the table below, "X" means "doesn't matter".

S3 S4 S5 Amp out 1
down X down Guitar
up X down Loop return
X down up Guitar
X up up Loop return
==================================

Similarly for Amp out 2:

S1 S2 S5 Amp out 2
down X down Guitar
up X down Loop return
X down up Guitar
X up up Loop return
==================================
OK, so how would you use this in real life?

S5 is the master switch that you step on.

By setting the switches S1 through S4, you can create presets that will send either your guitar or the loop return to one or both of the outputs when you press on the switch alternately.

One possibility:
S3 Down S4 Up S1 Up S2 Down - as you press S5, the looper is alternately patched to Amp 1 or Amp 2, while the straight guitar signal goes to the other amp. I don't think you can do this with a simple A-B switcher. If that's all you wanted to do, you could dispense with S1 - S4 and just hardwire it that way.

If you had a grounded 1/4" plug, if you jammed that into the FX return you'd have the function of an A/B switcher. Not that you'd go through all this trouble for an A/B switcher, just that you COULD use it that way.

S6 is supposed to be an extension of S5. The Eagle schematic/PCB package I was using didn't have s 4PDT switch handy so I just drew in 2 DPDT. The intention here is to illuminate some colored LEDs to let you know what's currently going on at the different amp outputs. E.g. Green = straight guitar, Red = Looper. However I haven't finished hooking that up.

Now there's another design around here I'll have to find that is a bit more complicated, which gives you the option of MUTING the effects loop send as part of a preset. In the existing design, whenever the Loop return is patched to an amp output, the Guitar signal is still going to the Looper input. So that would suck, because what I wanted was a way to put a loop into one of the amps, then switch over to using the other amp to play on top of the loop without having what I'm playing be routed to the looper input.

For example you could play some nice chords into a loop going to your clean amp, hit the looper button to keep it going, then switch over to the dirty amp to go all shreddy over your rhythm loop. Alternately you could play some line into the looper going to your dirty amp, then switch back to your clean amp to play some chords, chord melody, ambient volume swells, whale sounds, etc. without that all getting routed to your dirty amp as well.

Perhaps this design is approaching the limits of special interest as you'd really need to conform your performing approach to your amp layout. But isn't that what Tonefiend DIY is all about?

The thought that triggered all this was born from using a Digitech Jam Man into the front end of my Tech21 Trademark 60 and then realizing that if I put a loop in there with the clean channel selected, then wanted to play something over it using the amp's overdrive, then the loop tone would change as well. Of course, I could put the looper into the Tech21's switchable effects loop, but not all amps have effects loops. And, what with the myriad tube amps coming out these days, everyone doing anything even halfway serious is going to own at least a dozen amps, and how do you get those all into your performing rig?