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Re: Still Switching (sort of Tapdancing really...)

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12/15/1999 2:09 PM

Re: Still Switching (sort of Tapdancing really...)

quote:
"You may want to try optoFETs like it was suggested on a channel switching thread sometime ago."

Why would this be better? What part number would you use?

12/15/1999 2:20 PM
Kali	>>Why would this be better? What part number would you use? It accepts bipolar signals and is easy to turn on/off. I'd try the H11F1 Kali

12/15/1999 6:36 PM
Joe Fuzz	I was going to sketch up a 2 loop version with bypass - until I saw you wanted 6 loops! Are you thinking of one switch per loop? Or one switch that cycles through each loop? If you're going with 1 switch per loop: If switch 1 is on (for effect loop 1), what do you want to happen when you step on switch 2?

12/15/1999 7:02 PM

You need three single switches per loop - one to do the "bypass" and two to gate the stuff into and out of the effect. These make for one bypass switch per loop/effect.

Some other things have kept me from getting my switch setup up at GEO, but there's a switch matrix in front of the one switch per loop. The switch matrix selects which bypass switches get activated per row of the matrix. A six-by-six matrix is where I started, although you can do any-by-six if you have six effects loops.

From your earlier post and Kali's reply, the H11F1, F2, or F3 work fine. They are isolated photo-JFETs that look like an open circuit down to about 500 ohms depending on the amount of current in the led. There is little or no distortion in the full-on position, so it's a pretty good switch. The only real problem is needing three of them per loop.

The CD4053 works well as a bypass, costs about $0.50, and you can use one per bypass switch.

The true mess is the switch matrix. You need six switches per program, so a six-by-six is 36 switches. If you're using mechanical switches, you're into some money. The little toggle switches are $1.50 to $5.00 each, so that's not too practical. Mouser has a slide switch that's $0.20, so it gets reasonable for the programming matrix, but it takes more mechanical work to mount it to a panel.

12/15/1999 8:07 PM

But you can see the point that I'm making. A two-loop either/or switcher can be done fairly cheaply and easily with a Schmidt trigger (or JK flip-flop if you so desire). If you add a DPDT footswitch and use it in front as a true bypass of the switcher, you can get away with using only 4 CD4053s.

In other words, a 2 loop project could probably be done for 20-30 bucks (depending on the case you use). A 6 loop multiplexed ordeal...at some point, you have to say, "I'll spend the $300 for a switcher!"

12/15/1999 8:38 PM

quote:
"But you can see the point that I'm making. A two-loop either/or switcher can be done fairly cheaply and easily"

Absolutely. The problem with matrix and order switchers is that they in crease in complexity and cost as the square of the number of things involved.

quote:
"A 6 loop multiplexed ordeal...at some point, you have to say, "I'll spend the $300 for a switcher!""

Yep. I was actually hoping to do a modular design that you could do as many or as few as you want. The two-by-two you propose is indeed a quick and easy one. If you go to the bit of pain to make that carry the hardware for expansion - which really isn't all that much - they you can grow it to a four by four pretty simply, and four by four is pretty serviceable.

Noticing that each in/out is actually a loop means that you can trade some flexibility in the switch matrix for more effects in the loops if you want.

12/15/1999 9:10 PM
Joe Fuzz	I think what's implicit in my arrangement -- and it sounds like it's so in yours, too -- is that there is a common ground to the entire unit. In other words, all effects units and the guitar (and the amp for that matter, too) will have the same ground. We're only switching "Hot."

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