H11F1 instead of relay?

[tempus]

Hey all;

I was just wondering if there was any reason not to use a photo fet like the H11F1 instead of a mechanical relay or JFET switch for switching fx in and out of a loop. I haven't really seen any projects that use them so I was kinda wondering...

Thanks

[DiscoVlad]

Not sure on the exact chip(s) used - i.e. I'd have to open mine up, but the Boss FS-6 foot switch uses a cmos chip to select latching/momentary and optocouplers for switching.

[defaced]

They blip up from time to time on the amp forums I frequent. So yea, its been done.

[R.G.]

The H11F1 is an LED driving a photo-FET. The FET changes from a near-open circuit to a few hundred ohms when there is current through the LED. It's an OK-ish switch as long as the signal is below a few volts, and not much current.

You'd need two at least for "bypassing", in the sense that Boss and Ibanez pedals "bypass" using JFETs. They're modestly expensive, and need a fair amount of support circuitry, which is what probably accounts for their not getting much use.

They do have one advantage. The LED/photo coupling is much better isolation from the control signal switching than the standard JFET circuits.

[~arph]

Voodoo labs does this:

http://stinkfoot.se/archives/1005

I've tried it in a couple of pedals, where I needed some better switches than the standard 3PDT blue ones and only had DPDT available. Works great.

EDIT: Saw it in a catalinbread pedal too recently I believe.

[tempus]

Thanks for your replies everyone.

R.G., you mention that the signal needs to be below a few volts, but the datasheet gives the peak-to-peak maximum signal capability as 60V. Doesn't that mean that you could have at least a 20V RMS signal at its output terminals? Also, you mention not much current. Current is something I never really think of too much for guitar signals; would it be capable of handling the current being processed by an fx pedal?

You also mentioned the support circuitry - wouldn't you just need a resistor to set the current through the LED properly, or does it need some other stuff to make it work? I was planning on driving it with a PIC, so I was thinking of sending my PIC output through a 330 ohm resistor to the H11F1, and connecting the signal to the output terminals (obviously I'd need a few of these to use it as a relay). If they could switch totally silently, they'd be worth the extra bucks. I guess while we're on the subject, could silent switching be accomplished by the phototransistor variety of these things like a 4N25?

Thanks for the schem link too arph.