how do I interface to use a JFET as a switch?

I don't know what kind of noise/cross talk/distortion this might impose, in fact I didn't even go look at the datasheet, but did you take a look at the CD4066 and its variants? A multi channel analog switch that can be turned on/off using logic level control. Just google the part number and take a look.

Jim

Thanks for the replies.

When I first started working on this project, I had fully intended to use some type of analog switch. I looked at trygin things with multiplexers, etc., even got some ideas on paper before I realized there was a potentially serious problem. The on resistance of these types of devices is around 80 -

250 ohms. If I had only 1 effect on (and did not switch both input and output) I would only have 80 ohms in the signal path, which may or may not degrade the audio. However, if I had 3 effects on, I would have in the order of a several hundred ohms, which I think would cause at the very least an audible change in the signal leveif not a serious degradation of the tone. If I'm wrong in this assumption please let me know, because both of you guys are right - this would be way easier with some type of analog switch.

Thanks

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Hi Jamie;

My signal goes from guitar => 1st pedal => 2nd pedal etc => guitar amp, so there is no amp at the start of the chain. Is that what you were picturing when you said there should be no problems?

Thanks

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you would gain a lot of saved time by using something like the old stand by 4066 chip which is a bi-directional analog switch controlled by a simple logic level input. if you really want to get fancy with this, you could make it so that it latches/unlatches near the zero crossing point of the current output via comparator! but that would complicate things i know :)

--
Real Programmers Do things like this.
http://webpages.charter.net/jamie_5

if your driving an amp/pre'amp etc... you should not have any problems. actually the on R would help to prevent cross over impedance problems with other devices. the idea is to do this at the preamp stage and not at the main power stage.

--
Real Programmers Do things like this.
http://webpages.charter.net/jamie_5

Arp.. switching Audio is a pain in the bootocks. Don't suppose you could fit some nice bright shiny new relays....?

Eeebore probably wanted you to.......

Anyway all of that digital stuff is just an invitation for clicky shit what will detract from how crap your guitar playing is.

What you really want, since you are not bothered about power, is some of those VactecVactrols

And... once you have seen one of them you might be tempted to make your own. All you need to do is find a source for light dependent resistors, LDR's. LED's are easy. Then you put them in tubes, glue em up and heatshrink em to keep the light out.

Then you adapt your original relay thing to work with them.

Job Done.

Excellent

DNA

Eeeeh the days of the ORP12.

Bonza

DNA

Interesting idea - thanks Genome. Kind of a slow response time though, and even worse turn off (35 ms!!)

Hold the phone - Inspired by previous posts I did some Googling and came up with these from Maxim:

Now I would think that the 2-10 ohms that would be introduced to the signal line should have no effect on the tone. Wouldn't this be the equivalent of having a resistor of the same size in series? would this affect the sound?

Thanks

Not my problem... but nice cross fading scenario.

I'm sure you pick your geetar at about thirty picks per second but the rest of us have to spend time finding D having got used to E for 12.

DNA

This is why 9 bar variable Blues was invented. You use the time to draw breath for the next verse whilst getting your fingers right and it gives the drummer time to have a pull on his pint.

It's variable because chances are he'll lose his sticks so you'd have to drop down to 7 but since you are doing 9 variable no-one notices.

DNA

DNA

The switch resistance won't be a big issue.

What *will* be an issue is that an ac coupled signal will go 'below' ground and the bilateral switch won't like that on a single supply. In fact they don't like their ins and out close to supply rail at all. Look for the graph that shows Ron vs input voltage.

A jfet doesn't have this problem but as noted elswewhere a CdS/CdSe photocell might be easier to use. Farnell stock the very good Silonex parts btw.

I have no idea why it says 'unbranded' there ! For reference that shows what it looks like.

Graham