Making a circuit switchable

english_bob

I've just added a buffer to the pedalboard patchbay I made a while ago- it has an indicator LED that lights up when power is applied (which is currently all the time). I'd like to make the buffer switchable and have the LED indicate when it's in the circuit, but since my electronic skills extend to following diagrams and not burning myself with the soldering iron I'm not sure how to go about this without resorting to trial and error.

Currently the buffer sits between the first input/output jacks in the patchbay, so the signal from the guitar goes straight to the buffer before hitting the pedals in front of the amp.

I'm thinking:

DPDT on/on switch

1 - to buffer -> to audio output  
3 - audio input
5 - to audio output

2 - to LED +ve
4- 9v +ve
6 - unused? ground?

The 9v supply to buffer stays on the whole time.

Does that work, or am I expecting this to be simpler than it really is? I doubt anything bigger than a DPDT switch will fit in the enclosure...

Sporky

That looks like half-arsed bypass, which will hang the buffer circuit off the signal line. Like an original Crybaby.

You can get 3PDT toggle switches - even mini toggles. That'd let you wire up as true bypass and have an LED. You could even use a bicolour LED that's lit when the power is on, but is (fer example) green when the buffer is in the signal chain and red when it's bypassed.

robinbowes

This might be of use: http://www.geofex.com/article_folders/millenium/millen.htm

Also, this: http://www.dextersworkshop.com/shop/true-bypass-module-momentary-switch/

R.

english_bob

Sporky said:

That looks like half-arsed bypass, which will hang the buffer circuit off the signal line. Like an original Crybaby.

You can get 3PDT toggle switches - even mini toggles. That'd let you wire up as true bypass and have an LED. You could even use a bicolour LED that's lit when the power is on, but is (fer example) green when the buffer is in the signal chain and red when it's bypassed.

So will my half-arsed bypass have the same tone-crappening effect as the old crybaby when the buffer is bypassed?

Is a 3PDT toggle switch physically much bigger than a DPDT? There's not a lot of room left in the 1590B with eight plastic jack sockets, 9v socket, LED and the buffer circuit...

english_bob

robinbowes said:

This might be of use: http://www.geofex.com/article_folders/millenium/millen.htm

Also, this: http://www.dextersworkshop.com/shop/true-bypass-module-momentary-switch/

R.

Hmm. Millennium bypass might work...

Sporky

english_bob said:

So will my half-arsed bypass have the same tone-crappening effect as the old crybaby when the buffer is bypassed?

Is a 3PDT toggle switch physically much bigger than a DPDT? There's not a lot of room left in the 1590B with eight plastic jack sockets, 9v socket, LED and the buffer circuit...

It might not be as bad as a Crybaby, but I would expect it to be detrimental.

A 3PDT mini-toggle isn't huge, and you can use the existing LED hole for a bicolour LED. I'd suggest one of these (having tried a lot of different mini-toggles over the years):

http://cpc.farnell.com/apem/5656a/switch-3pdt/dp/SW03171

The body is about 17mm deep, 13mm wide and 17mm long.

ICBM

Whatever you do, don't connect pin 4 to +9V and pin 6 to ground… you'll short out your power supply when the switch is in the bypass position.

You've also got the switching on the input not the output, which won't work properly even for half-arsed bypass - the output impedance of the buffer will be very low and it will massively suck tone. 1 should be the output of the buffer, 3 should be to the rest of the pedals, and 5 the guitar input and input to the buffer.

Whether it sucks tone when it's on the output or not is dependent on the input impedance of the buffer (theoretically/ideally infinite, but it won't be in practice), but it's better to avoid it if you can.