sunn (fender) model t footswitch question (schem included)

[kismet78]

I've been hunting for this schem for days, yikes.

Anyway, this weekend I'm going to throw together a footswitch for my new used reissue Model T. The footswitch part of the schematic I've highlighted below. I think that's all of it... Would someone care to explain to me how this works? How are both the channel switching and the fx loop switching working from a mono jack? I really thought it would have been stereo, but thank goodness I always keep my receipts. I'm assuming it has something to do with the reversed diodes, but I don't understand the how. This really looks to be one of the simplest things I'll have built in quite a while, yet I think I understand it the least. Weird.

For S1A & S2A I'll used dpdt instead, so I can incorp LEDs. I'm assuming that's the least intrusive way of adding LEDs since the switching happening here doesn't appear to be a simple open/closed type situation. Correct?

Oh, do you think 1N4148 would be a suitable replacement for the 1N4448's? I happen to have a million of those lying around.


AND HERE'S A CLOSEUP OF THE SWITCH SECTION:

[drewl]

It uses different voltage levels (detemined by the diodes) to let it know what is being switched.

[kismet78]

Thanks. That makes sense.

I'm going to breadboard it with 1N4148s later and see if they'll work as a substitute.

[Andre]

It uses different voltage levels (detemined by the diodes) to let it know what is being switched.

To be more precise,  an AC voltage is sent to the footswitch.
The 2 switches short the positive, negative or both halves of the AC voltage to ground via the 2 LED's in the footswitch.
The switches in the area you marked on the schematic do exactly the same, only here diodes are used instead of LED's.

On the amp side there are 2 comperators to detect the absence of the positive and negative voltages and switch the DRIVE and EFFECT relays.

Here's a schematic of what I think is inside the footswitch:



André

[kismet78]

Alright, finished. Thanks for everybody's help. More photos and a build/finish report on my site: http://www.kyletompkins.com/wp/?p=573

[Andre]

Kismet78,

I like your footswitch.
Nice vintage look, but I see you are using a powersupply to feed the LED's.
In the little schematic I posted there's no need for an extra powersupply as the LED's are powered by the AC Voltage.
The current throught the LED's is limited by resistor R83 in the amp circuit.

The LED's in my (actually Fender's ) switching circuit have a double function.
They are used as diodes to short the switching voltages to ground and as indicator LED's at the same time.

This way you'd have one cable less to trip over on stage.

André

[kismet78]

Kismet78,

I like your footswitch.
Nice vintage look, but I see you are using a powersupply to feed the LED's.
In the little schematic I posted there's no need for an extra powersupply as the LED's are powered by the AC Voltage.
The current throught the LED's is limited by resistor R83 in the amp circuit.

The LED's in my (actually Fender's ) switching circuit have a double function.
They are used as diodes to short the switching voltages to ground and as indicator LED's at the same time.

This way you'd have one cable less to trip over on stage.

André

Ah, I didn't realize that would work, but it makes sense now that you point out R83 as a limiting resistor. If only I could go back in time before I started drilling...

I doubt I'll swap it now though cause I hate gaping holes.  It'll get daisychained on my pedalboard anyway, so I'm not too concerned with just using it as is.

Thanks for all your help!