Ampeg Footswitch Question

[bob p]

I'm looking for information about what's inside of Ampeg footswitches like the AFP-2 and the AFP-2B. These are fairly simple footswitches that use a 1/4" TRS phone plug to control two features of an amp by completing the ground connection in a circuit. They also contain an LED indicator, so I'm wonder what's inside of them.

I could be wrong, but I don't think that they contain any complicated logic circuits like some of the Mesa footswitches.

Looking at an SVT-2 Pro schematic, my educated guess is that each segment of the footswitch just completes the ground connection between a (+) voltage coming out of the amp and a ground connection, so that the footswitch wouldn't have anything more inside of it than an LED and a current limiting resistor in series with the switch.

Some other amps like the VOX AC30 reissues use footswitches that contain the LED+resistor in the footswitch box, though some other amps dispense with the resistor, only putting the LED in the box. Doing this would have to relocate the current limiting resistor to the innards of the amp itself.

Does anyone have tech info on how the Ampeg AFP-2 and AFP-2B footswitches are wired? A schematic would be appreciated. Even a guts photo would help. Or just a good description. I'd like to build a footswitch box to work with an old SLM-era 2 Pro.

Thanks.

[Enzo]

I don't know offhand, but some pedals have no resistor because the circuit they complete is already limited. They might be in series with a relay coil and its dropping resistor for example.

yes, all the FS need to do is ground the tip or ring for control of function.


Looking at the schematic, I see a 1.5k pullup at the jack, pulled up to +15. If I assume 1.2v for a red LED, that means the pullup limits an LED dead across it to 7-8ma. No extra resistor needed. If I put an LED across the switch, that input node is sitting at the 1.2v (or whatever your LED makes) and lit. Close the switch and the LED goes dark. If you series the LED and switch, when open the pullup yanks the thing up close to 15v, and a FS closure down to the 1.2v. A quick and simple experiment determines which makes sense.


I could be wrong, but I see no need for anything fancier inside the pedal.


I highly suspect the difference between AFP2 and AFP2B might be the labeling.

[alecjahn]

Old thread, but it asks the same question I had the other day.
Luckily, even though I'd already slapped my homebrew footswitch together, a buddy had an unused AFP-3 sitting around and graciously passed it to me.

It appears there are no resistors in the footswitch. I thought perhaps one was in-line between the PCB and LED, but I tested the resistance through the plastic thingies and it's dead straight ("~zero" ohms).

Here's some pictures as well and a redundant MS-Paint diagram of the wiring (third switch is easy to figure out from there, just uses the tip and sleeve - ring is NC on that jack).

Hopefully this will help someone out there in the future.











-Alec