Hi All,
I recently acquired a Fender guitar amp that has a footswitch function. The footswitch has two switches on it, one controls channel select and the other switches FX effect. The interesting part is that the cable to connect the footswitch to the amp can be any guitar cable, that is a cable with a mono jack plug at each end. So how does it control two functions? I found this description in another forum.

The amp will be sending out an AC signal on a TS jack, and depending on the footswitches selected, it will see either no signal, just the positive half, just the negative half, or the full signal (though slightly modified by the voltage drop across the diode).

This schematic was linked to the above.

I'm no electronics whiz, and I'm a bit confused by the illustration of the jack. It's just a simple mono jack, so what do the numbers 2, 4 and 1 relate to? Or is it just a case of connecting the tip of the jack, i.e. "2" to the diodes and the common switch end to the barrel? Also, I've found elsewhere that the amp supplies 48v AC to the switch. I don't need any leds, so what diode(s) would be appropriate for this circuit?
Thanks,
Ian

 

You can use any 1N400x diode such as 1N4001 - 1N4007.
You should still add the LED to maintain the same voltage when the switch is closed. It also indicates the status of the switch.

1 is Ring.
2 is Tip.

 

Pin 4 shows a NC connection to pin 1. I.e. it is connected to pin 1 when the jack is empty and not connected when a plug is inserted. It is not used in this schematic. It is there to ground the input when the jack has nothing plugged in.

 

@MrChips and @BobTPH thanks for the clarifications. Hopefully I can get it to work.

;-)

 

So how does it control two functions?

oscillator can produce AC and depending on switch state result will be none, positive, negative or AC. so this allows distinguishing 4 states, not just two.

 

1 is Ring.
2 is Tip.

That's a mono jack. There is no ring connection, only tip and sleeve.

ak

 

So how does it control two functions?

The amp impresses a control signal on the tip. The diodes modify that signal. The amp sees the modifications, decodes them, and uses that information to control analog switches that select input signals, bypass the effects channel, etc.

Four combinations of functions plus two indicators, all with one wire - cute.

What is the amp name / model number?

ak

 

That's a mono jack. There is no ring connection, only tip and sleeve.

ak

Correct. For a mono jack, I don’t differentiate between ring and sleeve.
The cable for a mono plug is just center core and shield.

 

oscillator can produce AC and depending on switch state result will be none, positive, negative or AC. so this allows distinguishing 4 states, not just two.

That's 4 states for two functions.

 

What is the amp name / model number?

It's a Fender FM212R. Oldy but goody. All solid state but still manages to produce that beautiful Fender clean tone, and the distortion is great too. Got it cheap from a pawn shop. ;-)

 

Hello,

You can download the complete schematic over here:
https://elektrotanya.com/fender_frontman_212r_sch.pdf/download.html

Bertus

 

My FENDER AMP has a three-button padal, with only two 2-wire plugs. The diode scheme uses a 2 wire cable, the diodes short out either the positive half wave of the AC voltage OR the negative half wave of the AC voltage, or both. The circuit inside the amp is a bit more complicated, but certainly less expensive than another plug and jack. The other switch has a rather normal circuit that would allow hum into the signal path.
SO the TS does not need a three wire plug and cord!!
YES, it did take a bit to figure out.