Building a simplified Fender Frontman 212R footswitch

[dazz]

Hey guys. So I want to build a simple footswitch for my 212R. The original one has two switches: clean-drive and drive-more drive.

Here's what I think the schematics are: http://music-electronics-forum.com/a...1-deluxefs.jpg

So what I want to do is a single clean-drive footswitch. I've come up with this, by trial and error, and it works. The only problem is that there's a half a second delay between the drive to clean transition



Is there a simple way of getting rid of that lag please?

Thanks in advance

ETA: I simplified the circuit. Turns out I only need 1 diode. Still lags though

[darkfenriz]

Maybe the always connected diode can be made zener, say 5-7V. May help somewhat, but more can be achieved modding the amp

[dazz]

Maybe the always connected diode can be made zener, say 5-7V. May help somewhat, but more can be achieved modding the amp

Yep, the Zener works better. Still a little bit of lag but I think can live with that. Thanks!

On the modding the amp suggestion, I've searched the web for a while but all I've found are clean channel mods. Any pointers please?

[darkfenriz]

C64, originally 0.22uF, is the timing capacitor. Somewhere in the 22nF to 68nF range can speed the whole thing up.
drive->clean should be fast in theory, clean->drive transition seems intentionally slowed down

[dazz]

C64, originally 0.22uF, is the timing capacitor. Somewhere in the 22nF to 68nF can speed the whole thing up.
drive->clean should be fast in theory, clean->drive transition seems intentionally slowed down

That's weird. Actually it's drive->clean that lags. But anyway, off to build the footswitch... with a plastic lamp footswitch I have lying around (man, am I cheap or what haha)

Thanks for the info

[Enzo]

Why did you leave out the resistors and caps in the pedal? Did you try them first?

[dazz]

Why did you leave out the resistors and caps in the pedal? Did you try them first?

Because those seemed to be part of the "drive/more drive" switch circuit, which I don't really care about.
But of course I have no idea what I'm doing.

[Enzo]

Look at the schematic. There are two switch circuits. Each one has its own cap and resistor. You have D41, but left out C62, R117, R118.

The drive/more-drive parts are C61 and R116.

[dazz]

Look at the schematic. There are two switch circuits. Each one has its own cap and resistor. You have D41, but left out C62, R117, R118.

The drive/more-drive parts are C61 and R116.

Oh, I see, thanks Enzo. I thought this was the schematics for the original footswitch http://music-electronics-forum.com/a...1-deluxefs.jpg

Also in my search before posting here I found a thread where someone said the footswitch circuit was missing from the 212R schematics.

OK, so I need a 2PDT switch... is that a 10 Ohm and 100 Ohm resistors? looks like it reads 1D (R117) and 10D (R118). I'm guessing 1/4 watt is OK for those?
And finally a 22F electrolytic cap? That can't be right... excuse my ignorance

[Enzo]

You don't need a 2PDT, note the extra set of contacts doesn't do anything. Fender just uses DPDT in all the switches, and ignores the unneeded contacts.

The circuit on the schematic is the panel circuit, but if you duplicate it in a pedal, it will work, same as it does on a panel. The real footswitch may well be different, it has LEDs lighting up.

22uf cap, that is what I see.

If you try to eliminate the LEDs from that design, you risk losing function. The sensing circuit in the amp works on voltage levels. LEDs have a larger forward drop that regular diodes. So in the circuit you just posted of a footswitch, the left switch shorts a red LED. Add in the plain diode, and the circuit sees a drop of either half volt or over a volt and a half.

I don't know that this will cure your delay, but it might. I guess the test is this: when you do not use a footswitch, do the panel buttons have the delay?

[Enzo]

The schematic also shows TP20, TP22 with expected voltages. Do your voltages come close to those? From the panel? From your FS?

[dazz]

You don't need a 2PDT, note the extra set of contacts doesn't do anything. Fender just uses DPDT in all the switches, and ignores the unneeded contacts.

The circuit on the schematic is the panel circuit, but if you duplicate it in a pedal, it will work, same as it does on a panel. The real footswitch may well be different, it has LEDs lighting up.

22uf cap, that is what I see.

If you try to eliminate the LEDs from that design, you risk losing function. The sensing circuit in the amp works on voltage levels. LEDs have a larger forward drop that regular diodes. So in the circuit you just posted of a footswitch, the left switch shorts a red LED. Add in the plain diode, and the circuit sees a drop of either half volt or over a volt and a half.

I don't know that this will cure your delay, but it might. I guess the test is this: when you do not use a footswitch, do the panel buttons have the delay?

Any chance you can upload your schematics please? Mine looks like this:



Just tried putting 3 zeners (1N4733 I think) in series, then shorting two of them. Also tried the same thing with three 1N4007 diodes, and finally a 1N4007 in series with an LED. Same result: when shorting 2 diodes or the LED the amp stays in the drive channel, so that didn't work

Using the buttons in the front panel of the amp produces no delay

I would need to take the amp apart to check those voltages in the panel, but FWIW I get a voltage drop of 1.8V across the zener and 3.6V across the 1N4007 if I use that instead

[dazz]

I replicated the circuit on a breadboard and it works like a charm. Apart of R117, R118 & D41 I needed D40 too. It works great even without the cap, but I'll put it there just in case.

Thanks so much everyone

[Enzo]

You have the same drawing I do, the amp itself, I just suggested stealing the same circuit for your pedal.

Your switch handles clean/drive. D40 if you left it out or not would determine which level of drive would come up.

[dazz]

You have the same drawing I do, the amp itself, I just suggested stealing the same circuit for your pedal.

And that worked great, thanks again. BTW, why don't electrolytic caps come with units in the schematics like the rest of the caps?

Your switch handles clean/drive. D40 if you left it out or not would determine which level of drive would come up.

Understood. I'll put it there to have drive instead of more drive.