Fender Princeton Reverb II
Reverb-only Footswitch Idea

(original Fender was p/n 017007 with 2 buttons - the switch described here only has 1 button and switches the reverb only)
back to main footswitch page
home

NB This footswitch is intended to work with the Rivera-era Fender amps from 1982-86.
It probably won't work with any other amps.
It fixes a problem which (I think) only exists for some PRIIs and some Super Champs.

I have built one for my PRII and I'm very pleased with the result - full clean tone and switchable reverb, all I've wanted since I got the amp 6 years earlier...

OBJECTIVE / THE POINT
Many Princeton Reverb II users (and some Super Champ users) experience loss of clean tone when they use the original footswitch (or any footswitch built for the same purpose, including the one I built). In addition many PRII users don't even like the 'lead' sound, which is one of the two functions on the normal footswitch. Therefore, for most users, the original footswitch (or clone) gives you a tone you don't want, and takes away the one you do want. So I thought, why not build a single-button footswitch which only switches reverb and avoids the loss of tone?

BASIC IDEA
The amp's reverb signal is sent to the ring terminal of the amp's plain footswitch socket. If that terminal is shorted down to to the amp's chassis (i.e., grounded or earthed) then the reverb is 'off'. Undo the grounding and the reverbed signal is allowed to continue through the amp.  You can test this by putting a MONO jack plug (e.g., a guitar cable with nothing connected to the other end) into the amp's plain footswitch socket; this defeats the reverb because the main section of the jack plug  shorts the ring (middle) terminal of the socket to ground. Remove the  mono plug, and reverb comes back. (Insert/remove the plug with the amp's master volume at zero to avoid a nasty noise.)

SIMPLEST SOLUTION
Wire the plain-socket ring terminal to ground via a switch and you've got a reverb switch. You could buy a simple, unbranded one-button footswitch ('latching' style, which means push-on, push-off) cheaply on eBay or at your local music shop. It probably comes with a mono jack or RCA/phono connector at the other end of the cable. Remove the connector and replace it with a STEREO 1/4" (6.35mm) jack plug. Connect the shield or braid to the body of the plug, and the inner wire to the ring or middle section of the plug. The tip is not connected. Do these continuity checks;
 
(1) when you work the switch, continuity cycles on/off between ring (middle section) and body of stereo jack
(2) tip never connected to anything else

Plug it into the amp's plain footswitch socket and (with the reverb knob turned to the desired reverb depth) you've got a reverb footswitch.

LED 'reverb on' INDICATOR
 I wanted a LED to tell me when the reverb is on. I built one using my diagram below, getting 'reverb on' indication with a 9v battery, a LED and a resistor. A DPDT latching switch is used so the reverb circuit and the battery circuit never meet but are switched simultaenously. The battery circuit uses the opposite pole of the switch, so the LED is on when the reverb signal ISN'T grounded (ie when the reverb is on). This sketch tries to get across how to wire up the components inside the box, so it's a view into the box with the bottom of the box removed.   Accidental battery drain is prevented by running the battery circuit through 2 terminals of a stereo jack socket, so that the LED can only come on when a mono (not stereo) jack plug is pushed into the socket. The sketch is not intended as a scale drawing and the internal layout is up to you. 

improved reverb-only footswitch

To complete this footswitch you need to wire up a cable as shown at the bottom of the above diagram. It could be made out of an ordinary guitar cable, replacing one end with a stereo jack plug as shown. Note the stereo jack plug tip is not connected. The stereo end goes to the amp plain footswitch socket, and the mono end goes to the footswitch.

PRACTICAL BUILD
When planning to make mine, I looked for a suitable box - it needed to be strong, with a 9V battery compartment. I suddenly realised I already had one on my desk - a faulty DI box! It was made in China by a company with a German-sounding name. It hadn't been very reliable but the aluminium extruded box and the four huge rubber corners looked great. All I had to do do was drill a hole in the top for the switch and another for the LED. There was already a hole for the jack socket and a 9V battery compartment with a handy little door held shut with a thumbscrew. Drilling and wiring took only an hour! (That same company made my band's PA mixer and it's great, by the way...)

If you have an old, faulty effects pedal, that might also give you the box you need.

TEST BEFORE USE
Fit a battery. Insert the cable mono jack into the footswitch's socket. Don't connect to the amp. Work the switch and check the LED switches on and off. Use a multimeter or continuity tester on the other end of the cable (stereo plug)  to check

(1) ring (middle section) connected to body when the LED is off
(2) ring NOT connected to body when LED is on
(3) tip never connected to anything else

FURTHER THOUGHT
If you want LED indication but you want to avoid using a battery, there is -6.2V DC available inside the amp on the red footswitch socket, tip terminal. Now we DON'T want to stick a jack plug in there because then we'll get the loss-of-tone problem again. But if you know you'll never use a normal footswitch again, maybe you could go inside the amp, block off the red socket so it can't be used, and move the -6.2V DC wire from the tip terminal of the red socket to the tip terminal of the plain socket; then design a whole new f/s with a 3-conductor cable up to the amp (stereo plugs at each end). The three conductors would carry -6.2V DC, reverb output, and ground. The resistor value would come down to about 390R.

The above advice is offered in good faith but I accept no responsibility for loss, damage, injury, death, blown up amps, etc etc. I'd appreciate it if you'd treat my write-up and sketches as copyright 2008 Andrew Waugh. Thanks.

back to main footswitch page
home