Fender SCX2 tap floor switch mod?

[harryevan]

Working my way to my last amp, I got a Fender Super Champ X2 head after a friend's demo. Nice and Fender clean with modeling. Sounds great with 2 10's, 1 or 2 12's or even a single 15.

But, and I see this one a lot these days on different makes - there's a "tap" button (interrupter switch) on the face, but nowhere to plug a simple foot switch to control the tempo. I mean, your hands are busy, and to adjust tempo you have to stop playing, if only for a couple of beats. No matter how fast you are, it would be simpler (and obvious) to use a floor switch. After watching Larry Carlton and Robben Ford interviews (Dumble guys) they keep it simple with a reverb pedal and a delay, but the delay has a tap button.

The SCX2 schematic doesn't give a lot of detail for the tap circuit, comparing it to the PCB and components after opening it up.. I was thinking a jack in line just before the onboard tap switch that would allow something like a keyboard's sustain pedal to set the tempo.

Getting in there, there's room for the jack on the faceplate under the tap switch, but that's as far as I got after staring at the PCB and the schematic for too long. The onboard switch has 6 posts and it's a bit difficult to see if I couldn't just cut the trace leading to the switch from R66 (after coming out of P29's 5th position) and wire the jack in there?

I don't need to switch modeling presets, but being able to change the tempo keeps the groove clean, and saves a couple hundred bucks for another delay pedal. Mssr.s Carlton and Ford can't be wrong.

Thanks,

Harry Evan

 

[Jeff Gehring]

You don't need to cut any traces to add a jack for the tap switch. All it does is momentarily place digital ground on the junction of R66 and R76. You just need to parallel the panel switch with the jack you add. You can tack a wire to the side of R66 that goes to the P29 connector, and add another wire tacked to digital ground (like at the low side of R72/73/74/75). Then run those to the tip and sleeve of an INSULATED jack you add somewhere, into which you'll plug a momentary SPST switch. I don't know if you might see difficulties with trying to run a long cable, I think I'd try to keep that short, and of course use shielded cable.

 

[harryevan]

All it does is momentarily place digital ground on the junction of R66 and R76. You just need to parallel the panel switch with the jack you add. You can tack a wire to the side of R66 that goes to the P29 connector, and add another wire tacked digital ground (like at the low side of R72/73/74/75). Then run those to the tip and sleeve of an INSULATED jack you add somewhere, into which you'll plug a momentary SPST switch.

Thanks for the quick reply, Jeff. For the foot switch, I have an old Yamaha sustain pedal for keys. The VOM (continuity) says the switch is open when you press on it. With the VOM on the panel switch, it appears to close when you press it. I guess I'll reverse the pedal. I'm using one of those plastic 1/4" jacks for the insulation, so I have to pull the main PCB - it's bein' stubborn. I'll let you know. Thanks, again.

Harry Evan

 

[Jeff Gehring]

Right, Harry, you need a momentary closure of the switch when you stomp on it.