MKIII Footswitch Questions

[ursinus]

My new NOS MKIII Blue Stripe did not come with footswitches as they were lost by the dealer some time ago, so i'm building a switching interface for it like I did for my old MKIV. My question is can I just use normal dry contact relays for all three switch inputs? I know that the rev/eq is a stereo plug, but can they all share the same ground? Or do I need to isolate them. Also, do I need the resistor and diode on the Lead/Rythm to make the load correct? Mesa sent me the schematics, but the eq/rev was fuzzy so I could not tell if the dry contact switching would work on either. The schematic does not look like it needs anything other than dry contacts to switch, but I thought I would ask here before I build my switcher.

BTW, I love this amp, I should gotten one of these a long time ago. Love it more than my old MKIV. :shock:
Also put 5881's in the outer sockets and NOS Sylvania's in the inner sockets. I'm in heaven.... 8)

 

[kaluablue]

Relays are ok, and you won't need the LED / Resistor load.
But the switches cannot (or at least should not) share ground. If reverb and channel switch share ground, this results in hum. Rhtyhm/lead and R1/R2 is ok although.
I built a simple switch for my MKIII with these three switches (don't have EQ) in one housing and wanted to use one stereo cable for R1/R2 and reverb, because they are both on the back, but that didn't work - great hum. Now I' using one cable per switch :?
My LEDs are powered by an external 9V power supply, because otherwise there would be no LED for the reverb switch.

 

[ursinus]

Thanks!

I built my switcher with isolated jacks, so no hum.