Guitar amp foot switch question

[loungedebaldy]

Hi everyone. Just a question about an old Fender Studio Lead guitar amp. I bought this amp in a pawn shop years ago and finally broke down and purchased a foot switch to turn the dirty channel on and off. I ordered a single on/off type foot switch. Now when I use this switch it does a great job of turning off/on the dirty channel but as long as the switch is plugged in to the foot switch jack at the back of the amp the reverb doesn't work. Question. Is it possible I purchased the wrong switch? Is there something wrong with the circuitry of the amp? Is this normal for this amp?

 

[KrisBlueNZ]

My guess (and it's just a guess) would be that the socket on the amp is designed for a dual foot switch - one switch for clean/dirty and the other for reverb on/off - and is supposed to be used with a tip-ring-sleeve plug. When you plug a mono plug into it, this shorts the ring contact to the sleeve, and this is what's turning off the reverb.

You can try making (or you may already have) a splitter cable that has a TRS plug (which you plug into the amp) and two mono (TS) sockets. If my guess is right, if you plug the footswitch into the "left channel" socket (which is wired to the tip of the TRS plug), it will control clean/dirty, and if you plug it into the "right" channel socket (which is wired to the ring of the TRS plug), it will control reverb on/off.

 

[loungedebaldy]

Thanks for the tips.
I happened to have a trs plug with two monojacks coming out of it and tried the single foot switch in each jack. The switch would turn on/off the d/chn in each socket but reverb would stay off.
I then tried the foot switch from my Ultimate Chorus amp. This is a double switch but has only a mono jack. The chorus switch had no effect on anything but the other one would turn on/off the d/chn but no reverb. I did notice that the red indicator light in the front of the amp would light/dim when this switch was activated.
I then experimented with the plug of the new switch by pulling it slightly out of the socket. This allows me to turn on/off the d/chn and the reverb stays on.

 

[KrisBlueNZ]

Hmm. Can you find out whether the socket on the amp is mono or stereo? You might be able to see into it with a bright light, otherwise you might have to open it up.

A double footswitch with a mono plug would probably work by having different resistances in series with each switch. If your amplifier is designed to work with a pedal like that, then you should be able to enable the reverb by putting the right resistance across the plug. Try values in the range 100 ohms to 47 kilohms or so.

 

[loungedebaldy]

Yes, the amp foot switch socket is stereo.

Hold the presses!! In playing with the amp tonight I figured out that the plug splitter that I used the other night had stereo outputs not mono., So that was definitely the reason that the test failed and produced the result of both sides of the jack switching the dirty channel but not the reverb. I'm sure that if I get the proper plug that it will work. I will be able to pick up a plug in a few days and will post back with the results. Thanks again.

 

[loungedebaldy]

Just a follow up to my last post. I did finally acquire the proper stereo to mono plug that Kris suggested and indeed that is what solved the problem. With this set up I need two single switches to turn the individual channels on and off. Works great! I will get a proper switch for the amp sometime in the future. Thanks again for your help!

 

[KrisBlueNZ]

Great! You're welcome.