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UNPLANNED DOWNTIME: 12th Oct 23:45

Footswitch question for electronics and amp builder wizards...

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EvoEvo Frets: 292
edited July 2023 in Amps
Hello all!

This isn't a troubleshooting or problem solving question, just a thought that I've had rattling around for a little while and figured somebody might help me learn a little something.

My EVH amp has a 4 button footswitch which connects via a regular TS guitar cable, and the Marshall JVM410 has a 6 button footswitch (each with 3 modes) connected the same way with a regular TS cable. If I remember rightly then the blackstar ID core range have an FS12 footswitch which has 5 preset buttons AND a tuner readout, so that needs to send a signal TO the footswitch as well as receive from it.

My question is: How do these switches/amps send the necessary signals over a TS cable? I can wrap my head around the idea of a tip signal, sleeve signal, and both together....but how are all these extra commands achieved?

Can anybody weigh in on this?
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Comments

  • Danny1969Danny1969 Frets: 9752
    edited July 2023
    There are a few ways.

    In additional to on  / off as in shorted in reference to ground you can add additional function by using an AC voltage not a DC voltage. 
    So now with TRS you have 

    TR both open
    Just T open
    Just R open 
    TR shorted together. 
    All 3 shorted

    Now with an AC voltage you have Pos and neg portions of the AC voltage so now you have the above with 2 more choices on every permutation. 

    Shorted or just pos portions of the waveform shorted or just negative portions of the waveform shorted. This is accomplished with simple diodes in the foot switch on some amps but more advanced ways using a PIC chip in other amps. This can be a pain as if the chip dies just replacing it won't help, you need the code blown in the chip first (Marshall DSL etc) 

    Some use simplified midi, some use analog switch chips switched via logic gates. 


    www.2020studios.co.uk 
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  • SporkySporky Frets: 23802
    You could also do a voltage ladder. So the sleeve is ground, the ring is a 9 volt supply, the footswitches each add a voltage to the ring (for example):

    FS1 - 0.1v
    FS2 - 0.2v
    FS3 - 0.4v
    FS4 - 0.8v
    FS5 - 1.6v
    FS6 - 3.2v

    So from 0v to 6.3v you can encode any combination of footswitches quite simply as DC. No idea if anyone does it that way though. 
    "[Sporky] brings a certain vibe and dignity to the forum."
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