How to use expression input as a 3rd switch pedal input!

Started by ianplaysguitar, May 15, 2011, 11:49:39 AM

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ianplaysguitar

Hiya,

I just thought I'd share this with you.

I was frustrated with having only 2 control pedal inputs on the VG99, and I wanted to see if I could plug a 3rd control pedal into the expression pedal input.  I tried it and it didn't work.  So I looked into a way to trick the VG99 into thinking that it was an expression pedal and checked out the schematic of the roland expression pedal.

After a bit of thinking and experimentation I came up with the following solution!

The two wires on the mono jack of a control/switch pedal need to be connected to a TRS jack, onto the tip and ring (doesn't matter which way round).  Then it's simply a matter of soldering a 10K resistor between the tip and sleeve (also known as ground or sleeve) on the TRS (stereo) jack.

This way the VG99 is tricked into thinking it's an expression pedal at either end of travel.  ie.  switch pedal down, same as expression 'volume full' position, switch pedal up, same as expression at 'volume lowest' position.

I used an old A/B switcher box and used the input jack socket on it and soldered that to a stereo cable with a TRS jack on the end.  That way I can leave the original mono plug on the control pedal and convert it to TRS expression as I need it.


Let me know if anyone tries this too, works like a charm!

Ian

drjoness2001

I don't know if you tried this, but you can use already use the VG-99 expression pedal input as a single foot switch, without having to modify any gear at all, or do any special wiring with resistors, etc.

If you own a Roland FS-6 foot switch, you can plug that into the expression pedal input on the VG-99, and foot switch "B" will work just as you describe, no mods necessary.

ianplaysguitar

Hi Drjones,

Thanks for your reply.

I tried replicating the boss FS-7 technique as you suggested by shorting together various combinations of pins on the stereo jack. This is the way the FS-7 does it but for me this didn't work reliably.

Have you really got this working properly?  I had it 'kind of' working in this way but the problem is that the VG99 is looking for a resistance of 10K.  In my experience this only worked most of the time, not all of the time. 
It was useful to assign the expression pedal to something like mixer [A] level and navigate to the mixer page to see how many out of a hundred the pedal is registering and get an instant reading.  I found thy simply shorting together some of the stereo connections wasn't consistent at registering 0 or 100 every time, sometimes it plain didn't work at all!
The VG99 expects that when one pair of connections (tip to ring) has no resistance (switch is on), the other pair (ring to sleeve) shows 10k of resistance.  It measures the relative voltages which pass through.   This is why to truly emulate an ON position, you need a 10k resistor in there.

Will you do me a favour and test your FS-7 in expression input again, I'd be interested to hear what number values your VG99 is registering, to see how it compares and figure out if I did something wrong when I emulated it's function, maybe it has resistors in it's topography, I can't find any schematics or that pedal.

Next I'm going to wire some pedals into the 13 pin cable and give me GK S1, S2 & GK Volume as foot pedals!

More updates to follow!

Ian