This is my semi-educated guess. I could be wrong.
I don't have an ABM but I have an EVO III OM and a set of EVO III preamp schematics. They may not be representative of all EVO III variants.
If I understand, the EVO III 500 and 900 use a digital footswitch that sends serial data to the amp.
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If your amp has a single jack for the footswitch, like the image above, I believe the FS-4 is the model you need. FYI, they are available new for $79 and occasionally pop up used for about 1/2 the new price.
Thanks for the info! I wish the 4-way footswitch had a mute switch instead of the EQ switch, that would be more useful to me but let's see if I can grab it and somehow fit it into my rig... it's more the bulkiness and the fact that I'll probably never use two of the switches (EQ and Comp) that bugs me, but I really like the Subharmonic generator and would like to be able to switch it on and off.
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