Vintage Simmons Drums (UK) Users Group

Hey everyone.
I just uploaded some pictures of the Simmons 20-85 card. This is the daughter card that 
allows the SDS 7 modules to access four different eproms. The different eproms are selected 
using the resonance control - which kind of sucks because it means you lose that control, 
but but being able to access the different eproms is awesome.
I do have one question, though... There's a variable resistor on the card that I have no idea 
what it does. Resonance control, perhaps?  Any help would be greatly appreciated.
Many Thanks.
Ed