| I think it's meant to balance the volumes of the two pickups. Would be especially important if the pickups are wound differently for tone reasons and have different impedances.
Both my pre-Gib Classic and Signature have those, but I can't remember if my Basic 6 FL has one or not. That's the only one I have with a TCT. A Gibson Classic 5 that I used to own also had a DTA1.3 fitted with a TCT-LZ circuit.
Cheers,
EG |