Originally Posted by lozion
The Rv-1 is a great sounding albeit noisy unit, hence trying to improve the signal path by balancing it. As noted, there are already sockets cut into the frame for XLR connectors...
Most (all?) Furman gear of this era (late '70s to mid '80s ish) is pretty noisy internally. You may not see much improvement in the noise floor by balancing the I/O, especially if your cable runs are already short.
You might try swapping the opamps (most likely 4558s stock) for something quieter (burr brown opa2132?). On the PQ3 and PQ6 at least, and probably the RV-1, these chips are already socketed, so the swap is very easy to do.
Three things I did/do to my pair of EQs to quiet them:
1) swapping the original power transformers for new ones. In my case, both transformers were mechanically resonating @ 60Hz, inducing this into the signal. (~$25)
2) replacing the electrolytic caps in the box (all four of them!). This further reduced the mains hum in the units. (~$4)
3) I drive them as hot as possible.
Do contact Furman for the schematics though. IIRC, their balanced versions have more opamps in the circuit than their unbalanced versions, so it might not be as easy as just a few wires. Don't know if they used the same PBC or not either. Ignore this if you're just going to slap a couple of transformers inside.