Hi Andrew, sorry for the delay but I am in NY and computers don't work to well without electricity.
It sounds like you may have an early 502B if it arrived in an "A" box or if you have had it fdor some time.
As far as sub out mods go. I have been working on a proper network that does not take away from the output of the amplifier itself while allowing plenty of gain to the sub amp. I have come up with the proper setup that has been working out nicely for the pass few weeks. I just relayed this info to Jolida themselves yesterday.
Basically, the sub out is the same as a pre out.
I would only have to drill into the back if you required keeping all four inputs that are currently on your amp. If not, I can use one of the existing RCA sets and convert it into a sub/pre out.
As far as improvements on a budget, some of the upgrades that make a difference are as follows: Soft recovery diodes, Couplings capacitors, PS bypass capacitors, and resisistors.
From there you would look into the volume pot, signal wiring, source selector and bypassing the balance.
There are obviously various levels of what you want to do within the amp to bring out more of the potential these products have to offer.
Please feel free to give me a call or send me an email for further information or pricing on upgrade packages.
