I have an FX-500 that I bought new in 1989! 24 years ago, man.
I never took much of an interest in the internals.
A few days ago, I ripped out the six RC4558's that make up most of its analog audio path, and put in NE5532's.
Quite an improvement; it doesn't sound so cheap and boxy any more. I mean there are limitations on the digital side, but at least now they are laid bare.
The reverb is smoother, less irritating and less grainy sounding. Now when I heap on lots of reverb (externally, via analog mixing), it does not seem to occlude the dry signal as much as it did before.
Yet the basic character of the unit is retained; it still sounds like itself, just better. Clearly, its "personality" is from the digital side; and the analog side is just another op-amp selection cluster-funk.
It's a nice board to work with. The component side pads are solder-masked and so the solder did not capillarize through to the other side to make a double joint, as can happen with plated through-holes. The chips gave way quite easily after just pumping solder away; they just needed a little twist. No component side solder manipulation (pumping, wicking) was needed at all. The holes came out mostly clean. A .028" drill bit went through most of them easily. And so all six were done in under an hour.
Now it's obvious why the headphone output was better at driving a power amp (less tone suck): it's an NJM4556 which can drive 150 ohm loads. I kept that one in there.
I didn't consider if the power supply has the margin for the bigger current draw times six op-amps. I didn't check the temperature of the 7809 regulator, or take any measurements, like ripple on the input side, taking instead the empirical route of: close it and stick it back into the rack and if it works it works.
