Nice: op-amp swap on Yamaha FX-500 processor.

[Kaz Kylheku]

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. 

[Roly]

a) I hate it when people remind me that 1989 is now 24 years ago.  Seems like only yesterday. 

b) advertise the six RC4558's on e-Bay for the cork sniffers - should be able to make a major dent in your mortgage/buy that git/amp you have been dreaming of/have one hell of a night out on the town on the proceeds.   

There's quite a gap between 4558's and 5532's quality wise, so times six I'd expect to hear a difference.

Generally speaking the trend has been for op-amps to draw less operating current, and most of it goes into driving the load anyway.

I ripped all the old IC's out of a 24-channel Jands mixer a while back, replaced them with LM833's, and the difference was quite significant, better clarity, but particularly a much reduced noise floor with everything up - well worth the effort.   

[alfie]

I ripped out the six RC4558's that make up most of its analog audio path, and put in NE5532's.

Hey Kaz, could you please tell me the exact NE5532s you used here, or which kind are more generally suitable (e.g., https://www.digikey.com/products/en/integrated-circuits-ics/32?keywords=NE5532&pkeyword=NE5532&v=)? Thank you! 

[Enzo]

If you look at that link, Digikey only has two 5532 in stock, both from TI.  The 5532 and 5532A.  Both have the same data sheet.  Take your pick.

All the others there are not in stock, or special order, or not in the DIP form your board wants.

[alfie]

thank you, Enzo!

[66cccfff]

Ha, double-precision NE5532s, great idea. They're usually used in HI-FI audio products and you used it, inside a guitar effects module!