Have an old analog synthesizer that doesn't work. Was told to replace the RC4558N and RC4558NB op amps. Tried looking at several online electronics parts places but no luck. Is there somewhere that I can look up a suitable replacement part for these? I assume that these parts are no longer produced.
Was also told to try replacing a couple of 1.8K thermal capacitors that are affixed to the top of some other ICs.
Any suggestions on where to find either of these components?
Thanks in advance.
unicornelectronics.com
These are normal wideband opamps, can easily be replaced by new(er) ones.
The thermal capacitors, don't you mean resistors?
Pieter
Yes. Sorry. I did mean resistor. I'm a newbie.
My recollection is that the 4558 is a standard jellybean part - a low-noise dual op amp, bipolar, standard pinout, intended for audio applications. The RC is a manufacturer prefix, the N just means DIP-8 package, and the B is a version number. Several companies still make this part.
Digi-Key sells the Texas Instruments RC4558P for $0.46 in onesies. They also have the NJM version of the part for $0.36.
The specs are nothing exceptional, I think, and almost any standard
15-volt-capable dual op amp in the same package would serve as a substitute.You could try popping in some TL072 or TL082 parts as a functional replacement. These are JFET rather than bipolar but the chances are that this won't make a difference in your application. Even Radio Shack sells these (at a $2 price, ouch!).
"Thermal capacitors"? Beats me what those are!
For any old equipment of this sort, I'd strongly encourage you to check all of the electrolytic capacitors. Chances are good that at least some of them have dried up, and have developed a high series resistance or have lost most of their capacitance. This can lead to power-supply ripple and noise, and a failure of signal coupling between stages. It's possible that "re-capping" the board with modern 'lytics might be all you need to fix it.
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Mouser has the JRC NJM4558 equivalents, which, AFAIUI, are actually prized by some audioph**ls. Also the Fairchild (KA** made by a Korean company), KA4558, and the ST MC4558. MAKE sure you get the correct IC package. They're sensitive to compensation capacitor breakdown, which causes the output to go to one of the rails.
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