Another 4558 Question

Grant Richter grichter at
Thu Mar 23 08:40:54 CET 2000

There are a few different failure modes that 
might take out an op-amp which has been functioning
normally in circuit.

The most likely cause is a static zap from the outside.

Those sparks your sweater gives off in the winter
can go as high as 30,000 volts. Thats one of the reasons
for the 1K resistors on the output of op-amps.
To help prevent limit current coming back in.

That can blow holes in the internal metalization
that may not disconnect a pin but will weaken it
by making the metal thinner.

The increased current density in the thinned metal
area will cause electroplating where the metal
is carried away by the electrons and gets even thinner.

If the mains power fluctuates in some odd way this
can either cause a spike or bad supply timing
that might take out an already weakened op-amp
(for the above reasons)

At least thats the way the military justified spending
umpteen million dollars on anti-static programs.

> From: Tim Curtis <vampope at>
> To: DIY <synth-diy at>
> Subject: Another 4558 Question
> Date: Thursday, March 23, 2000 12:09 AM
> I just resurrected my Moog Prodigy from the dead - it was the 4558 Op
> Amp at U16 if anyone cares.
> I can't find a replacement here n town, so I got it up and running with
> a 1458.  Since I have ti order a replacement 4558, would it make sense
> to get several and replace all the 4558s in the unit?  (I don't know if
> those things go over time.)  If so, should I also replace the TL072s?
> Thanks,
> Tim

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