Neumann v472 op-amp OA20

[NoisyIndividual]

I have here a racked v472 with one faulty op-amp.
I assume these are OA20's with the covers removed for some reason, as the photos seem to indicate.
(Covered OA20 photo copied from Interweb)

Question, are these really OA20, and what are the options/hacks here if any?
OA20's seem thin on the ground to find/buy.

 

[rock soderstrom]

I assume these are OA20's with the covers removed for some reason, as the photos seem to indicate.

Question, are these really OA20, and what are the options/hacks here if any?
OA20's seem thin on the ground to find/buy.

I could imagine that these are the ones that were produced a little later. Probably the covers weren't really necessary and they could save a few bucks without?

Member volker @silentarts is more familiar with these parts.

Regarding your problem, you may also be dealing with faulty capacitors. I've had several cards like that with dried out caps, the dark red frakos are notorious. I would replace them, and probably the tantalum capacitor too.

 

[NoisyIndividual]

Thanks, I've done all the cap stuff, several were bad.
I swapped both op-amps around to prove beyond doubt one is noisy.

 

[rock soderstrom]

Thanks, I've done all the cap stuff, several were bad.
I swapped both op-amps around to prove beyond doubt one is noisy.

Okay, than you are one step further. Good luck!

As already mentioned, Volker is very familiar with these OPamps, he also has some DIY versions on offer, I can't say to what extent these are compatible. Ask him.

Discrete operational amplifier (one needed):
OA06 DIY kit: EUR 10,00 (+ VAT where applicable)
OA11N DIY kit: EUR 20,00 (+ VAT where applicable)
OA12N (built & tested): EUR 45,00 (+ VAT where applicable)

 

[beatnik]

Get your heatgun and razor knife out and strip it down.

You could even try an acetone bath first as it might loosen the goop a bit.

First make sure schematics and spare parts are available.

 

[TwentyTrees]

Those op amps appear to be OH100, the thick-film successor to the OA20 in the V472, on a daughterboard to match the OA20 pinout. An OA20 would be be a drop-in replacement. I've worked on V472 modules with both, and even had one in factory-fresh condition which had an OH-100 in one channel and OA20 in the other. No appreciable difference in sound quality.



I second the recommendation to speak with Volker (silent:arts), he knows this stuff inside out.

 

[NoisyIndividual]

Ah thanks, that's now making more sense.

 

[[silent:arts]]

The OH100 thick-film op amp was the latest of Neumann Op Amps, used directly in late V457 / V470 / V472 cards. It was used with different daughterboards for OA10 / OA12 / OA20 DOAs replacements too.