neumann opamps and more stuff

[rafafredd]

So, I got a bunch of nice transformers today (yes, more! And I know, I know... I´m sick), and some other things came on the same package.

I´m out of a digicam right now because I have already FU$$$D two of those. One just died and the other got a shower. So I´ve just the objects of this thread directly in my scanner. Sorry if the pics are bad...

Here they are:

Those are neumann discreet opamps. Ther are two plastic case and two metal cases. I´ve got the schematics on the Gyraf site for OA10, that seems to be different. Would anyone happen to have the OA12 schem?

This is a Point to Point board. Probably a line amp, with an opened OA12 there. I´ve reversed the board schematics, so I think I can reverse the OA12 schem also, if no one has it already.

The neumann board schem looks awfull to me. The opamp runs on a single power supply (probably +24v) and the opamp input is biased high above ground. I´m not a good circuit analyser, so forget me if I´m talking bullshit. I´m still very new in all this stuff.

So, Do you think this board is useable as it is, or should I take it apart and use the transformer and the opamp in another circuit? Maybe this neumann opamp would work just fine in an API kind of circuit??? I thinking about running this opamp with a dual power supply and get rid of both input bias and the 2.2uF input tantalum cap?

There was also a strange thing that came with all those nice trafos and opamps that I would love to know anything about:

As always, Thanks a lot!

 

[rafafredd]

Yes, I have already seen opamps working like this. Now that you described it, I remenber...

So it would run fine at +-12v with no bias at the input, and no coupling cap at the input, like any other opamp, I guess. Or should I try a higher dual supply?

 

[rafafredd]

Here are some more pics of that strange thing showing better angles. Is it a trafo? I don´t think so, because I´ve tried to Ohm it as a trafo but it didn´t work):

 

[rafafredd]

Thanks for the suggestions.

Yes, I´ll remove all the biasing circuit, including C2, C4, R4 and R5, but I think I should let R2 where it is, because it seems that it´s reflecting a impedance at the secondary of the transformer. Correct me if I´m wrong, or if you think that I should get rid of this anyway.

Also, I always see a cap at the feedback path (C3) even with split supply circuits, and I think I should leave it there because I´ll use a pot for variable gain. Again, correct me if I´m wrong.

Many thanks!

 

[ciminosound]

Wasn't the OA-12 available on Jakobs page at one point? I don't have my links available right now but the scematic was somewhere...

Gerry

 

[rafafredd]

On the Gyraf site there is just the OA-10 schem that seems to be very different then this one. In fact, OA-12 looks simpler.

 

[Gus]

When electro caps are used a single supply might be the best way to build something. Unless you are goig for an all DC path you don't need + and -.

FWIW I want to build a single supply f 110 circuit. If I use an opamp that can handed +-24Vdc, I could run the circuit off one good 48V supply.

Remember to keep the oxides formed in electro caps

 

[DrFrankencopter]

Well, I don't know anything about the Neumann op-amp, but that otherthing that you showed a picture of looks like it's an attacement for the KM84 series of mics. Maybe it's a bit of test equipment for checking out the amplifiers of the KM series mics...or maybe it's a strange capsule. But it definitly looks like it's KM84 compatible.

Cheers,

Kris

 

[rafafredd]

Please do so!

BTW: Did you have a chance to check the OAs performace? How is it doing?

kubi

So, I´ll reverse the one that is opened and I´ll let you know how it sounds as soon as I get it tested.

 

[rafafredd]

[quote author="DrFrankencopter"]Well, I don't know anything about the Neumann op-amp, but that otherthing that you showed a picture of looks like it's an attacement for the KM84 series of mics. Maybe it's a bit of test equipment for checking out the amplifiers of the KM series mics...or maybe it's a strange capsule. But it definitly looks like it's KM84 compatible.

Cheers,

Kris[/quote]

mmm, almost sure... Maybe a pad or adaptor of some kind?

 

[sismofyt]

It's looks abit like a KM100 extender, the one you use when you want the capsule on a cable. I dunno if Neumann made one for the KM84s. Try the asking at the Neumann forum!

 

[mik]

I guest that the different between theOA10, and OA12 is the the OA10 got the voltage divider on board, so is possible tu use it with a single suplly with only a pins arrangmen, for DC servo operation
OA12 got it out board, M100 is quite similar to OA10 both model can Handle low inpedence.
The OA10 is present in all PE, W495/a/b EQ series.
Mik.

 

[rafafredd]

Does anybody knows anything about those old red electro caps? Are those tants or aluminum lytics?

 

[sismofyt]

Electros I believe. Used to be very common in european gear, like the gold Frakos and blue Philips..

 

[rafafredd]

Always thought they were tants...

 

[[silent:arts]]

they are electros.

you should exchange them, because they like it this way :green::

 

[rafafredd]

What are those little modules? Lots of transistors!

 

[[silent:arts]]

[quote author="Viitalahde"]Those are w689 M/S decoders.[/quote]

Yes, and what I told you: recap it!

We have units working for more then 15 years. But any gear with this red caps waiting for years to be powered on will fuck up after a few days - like 12 W689 (most of them NOS) the last 4 weeks.

 

[David Satz]

Rafafredd,

This is my first posting here, so I hope that this message will show up in the right place.

The Neumann object which you were holding in your hand late last June, with a pin coming out of it, is a measurement adapter for a small cylindrical microphone. It could well be an MA 84, for example, or a predecessor model for an earlier version of their KM-series microphones. It is used when testing an amplifier; you can inject a microphone-level signal into the front end of the circuit and measure the distortion, frequency response, headroom, etc. of the amplifier. With a shorting plug you can measure the output noise of the circuit.

See the MA 80 instruction booklet http://www.neumann.com/infopool/download.php?Datei=opin0033.PDF on the Neumann Infopool for instructions on using one of these useful items.

Best regards,
David Satz

 

[gyraf]

Hi David!

Welcome to the Lab!

It's great to have people like you around here - I always enjoyed your to-the-point answers about microphones, e.g. at Klaus Heyne's forum.

Hope you will stick around - there's a lot of wierd mic-related experiments going on here - we need all the help and info we can get...

Jakob Erland