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Author Topic: M221b schematic  (Read 3012 times)

Ooooeeee

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M221b schematic
« on: October 16, 2016, 01:16:04 pm »

Hi all,
  So, I have been duped on EBay and inadvertently bought a pair of the infamous "Hungarian Schoeps m221b's". I am attempting, in my post, to turn a sow's ear into a silk purse. In listening to them, 1 sounds quite good and the other lacking in bottom end. The one that sounds good has been highly modified. The one that lacks bottom looks original. My questions are; Does anyone have a schematic that is legible for the original m221b? The only original one that I can find the values are all illegible. And, in the case that I may need it, who makes a suitable transformer substitute?
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David Satz

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Re: M221b schematic
« Reply #1 on: October 16, 2016, 10:09:00 pm »

There are a few different circuits for the M 221 B, but here is the main one. For many years Schoeps' schematics and part lists were separate, as in this case.

Schoeps built and wound the transformers themselves for this model, numbered and tested each one (with written test protocols), and selected them for lowest distortion. I don't know of any generally available third-party substitute.

The worst things about the Hungarian forgeries are generally their unselected tubes and carelessly assembled transformers. You might be better off waiting until the real thing comes around. Genuine M 221 Bs aren't all that rare, and (except for the MK 26 three-pattern capsule) the factory still maintains them to a great extent. But they will not accept the counterfeits for repair or upgrade.

Question: What is the model of capsule that you have? In addition to the amplifier scam, were you also sold an MK 240 capsule as a "cardioid"--which it is, of course, but designed for close speech pickup. It has a severe low-frequency rolloff in more general studio applications (e.g. -12 dB at 50 Hz when measured at the usual 1-meter equivalent distance for general-purpose studio microphones) plus a high-frequency emphasis chosen for speech intelligibility, which is not ideal for most music recording. Have you tried exchanging the capsules on the two bodies to see whether the lack of bass "travels with the capsule" when you do so?

--best regards
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Timjag

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Re: M221b schematic
« Reply #3 on: October 17, 2016, 02:09:53 pm »

Actually I take that back 3,9M in metal film from eBay

http://pages.ebay.com/link/?nav=item.view&alt=web&id=161148522176&globalID=EBAY-US
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Ooooeeee

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Re: M221b schematic
« Reply #4 on: October 22, 2016, 03:05:10 am »

    David, thank you for the Schematic! The capsules are both M934b switchable Omni/ cardioid. The problem does not follow the capsule. There is no apparent noise floor issue so I am assuming it is not the tube. At this point I surmise it's either the old resistors/ caps or the transformer.
Since the 1 good one sounds so good, to my ears, I feel that I will give a shot at changing out the resistors and caps in the one lacking bottom end, keeping my fingers firmly crossed that it's not the transformer!

   Tim, thanks for the links.. very helpful! The only problem is the minimum 100 piece order on the 180 Mohm resistors! Anyone else want to join in on my order?

   Klaus, fantastic blog... enormously helpful, thank you!
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klaus

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Re: M221b schematic
« Reply #5 on: October 22, 2016, 04:49:05 am »

What complicates matters of troubleshooting in this case is the fact that the fake Schoeps mics used sub-standard passive components. Your search, therefore, will not be easy.
While stock transformers never would display the symptom you describe, even that (fake) component cannot be excluded from being under suspicion.

Good luck, and let us know once you have identified the culprit!
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Klaus Heyne
German Masterworks®
www.GermanMasterworks.com

Jim Williams

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Re: M221b schematic
« Reply #6 on: October 22, 2016, 01:30:14 pm »

Dale makes their CMF55 series up to 4.99 meg ohms. I suspect a 3.9 meg ohm is in their catalog. Those are excellent replacement parts, better hf operation,. lower noise plus non-ferrous construction. If size is a problem use the excellent CMF50 series.
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Timjag

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Re: M221b schematic
« Reply #7 on: October 23, 2016, 11:57:21 am »

Clark,

I have 4 of those 180meg dales, I bought them when I couldn't find 250M Sfernice for a C28 restoration, which I now have. Can you PM here? If so get in touch. You're probably going to need dogbone caps or tiny polyester ones if you want to be authentic, there's a guy I've used for that sort of thing otherwise the new tantalum beads are tiny enough.


Tim
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