[Gus]

Found this thread
http://repforums.prosoundweb.com/index.php?topic=36964.0
I drew this up.
? by parts indicate made up values I could not read the values from the pictures. I don't know where the ceramic disk would be used and I am not sure if there is any more parts in the bottom that are not visible.
I guessed the transformer would be wired in series for the primary and in parallel for the secondary because of the 47K drain resistor.

 A lot of it is a guess. Anyone else have any ideas about the values or anything to add?

I guessed it could be a variation of a KM84 like circuit because of the number of parts and some values I could read.
Used stock parts in the LT spice program that is why two zeners the program did not have a 33VDC one.

EDIT 1/18/2020 replaced missing circuit diagram

[kingkorg]

Interesting part of original thread is manipulating capsule as well. Great topic alltogether.

[Moby]

Excuse my ignorance but I can't see anything fancy/innovative  in this schematics?  What exactly you expect from this circuit? To replace FV14?

[Gus]

Excuse my ignorance but I can't see anything fancy/innovative  in this schematics?  What exactly you expect from this circuit? To replace FV14?

I posted this as a kind of history lesson.

S.P. worked on microphones.

I saw the thread and traced(as best I could from the pictures) the circuit for fun.

I did not post what I think about this circuit.

[Moby]

I posted this as a kind of history lesson.

S.P. worked on microphones.

I saw the thread and traced(as best I could from the pictures) the circuit for fun.

I did not post what I think about this circuit.

Oh, then OK BTW, BV.08 primary is wired in series in both arrangements, 6.5:1 and 13:1. Here, it looks like the sec is in parallel, so expected to be 50ohm terminated for the  proper reflected impedance.
EDIT:
I just checked the thread you posted. Dear God why somebody ruined this mic? Guy claims that:  "It sounds fantastic, even without the VF14 M telefunken tube"
Well, I believe that it works, but I don't believe that it sounds better than cheapo U47 Chinese copies. 3um membrane? I dont get it!

[Recording Engineer]

I just checked the thread you posted. Dear God why somebody ruined this mic? Guy claims that:  "It sounds fantastic, even without the VF14 M telefunken tube"
Well, I believe that it works, but I don't believe that it sounds better than cheapo U47 Chinese copies. 3um membrane? I dont get it!

Well, this was 1989... There was no cheapo U47 Chinese copies. Not sure what year BPM Microphones (the “other” German mic company that was really from China, and no one knew it) started rearing their head, but I’m guessing it still was a few years until Alan Hyatt started importing them into the United States from Germany. Aspen Pitman didn’t release the Groove Tubes’ first mic until 1992. Audio-Technica didn’t release their first studio mic until 1994, the 4050.

It was a time when their still wasn’t any other large-diaphragm condenser mics other than the long-standing Europe manufacturers. At the time, it had already been a full decade of Stephen Paul modding “secretive and sacred” European microphones, along with his signature 3-micron Mylar that Neumann still maintains in not stable for large-diaphragms.

This was at a time when Stephen Paul Audio was the first and only -ever authorized Neumann repair shop outside of Neumann for aluminum-diaphragms since Neumann themselves are no-longer capable; hence their titanium capsule at Stephen’s suggestion when approached by Neumann.

Now, I don’t know if it was fancy/innovative for that time, but I can guarantee his work is a huge piece of why it may not be fancy/innovative today.

I haven’t heard it, but I for one, fully believe the guy when he says it sounds fantastic!

[Moby]

I remember those days, I'm 51 And I still think it's ruining the classics. True, cheap mic's was not vailable and U47 was the best available, same like today. VF14 was affordable and so on. My commemt about the China mic's is because topology remindes me, all together with thin membrane

[Timjag]

I though "Bloody he'll, Moby is 51!!" But then I remembered I'm 46 and not 30! Hey a boy can dream! I remember those days. I loved them in fact. People really did believe certain pieces of equipment had magic fairy dust in them, and I honestly believe that this naive thinking added to the creativity within studios.

My partner has a Vox AC30 that sounds better than every other one we've ever heard. She picked it out of a line up of 110 ac30s 25 years ago, all straight out of crates imported to the US from the UK and Ireland. This one out shone all the others, and in my opinion still does. She believes it has magic fairy dust.  Ironically she then got a deal with virgin records and brought the Amp back to London! And here it's stayed ever since

*I* know why it sounds so good and different from others, but she doesn't want to know. She wouldn't even let me service it for 10 years! But it went wrong and I finally got my evil way with it!

I miss those days. Magic mics, magic amps, magic people and most of all magic music. Everything just seems so, well... explained these days

Anyhow I digress sorry for hijacking the thread

Happy Christmas

[Moby]

I though "Bloody he'll, Moby is 51!!"

Wow, I also  can't believe it !
Happy Christmas

[Gus]

There was a forum that Stephen Paul moderated or ran.  Anyone remember the name so we can look for it on the wayback machine?

To be clear about the screenshot of the sim. ? by a part means guesses.

It has a few GUESSES, however the guesses are some things I might do with a KM84 circuit for the body and capsule.

I posted the sim with two 15VDC zeners because they are in the download of LT spice and a 33VDC is not(Yes you can add parts but this is so people can make a sim with download included parts)

KM84 with a 24VDC zener has 10k and 47K after 56K for a series string of 113K total 
I saw 47K and 18K resistors by the zener and guessed the two block resistors in series under the PCB might be two 22K resistors(109K total) and a 33VDC zener moved along the series string more positive.
I could be a 24VDC zener with 44K so the zener is shunting more current.

I might be 24VDC instead of 33VDC because I don't like the drain to gate voltage in the screenshot.

I see what looks to be two polystyrene caps that is why the 1000pF and 15pF guesses.

10K carbon comp as a source resistor would be OK because it is bypassed by a cap, this would reduce noise from the CC resistor, also 10K is in the range of biasing a 2N3819 I have seen up to 11K in older 87s and it looked to be stock

The circuit looks like it might sound very good. I have not heard a SPA microphone in a room (I would guess I have heard some on recordings). It is hard to go wrong with a KM84 like circuit.

[Gus]

A bump This was a SPA microphone adjustment so I thought people would be interested

Funny I posted this to start a discussion
What is good about this microphone?
What can be improved?

[Recording Engineer]

There was a forum that Stephen Paul moderated or ran.  Anyone remember the name so we can look for it on the wayback machine?

Wasn’t that on recording.org?

[Gus]

Recording Engineer 

Thanks, found some threads
https://recording.org/threads/neumann-kms-85i.5516/#post-45402

https://recording.org/threads/neumann-u67-reissue-vs-original.5520/

[Gus]

Bump

added the missing schematic to the first post

[Gus]

Bump

Wanted: Roland SPA-120 (Power Amp) Schematic

Started by matta The Lab

fostex spa powered monitor

Started by wkrbee The Lab

KH and SPA u87 etc adjustments

Started by Gus « 1 2 » Microphones

SPA picture u47

Started by Gus Microphones