M49C circuit details / questions

[geareyes]

Dear Wulf,

Thank you so much for your contribution.

Simply incredible !!!!

Best wishes,
Mike

 

[hop.sing]

The third article is about the creation of the MS2 valve that had to be created especially for the M49/M50 by the small company Hiller in Hamburg, because the big valve-producing companies were unable to fullfil the task at the time.

I hope you find the articles informative or interesting but I´d be happy if they just raise a smile,

Best wishes from Bremen,
Wulf

Really great information in those articles, thank you.
By the way, I own and use a Hiller m69 small membrane microphone with the msc2 tube installed and have a backup tube assembly with another msc2 for that mic and both tubes work still within or close to their specifications, a little noisy for very quite sources but totally usable for something like a strummed acoustic guitar.
70 years after they where built, incredible...

 

[telewulf]

Really great information in those articles, thank you.
By the way, I own and use a Hiller m69 small membrane microphone with the msc2 tube installed and have a backup tube assembly with another msc2 for that mic and both tubes work still within or close to their specifications, a little noisy for very quite sources but totally usable for something like a strummed acoustic guitar.
70 years after they where built, incredible...

Really? You do own a Hiller Mik? An even with a spare MSC2? - WOW!!!

... you don´t by any chance have some pics at hand?

best wishes from Bremen
Wulf

 

[bremusound]

https://www.tapatalk.com/groups/pro...ors-of-hiller-tubes-in-hiller--t19405979.html

In this thread you can find infos and pictures of Hiller mics

 

[OneRoomStudio]

Also of interest: https://groupdiy.com/threads/nwdr-neumann-b-m49.85289/

 

[hop.sing]

Really? You do own a Hiller Mik? An even with a spare MSC2? - WOW!!!

... you don´t by any chance have some pics at hand?

best wishes from Bremen
Wulf

The Mic looks like a typical Hiller miniature mic with the phase ring. Andreas Grosser rescued it and built a fitting power supply with the electronics and a Haufe transformer. The original aluminum membrane was shot, so he had it reskinned from Thiersch with a nickel membrane. So I have no idea if it sounds like it should, but it sounds very nice on transient sources, but is a little light on the bass.
The tube assembly is interesting as it contains the complete electronics in the m69 which is the tube and the grid resistor, as well as the plug and the spring which connects to the capsule. It is a very small microphone indeed The assembly seems to be an unused spare and works perfectly. It was a very lucky find on Ebay for 180 Euro....

 

[telewulf]

The Mic looks like a typical Hiller miniature mic with the phase ring. Andreas Grosser rescued it and built a fitting power supply with the electronics and a Haufe transformer. The original aluminum membrane was shot, so he had it reskinned from Thiersch with a nickel membrane. So I have no idea if it sounds like it should, but it sounds very nice on transient sources, but is a little light on the bass.
The tube assembly is interesting as it contains the complete electronics in the m69 which is the tube and the grid resistor, as well as the plug and the spring which connects to the capsule. It is a very small microphone indeed The assembly seems to be an unused spare and works perfectly. It was a very lucky find on Ebay for 180 Euro....

A very lucky find indeed! And the 1955 labeled replacement-assembly - wow! - that´s what I call real audio-archaeology. Congratulation!

 

[tomas.borgstrom]

Here’s some pictures of the other part of that Hiller microphone and my schematic of it. The small pencil is just the tube, capsule and a 2G resistor with a quite unique look. This particular microphone is in very good shape, everything original, and it sounds really good. Unfortunately it’s not mine.

 

[tomas.borgstrom]

The schematic is not complete. There’s a 2G resistor between grid and ground.

 

[telewulf]

Hello Tomas,

are you certain about the 2 GOhm Resistor? As far as I know, that one is supposed to be 7 GOhm. Even more unlikely but true. Have a look at the tapatalk-link that Bremusound supplied, you´ll find the original schematics there.

Great pictures by the way, I have never even seen any Hiller mik in my live and so I´m very curious

 

[telewulf]

Among the documents you find at tapatalk, you find a brochure about the company of Albert Hiller, that had been editedin 2000 by the NDR. I took the liberty to translate that brochure into English - here it is. Hope you have as much fun with it, as I had.

best wishes from Bremen,
Wulf

 

[tomas.borgstrom]

Hello Tomas,

are you certain about the 2 GOhm Resistor? As far as I know, that one is supposed to be 7 GOhm. Even more unlikely but true. Have a look at the tapatalk-link that Bremusound supplied, you´ll find the original schematics there.

Great pictures by the way, I have never even seen any Hiller mik in my live and so I´m very curious

I haven't measured it but for some reason I've written down 2G. The schematics of M59 says 7000Mohm but it does not have the same flat resistor just beneath the contact of the capsule.

 

[bremusound]

Here is the Braunbuch file of the Hiller M59/60 microphones

 

[rock soderstrom]

Here is the Braunbuch file of the Hiller M59/60 microphones

Very interesting

 

[Murdock]

Maybe I missed it and it was already said but according to my simulations the value of R3 (5Meg) has to be altered when omiting or reducing the feedback cap C4 to get the same curve as originally intended or you get a more drastic low cut.
In the original configuration (5Meg and 8pF) the -3dB point is at about 20Hz.
When completely omiting the feedback cap C4 the -3dB point shifts up to around 50Hz. To have the -3dB point at 20Hz you have to increase R3 to 15Meg or increase C3 from 10nF to 33nF.
At least according to my simulations. Will also test it with my actual circuit.

 

[Roman Beilharz]

Maybe I missed it and it was already said but according to my simulations the value of R3 (5Meg) has to be altered when omiting or reducing the feedback cap C4 to get the same curve as originally intended or you get a more drastic low cut.
In the original configuration (5Meg and 8pF) the -3dB point is at about 20Hz.
When completely omiting the feedback cap C4 the -3dB point shifts up to around 50Hz. To have the -3dB point at 20Hz you have to increase R3 to 15Meg or increase C3 from 10nF to 33nF.
At least according to my simulations. Will also test it with my actual circuit.

Murdock, thank you so much for sharing; your post finds me just in time as I finished building a M49c clone without the 5M/R3 feedback/low cut, but still using a 3-12pF trim cap for C4.

As I am building a matched pair, I was assuming, I could simply level match both mics using C4. Now looking at the schematics again, I realize C4 is part of the feedback loop and now I am wondering, whether I should rather abandon C4 completely?!? A side effect would be I could get rid of the specific trim cap, which is a little too high, so that I was about to dremel away a couple of mm of the headbaskets's interior rim to make this bugger fit into the body...

Any recommendations, anyone?

 

[Migs 31]

I finished building a M49c clone without the 5M/R3 feedback/low cut, but still using a 3-12pF trim cap for C4.

As I am building a matched pair, I was assuming, I could simply level match both mics using C4. Now looking at the schematics again, I realize C4 is part of the feedback loop and now I am wondering, whether I should rather abandon C4 completely?!?

Hey Roman,

Well done on your build.
I'm working on a pair of M49 C (striped down circuit) myself at the moment.
I omitted C4 AND R3 completely, no problem from what I can hear : good volume & plenty bass.
This is my 2 cents, based on real life circuit.

M

 

[Roman Beilharz]

Hey Roman,

Well done on your build.
I'm working on a pair of M49 C (striped down circuit) myself at the moment.
I omitted C4 AND R3 completely, no problem from what I can hear : good volume & plenty bass.
This is my 2 cents, based on real life circuit.

M

Hey Migs, thank you for your reply. Yes, I also thought about omitting C4 and R3 - just as all the other measurement input related parts - to preserve maximum gain and bass, but for a first shot I wanted to keep the option to maybe be able to level match my pair a little better with C4.

By the way, did you stick with two 10nF caps C2/C3 (=5nF in total) regardless of the missing R3 output link? Right now I just used a single 10nF cap from backplate to ground as Neumann had used it for the first M49 versions, that didn't have the R3 LC filter.

My current understanding is, that C4 creates an Anode feedback, which simply attenuates the signal. But Murdocks statement could imply, that C4 also might apply some kind of filtering even when not flanked by R3. Could some of the experts maybe shed some light onto this?

 

[bremusound]

Looks like a Phaedrus 701, right?

 

[Roman Beilharz]

Looks like a Phaedrus 701, right?

Yes!