Small Diaphragm Condenser Mic Haun MB-C540 + MB C 92540 capsule Information

[rock soderstrom]

Hello girls and boys,

I bought an untested MB-C540 from Haun for 30€. Unfortunately the mic set is no longer complete and is quite heavily used.


The MB-C540 could be a good canidate for a tube mod , spontaneously the S52 design comes to mind. Before I would do something like that, I would give the mic first a chance and also test its original function. Is it still alive?

In this thread I want to collect and post all the info I found about the mic.

The MB-C540 was manufactured in the 70s by the company Mikrofonbau GmbH from Obrigheim/Germany. The company is still active today and known under the current name MBHO (GmbH), which means Mikrofonbau Haun Obrigheim (LLC, Ltd.).

MBHO has produced since its foundation in 1962, in addition to its own microphones, for numerous microphone manufacturers and OEM resellers microphones or parts of them.

Quote from the MBHO site: "Many well known industry customers like Telefunken, Strässer, Dual, Grundig, ITT, Saba, US-Clearcom, Audix and the highly acclaimed Brauner valve tube microphones have been satisfied partners of MBHO.

The main figures of MBHO are Herbert Haun and Manfred Schneider, who can be considered without doubt as heavyweights of the German microphone industry.

Most of the info I found regarding the MB-C540 is based on the following german article I found here.



Since not everyone understands German, I will summarize this very informative article with my humble skills in English

The MB-C 540 is a true condenser microphone system with interchangeable capsules.



The capsules are based on gold coated Mylar foil and the following variants were available:

91540 - Omnidirectional
92540 - cardioid
93540 - cardioid with increased sensitivity 11mV/mubar
94540 - cardioid with (in this article not further specified) special characteristics



The headamp is based on a single FET transistor in a source follower circuit, see schematic. If the amplifier is powered by batteries (2x Pertrix 74 IEC 10 F 15, 15Volt each), pin 4 must be connected to pin 5, which was originally done by a system cable named MB-A9541, which I don't have. The batteries are probably also rather rare today.



The microphone can be powered by the internal batteries or also external PSU via pin 5. The voltage must be between 20-50V and must not exceed a rest ripple of 1mV. With this type of power supply, which is standardized by DIN45594, supply lines up to 30m are possible.
If longer cable lengths are required without battery power, an additional adapter (MB-C548) and phantom power can be used to realize cable lengths of up to 100m.

This adapter also contains a stepdown transformer, which transfers the 500 Ohm output impedance of the microphone to 200 Ohm.

Other accessories such as 10dB pad, external power supply switch and low-cut (rumble) filter are available as external accessories, see photo.

In this magazine's test, the MB-C540 performed very well for the price (435FR swiss francs in 1975/76!). In direct comparison with unspecified professional studio microphones (probably Neumann and/or Schoeps), reduced bass response and slightly increased noise were noted.

Armed with this information I will now build an adapter cable and a temporary power supply to test the mic.

to be continued...

 

[McIrish]

Very interested in this. Great work so far.

 

[Tim Campbell]

If you have any questions write Herbert. He is a sweet guy and usually very helpfull. I visited them quite a few years back.
Herbert must be getting close to 80 years old and I am sure Manfred must be retired. He was in his 80's when I met him 10 years or so ago

.

 

[phetus]

Did you get any further? I have a pair of these with both the cardioid and omni capsules, they seem fairly noisy... was considering making new preamps for them...
If you want me to check anything on mine/compare let me know.

 

[rock soderstrom]

Did you get any further? I have a pair of these with both the cardioid and omni capsules, they seem fairly noisy... was considering making new preamps for them...
If you want me to check anything on mine/compare let me know.

I've only been able to do a little testing with a makeshift PSU so far.
My result was similar. Little level and rather noisey. On the weekend I have more time and will post my results. I also plan to replace the headamp, probably with a 5840/6s6b.

Edit: The basic sound was good, maybe I did something wrong regarding the impedance matching??? We will see.

 

[phetus]

I've only been able to do a little testing with a makeshift PSU so far.
My result was similar. Little level and rather noisey. On the weekend I have more time and will post my results. I also plan to replace the headamp, probably with a 5840/6s6b.

Edit: The basic sound was good, maybe I did something wrong regarding the impedance matching??? We will see.

ah, shame, was hoping maybe my batteries where low or something - i guess not.
oh interesting! will you run it on phantom power or have an external supply? i would like to try the c480 headamp, but couldnt find a complete schematic yet. i had a look at the km84 schematic and it seems very similar to the original... maybe it's also worth a try, definitely simpler

 

[rock soderstrom]

ah, shame, was hoping maybe my batteries where low or something - i guess not.
oh interesting! will you run it on phantom power or have an external supply? i would like to try the c480 headamp, but couldnt find a complete schematic yet. i had a look at the km84 schematic and it seems very similar to the original... maybe it's also worth a try, definitely simpler

My test was with a crude Phantom Power adapter cable. As I said, my noisey result may also be related to my test setup. I don't want to make a final conclusion yet.

KM84 circuit would certainly be worth a try.
Very interesting is also the S52 circuit with a tube. Check that here in the forum. The original designer used a same or very similar capsule at that time and was very satisfied.

 

[Gerard]

Could it be trying to draw more current than a P48 supply can deliver? That would pull the voltage down.

I am doing something similar with an NTI 3382 measurement mic. In the case of the 3382 it requires a 10-30 V phantom supply at up to 12.5 mA. For that, the feed-in resistors need to be 1 kΩ, not the usual 6.81 kΩ for P48.

 

[MicUlli]

Hello Rock,

that's amazing, only 30 €

If the capsule is okay and a good input stage is used you can expect a sensitivity around 12..15 mV/Pa and a self noise figure smaller than 14 dB(A). The frequency response can be easily corrected in the DAW. These capsules are very well known for their perfect off axis frequency response consistency. I use them for ORTF recording (piano, choir, organ), sometimes assisted by an omni SDC for "rounder" low frequency performance.

 

[phetus]

Hello Rock,

that's amazing, only 30 €

If the capsule is okay and a good input stage is used you can expect a sensitivity around 12..15 mV/Pa and a self noise figure smaller than 14 dB(A). The frequency response can be easily corrected in the DAW. These capsules are very well known for their perfect off axis frequency response consistency. I use them for ORTF recording (piano, choir, organ), sometimes assisted by an omni SDC for "rounder" low frequency performance.

14dB(A) does sound good! what input stage would you suggest?

 

[rock soderstrom]

Could it be trying to draw more current than a P48 supply can deliver? That would pull the voltage down.

I am doing something similar with an NTI 3382 measurement mic. In the case of the 3382 it requires a 10-30 V phantom supply at up to 12.5 mA. For that, the feed-in resistors need to be 1 kΩ, not the usual 6.81 kΩ for P48.

Thanks for input, but I guess this is not my problem. I have to check this next time I will find free time to play with this mic.

 

[rock soderstrom]

Hello Rock,

that's amazing, only 30 €

If the capsule is okay and a good input stage is used you can expect a sensitivity around 12..15 mV/Pa and a self noise figure smaller than 14 dB(A). The frequency response can be easily corrected in the DAW. These capsules are very well known for their perfect off axis frequency response consistency. I use them for ORTF recording (piano, choir, organ), sometimes assisted by an omni SDC for "rounder" low frequency performance.

Yes, 30€ was pretty good. I like ebay Kleinanzeigen

Thanks for Info! Sounds promising.

 

[rock soderstrom]

14dB(A) does sound good! what input stage would you suggest?

I guess MicUlli uses his own design, you can find here.

A very versatile input stage for SDC mics

 

[MicUlli]

That's correct