sennheiser mhk30 capsule

seavote · May 31, 2006

i recently won 2 capsules for the sennheiser mkh30 microphone. i was planning on building 2 of the same mics from the mkh30 schematic. i learned that these mics use inductors in the circiut to excite the capsule. there is a lot going on inside this mic. the circuit is called an rf circuit for ralf falk the engineer i think? any info on this type of circuit is welcome. but i was also told that these mics would not be good to use in a tube microphone and i was thinking of using the capsule in a d.i.y. g7 mic. mainly because i believe that these capsules are probably of much better quality to the chinese capsules that are all over the place and better than a peluso(who seems to be the only alternative,if you know more sources for some high quality capsules please let me know. does any one who is familiar with this mic or type of circuit know if this capsule is constructed differently than those used in tube mics and if so can they be modded to work in a tube mic and still maintain their quality. any help or ideas are appreciated........ thx, an ambitious newbie

BradAvenson · May 31, 2006

That capsule won't work for a G7. You have to use an RF (radio frequency) signal to charge the capsule. They work really well with the sennheiser electronics, but I think you will have a hard time finding many of the parts.

seavote · May 31, 2006

i believed i'd located the parts but i was uncertain .maybe you can clear that up for me. the inductors i found are tdk brand "smd type" i dont know what that means.(are they the correct"type" for an rf circuit) all the values of the inductors are as called for in the schematic. the transistors bc 850 b , bc 860 b and bc846b are fairchild npn and pnp amps. one small signal fairchild diode, 2 schottky barrier diodes and the rest zener diodes. does this sound like the correct type of components one would find in an rf mic circuit??? i hope so. if not its back to the drawing board. thx

seavote · Jun 1, 2006

can anyone who is familiar with an rf circuit or owns this mic help me out and confirm that ive located the correct components. i see that smd inductors have a lower profile than other inductors which makes sense in a mic body. thanks

Mendelt · Jun 1, 2006

SMD means surface mounted if i'm not mistaken. I'm not sure if those are the inductors you'd want.

I opened a sennheiser mkh110 once (similar rf design i think) and they had 1cm high inductors with adjustable cores.

I'm curious. How exactly are these capsules different from normal capsules?
As far as I understand the principles of operation are similar as with a normal capacitor microphone. The trick was that sennheiser used an rf ac signal to charge the capsule instead of dc and that this somehow got around the problem of needing the high impedance of a tube grid or fet gate. That way they could use low noise bjt's (which was very important in a time when jfet-quality wasn't as good as it is now).

seavote · Jun 1, 2006

just double checked the schematic. no adjustable core inductors are called for in the mkh30. i could get a schematic to anyone who is interested in seeing how the circuit works. i know what the symbols stand for but how the circuit works is beyond me.

pstamler · Jun 2, 2006

As I understand it, the way the circuit works is that the capsule is part of a radio frequency (RF) oscillator. As the diaphragm moves in and out in response to sound, its capacitance changes, which changes the frequency of the oscillator. The RF signal, therefore, is frequency modulated. The rest of the circuit then demodulates the signal, extracting the audio and sending it out the outputs.

One advantage, aside from the design's ability to use bipolar transistors, is that the mic doesn't mind working in high-humidity environments as much as most condenser mics.

Whether the capsule could be used in a conventional design, I have no idea.

Peace,
Paul

Mendelt · Jun 2, 2006

Voltages on the capsule are a lot lower in these sennheiser mic's. I can imagine they won't like the higher voltages in a normal capacitor mic.

gyraf · Jun 2, 2006

The HF-mics are not something that I would take on as DIY - there is a very good reason why so few companies got it right - and it ain't to do with the capsules.

So don't expect this to be a matter of throwing together the right components on a strip of veroboard!

Here are some HF-mic schematics:

http://www.gyraf.dk/schematics/SennheiserMkh-105.jpg
http://www.gyraf.dk/schematics/Sennheiser_Mkh-405.jpg
http://www.gyraf.dk/schematics/Sennheisser_MKH-435.GIF

Jakob E.

Guest · Jun 2, 2006

[quote author="BradAvenson"] You have to use an RF (radio frequency) signal to charge the capsule. [/quote]

What do You mean about this?:
http://www.beis.de/Elektronik/HF-Mic/HF-Mic.html

xvlk

Guest · Jun 2, 2006

[quote author="Mendelt"]Voltages on the capsule are a lot lower in these sennheiser mic's. [/quote]

Some 40 V AC...
It is symetrical capsule, works in Hibbing s connection (without quartz)
Look at modern Sennheiser schematics, I can scan something.

xvlk

seavote · Jun 2, 2006

gyraf,i am to ignorant to know why.(newbies even laugh at me) could you tell me why this project will not work if i get all the correct components and wire them as per the schematic for the mic. or is aquiring the correct components the difficult part. the 2 capsules are mine and i cant use them for a tube microphone. xvlk, your info was very interesting and makes me believe this might work. may i email you with some questions. you seem to know these circuits well.

Guest · Jun 2, 2006

[quote author="gyraf"]
Here are some HF-mic schematics:
[/quote]
Griese - Hibbing s mic:
http://www.rudolfinea.cz/mkh20.gif

But, why not to transform this mic into tube HF mic.
There was famous tube HF mics in the world, somebody older
can remember... ?
Some Japaneese one:
http://www.rudolfinea.cz/s204.gif

xvlk

rodabod · Jun 2, 2006

This is the first time I have ever heard of RF microphones.

That's clever how they use FM modulation.....

Xvlk, you always surprise me how much you know about all sorts of microphones! A tube RF mic could be cool.....

Guest · Jun 2, 2006

[quote author="pstamler"]
Whether the capsule could be used in a conventional design, I have no idea.
[/quote]
Conventional design == constand charge
HF design == constant voltage.
Some shifts in negative compliancy can occurs, it would not
have much affect on freq response.
But capsule is not constructed to DC, may behave like old Wente s mics
from 1920-ies (may be too noisy)
But it depends on sennheiser technology.
I had constructed some capsules year ago, and its was usable in the
HF circuit, but absolutely unusable in classical circuits with DC charge.

xvlk

Guest · Jun 3, 2006

[quote author="rodabod"]
Xvlk, you always surprise me how much you know about all sorts of microphones![/quote]
Some nonclassical sorts of microphones can perform better in locations.
I always study before buying new mic.

But for MKH capsule... I think, that original Van Zelst schemo is
well adaptable to symetrical Griese capsules. And it can be done as DIY
(if someone have some basic HF measuring equipment like polyscope)
It is Phillips microphone from 1940-ies, Van Zelst had 25 - 50 mA of AC current trough the capsule
Here it is:

http://www.rudolfinea.cz/zelst.gif

xvlk

sennheiser mhk30 capsule

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