Neumann M50

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riggler

Well-known member
Joined
Jan 24, 2006
Messages
1,076
Location
Pennsylvania, USA
Hi all,

It looks like the mic schematics from the Silent Arts website are all down. I was wondering if anyone could send me the schematics to the Neumann M50 or M50b mic. I'm going to start a DIY project. :twisted: Also, if anyone has information on the power supplies for these units, I'd be grateful for that as well!

Thanks,

-Damian
 
in the microphone meta there's:

http://www.sdiy.org/oid/mics.html

you can find 2 M50 schemos, one with the Hiller MSC2, and one with AC701...

Axel
 
Thanks all! :grin:

So, my plan is to layout a pcb and make a parts list for the mic using a new tube. Thinking a Peluso capsule may be a good fit for this project, although I already have a set of MXL omni capsules that could be used.

I got more information I will post tomorrow on the mics.

Anyone else interested in doing an M50 clone project? I'll need some help in determining a good, new tube for it. The PSU should be straightforward, and we should be able to build a unit with lower self-noise with today's components.
 
[quote author="riggler"]Thanks all! :grin:

So, my plan is to layout a pcb and make a parts list for the mic using a new tube. Thinking a Peluso capsule may be a good fit for this project, although I already have a set of MXL omni capsules that could be used.

I got more information I will post tomorrow on the mics.

Anyone else interested in doing an M50 clone project? I'll need some help in determining a good, new tube for it. The PSU should be straightforward, and we should be able to build a unit with lower self-noise with today's components.[/quote]

At some point you might find yourself completely stuck, as there is no quiet enough tube on the market to work with SD capsule... unless you are willing to get whole bunch of 5840 (etc.) and try to select one... untill you give up.
I'd recommend not to clone M50, but get a nice omni pencil mic and make a couple of spheres of different diameters (for defferent peaks), make nice through holes and slide them on the mic--acoustically the same effect as M50.
I'll later post a pic what I did.

Best, M
 
M,

I've made spheres for my modded MXL 603's and Altec 201B's. They do sound good. I have omni capsules for both mics.

But I really want to build a tube mic. Maybe the better approach would be a G7, mounting the capsules in a sphere like the M50.

Is there a relatively inexpensive modern-day replacement for the 701 tube? I didn't mean to imply I'm after a very quiet mic.
 
[quote author="riggler"]
Is there a relatively inexpensive modern-day replacement for the 701 tube? I didn't mean to imply I'm after a very quiet mic.[/quote]

AFAIK, there is no... at least readily available. I think Allegro, though, sells selected for low noise tubes of any type--expensive, but might be a good option.
 
Hi all,
I'm very interested in this this project. I do not claim to build a M50 or preferably for me a M49 clone... There are so many problems to solve to design a mike of this class.. First of all mechanical parts are expensive (see Flea mechanical kit : about 1200EUR here in France) and we now that head design is so important for acoustical behaviour. So if someone could build this parts, I'm in !! (ok, that's a joke!)
Secondly, original M7 are now unavailable but we can test M7-like capsules (like Dale's capsule I own .... thanks again Dale to share your great work).
The tube now: AC701K are now quite expensive (I pray for my 2 * M367 tubes) and those found on Ebay (for example) were rejected by Neumann... so maybe it's better to look for a substitute (selected 5703WB?).
Transformer and psu are not really a problem (see Tab Funk).
I'm really waiting for your answers in this topic because I'm not an expert in microphone design and building (though I've modified my Apex 460 like many others..).
And I apologize for my poor english...
All the best.
Eric
 
After some investigation, the AC701 tubes are prohibitively expensive, and will only become harder to get. This isn't the best for DIY.

So, another idea. A 6072 tube can be used in place of the AC701 if we up the heater voltage to 6.3 volts. If we make that jump, than we may as well move to the EF86 G7 design, which is based on the Neumann architectures of the period.

Jakob saves the day. :!:

So, I'm thinking we could:

1. Remove the pattern switching from the G7 design for straight omni. This would include PSU mods and also mic mods.

2. Use a Peluso CEK 89/S, found for $105 American. This is a single sided capsule, which gives us omni, correct?

3. Make a sphere out of hardwood, a golf ball, etc to mount the capsule.

I need to re-read the theory of operation and do some learning before I can modify the schematic. Do we still need to bias the capsule with 160V if it's single sided for omni operation? I assume it has to be biased with *something*...

At the end of the day, will the G7 design sound close enough? For me, probably. I'm very good at drafting and design and have access to a metal shop, so I could come up with an easily-built design. We must follow the M50 grille design. That will be the toughest but I have some ideas for making that possible already that should not affect the acoustics *too bad*, all things considered for a DIY project.

So, do we do 6072 tube, 5703WB tube, or the Gyraf EF86 tube & design?
I think the EF86 using the Gyraf layout may be the best choice for now.
I can't find a clean, legible, schematic for the M50b... working on that.

Capsules --- How much is the Dale capsule and is it readily available?
 
The 5703 or EF86 will work fine in this application. There is another tube, an ECM1000, I think, which looks just like an AC701 that was used by Bruel & Kjaer in some of their tube mikes. I have purchased them in the $50-60 range.

Does anyone know how the M50 capsule is constructed? Hole pattern, depth, diameter for a possible recreation? The original capsule appears to have a 12mm diaphragm.
 
Were are you going to get a BV11 or a real M50 capsule?

G7 is cathode biased and 50b is fixed bias

Low noise tube?

I would reread Mariks posts that might be even better because of the different size spheres.

You will not be building a M50 but something kind of like a M50

Details count.

There is a part that needs adjustment for the overall gain control Neumann DESIGNED into the circuit. Do you understand how the M50 circuit works?

An EF86 is not a AC701.

If I was building a M50 clone I would design my own supply not use the G7.
 
[quote author="riggler"]

2. Use a Peluso CEK 89/S, found for $105 American. This is a single sided capsule, which gives us omni, correct?

[/quote]

This is a cardioid capsule. Also, the original M50 has nothing to do with aforementioned M7 and had aluminum diaphragm. I don't know any true omni capsule on the market of M50 size.

[quote author="riggler"]Darn. I just realized that Peluso capsules are too big. We need to stay SDC here. So.... I think between 10-15mm would suffice.[/quote]

If you are going a tube route and 10-15mm capsules I highly doubt you will find much signal in the noise. You could try omni from MXL603--it is very cheap, but I could not find graphs to see if it is already free field corrected or not. Other readily available options are AKG CK62-ULS and MBHO.

Best, M
 
First off, let me say that this will not be a "clone". Let's say M50 - style at this point. "Cloning" this mic is just too expensive, at least for me.

[quote author="Gus"]Were are you going to get a BV11 or a real M50 capsule?[/quote]

I just got off the phone with Peluso. They make a SDC omni capsule, about 18mm in diameter, $90 each. Any other reasonable suggestions?

As far as transformer and other electronics, the BV11 is $350, too much $$ for me, but maybe not others. But, we are still tied to a very expensive AC701 anyway. This is why I think we should opt for the G7 basis for the design. That, and I do not have the skills to redesign the electronics as far as matching tube to transformer, etc.

G7 is cathode biased and 50b is fixed bias.

How does this affect the sound? I would think we'd get less color/saturation based on what I've read, but I am not an expert here. We would get more gain -- all else being equal -- with a fixed bias design, right? OTOH, cathode bias uses negative feedback which could smooth things over and lower distortion, correct? I am learning here....

Low noise tube?

Can someone explain to me the relationship between capsule size and noise? I've never really understood this. A larger capsule generally will have a higher capacitance, is this reflected in noise figures?

When I originally mentioned lower noise, I was thinking a clone could have a lower noise floor due to because of better tolerances on components we have today. I fully realize that a tube mic will not be a "quiet" mic, comparatively speaking. The goal here, for me, is to get some of the character from the M50.

I would reread Mariks posts that might be even better because of the different size spheres.

The spheres I have to work on existing SDC stick mics, like the 603. But I want to try this with a tube mic. The Royer mod on the 603's would be an option if this doesn't pan out.

You will not be building a M50 but something kind of like a M50

Details count.

Correct on both counts. I am hoping to get "enough" character to be "close enough". We know we won't make a 100% piece without a lot of $$$ and skill.

There is a part that needs adjustment for the overall gain control Neumann DESIGNED into the circuit. Do you understand how the M50 circuit works?

Not completely. Looking at the M50b schemo, between C1 and R2 there is a calibration input. How does this function? Is there a trimmer on the PSU?

An EF86 is not a AC701.

Understood.

If I was building a M50 clone I would design my own supply not use the G7.

I think we're at the point of not really cloning the mic. Unless someone chimes in with some skills. For me, it's easiest to work back the G7 by changing the capsule (the Peluso is 37pF BTW), drop the polarization switch on the PSU, etc.

What do you think?
 
The capsule size affects noise because the SDC capsule is ~1/4 the area of an LDC capsule. This means the capacitance and consequently the area available for signal generation will be less.

An actual M50 capsule diaphragm to back electrode spacing is roughly half that of a normal LDC at 10um. This accounts for why its actual capacitance is half that of a typical LDC rather than 1/3 to 1/4 the capacitance of a typical SDC capsule, which would be expected. This will also cause it to be more sensitive.

The desirable characteristics of the M50 arise from the smaller diaphragm which will produce faster transients. It also has a relatively flat frequency response except for a +6db rise at 8KHz. By comparison, LDCs have all kinds of subresonances and front to back cancellation that is dependent on frequency and angle of incidence. The omni capsule in an almost ideal mount (the sphere) presents a uniform aerodynamic front to the oncoming pressure wave and functions as a more perfect pressure transducer (as opposed to gradient, or differential pressure transducer of the typical LDC).

The original capsule used an aluminum diaphragm but later production models used a gold coated polyester diaphragm.
 
riggler

I suggest you read some of the good PDFs at the Neumann site. Also look at Klaus's and others forums at REP prosoundweb. There is more stuff on the web to learn from with tubes. Look around the Schoeps site and DPA and......

Marik posted about MXL omnis did you check the prices?

fixed vs cathode bias sometimes you just need to build stuff to learn.

Look at all the tube microphone schematics you can find.


Have fun
 
Interesting project, but a tough one...!

Have you considered a half inch measurement capsule? One that operates with 200V polarization might give you enough S/N despite the low capacitance, and it's about the right size too! Might even be able to find these second hand. Used some from B&K a long time ago with good results.

Have my doubts you can build anything good without spending at least some money on the capsule. There's a reason a Peluso capsule from China is only $90, even if an omni capsule is generally easier to build than a cardioid. Why not ask Dale Ulan to consider making a batch of special omni capsules for us?

Martin
 

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