Leftover capsules. Any ideas?

[HellfireStudios]

I've done quite a few mic mods so far, and I had lots of dual-diaphragm Chinese 32mm K67 capsules laying around. Does anyone have any ideas what these capsules could be good for? I'm still on the fence about whether I should go for another high-end style mic, or something a bit trashier... Any thoughts welcome.

-James-

 

[MagnetoSound]

Why not go for poctop's D-U67?

 

[HellfireStudios]

I wouldn't disgrace a U-67 circuit with a cheap Chinese capsule. Also my intended mic body will be G7-ish in design (straight tube with grill area cutout), so the capsule-to-grill acoustics wouldn't be the same as the U-67. I do intend on getting the DIY67 project in the near future, so I don't need another tube circuit right now. Although, a ELA M251 circuit with a larger smoothing cap is looking very tempting...
I have the PCB and transformer for a Carvin CM-87S left over from a DIY87 project. Would this circuit be worth modifying? How easy would it be to implement multi-pattern capability? Thanks.

-James-

 

[MagnetoSound]

I wouldn't disgrace a U-67 circuit with a cheap Chinese capsule.

I thought you might say that.  ;D

But then, if this capsule is not worthy of the very circuit for which it was designed, perhaps it's not worth using at all ...?

The Carvin is supposed to be a U87-type circuit, right? It's probably designed for non-isolated backplates, anyway. Since you have it, why not use it ?

 

[HellfireStudios]

Actually, I will be using a reskinned 34mm K67 capsule for the DIY67 project. So I couldn't use a lesser capsule for such a fine mic, but I also can't waste anything (I might have a touch of OCD). To that end, an idea came to mind earlier today. Since these capsules have an inherent rise in the high frequency response that can actually sound ok with acoustic intstruments. I was thinking of using this capsule for a distant mic with a sort of Fletcher-Munson compensation curve design. This could allow for more apparent detail at further distances (mainly due to the high frquency rise).
The head amp would need to be very quiet and have high sensitivity. A boost in the low end from the amp would be needed as well. The high end may still need some attenuation too, if harshness is encountered in use.
Could the stock Chinese U-87 style circuit (Aurycle a460, Carvin CM-87S, etc.) be modified to accomplish these goals? If not, would starting with a Shoeps style circuit be a more fitting match? Finally, what would I change in either of these circuits to boost the lows and attenuate the highs? Thanks.

-James-

 

[MagnetoSound]

Could the stock Chinese U-87 style circuit (Aurycle a460, Carvin CM-87S, etc.) be modified to accomplish these goals?

The frequency response tailoring in the U87 is accomplished using NFB. Referring to the MXL2001 circuit attached below, let's look at C5. This is the global feedback cap that couples the drain signal into the feedback network (R3, C3) leading to the capsule. It also forms a high-pass filter with R17 (which effectively acts as a shunt via C13). Reducing the value of C5 will allow less LF into R3, resulting in less LF attenuation (in other words a low end boost).

C3 is the treble rolloff cap. It bypasses R3, increasing HF feedback into the amp via the capsule. Removing this will linearize the top end of the amp and restore the HF rise of the capsule at the output.

 

[HellfireStudios]

Excellent. You are, as always, a big help. I think I may have a great starting point.

Quick question:
Would a change at C3 alter the corner frequency or the amount of attenuation (my guess is corner frequency)?

Thanks again.

-James-

 

[gemini86]

If you still have capsules sitting around being useless... I'd take a couple off your hands

I'm not afraid to disgrace a DIY U67 with a cheap capsule.

 

[gyraf]

Make a Soundfield setup?

Keith SSLTech has a schematic of matrix etc somewhere around here...

Jakob E.

 

[MagnetoSound]

Would a change at C3 alter the corner frequency or the amount of attenuation (my guess is corner frequency)?

You guessed correct.

I forgot to mention, you can remove C5 altogether and linearize the response that way, although the result is a lot more gain and less headroom. This may be too close to overload on loud sources, but will be fine for distant applications.

 

[DerEber]

If your not going to build something with it.
Just keep it for some time.
From time to time people will pop up here having problems with their Mic's and would need a spare capsule to snap in for testing. You can make them very happy.

 

[HellfireStudios]

Great ideas. I think I'll start with building the mic body. By the time I finish with that (my last full DIY to over a year), I may be in a better place financially. Then, I could possibly purchase more high end capsules to relieve my G.A.S.
The distant mic idea is the idea that sticks out the most. I'm trying to fill any gaps in my collection. A diffuse soundfield mic, a large diaphragm dynamic (SM7B, RE-20, etc.), and maybe a carbon mic are what I need to round out my mic locker (for now).
Unless someone knows how to make a LDC sound like an SM7B, I'll probably start with the diffuse soundfield mic. Thanks.

-James-

 

[tchgtr]

  Assuming you saw this thread:
http://www.groupdiy.com/index.php?topic=51640.0
RuuDNL did a very nice job.

  Also, I tried the Oktava MK-012 circuit in a mic with a LDC capsule, and it's a bit hyped in the mids, but adjustable to some degree. There is a nice thread about it somewhere, where PRR chimes in with a good analysis of the circuit, and Gus suggests a way to tone down the high end for LDC use.

 

     

 

[HellfireStudios]

  Assuming you saw this thread:
http://www.groupdiy.com/index.php?topic=51640.0
RuuDNL did a very nice job.

  Also, I tried the Oktava MK-012 circuit in a mic with a LDC capsule, and it's a bit hyped in the mids, but adjustable to some degree. There is a nice thread about it somewhere, where PRR chimes in with a good analysis of the circuit, and Gus suggests a way to tone down the high end for LDC use.

 

I did see that thread. Unfortunately, RuuDNL ended up using a K47 style capsule in his build. My only leftover capsule is a K67 type. Though, I can see how we had a similar intent.
After MUCH internal debate, I think I'll optimize a stock Chinese U-87ish circuit I have lying around, relam the x-former, and make it bi-polar (I mean cardioid/omni not the mental condition). Other than the SPST switch needed to bring the back diaphragm into the circuit, is there anything else needed to make a cardioid-only mic multi-pattern? Also, where do I find info on re-laminating a x-former? Thanks.

-James-

 

[MagnetoSound]

Other than the SPST switch needed to bring the back diaphragm into the circuit, is there anything else needed to make a cardioid-only mic multi-pattern?

Unless you can derive a separate supply rail to polarise the rear diaphragm, you would require a K87-style capsule with isolated backplates and a more complicated switching system (and blocking cap) to achieve figure-8. The U87 schematic will illustrate this.

Also, where do I find info on re-laminating a x-former? Thanks.

CJ?  ;D

 

[dmp]

Unless someone knows how to make a LDC sound like an SM7B

This would be an awesome DIY project, to develop a multipattern LDC mic that sounds like a sm7b.
I tried with a donor AT body, front address, MXL donor capsule, and 5840 tube circuit. Didn't work well at all at first listen, but I'd like to get back to it.

 

[HellfireStudios]

Unless someone knows how to make a LDC sound like an SM7B

This would be an awesome DIY project, to develop a multipattern LDC mic that sounds like a sm7b.
I tried with a donor AT body, front address, MXL donor capsule, and 5840 tube circuit. Didn't work well at all at first listen, but I'd like to get back to it.

Kel Audio have claimed just that. It's the HM-2D, and they say that this side-address condenser mic sounds like a large diaphragm dynamic. There are even audio samples on their site. As I have never had the opportunity to use a SM-7B, I could not comment on the legitimacy of their claim. Still an interesting idea, though.

-James-