Stereo Valve/Tube Mic

[Migs 31]

I know ... it’s just a rip-off of an old old so so design from Austria. (C-24)
But it’s alive, two PCB’s with a 12AY7 sandwiched in. Will change capsules & valve once all the debugging done.
Top capsule rotates 90 degrees.

M

 

[brndvnrdn]

Looks amazing. What body did you use ?

 

[Migs 31]

Looks amazing. What body did you use ?

Got it from China. Something similar to his, but without the pad switches etc:

https://groupdiy.com/threads/heres-a-group-buy-opportunity-for-stereo-ldc-bodies.86700/

 

[Migs 31]

Bit of a problem here.
The top capsule (back-diaphragm) receives Bias voltage through an SPDT Switch and a 200 MG resistor. Front Diaphragm gets 0V - Backplate ~ 60V.

Even when no audio cable is plugged-but with HT & Heaters on, I hear an electrical scratching noise coming from the diaphragm, from time to time ? Just from top capsule, not bottom one !?!

What is going on here ???
M

 

[Paul W]

This got me to thinking. Is a stereo tube mic a good idea?

I assume that the tube is so that you get nonlinearity and some kind of nice-sounding distortion.

But if the stereo signal is asymmetrical (which it probably is, at least a little, or you wouldn't need stereo) the two amps are going to distort differently, maybe very differently when the signal is very asymmetrical. I'd think that'd mess with stereo imaging.

Would a mid-side tube mic make more sense, with distortion mostly on the mid signal?

 

[Barry Hufker]

Having used stereo tube mics for years, in my experience the concerns you express haven't dissuaded me from using them in X/Y or M/S. I think M/S is more flexible as a technique but the sound has been good either way.

 

[Migs 31]

This got me to thinking. Is a stereo tube mic a good idea?

Yes I get your point.
And for some ultra clean Stereo applications i would go for my Schoeps in an ORTF or NOS config.

But as @Barry Hufker said, it never stopped him & many more to use valve/tube mics in a Stereo application.

Well, look at Orchestra people using M50´s in a Stereo or Decca Tree pattern and the results they usually get. I mean, wow!

Thé AKG C-24, I heard one last time in Tampere Jazz Festival, Finland on a Grand Piano. And Ouch! What a combo!!!

Im trying to get the pattern switch working correctly on my prototype, so I can use it either in X-Y, MS or maybe Blumlein. Then i’ll get good decent capsules on it when done.

M

 

[klem]

It's way down on the project list, but I would LOVE a DIY project that is akin to either a C24 or Neumann SM2. I have rarely heard a better sounding mic(s) for drums front of kit, and so accurately defined stereo image (usually Blumlein or M/S)

 

[Migs 31]

It's way down on the project list, but I would LOVE a DIY project that is akin to either a C24 or Neumann SM2. I have rarely heard a better sounding mic(s) for drums front of kit, and so accurately defined stereo image (usually Blumlein or M/S)

Oh ok, really?
On a drum kit, I have tried Coles & others as spaced Stereo pair, before.
And yes, M/S is a useful technique for various reasons.
Now I can’t wait to try that, once my mic is working properly.
M

 

[Accelerator]

This AKG C24 Manual may help you to your task…

 

[Migs 31]

This AKG C24 Manual may help you to your task…

Thanks Accelerator!
I have the schematics for the C-24.
Mine is a souped-up/illegitimate son.

I’m working on a 2 or 3 patterns basis.
Cardioid & Fig. 8 (Omni If faisable)
But thank you all the same.
I have never seen the “cutsheet”

M