Oktava MK319 mod and new capsule - question

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McIrish

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Hi, I have three Oktava MK319 mics that I did the usual modifications to: replaced caps, some resistors, removed the inner screen in head basket, applied silicone to dampen the body and head basket, removed the resonator disc from the capsule, removed the switches. I can't remember if I changed the FET or not, as this was three years ago. For a while, I was pretty happy with them and I used them in many different situations but they were never my favorites. (current favs are a modded CV4 and a CM7GTS/M7.
So the other day I decided to install a M7 capsule and wire up one of the switches so I could get it to be both cardioid and omni. I only did a quick test so far and it seems to work fine and sounds good. But I have a question.

I'm curious about the polarization voltage on the capsule. Being a FET mic, I believe the voltage can't be any higher than 48V. What effect does that have on the capsule? I've read that higher voltages will decrease the noise floor and decrease the low end. Is the only possible issue an increased noise floor and possibly more bass response? The U48 only had 52V and sounds great.

thanks for the info.
 

Khron

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Well, that 48V is just in theory - since it's supplied through a pair of 6.8k resistors, and the impedance converter needs some current to function too, something in the region of 30-35V is a more realistic expectation.

That being said, in addition to lowering the noise floor, raising the polarization voltage may very well push whatever inherent resonance frequency the capsule has, a bit higher on the spectrum. This kinda makes sense - a higher bias voltage leads to a more taut diaphragm, at idle. Same as if you stretch / tension up a guitar string, the pitch goes up.

The amount of effect that has in real life, though, is up for debate (or measurement, whichever you prefer) ;D
 

McIrish

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Thanks for the reply. I will put it up against the usual suspects in the next session. I'm kind of hoping it is slightly darker than the other mics  (U47 type) for use on a violin. I know I should get a ribbon, but I'll give this a shot first. Heck, I may end up loving it. or not...
 

Moby

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McIrish said:
I'm curious about the polarization voltage on the capsule. Being a FET mic, I believe the voltage can't be any higher than 48V.
Of course it can be. Most of the PH powered mics use voltage booster circuits. So, do a search about it and you can add that mod to your list , of course if you want more than 48v.
 

McIrish

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Great point. I could add that if I felt i wanted to do more mods. I'll see what its like now and then cross that road. Modding mics is kind of addicting. I have to watch myself or I'd never get any recordings done. Ha!
 

McIrish

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Jun 15, 2016
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Well, I tried the mic in a session. i put it up against a Miktek CV4 with a BN K7 capsule. The oktava with the M7 sounded a bit harsh. I didn't care for it at all. I'm pretty surprised. I'm not sure if raising the voltage to the capsule will sweeten the sound.  That was a disappointing outcome. An old ADK A51 (typeII) actually sounded warmer and smoother.
Oh well. Maybe I will look for some used tube mic to use as a donor. I'm sure this M7 sounds better than what this mic sounds like.
 
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