DIY home made P2P Oktava Mk012.......circuit questions & observations

[pasarski]

I luv it! 

Hope the foam doesn't crumble and contaminate the capsule BTW.

 

[Gus]

A screen shot of a condenser microphone follower circuit(no capsule or grill) sim frequency response .  Phantom powered solid state.  Who needs tubes?

 

[Rybow]

I luv it!  

Hope the foam doesn't crumble and contaminate the capsule BTW.

Thanks pasarski! I am glad you like it! I'll have to keep an eye on the foam. I put it in to see if I there were any reflections in the head basket that needed taming. Honestly, I don't know if it made any difference.

EDIT: Hooked up the mic today after cleaning the high impedance area with a flux remover pen. It seems that isopropyl alcohol reduces output level when used on the high impedance area. Anyway, I was greeted with some wacky noise, and i am not sure where it's coming from. Sounds like wind, not the usual white noise/noisy circuit sound, but like wind is rushing by the capsule, then there are some crazy thumps that happen, and not from me banging the stand either. I made a recording of the noise. I don't know, dirty capsule?

http://dl.dropbox.com/u/11106120/mk%20012%20noise.m4a

Gus- Who needs tubes? Tubes!? Blasphemy!

All joking aside, I like these FET circuits so far, and don't have an overwhelming urge to deal with tubes at the moment. They sound really nice, and are so cheap to build. A little work on biasing, and you are good to go. My biggest issue with FET phantom powered mics, implementing figure 8.

I am really interested in discussing FET circuits in mics further. Would anyone mind if I started a thread in the drawing board? Just to keep this thread clean maybe.

 

[Oceano99]

The modded mk 012 circuit sound really intresting.
Does any one know any LDC that works well with this circuit?
Seems polarization dosn't mather so did anyone tried a copy of the CK12 capsule with this circuit?

Johan

 

[gary o]

Hi Johan Im in the midst of trying capsules with mic circuits, I just tried a ADK vienna capsule with oktava circuit......I have read the Vienna capsule is a copy of the C12 capsule......its sounds good sounds pretty much same as th complete ADK mic with its transformer.....tho the ADK is a cheap mic it has good components & I read good things about it

On the other end of scale I just tried a RK47 a cheap K47 from china... it as expected sounds more mellow & still good......that combo is cheap to DIY........need to try a RK12......also cheap china but maybe good...

Im trying to make best possible vocal mic from these parts....Oktave circuit,Oktava MK101, Expesive Violet vin 67,RK47,Lomo K47 ish,ADK C12ish  maxes MK47, C12 ish circuit, Royer circuit

 

[Jean3030]

Hello, I have great interest to modify Superlux S502 circuitry and replace it with Oktava MK12 input preamp style, so, in the Superlux, there is really no place and it needs 2 similar circuitry.
I suppose you know well Superlux S502, it's an ORTF Chinese stereo microphone (like Schoeps, but not the same quality) and the price is very low for the rather good quality. I just find it too noisy.


I suggest this modification to reduce the number of components, but i did not try it :



If there is a problem ,I will put again the 2X13k resistors instead of single 3K and I will add again the 2X 10nF filtering XLR outputs.

84K resistor is not a common value, so I found 84.5K or traditionnal 82 K value, it seems to me not very critical. If somebody have an idea about that ?

The evental small improvement compared to original MK12 input, is to obtain a real 48V voltage for the capsule. The problem is to loose the balanced phantom power principe.

In the original Superlux S502 circuitry, there is noise lever higher than oktava mk12 and not a good response for hi frequencies (perhaps the capsule) and small decrease for low frequencies (wich is rather good for general use). Input capacitor of Fet is 470pF, a 1nF is better but does not solve the noise problem.

I tried today to improve original Superlux circuit and it seems very easy to have more low frequencies but the noise is the problem because FET have fixed bias throw a resistor divider and the 2 FET's are not similar. 2 tantalum caps are used before the 2 symetrical current driver stage. Sound becomes better replacing them but I'm really sure now that the more simple is to remplace everything with the Oktava circuit.

My best regards from France.

Jean

 

[Jean3030]

Forgot my schema, I think to don't use the symetrical phantom power is a bad idea. Perhaps the 2 X10 nF close to the XLR outs can be removed.

Finally, there is no place in the Superlux S502, it would be able to modify but very difficult because of the 3 chemical capacitors (X2 in this case). I just improve it changing the input capacitors with polyethylene film 470pF, putting out the 10nF out capacitors and reducing the lenght of the capsule wire. This last and very simple modification gave the more audible and efficent result. more definition in the high frequencies but with that, the small differences between the 2 capsules are now easy to ear, stereo image stay very good, but it's far from a Schoeps (Price is only 98Euros)

 

[emrr]

high pass experiments:

I just simmed some values. Try a >= .01uf in series with a 50 meg. Connect one side to the center and the other side to ground. The high pass circuit a guess as to what Oktava might be doing

I think I get it - If I understand it is like you use a big enough capacitor to appear as a short circuit to all frequencies, then you put a resistor in to work as an RC network High Pass filter with the capsule capacitance of 40PF.  is that right?

So the knee you chose was 79Hz?

I changed that and put .020uf and 22Megaohms, which is giving me a 180 Hz knee (down 3 db at 180 and 6DB per octave below that?).  I think the .010uf would have worked.  But 55Meg is too much (that means it is only down 9DB at 36HZ, and it doesn't seem like that is not enough to prevent overloading the head amp when wind hits the capsule).

It is very hard to measure but I can hear it, and it sounds right gentle and good, and really reduces pop clunk bam wind noises to just noise.. no overload.  I may need to lower the frequency of the Knee a little, it cuts the proximity effect bass a lot.

But it works great, and is a great use for all these Oktava Mk12 pads, which I hardly ever use.  Maybe I will make a couple of different knee frequencies in different pads. 

I'm curious where you landed in the end on this HPF mod? I'm chafing at the official HPF cost. 

 

[bruce0]

I use it occasionally, when I am worried about wind or AC or other airflows.

I left the values as described in the last post.  Never changed them.
I have a photo somewhere, if you want.

The problem with this filter ( and I think that must be what Oktava is providing as well, though It would be nice for someone to open up the end and get the values off the cap and resistor.) is that it is passive.  It must be because there is not power passed out (other than signal) of the body.

The nice CUT1 filter on Schoeps SDC's have 5! (really 5) connections between body and capsule, so the cut 1 filter, while larger can do a lot more.

b

 

[emrr]

Schoeps!  I hadn't been able to find anything else with an inline filter. They look like very different devices, with steep cut-off and variable proximity control. 

I got a comment the official Oktava filter adds a bit of hiss, which seems likely with a passive filter.  I'd be interested to hear other reports.  It doesn't seem like a good $95 purchase, maybe a decent $25 DIY.

 

[bruce0]

Those 5 contact rings put power out beyond the body, so they can make an active filter like the CUT1.

The Oktava one has to be simple, if anyone has one it would be interesting to know what is in it.

I can't speak to the his, the conditions when I use the low cut generally involved wind, and I don' t have that much experience with it.  if there were hiss, it would be buried in the wind.

 

[emrr]

Yeah, I think you wouldn't notice hiss if dealing with wind noise.  An acoustic guitar in a controlled room might be another matter. 

Found some other comments here:

http://www.audiobanter.com/showthread.php?t=127763

useful posts maybe start with #9; the usual caustic "everything is useless garbage" Dorsey take.

 

[emrr]

Have one of these HPF in front of me, recent production. 

Looking around again, I find a comment that Oktava claims the parts values are 30 MOhm and 1000 pF.  The cap at least sounds mis-quoted to me. 

I would confirm 30M appears right, and 22pfd is what I measure. 

Connection is 'center pin / C / R / shell'.

With simple voice tests, I haven't yet found the increased noise to be a problem. 

A quick and dirty pink noise comparison test appears to show roughly 80Hz -3dB point, -9 somewhere around 33Hz. 

 

[emrr]

Tried converting a pair of the pads to the HPF's.  Cleaned up everything with 99.9% alcohol afterwards. 

To the ear they all work.  Revisiting, there is a rushing sound on the stock and DIY units which is not present without the filter, so it is noticeable.  Would it hide in a recording?  Probably. 

Pink noise comparison test shows one isn't right at all, sensitivity is down -6 and there's really not a rolloff.  I must just be hearing the reduced sensitivity.  The other has sensitivity closer to the stock HPF, but slightly lossy, and the rolloff is not as great, more like -3 at 45Hz.