Oktava mk012 problem

A

AneriaFilms

Member
Sometimes when I use my Oktava mk012, i get some sort of wind noise even though there is no wind (I'm using it indoors, nobody's breathing on it, mic is stationary). It's a steady "swooshing" sound that is just like somebody blowing on it gently. I'm using it with a DVX100a...

Anybody have this problem? Is the mic going? I don't have a problem with any other microphone, so I'm thinking it must be something with the oktava...

Any ideas??? Similar issues/solutions??? Do I need a new mic?

--davy
 
This is a problem that happens to a number of mics if you don't feed them 48V phantom power. Some devices don't put out a full 48V. Phantom power does not "have to be" 48V to be in spec but it is the semi official standard. Oktava is one of the mics that NEEDS 48V. I think the problem is not so much the mic as it's interaction with the preamp/ phantom power unit. There is some documentation on this on Sound Devices web site. The MixPre (maybe others) can be switched to 12V phantom power (many mics don't care) to save power. So a number of people got what you describe. If I remember correctly the things that can "fix" it other than more power is a low pass filter and lowering the gain.
 
I know you just said indoors w/o any wind... but what windscreen and shockmount are you using? The Oktava should NEVER be bare in the air. Are you sure that the mic isn't picking up vibration or something else through the stand/or mount? Does "stationary" mean that it's mounted on the DVX in the stock mount? (If so then it's probably tape transport noise instead of wind).
 
From the SD website (since it isn't as easy to find as I thought).
Oktava isn't listed which is puzzling since I know a number of folks including me that had this problem with the Oktava??? But if this sounds like your problem, here's your answer - sort of.

-----------------
Oscillation with Transformer-Balanced Inputs
Sound Devices Support Oscillation with Transformer-Balanced Inputs
Problem
Depending on several conditions, chiefly the microphone, the transformer-balanced inputs, such as those on the 302, 442, MixPre, MM-1, MP-1, and MP2, can get into an oscillating condition with a microphone that renders the audio unusable. This oscillation is often described as a "motorboating" condition since this low frequency oscillation sounds like a motor boat.
Cause
Microphones with low rejection to common-mode phantom voltages fluctuate their output level based on the phantom voltage supplied. This variation "wiggles" the bipolar +/-15 volt audio rails -- which subsequently fluctuates the phantom voltage rails, which fluctuates the output level and sets up the oscillation.
Sound Devices field mixers and preamps are very portable products and have compact, efficient power supplies. The AA batteries in the product supply several voltages including, ±15 volts for audio, 48 or 15 V for phantom power, and 5 V for LED's. The power supply is suitable for most microphones, but is susceptible to oscillation with microphones prone to drawing current based on output level.
Remedy
With microphones prone to this condition, several things can be done to minimize and/or prevent the condition.
Engage the high-pass filter.
Use 48 V phantom even if not required.
Power the microphone(s) from an external phantom supply.
Power the mixer from an external, DC power supply.
Additional capacitance in the mixer would also help the condition, however, these units have the most capacitance that will fit into their chassis.
The same microphone that exhibits this condition with the MixPre or MP-2 may not exhibit the problem with another preamp with a larger phantom supply with more capacitance.
Microphones Know to Exhibit this Problem
AKG Blue Line Series
AT 4073
Sanken CUB-01, CS-1
If you have experienced the above condition with a microphone not listed, contact Sound Devices so we may make this list inclusive.

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THey call it motor boating but my experience was more whoosh, whoosh... sort of like someone blowing on the capsule gently at a pretty slow rhythm. 48 on the MixPre solved the problem.
 
For the record I have both a new 302 and an old mixpre... and I've had 4 Oktavas... and I never had this problem.
 
MattinSTL said:
For the record I have both a new 302 and an old mixpre... and I've had 4 Oktavas... and I never had this problem.
Click to expand...

Were you running with 48V phantom or 15V? I've never had this happen at 48V. It also, on the mix Pre anyway, doesn't happen if any of the low cuts are on. And I was using a pair so that may have had an effect. But I was seeing a bunch of posts on this issue with Oktavas on the CAS site a few years back when the MixPre's were fairly new.

Or Matt may have nailed your issue.
 
Davy,
It sounds like humidity could be the problem. If you have another capsule, try it with your preamp body just to be sure it's the capsule at fault. Most likely your capsule is the issue. When there is excessive humidity the noise you are describing is what is sounds like. A "swooshing" sound is a good description.

(shhh... don't tell anyone I told you to do this to a condenser microphone, but the best remedy is a hair dryer)

Attach the capsule to the body, fire up the hair dryer, don't point it directly at the capsule end, but blow hot air across the front, a few inches away. Do this for a minute or so... let it cool for a minute. Test the mic. If the swooshing sound is still there, use the hair dryer again. It should ultimately dry up the condensation on the capsule.

This time of year it's a good idea to put a little dessicant pack in your mic's case.

Or if you'd rather not do this, and if the mic came from me, just send it back and I'll send you out a brand new one. That's the easiest fix of all.

All the best,
Paul
 
Wow! I can't believe that you are monitoring the forum and offering help! I know you are good Paul (you helped me a ton) but wow!!

I feel like ordering something else just because you are cool!
 
Thanks everyone for your replies. I don't get that sound issue all the time, just some of the time. Humidity might be the culprit as was mentioned above, but I havn't kept track of humidity levels when I'm using it. It's been humid lately, though...

I'm not sure about the 48v Phantom power unless my DVX100A isn't giving the mic the full 48v...

Thanks again, you've all gave me some good info to check out. Hopefully I can correct his so I can keep using this wonderful microphone.

--davy
 
the sennheiser mkh50 is known to work well in humidity, but it is $1300. People use that mic instead of the schoeps in that kind of enviornment.
 
The Sound Room said:
Attach the capsule to the body, fire up the hair dryer, don't point it directly at the capsule end, but blow hot air across the front, a few inches away. Do this for a minute or so... let it cool for a minute. Test the mic. If the swooshing sound is still there, use the hair dryer again. It should ultimately dry up the condensation on the capsule.
Paul
Click to expand...

Sorry to bring up old threads - Paul I got my octava from you - umm year ago? Has worked perfectly btw.

If it is moisture, I usually stuff those packets of silica gel in my audio bag - keeps everything on the up.
 
I am sure the 50 sounds wonderful! I just wanted to point out the humidity resistance. I guess I have just always heard that the schoeps is "the" hollywood interior dialog mic, but the mkh50 is overtaking it recently in some situations (like high humidity).
 
bwest said:
yea, but is this mic in question a bona-fide Oktava?
Click to expand...

Asking Matt if his Oktavas are "bona-fide" is like asking if the Pope is Catholic.

Just to clue you in, Matt is the Godfather of all things Oktava as far as use and advice. He is responsible for more adoptions of Oktava's than Agelina Jolie is of kids.

And yes, it is great to see Paul here who is the King of all things Oktava when it comes to purchasing the mike. I am one of many happy customers of Paul's who got their "Bona-Fide" Oktavas from him.
 
Kelly Olsen said:
Asking Matt if his Oktavas are "bona-fide" is like asking if the Pope is Catholic.

Just to clue you in, Matt is the Godfather of all things Oktava as far as use and advice. He is responsible for more adoptions of Oktava's than Agelina Jolie is of kids.
Click to expand...

I think bwest was asking if the original posters were bonafide - not Matts.

But youre right about the other thing, Im another person who picked up an Oktava based on Matts enthusiasm for it. Have to say , it really has been a little champ for me. I use it in a softie at all times, but other than that.
 
So far I have only used mine to record fireworks, but it was a must have sound for my film and I got it crystal clear. The report, the echo, perfect.
 
Just FYI:
My pair of MC-012s always cause "motorboating" with my MixPre, but never on my console preamps or DVX preamps (transformerless). I'm sending an email to Sound Devices to see if they could update their FAQ to include Oktavas. (Their advice is 100% correct: HPF fixes it, external MixPre power fixes it, haven't tried external P48.) It's worthy of note that Scott Dorsey's Oktava mod article from Recording Magazine Sept 2003 mentions that the output of the MC-012 is effectively unbalanced, and that a 68uF cap designed to shunt pin3 to ground actually becomes part of the signal path when the mic is used with a transformer-balanced mic pre. (Not sure if this would aggravate the problem, but it's interesting nonetheless.)

About "swooshing": It might be the capsule, but it also might be the head end of the electronics. Many of these mics shipped without a conformal coating on the PCB, and with quite a lot of leftover solder flux. The extremely high-impedence of the capsule-to-FET part of the PCB is susceptible to humidity changes if dirty or uncoated. (This happened to mine, and while I had it opened up to do an electronics mod I cleaned and coated it. No more humidity problems!

OT: I received a brand new MXL 603S that squealed uncontrollably until I used denatured alcohol to clean the flux off of the PCB. Since then it's been dead quiet.
 
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