Oktava MK-012 high pitched tone. Need help.

[stason99]

Cause of fault found.

Finally my multimeter arrived so I measured 47uF cap. It measured 28uF. I tested the mic with 47uF cap open (one pin unsoldered) and the tone is gone. Looks like the cap was bad. Panasonic radial electrolytic caps will arrive next week, so I'll replace all 3 in each mic. Thanks for pointing to the 47uF being the cause!

Now that the mic is fixed, I want to concentrate on the rest of the components. Many of you have disagreed with Joly's choose of the Silver Mica (is that the Big brown cap on my photo? )  instead of a C0G. Is C0G definitely better, should I replace silver mica with this one (I've ordered it already just in case)?

https://www.digikey.it/product-detail/en/murata-electronics/RCE5C2A821J0M1H03A/490-7493-1-ND/4277410

If C0G is better, then what's the logic of a knowledgeable guy like Mike Joly behind using a silver mica? Do they have any advantages over C0G for sound?

Lastly, I want to replace the Russian FET with Toshiba 2SK170 BL. But I hope to get your guys clarification about the C0G vs Silver Mica.

 

[dbelousov]

Silver Mica caps are fine except for the microphonic effect, this is the reason why mic producers avoid using them in, actually, microphones.

Polystyrene and polypropylene caps are the usual suspects in this position for "high quality" gear. Wima FKP2 should be fine. I usually use ERO NOS PP caps, though, which I bought in a very unreasonable amount once.

I, actually, replace the 2SK170 in these mics. It sounds dull (because of its high capacitance I believe) in mics and any noise benefits are questionable (I didn't find any) since its noise rises with the source impedance.

The main question is what do you want from the mics? I, personally, strive for the clearest, fastest, and most accurate sound possible from my SDCs, I have tubes, ribbons, etc. for other tasks. But people seem to love the 012 for its soft, slightly muffled sound.

 

[stason99]

Polystyrene and polypropylene caps are the usual suspects in this position for "high quality" gear. Wima FKP2 should be fine.

What are FKP2?

Are these fine? :
https://www.digikey.it/product-detail/en/murata-electronics/RCE5C2A821J0M1H03A/490-7493-1-ND/4277410

Also, why would a guy who specializes on microphone mods (Mike Joly) use a cap that is the worst choice for mics due to being microphonic? Is there something we overlook in Silver Mica, any advantages?

 

[Gus]

Polystyrene is microphonic as well. I installed a polystyrene in place of a capsule in a microphone and it picked up sound. It is always good to test things if possible

I avoid 170's at the input of a microphone

 

[stason99]

Polystyrene is microphonic as well. I installed a polystyrene in place of a capsule in a microphone and it picked up sound. It is always good to test things if possible

But the cap I linked is not a Polystyrene but C0G, isn't it? This one:
https://www.digikey.it/product-detail/en/murata-electronics/RCE5C2A821J0M1H03A/490-7493-1-ND/4277410

 

[Gus]

Try different cap types at the capsule to gate they do not cost much think of it as a learning experience and that you will be less likely to think what someone posts if they don't post a preference.

Sometimes with audio stuff I use a "BAD" cap because it is microphonic or

This is one of the few places in a microphone that the type might matter. This is due to the voltage difference between the capsule and gate. Look up dielectric stress.

One time when thinking about adjusting 012s they were left totally stock because they sounded good that way compared to an adjusted set.

In tube microphones you also have the plate to transformer coupling cap with the voltage difference

 

[dbelousov]

Polystyrene is microphonic as well. I installed a polystyrene in place of a capsule in a microphone and it picked up sound. It is always good to test things if possible

I had a very audible problem with them once in a pair of Chinese tube mics. I just glued them to the PCBs with a drop of some soft and not aggressive glue in the end.

I haven't found a cap that is not microphonic at all, so it's about an "acceptable" degree I suppose, and this effect is hard to measure.

I glue caps in my modded/refurbished mics with a hot glue gun. It doesn't look fancy but reduces ringing close to non-existence.

What are FKP2?

Are these fine? :
https://www.digikey.it/product-detail/en/murata-electronics/RCE5C2A821J0M1H03A/490-7493-1-ND/4277410

Also, why would a guy who specializes on microphone mods (Mike Joly) use a cap that is the worst choice for mics due to being microphonic? Is there something we overlook in Silver Mica, any advantages?

https://www.digikey.com/en/products/detail/wima/FKP2G011001D00KSSD/9370222

Who knows Joly's motives. Micas are used intensively by guitar amp builders in EQ sections. I believe, according to what he has done, he aimed to "open" the sound, but the major problem here is RFI filtering caps, which were remained untouched.

 

[stason99]

It drives me crazy.. It was not the 47uF cap...

I replaced all 3 electrolytic caps in both mics to radial Panasonic but the tone didn't only remain but started appearing in the other mic, the one that was "good"...

Then in the "bad" mic I removed two additional red 10nF each in parallel to 68uF that Joly put there, and the tone became weaker.

It drives me nuts... Nothing is shortening to the casing, but it seems like location of some components or proximity to each other may be responsible...

Another extremely weird thing is that the tone is louder when the mic is in certain position up in the air, but when I move it closer to any equipment that may cause interference - the tone diminishes. It's usually louder when I hold the mic (in its casing) in my hand. Additional jumper between connector and the tube makes no difference whatsoever, so it can't be grounding.

Any idea what the hell is going on with these mics?

P. S. The old 47uF that measured 28uF turned out to be 33uF, not 47uF.

 

[rackmonkey]

If all else fails, you can try the old hack of creating a special cable for the mic by desoldering pin 1 from the cable’s female xlr jack and soldering it to the xlr ground lug. Just use that cable with the mic and it’ll shunt the recitified RF so that you don’t hear it any more.

Ideally, you can track down the problem in the mic, but when you’re finally ready to throw up your hands, this redneck engineering exercise will at least make the mics usable again the majority of the time.

 

[Gus]

Do you have another audio interface to test the microphones with? Maybe something is wrong with the interface.

Have you tried other microphones with the RME Babyface Pro?

Have you tried the RME Babyface Pro with another PC or Mac? To test if it might be an USB issue if you are using USB to power the interface.

Have you tried an external power supply?

Have you tried another USB cable if you are powering from USB?

Can you test both microphones at another location with a known good interface? This can help  to find out if it is interface and/or RF issues

How are you powering the RME Babyface Pro, USB 3, USB 2 or external power supply?
USB 2 has unit load of 100mA and is speced at 5 total unit loads for 500mA

 

[stason99]

If all else fails, you can try the old hack of creating a special cable for the mic by desoldering pin 1 from the cable’s female xlr jack and soldering it to the xlr ground lug. Just use that cable with the mic and it’ll shunt the recitified RF so that you don’t hear it any more.

Wire from Pin 1 to ground should be only on the female cable side, right? I tried as you suggested - no difference...

Do you have another audio interface to test the microphones with? Maybe something is wrong with the interface.

Have you tried other microphones with the RME Babyface Pro?

Have you tried the RME Babyface Pro with another PC or Mac? To test if it might be an USB issue if you are using USB to power the interface.

Have you tried an external power supply?

Have you tried another USB cable if you are powering from USB?

Can you test both microphones at another location with a known good interface? This can help  to find out if it is interface and/or RF issues

How are you powering the RME Babyface Pro, USB 3, USB 2 or external power supply?
USB 2 has unit load of 100mA and is speced at 5 total unit loads for 500mA

None of my other mics (Sennheiser MKH416 and MKH-50) do that on the same interface.
The Babyface is powered from USB2. I tried powering it from an external power supply with USB plug disconnected - no difference.

At the moment my only other preamp with phantom power is an old Zoom H1. I'll try it but I'm sure it won't make a difference.

Another piece of clue is that I found that it's not the position of the mic in the air that causes the tone, but position of the cable. In certain positions of the cable the tone is lowder or disappears completely, as if it's capacitance or inductance caused a self excitement of the mic or something like that.

This happens with known good cables, long and short, new and tested with a proper tester - so definitely not a cable. And the same cables are totally fine on the other mics.

I wonder if that is because MK-012 has an unbalanced circuit and this happens to all of them but nobody ever paid attention??

 

[Khron]

Is the computer the Babyface is connected to, earthed?

 

[stason99]

Is the computer the Babyface is connected to, earthed?

Should be, through AC plug. But no other mics have this problem except these two.

 

[stason99]

Can you test both microphones at another location with a known good interface? This can help  to find out if it is interface and/or RF issues

Tried with another preamp, this time Zoom H1. Same exact thing... The intermittent tone is there.

 

[Big Valley Audio]

Sounds similar to a problem I am dealing with here in Vancouver BC. In the last 6 months I've had numerous clients contacting me with noisy microphones and one client has been severely affected so I've been working on this issue for them.
Download a cell tower locator app on your phone and see what is around you. That could be your issue.
Cell phone companies have started adding "RF density" to most areas when they upgraded to 5G and around here they are actually using lower ( 600MHz) frequencies to transmit and receive because they have better penetrating power than the higher (2100MHz). The mics that have up till this point been fine in close proximity to a tower are now being overloaded with RF and are acting like AM demodulators. Usually you will hear a 4KHz tone with harmonics travelling up the spectrum (6, 8, 10, etc) that is the frequency that the signal is being switched at and unfortunately it's in our audio zone.
This is going to be a big problem for commercial studios moving forward I think.
Try pointing the side ( expose the most surface area ) of the mic towards the tower if there is one close and see if that is the noisiest, turn the mic like a clock dial you should hear the noise get quieter as you do.
I hope this helps pinpoint your noise issue!

Corey

 

[mrgrooves666]

I'm sure you already checked this, but 012 capsules are prone to caught humidity. I've had this happen many times. The end result is garbling noise and a lower output/muddy sound. I've experienced this with both 012 cardioid capsules and the 103 mid size capsule. Dissasembly of the capsule and putting the electrode under light for an hour or two fixes it.

 

[calaverasgrande]

Sounds similar to a problem I am dealing with here in Vancouver BC. In the last 6 months I've had numerous clients contacting me with noisy microphones and one client has been severely affected so I've been working on this issue for them.
Download a cell tower locator app on your phone and see what is around you. That could be your issue.
Cell phone companies have started adding "RF density" to most areas when they upgraded to 5G and around here they are actually using lower ( 600MHz) frequencies to transmit and receive because they have better penetrating power than the higher (2100MHz). The mics that have up till this point been fine in close proximity to a tower are now being overloaded with RF and are acting like AM demodulators. Usually you will hear a 4KHz tone with harmonics travelling up the spectrum (6, 8, 10, etc) that is the frequency that the signal is being switched at and unfortunately it's in our audio zone.
This is going to be a big problem for commercial studios moving forward I think.
Try pointing the side ( expose the most surface area ) of the mic towards the tower if there is one close and see if that is the noisiest, turn the mic like a clock dial you should hear the noise get quieter as you do.
I hope this helps pinpoint your noise issue!

Corey

When I worked in television we had a Faraday cage around the entire studio, and cell phones went in a bucket at the door.
I understand some recording studios in NYC do this as well.

 

[Big Valley Audio]

When I worked in television we had a Faraday cage around the entire studio, and cell phones went in a bucket at the door.
I understand some recording studios in NYC do this as well.

I've been looking into that and I bet it would probably do the trick. Insanely expensive to retrofit in the location I'm dealing with (This studio has been around for almost 30 years) Luckily, the cell phone company is actually turning off the antenna that is pointed at the studio.......for now.

 

[bdamiano]

I had a very interesting problem with two of my builds (schoeps style circuit with LDC). I made a matched pair for a customer and when the two were plugged into the same interface and powered up, I would get a 14K whine in the output of one of them. It drove me crazy for days but then I had a hunch. I wondered if this 14K was a "difference" (beat) frequency caused by the two mics' oscillators modulating each other. Sure enough, I measured both oscillators and although they were both around 2MHz, one was exactly 14KHz higher than the other. As a quick experiment, I retuned one to make it about 200K higher than the other and the problem went away (or at least went well above the audio range). I had never seen this happen before with any other combination of my mics plugged in. I ended up replacing the board anyway before I shipped it out, but I thought it was a pretty interesting phenomenon.

 

[ccaudle]

The mics that have up till this point been fine in close proximity to a tower are now being overloaded with RF and are acting like AM demodulators.

Generally a combination of lack of RF filtering on pin 2 and 3, and improper connection of pin 1 go case.
See a copy of "Radio Frequency Susceptibility of Capacitor Microphones" from the web site of one of the presentation authors:
http://www.audiosystemsgroup.com/AES-RFMicrophonesASGWeb.pdf

You can sometimes correct the problem by rewiring the pin 1 connection point, or use Neutrik RFI XLR connectors on the cable.
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