Noise with AT 4060 tube microphone

HI,

I'm getting unwanted noise with my AT 4060, I thought it was the tube so I changed the stock one with a NOS Philips JAN 6922, and the sound is much better but the noise is still there. This is not hum or buzz but a kind of strange modulating blowing noise, like  the wind, difficult to explain, I'll try to send an audio file of it ASAP. I don't know if it comes from the mic circuit or the PSU. Any help would be welcome.

check the capsule.....  At an old studio i worked for we had an at4060 and the capsule was real susceptible to temp and humidity.

Hey Pucho thanks for the reply.

So I opened the mic and checked the capsule and I'm not sure I'm able to make a diagnostic. The capsule has tiny traces on the capture's side, probably because I use this mic generally for vocals, but it seems to be in good shape. How could I be sure it needs replacing or repair...? Do you know if this mic can handle other capsules than the stock one ? and do you know how to change it ?

Thanks

oh you won't see any physical damage usually, but the sound you describe is often associated with condensation or other dirt and gunk trapped in  the capsule.....

the sound you describe is often associated with condensation or other dirt and gunk trapped in  the capsule.....

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Ok, so what is the cure ? if there is, otherwise what to do... change the capsule ? I already contacted Audio Technica to get a quote for a new capsule, and I received it with a very bad surprise. They ask me to pay 329€ inc VAT for a spare stock capsule, without the mounting job (I need to replace it by myself)... So I definitively  search for a cheaper alternative.

do some  google searching on cleaning and drying mic capsules. But be careful, only proceed with any of that action if you are ready to get a replacement capsule, your first time might not go so well. You can also take to a mic repair shop and have them clean and dry out the capsule. It does take time and patience.

OK, I did some research about how to clean a condenser mic capsule. The problem with the 4060 is that there's no access to the diaphragm itself. There's a grill in front of it with holes letting only see tiny part of the membrane. I guess it's possible to remove this grill but I'm not sure being ready to take the risk of damaging the capsule when trying to do that.

Here's a picture of the 4060 capsule

It is true that most of the times it's impossible to see the dirt that causes the problem.
However, I'm not 100% certain that it's the cause of your problem.
In order to know more decisively, you should thoroughly dry your microphone, by putting it above a heater or in an oven at about 50°C, with the mic protected with a cloth. Check the mic after 1-2 hours of drying. If the problem is still there, that rules out the capsule. Then that would direct the investigation towards a leaky cap, either in the mic or in the PSU.
In the mic, I would suspect first the output cap (47u) but I would not rule out the two other 'lytics.
Another way to rule out the capsule would simply be to disconnect it; if the random noise is still there, that rules out the capsule. Constant-steady hiss will be significantly higher though, unless you connect a 50-100pF cap.
I have posted the schemo of the 4060 in the Technical Documents. I'll try to get the PSU schemo.

Some good information was posted earlier - again, make sure that the capsule is actually the problem. Also consider that if a bias resistor is dirty, it too may quiet down when the mike is dried. So, it may be worth cleaning the components directly attached to the capsule and the impedance converter circuit, if only because that's generally a lot easier and safer to do. Then, dry the mike and see what problems remain.

Another idea is that the diaphragm itself may not need to be cleaned directly. If the sputtered metal is on the outer surface of the diaphragm, then it is already conductive (and needs to stay that way). What you could do instead is to clean the insulators that separate the diaphragm and electrodes, since this is where the bias voltage is present, and it's where there needs to be extremely low leakage. These parts are usually at the periphery of the capsule, and also possibly the mounting post or clamp.

The danger is that if you get any fluid in any of the capsule breather holes and it gets drawn inside of the capsule by capillary forces, the fluid will slowly evaporate and build up pressure inside of the capsule, swelling the diaphragm and probably destroying it. You can guess how I figured this out! :-/

So, the cleaning process is still not such a safe or simple procedure, but since the insulators are the primary item to keep clean, you can generally avoid cleaning the diaphragm itself. Of course, some mikes that have been used without a windscreen can have a lot of dried spittle on the diaphragm, changing its mass. Those diaphragms can be cleaned, but you run the risk of destroying the capsule if you're careless.

I'd try to  read as many accounts of capsule cleaning as you can, but the general idea is to use an ultra-clean solvent and an ultra-clean applicator. Apply the solvent sparingly to the applicator and apply extremely little pressure while you move it around the surface. I've used cotton swabs that I've pulled the fibers away from the stick, then rinsed it with clean solvent, and then gently applied it to the capsule, allowing surface tension and not deliberate pressure to guide it along the surface you want to clean. Work slowly and make sure that solvent can't run into the capsule as mentioned above. Best of luck!

I've posted the 4060's PSU schemo in Technical Documents.

I'll check the file cabinet but I may have a full schematic for the mic.

Hey, thank you guys for your good advices... I put my mic in an oven for 1 hour and a half at 50° (Celsius). I haven't been able to test it yet. As soon as I can, I'll let you know.

Pierrick

pucho812 said:

I'll check the file cabinet but I may have a full schematic for the mic.

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I've already put it in the Technical Documents.

never mind then

Hi everyone,

I finally been able to test my mic, and unfortunately, putting it in an oven at 50° for almost 2 hours didn't solve the problem.

Then that would direct the investigation towards a leaky cap, either in the mic or in the PSU.
In the mic, I would suspect first the output cap (47u) but I would not rule out the two other 'lytics.
Another way to rule out the capsule would simply be to disconnect it; if the random noise is still there, that rules out the capsule.

Click to expand...

I'll first try this and also try to clean the insulators

So I disconnected the capsule, plugged the mic and the noise is still there, so that rules out the capsule.  I also unplugged the mic from the PSU but letting it connected to the input of my console via the xlr audio output of the psu, and no noise. So does it mean that it rules out the PSU ? I guess not.

I checked the caps inside, the 47uf and others, they are in good shape and have no sign of malfunctioning or whatever. They are Nichicon caps which is a good quality brand right ?

Where do I go on investigations... Bad cap on mic's circuit ? PSU ?

innercityman said:

So I disconnected the capsule, plugged the mic and the noise is still there, so that rules out the capsule.  I also unplugged the mic from the PSU but letting it connected to the input of my console via the xlr audio output of the psu, and no noise. So does it mean that it rules out the PSU ? I guess not.

I checked the caps inside, the 47uf and others, they are in good shape and have no sign of malfunctioning or whatever. They are Nichicon caps which is a good quality brand right ?

Where do I go on investigations... Bad cap on mic's circuit ? PSU ?

Click to expand...

Modern caps, even leaky, look in good shape; there's no way to tell other than replacing them temporarily. It's fastidious and messy, but there's no other way (at least for DIY).
That could be the tube (that's often the case); you have to replace it also. I would think you really need to find someone in your environment that would lend you a working set and that you proceed to swapping elements.

That could be the tube (that's often the case); you have to replace it also

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I replaced the tube few month ago when I encountered this issue, thinking it was the reason. I put a NOS Ian Philips tube but the issued remained.

Still can be the tube, one tube is not a good test unless you know it works well in another 4060.

What type of noise is it?

Have you checked the power supply? Take note that the microphone  uses super caps as filters for the heater.

The microphone used diodes instead of high value resistors at the capsule to grid section.

What I might do to test if trying a few more tubes does not fix the noise

disconnect the two caps between the capsule charge voltage section diodes and the grid biasing diodes and check for noise

However reading the following

"So I disconnected the capsule, plugged the mic and the noise is still there, so that rules out the capsule.  I also unplugged the mic from the PSU but letting it connected to the input of my console via the xlr audio output of the psu, and no noise. So does it mean that it rules out the PSU ? I guess not."

You will have no noise with no power to the microphone

What does AT charge to repair the microphone?

What type of noise is it?

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A kind of blowing noise, like if I could here the wind or even the sea, something like that.

Have you checked the power supply?

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I've just open it and had a look... No blown or brun cap or resistor... I didn't go further in my investigations.

What does AT charge to repair the microphone?

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I have no idea. What I know is the price of a new capsule and it's very expensive, more than 300€.

What I'll try first will be to put back the original stock tube and see if the noise is less or more present, that could give me an idea.