You are here

Noisy Mic Issue

All about the tools and techniques involved in capturing sound, in the studio or on location.

Noisy Mic Issue

Postby blinddrew » Wed Jun 10, 2020 7:05 pm

My 'go to' vocal mic is a SubZero valve mic ( https://www.soundonsound.com/reviews/subzero-sz-v12c ) that I've had for 4 or 5 years. However I noticed last night that it seemed a bit noisy. It was late so I ignored it but this evening I've checked it again and it's definitely much noisier than it should be.
This file shows the subzero vs a ribbon mic (the next thing to hand) at roughly the same level and you can clearly hear the difference in noise: https://soundcloud.com/blinddrew/noisy- ... 9HTn4tPwMk

Any suggestions on what the cause might be? I don't think it's condensation as the room is a very consistent temperature at this time of year, and it doesn't get used particularly closely or without a pop shield so there shouldn't be too much in the way of waper vapour from my mouth. There does seem to be a bit of a resonant frequency at about 75Hz (and harmonics).
Any ideas from the better brains out there?
User avatar
blinddrew
Jedi Poster
Posts: 10852
Joined: Sun Jul 05, 2015 12:00 am
Location: York
Ignore the post count, I have no idea what I'm doing...

Re: Noisy Mic Issue

Postby resistorman » Thu Jun 11, 2020 5:07 am

You could try cleaning the valve pins and socket with deoxit. I like to use a pen dispenser to coat the pins and insert/ remove the tube a few times.
User avatar
resistorman
Frequent Poster
Posts: 951
Joined: Sun Nov 22, 2015 1:00 am
Location: Asheville NC

Re: Noisy Mic Issue

Postby ef37a » Thu Jun 11, 2020 7:07 am

Yes try a pin scrub.
Could be the valve of course. https://www.karltone.co.uk/jj-12ay7-6072-720-p

That ^ is an exact electrical equivalent to the 6072 but not the selected, ultra low noise type SAID to be fitted in the microphone, it should however give you some idea of the condition of the original?

Looking around, peeps want silly money for NOS examples of the 6072A and there is of course no guarantee that they will actually be very low noise samples.

Do NOT be tempted to fit another variety of double triode! E.g. the 12AT7 worse the 12AU7. The components in a mic are probably quite wee and a wrong valve can pull enough current to burn them out.

Dave.
ef37a
Jedi Poster
Posts: 11780
Joined: Mon May 29, 2006 12:00 am
Location: northampton uk

Re: Noisy Mic Issue

Postby blinddrew » Thu Jun 11, 2020 8:35 am

Thanks gents, will give the pins some tlc first.
Cheers
User avatar
blinddrew
Jedi Poster
Posts: 10852
Joined: Sun Jul 05, 2015 12:00 am
Location: York
Ignore the post count, I have no idea what I'm doing...

Re: Noisy Mic Issue

Postby blinddrew » Thu Jun 11, 2020 6:01 pm

I assume a generic maplin switch cleaner will do the job?
User avatar
blinddrew
Jedi Poster
Posts: 10852
Joined: Sun Jul 05, 2015 12:00 am
Location: York
Ignore the post count, I have no idea what I'm doing...

Re: Noisy Mic Issue

Postby Dan LB » Thu Jun 11, 2020 6:22 pm

blinddrew wrote:I assume a generic maplin switch cleaner will do the job?

Yep, should do. :thumbup:

I use Ambersil Ambertron for general contact cleaning duties.
Readily available from Radionics.

Image
User avatar
Dan LB
Frequent Poster
Posts: 1429
Joined: Sat Jan 28, 2006 1:00 am
Location: Wicklow, Ireland

Re: Noisy Mic Issue

Postby Ben Asaro » Fri Jun 12, 2020 1:24 am

My Rode NTK was getting very noisy as well. I replaced the 6922 valve, and it’s good as new now!
Ben Asaro
Frequent Poster
Posts: 772
Joined: Thu Feb 26, 2009 1:00 am
Location: NYC

Re: Noisy Mic Issue

Postby blinddrew » Fri Jun 12, 2020 9:46 am

Well I gave it a bit of a clean up last night so hopefully I'll get time to give it a test tonight.
User avatar
blinddrew
Jedi Poster
Posts: 10852
Joined: Sun Jul 05, 2015 12:00 am
Location: York
Ignore the post count, I have no idea what I'm doing...

Re: Noisy Mic Issue

Postby blinddrew » Fri Jun 12, 2020 3:19 pm

Interesting. Whatever I did last night did not fix it.
It kind of did the opposite in fact. I now have noise but no signal. Must have screwed something up getting the valve out. I shall have a better look tonight.
User avatar
blinddrew
Jedi Poster
Posts: 10852
Joined: Sun Jul 05, 2015 12:00 am
Location: York
Ignore the post count, I have no idea what I'm doing...

Re: Noisy Mic Issue

Postby Hugh Robjohns » Fri Jun 12, 2020 3:48 pm

A permanent fault is easier to fix than an intermittent one! ;-)

Check that you have seated the valve the right way around. It should only fit in the base one way, of course, but not all bases are made equal! And make sure that it is pressed fully home.

It also possible that in removing or reseating the valve you have fractured the PCB or a wire joint. And it's also possible that the cleaning solution you used has spread to the high-impedance areas of the circuitry causing signal loss through leakage.

And, obviously, make sure the PSU was connected and powered up! :-)
User avatar
Hugh Robjohns
Moderator
Posts: 27902
Joined: Fri Jul 25, 2003 12:00 am
Location: Worcestershire, UK
Technical Editor, Sound On Sound

Re: Noisy Mic Issue

Postby blinddrew » Fri Jun 12, 2020 4:20 pm

Hugh Robjohns wrote:Check that you have seated the valve the right way around. It should only fit in the base one way, of course, but not all bases are made equal! And make sure that it is pressed fully home.
Yep, it only goes in one way. It was really stiff to get in and out though, so...

Hugh Robjohns wrote:It also possible that in removing or reseating the valve you have fractured the PCB or a wire joint.
... I suspect this may be the case. Will fish out my magnifying glass later.

Hugh Robjohns wrote:And it's also possible that the cleaning solution you used has spread to the high-impedance areas of the circuitry causing signal loss through leakage.
I was reasonably sparing with this, spraying it onto a cloth and then wiping the pins so I'd hope not.

Hugh Robjohns wrote:And, obviously, make sure the PSU was connected and powered up! :-)
Yep, I can confirm that the noise part of the content is still present and correct, just the signal part that's now missing!
User avatar
blinddrew
Jedi Poster
Posts: 10852
Joined: Sun Jul 05, 2015 12:00 am
Location: York
Ignore the post count, I have no idea what I'm doing...

Re: Noisy Mic Issue

Postby Hugh Robjohns » Fri Jun 12, 2020 4:27 pm

Hmmm...

So if it's generating some noise that implies the output side of the circuitry is working as intended. So I'd be looking around the capsule connections and the switches to make sure they are all intact and not trapped or shorted out on the case.
User avatar
Hugh Robjohns
Moderator
Posts: 27902
Joined: Fri Jul 25, 2003 12:00 am
Location: Worcestershire, UK
Technical Editor, Sound On Sound

Re: Noisy Mic Issue

Postby ef37a » Fri Jun 12, 2020 4:49 pm

I WAS going to say that it might be important to wash off any cleaner residue with a very pure alcohol?
As Hugh say, the impedances in the grid circuit are extremely high so almost any trace of anything could effectively 'short' the signal.

I know for instance that the GigOhm bias resistors for FET mic inputs come in sealed containers and must not be touched by human hand!

Dave.
ef37a
Jedi Poster
Posts: 11780
Joined: Mon May 29, 2006 12:00 am
Location: northampton uk

Re: Noisy Mic Issue

Postby blinddrew » Fri Jun 12, 2020 6:07 pm

I found a loose wire...
User avatar
blinddrew
Jedi Poster
Posts: 10852
Joined: Sun Jul 05, 2015 12:00 am
Location: York
Ignore the post count, I have no idea what I'm doing...

Re: Noisy Mic Issue

Postby blinddrew » Fri Jun 12, 2020 6:49 pm

Resoldered and now working. Not as noisy as it was earlier in the week but noisier than it used to be. Almost a pink noise profile. In comparison my ribbon has something closer to a white noise profile and my old sE2200a has something closer to a brown noise profile.

Guessing it might be time for a new valve?
User avatar
blinddrew
Jedi Poster
Posts: 10852
Joined: Sun Jul 05, 2015 12:00 am
Location: York
Ignore the post count, I have no idea what I'm doing...

Next