Condenser Mic Maintenance 101

[Nate74]

I just picked up a cheapy Samson C01 mic for $5 at a pawnshop. Guy told me “it works, but it’s noisy.” I do my own amp work and would like to pop it open and see if I can fix it. More as a project than to get a “great” mic out of it.

What should I look for when I get it open? What other info can help figuring out what’s wrong with it?

Thanks.
Nate

[Harvey Gerst]

Originally Posted by Nate74

I just picked up a cheapy Samson C01 mic for $5 at a pawnshop. Guy told me ?it works, but it?s noisy.? I do my own amp work and would like to pop it open and see if I can fix it. More as a project than to get a ?great? mic out of it.

What should I look for when I get it open? What other info can help figuring out what?s wrong with it?

Thanks.
Nate

First of all, don't open it. Plug it in and see if the pawnshop owner was right. He may have been testing it with some noisy equipment. If it REALLY is noisy, then we can talk.

[Nate74]

Yup,

It's noisy. The sound comes through just fine, no loss of signal strength. The "noise" is in the form of sporadic pops and crackles. I was actually expecting 60Hz hum, but this is different.

Whadya think?

N

[sdelsolray]

Originally Posted by Nate74

Yup,

It's noisy. The sound comes through just fine, no loss of signal strength. The "noise" is in the form of sporadic pops and crackles. I was actually expecting 60Hz hum, but this is different.

Whadya think?

N

The capsule is likely soiled, or could simply be damp. Dry the thing out for a few days and try it again.

[Harvey Gerst]

Originally Posted by Nate74

Yup,

It's noisy. The sound comes through just fine, no loss of signal strength. The "noise" is in the form of sporadic pops and crackles. I was actually expecting 60Hz hum, but this is different.

Whadya think?

N

Try placing it a couple feet above a 50 watt lamp for a few hours.

"pops and crackles" are often a sign that the diaphragm has become dirty, and that the dirt is absorbing moisture and becoming conductive. Capsule cleaning would not hurt either, once you have verified that drying it out fixes the problem.

If that doesn't fix it, we can get into other stuff you can do.

[Nate74]

By dry out, you probalby don't mean hair dryer... But should I take the screen off?
N

[Nate74]

Oops, posted my hair dryer joke before reading about the light bulb, I'll give that a try. THANKS!

[Nate74]

BTW, is capsule cleaning something a newbie can do...? it is only a $5 mic at this point. Thanks.

[Harvey Gerst]

Originally Posted by Nate74

BTW, is capsule cleaning something a newbie can do...? it is only a $5 mic at this point. Thanks.

Distilled water and a very light touch. If your hand ain't very steady or you press too hard, you'll rub off the gold.

[Nate74]

Q-tips, cotton balls, old clean T-shirt? Any "how to" resources on line?
Thanks again for everybody's input.
N

[Harvey Gerst]

Originally Posted by Nate74

Q-tips, cotton balls, old clean T-shirt? Any "how to" resources on line?
Thanks again for everybody's input.
N

Sorry, usually Q-tips.

[Nate74]

Thanks.

Another bit of info:

After an hour over the bulb, I thought I'd put it back together and try it. The noise level when powered up was the same, but when I turned the phantom power off, I didn't pull the volume on my board down, and the crackling when crazy!

All my other mics just gradually stop working, with no noise.

When my tube amps do that when powered down, I usually suspect either an op-amp or a capacitor. Does that change the diagnosis?

[Harvey Gerst]

Originally Posted by Nate74

Thanks.

Another bit of info:

After an hour over the bulb, I thought I'd put it back together and try it. The noise level when powered up was the same, but when I turned the phantom power off, I didn't pull the volume on my board down, and the crackling when crazy!

All my other mics just gradually stop working, with no noise.

When my tube amps do that when powered down, I usually suspect either an op-amp or a capacitor. Does that change the diagnosis?

If the mic has a transformer, it could be bad.

[Nate74]

So from tracing the routing on the PC board, this 7 prong fellow looks like the transformer.

I requsted a schemait from Samson, but I'm not hopeful. Is there any kind of stardardization for these transformers, or is each manufacturer unique?

There can't be more than about $5 worth of components on this whole darn board, replacement should be fast and cheap, just what to replace...?

[Harvey Gerst]

Should be a silver looking can near the base of the mic.

[Nate74]

OK, then I don't think this little guy has it's own transformer. The everything it has is pictured... maybe it's $5 down the drain

Anything else to try...?

[Marik]

Originally Posted by Nate74

So from tracing the routing on the PC board, this 7 prong fellow looks like the transformer.

There can't be more than about $5 worth of components on this whole darn board, replacement should be fast and cheap, just what to replace...?

No this guy is not a transformer, but dual monolithic BJT. Most likely 2SA1349, or similar. This is a transformerless design. Before you do anything, put the mic into a zipped bag with fresh silica pack and leave it overnight. Make sure that the pack is FRESH. Then we will see.

[crazydoc]

Here's what I would try, just out of sheer ignorance.

With the case off, I'd plug it in to the preamp as usual, to power it up with phantom (though no gain necessary - only using it for phantom.)

Hook a probe (guitar cable) to the unbalanced input of another pre, with a ground from that pre (shield of the guit cable) to mic ground.

Hook a capacitor (for DC blocking - best non-polarized - 0.5 to 1uF or so) to the tip of the guitar cable, and start probing from the FET on back through the mic circuit, listening through the second pre until you find the point where the noise starts. The component just upstream in the circuit is the offender.
(I guess I'd discharge the cap between each movement so as not to zap anything in the circuit).

I'd think the most likely culprit would be the FET or one of the caps. You could probably replace the FET with a 2SK170 type which are cheap and easy to find.

Attached is another view of the board showing the traces, just for shits.

[Marik]

Actually, on a second thought to rule out the capsule try to unsolder its lead (the one, which goes to capacitor). Fire the thing up, keeping gain low. If there is hum only, then it is capsule, if the noise persists, then... something else....

[Harvey Gerst]

Nate, at this point I was gonna suggest that Marik and crazydoc might be your best sources for answers, but I see they're here already, so you're in good hands.

[Nate74]

OK,
I unsoldered the lead to the capsule and powered up, still had the crackling & popping. So it must not be the capsule.

Will swing by the electronics store this afternoon after work and picking up the required capacitor for crazydoc's test procedure. I'll probably pick up a replacement FET and set of caps as well.

Will get a chance to try it this evening. Thanks to all for your help!!!
N

[Nate74]

BTW,
I meant to ask this also... is there an online source for manufacturer specific mic parts. I have 5 or 6 mics from a studio that closed down near me, and most are missing various components: shock mounts, stand adapters, etc.

I know I could contact the mfgs directly (Rode & Shure mostly) but wondered if there was another source.
Thanks

[Marik]

Originally Posted by Nate74

OK,
I unsoldered the lead to the capsule and powered up, still had the crackling & popping. So it must not be the capsule.

Then I'd say you are lucky. The capsule is by far the most expensive thing here.

Originally Posted by Nate74

Will swing by the electronics store this afternoon after work and picking up the required capacitor for crazydoc's test procedure. I'll probably pick up a replacement FET and set of caps as well.

Please note that Crazydoc exellent suggestion would not work if one of the electrolytic caps is busted. Because they are in PSU filtering all the stages will be affected. If you don't have cap tester, I'd suggest to replace them all with the same values and voltage rating--since there are only three of them, you spend a couple bucks at the most.

Oh yeah, be very careful not to lift traces.

[crazydoc]

Originally Posted by Marik

Please note that Crazydoc exellent suggestion would not work if one of the electrolytic caps is busted. Because they are in PSU filtering all the stages will be affected. If you don't have cap tester, I'd suggest to replace them all with the same values and voltage rating--since there are only three of them, you spend a couple bucks at the most.

Good point, Marik. Thanks for pointing that out. It hadn't occurred to me - live and learn.

[Nate74]

OK,
Home from work and the electronics shop. All three caps and both FETs set me back all of $4.30. Will try replacing the FETs first, then work my way through the caps.

Again, I have to say a HUGE thank you to everyone for their suggestions. This board is an incredible resourse!!!
Nate