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Tube mic "clicks" when signal drops? Condenser Microphones
Old 27th December 2010
  #1
Gear Head
 

Tube mic "clicks" when signal drops?

Hey there,

I have two Apex 450 Tube mics, and I've noticed a faint kind of clicking/popping sound when I use them. The mics seem to work fine, I don't have to crank the gain on Mackie board to get a workable signal out of them, and the audio that comes out is not distorted or anything like that. There is no noise/hum at low gain levels. It seems like when the signal stops hitting the mic (stop singing, for example), there is a little click a couple of seconds later. Almost like a gate closing or something.

These are the only tube mics I have experience with, so maybe it is just normal? Maybe I'm not gain staging properly? I have swapped the mics, cables, and power supplies into every combination, and it still happens on both mics.

Any ideas would be greatly appreciated!
Old 27th December 2010
  #2
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2N1305's Avatar
 

I would email customer support to ask them about that. Seems strange.
Could it be something in your mixer or preamp?
Old 27th December 2010
  #3
Gear Head
 

Could be the preamp on the Mackie mixer I guess, but I only notice it with these two mics. I doubt I'll have much luck with support on them... I bought them used a few years ago, and I think they're discontinued now. Thanks though.
Old 28th December 2010
  #4
Gear Head
 

Bump.

Would definitely be interested in the thoughts of anyone with a little more tube mic experience than I have.
Old 28th December 2010
  #5
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DrFrankencopter's Avatar
Possibly DC leaking out from somewhere???? Try using a voltmeter set to DC between pin 2 & 3 of the output XLR ...

Just a guess.

Cheers

Kris
Old 28th December 2010
  #6
Gear Head
 

Thanks Frankencopter... I will do that. Excuse the noobe question, but basically I'd just be looking for any DC voltage on those pins, correct?
Old 28th December 2010
  #7
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2N1305's Avatar
 

We are eagerly awaiting the results of the D.C. voltage check!

Actually you should have dc on pins 2 and 3, relative to pin 1, or else your condenser mics will not work obviously.

I think, if the dc is present on only one of those pins (2 or 3) then it might be that it's charging a coupling capacitor and that cap is slowly discharging while it's hooked up. Or doing something else weird. Let's just find out what the dc check reveals. Remember to switch it on on your Mackie!

Last edited by 2N1305; 28th December 2010 at 10:16 PM.. Reason: corrected information.
Old 28th December 2010
  #8
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2N1305's Avatar
 

Quote:
Originally Posted by chille01 View Post
Thanks Frankencopter... I will do that. Excuse the noobe question, but basically I'd just be looking for any DC voltage on those pins, correct?

You'd like to see anywhere between 47 and 50 volts on pins 2 and 3 with respect to pin 1.
Old 28th December 2010
  #9
Gear Head
 

Thanks guys. At work right now, but I'll do this tonight. Just to be clear, these mics have a power supply box... so the chain is:

Mic
5 Pin XLR
PSU
3 Pin XLR
Mackie Strip

Where exactly in that chain should I be checking this voltage? Pin 2 and 3 on the output of the PSU, or on the output of the mic? Not sure what the extra two pins are for in that cable, but I can only assume they have something to do with delivering the power to the mic.
Old 29th December 2010
  #10
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2N1305's Avatar
 

Quote:
Originally Posted by chille01 View Post
Thanks guys. At work right now, but I'll do this tonight. Just to be clear, these mics have a power supply box... so the chain is:

Mic
5 Pin XLR
PSU
3 Pin XLR
Mackie Strip
Ah, well this changes my suggestion. You don't have to have the Mackie's phantom supply switched on. At least check in the owner's manual of the 450 to see if they allow the power supply to have phantom power switched on. They should because if you have other condenser microphones plugged into the board (which ever board that may be) then they need to be powered.
Whatever, the fact that these have an individual power supply (I should have noticed that when you said tube mic) means that the problem could lie there.

Like I said try contacting Apex, they might be able to help you out.

Quote:
Originally Posted by chille01 View Post
Where exactly in that chain should I be checking this voltage? Pin 2 and 3 on the output of the PSU, or on the output of the mic? Not sure what the extra two pins are for in that cable, but I can only assume they have something to do with delivering the power to the mic.
Actually, everywhere. My hypothesis (and that's only from experience and what I've learned) is that pin layout on this connector is the same as a three pin XLR, except the two other pins are in between pins 1&2 and 2&5

O 1 O 5
O 2 O 4
O 3

But AGAIN! Check with the manual.

The reason there's a power supply is because you have to power the tube inside the mic with high voltage, higher than 48V.
Old 29th December 2010
  #11
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2N1305's Avatar
 

Sorry my ascii drawing got reformatted and it isn't clear but I am trying to represent the half circle layout of the Cannon type connector.

BE CAREFUL when measuring the voltage on the five pin connector, you will most likely have over 200 volts present on one of those pins! Make sure you know what you are doing!!!
Old 29th December 2010
  #12
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DrFrankencopter's Avatar
My suggestion is that you unplug the 3 pin XLR coming out of the power supply, and make the following measurements with your meter set to DC milivolts:
----> Common mode Voltage to ground
-Pin 1 to Pin 2
-Pin 1 to Pin 3

----> DC signal voltage
- Pin 2 to Pin 3

Try replicating your audio test....generate a signal on the mic, and look at the DC output. Is it floating up/down to some static value, or is it near zero? There might be some common mode voltage relative to pin 1, but there should be no DC between pin 2 & 3.

It's quite possible that there is a DC problem inside the mic, which might be masked by output stage coupling capacitors....in which case you'd need to start poking around inside the mic.

Cheers

Kris
Old 29th December 2010
  #13
Gear Head
 

Thanks Copter. That gives me an idea of what I'm looking for. I did try earlier, but I was just poking blind and I didn't generate a signal to the mic. Will do so this afternoon.

One other thing I did notice is that it seems to only happen at lower gain settings on the preamp. For instance, if I hit the solo button and set my gain so that it is just peaking at 0 when I speak into the mic, I get this problem. If I crank the gain a little higher, it seems to go away... but by then it is pretty noisey overall.
Old 30th December 2010
  #14
Gear Head
 

Ok... so did this test.

Pin 2 or 3 to Pin 1, there is indeed a floating voltage, that seems to peak all the way up to about 35mv or so.

Between pins 2 and 3, there is a minor voltage that seems to jump between .1 and .2 mv, and not in any kind of correlation to signal on the mic. I'm thinking this minor voltage is not likely the cause of my problems.

I will email Apex, and see what they say.
Old 30th December 2010
  #15
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2N1305's Avatar
 

Quote:
Originally Posted by chille01 View Post
Ok... so did this test.

Pin 2 or 3 to Pin 1, there is indeed a floating voltage, that seems to peak all the way up to about 35mv or so.
This is your signal voltage, your mic is just picking up random sound and your multimeter tries to measure it. A multimeter cannot measure ac voltages that are above 60hz. An oscilloscope would be the instrument to use, if you have one.

Quote:
Originally Posted by chille01 View Post
Between pins 2 and 3, there is a minor voltage that seems to jump between .1 and .2 mv, and not in any kind of correlation to signal on the mic. I'm thinking this minor voltage is not likely the cause of my problems.
No it is simply the differential output ac voltage that your multimeter cannot track. I don't know why it is lower than the 35mv mentionned earlier, and it also should be in correlation to the signal, since it is the signal voltage. As a matter of fact, it should twice as big as the voltage you would read on your meter (assuming it could properly read audio frequencies) between pin 1 & 2 and 1 & 3.

Quote:
Originally Posted by chille01 View Post
I will email Apex, and see what they say.
yup. They know more than we do.

Last edited by 2N1305; 30th December 2010 at 05:36 AM.. Reason: corrected spelling.
Old 30th December 2010
  #16
Gear Head
 

No oscilloscope here, and no word from Apex thus far. Not sure they'll know much more... I think they basically just buy the Chinese mics and throw an Apex badge on them. We'll see though.

I am considering swapping the tubes from 12ax7 to 12au7 though. I figure for the $20 in tubes it will cost me, it's worth a shot. Worst case I can always put those tubes in one of my guitar amps.
Old 31st December 2010
  #17
Gear Head
 

Actually talked to Apex today, and they were stumped as much as anyone. He said it could be static electricity discharging, which I guess is possible. Other than that, all he could suggest was opening it up and making sure all the contacts are clean.
Old 4th January 2011
  #18
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2N1305's Avatar
 

Quote:
Originally Posted by chille01 View Post
Actually talked to Apex today, and they were stumped as much as anyone. He said it could be static electricity discharging, which I guess is possible. Other than that, all he could suggest was opening it up and making sure all the contacts are clean.
Hmm. Well at least they answered you. I think that reseating the connectors, and cleaning them, could probably help. Static electricity buildup, yeah, but in what? I guess you could put a ground wire from the mic to your main ground connection, and see what it does...

Cheers and good luck!
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