ProSoundWeb Community

Please login or register.

Login with username, password and session length
Advanced search  

Pages: [1] 2 3  All   Go Down

Author Topic: Condenser Mic fault explanation.  (Read 2456 times)

Ken Webster

  • Jr. Member
  • **
  • Offline Offline
  • Posts: 50
Condenser Mic fault explanation.
« on: February 19, 2018, 07:17:59 am »

The church has an old condenser mic that I repaired and got working well maybe 20+ years ago but recently found not working properly now.  It is an Electret Rapar EMC-1017 50 kohm & 600 ohm.  (waiting for laughter to subside).........OK I did say it is old but these were once pretty will known.  The thing is that it picks up breath at a normal level but not voice.  It's not a proximity issue, it's like it is responding to turbulent air movement but not actual sound wave SPL.  Can anyone explain what has happened?

I know it's probably toast and long overdue to replace but there just isn't great need ATM.
Still, it might be handy if I can get it working again but I would need to understand the fault.

The original issue was corrosion from a leaking battery btw.

Ken
Logged

Steve M Smith

  • Hero Member
  • *****
  • Online Online
  • Posts: 3086
  • Isle of Wight - England
Re: Condenser Mic fault explanation.
« Reply #1 on: February 19, 2018, 07:20:49 am »

Does it have foam behind the grille?  If so, has it turned into goo?


Steve.
Logged

Ken Webster

  • Jr. Member
  • **
  • Offline Offline
  • Posts: 50
Re: Condenser Mic fault explanation.
« Reply #2 on: February 19, 2018, 07:34:34 am »

Does it have foam behind the grille?  If so, has it turned into goo?


Steve.

Ta Steve, can see through the grill and no sign of foam.

 I haven't taken it apart yet cos I recall the last time it was tricky.  Just hoped someone might recognise this symptom before I invest too much time on it.
Logged

Todd Friemuth

  • Newbie
  • *
  • Offline Offline
  • Posts: 39
Re: Condenser Mic fault explanation.
« Reply #3 on: February 19, 2018, 07:56:20 am »

Have you replaced the battery with a known good one?
Logged

Ken Webster

  • Jr. Member
  • **
  • Offline Offline
  • Posts: 50
Re: Condenser Mic fault explanation.
« Reply #4 on: February 19, 2018, 04:59:06 pm »

Have you replaced the battery with a known good one?

Yes of course, checked voltage, cleaned and conditioned (deoxit) the contacts as well.
It is giving a good solid signal level from breath but no detectable signal from voice.

Ken.
« Last Edit: February 19, 2018, 05:01:34 pm by Ken Webster »
Logged

Mike Caldwell

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 1043
  • Covington, Ohio
    • Mike Caldwell Audio Productions
Re: Condenser Mic fault explanation.
« Reply #5 on: February 19, 2018, 06:23:58 pm »

Are you using a 1/4 plug or an XLR connector with that mic?
Either way double check the cable.

I looked that mic up and to honest it may be time to put it on the shelf as a conversation piece!

What mixer are you plugging it into, does it have phantom power available?

What it this mic used for?

Ken Webster

  • Jr. Member
  • **
  • Offline Offline
  • Posts: 50
Re: Condenser Mic fault explanation.
« Reply #6 on: February 19, 2018, 06:48:51 pm »

Are you using a 1/4 plug or an XLR connector with that mic?
Either way double check the cable.

I looked that mic up and to honest it may be time to put it on the shelf as a conversation piece!

What mixer are you plugging it into, does it have phantom power available?

What it this mic used for?

This mic has a 4 pin connector in it's base to handle dual impedance.  You just wurn the plug around to engage the appropriate pins for the impedance you want.  The original cable connector was damaged and replaced 20 years ago with a single core cable and 1/4 inch TS plug.  This all appears to still be in good order with good electrical continuity.  As I said it is passing a signal which appears to be generated from the capsule (blowing breath into the screen).  It seems to me the capsule is responding to turbulence associated with breath but not to sound SPL.  I don't get how that is possible though.

I have started disassembling the mic and testing internal wiring.  At the base plug, there are 4 pins in a square.  2 diagonally opposite pins are bridged earth shield zero ohms between them.  The other 2 pins appear to be from what I assume is an audio transformer windings and measure 45 ohms and 2 kohms to earth. So switching the plug around 180 degrees selects which of these impedances is used to tap signal.  Currently, the cable is bridged to tap both signal pins at the same time which is wrong as it defeats the impedance selectability of this plug.  However it has been working for many years so this is not the problem.

There are 2 wires running up the body to the capsule, one is earthed and there is 45 ohm to earth.  I assumed these are the other side of the transformer so should be isolated from the plug signal pins.  However, there doesn't appear to be any isolation so either there is no transformer or if there is, it may have shorted or I need to isolate the capsule from these measurements.  What do you think?

Ken
« Last Edit: February 19, 2018, 08:02:34 pm by Ken Webster »
Logged

Mike Caldwell

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 1043
  • Covington, Ohio
    • Mike Caldwell Audio Productions
Re: Condenser Mic fault explanation.
« Reply #7 on: February 19, 2018, 08:07:43 pm »

This mic has a 4 pin connector in it's base to handle dual impedance.  You just wurn the plug around to engage the appropriate pins for the impedance you want.  The original cable connector was damaged and replaced 20 years ago with a single core cable and 1/4 inch TS plug.  This all appears to still be in good order with good electrical continuity.  As I said it is passing a signal which appears to be generated from the capsule (blowing breath into the screen).  It seems to me the capsule is responding to turbulence associated with breath but not to sound SPL.  I don't get how that is possible though.

Ken

A blast of breath blowing on to the mic capsule results in a large output from the mic, talking into the mic is much lower in level. That larger output level makes it through to some degree the bad section of the mic or the cable or the input that it is plugged into, have you tried it plugged into another channel on the mixer.

The mic capsule in a condenser mic does not output voltage as such, in a nut shell when it picks up sound but changes in it's capacitance and the voltage across the plates, the pre-amp in the mic takes that very high impedance signal from the mic capsule amplifies the signal and converts it to lower more usable impedance.

My guess would be it's the pre-amp section that is bad.

Ken Webster

  • Jr. Member
  • **
  • Offline Offline
  • Posts: 50
Re: Condenser Mic fault explanation.
« Reply #8 on: February 19, 2018, 09:58:38 pm »

A blast of breath blowing on to the mic capsule results in a large output from the mic, talking into the mic is much lower in level. That larger output level makes it through to some degree the bad section of the mic or the cable or the input that it is plugged into, have you tried it plugged into another channel on the mixer.

The mic capsule in a condenser mic does not output voltage as such, in a nut shell when it picks up sound but changes in it's capacitance and the voltage across the plates, the pre-amp in the mic takes that very high impedance signal from the mic capsule amplifies the signal and converts it to lower more usable impedance.

My guess would be it's the pre-amp section that is bad.


OK, I have been doing sound here more than 20 years so I have a good idea how much of a breath is need to get a response.  I'm not blasting air at it, just enough breath to see if there is any response.  In this respect it appears quite normal.  I don't like pulling mics apart but it's dead anyway so may as well try.   I'll have to unsolder the capsule to pull all the wiring through and take a better look.  There is something in base of mic and a board with a couple of caps on the back of the capsule someone told me they used a transformer for amplification.  That's doesn't appear to be correct as I am getting DC continuity past where such a thing could be.  I do know that caps can go bad over time, it's old enough for that I guess.  We have only used this mic a couple of times a year and I have never stripped it down completely before.

Ken
Logged

Scott Holtzman

  • Hero Member
  • *****
  • Online Online
  • Posts: 5037
  • Ghost AV - Avon Lake, OH
    • Ghost Audio Visual Systems, LLC
Re: Condenser Mic fault explanation.
« Reply #9 on: February 19, 2018, 11:56:30 pm »



OK, I have been doing sound here more than 20 years so I have a good idea how much of a breath is need to get a response.  I'm not blasting air at it, just enough breath to see if there is any response.  In this respect it appears quite normal.  I don't like pulling mics apart but it's dead anyway so may as well try.   I'll have to unsolder the capsule to pull all the wiring through and take a better look.  There is something in base of mic and a board with a couple of caps on the back of the capsule someone told me they used a transformer for amplification.  That's doesn't appear to be correct as I am getting DC continuity past where such a thing could be.  I do know that caps can go bad over time, it's old enough for that I guess.  We have only used this mic a couple of times a year and I have never stripped it down completely before.

Ken

Transformers don't amplify, they step up or down voltage.  Total energy stays the same (less a little bit of coupling loss).

The explanation of how a condenser microphone works that was given to you by Mike is very good.  It's important that you understand that before you try and fix it.  Repairing items is a great way to increase your electronics knowledge.

Are you using a good high impedance meter?  One thing that you have to get over is that measurements are mostly relative.   Your meter measures resistance, without loading the circuit, impedance, while expressed in ohms is resistance to alternating current and changes depending on frequency.

Logged
Scott AKA "Skyking" Holtzman
River Delta Audio is now:

Ghost Audio Visual Solutions, LLC
Cleveland OH
www.ghostav.rocks
Pages: [1] 2 3  All   Go Up
 


Page created in 0.086 seconds with 24 queries.