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Church and H.O.W. Forums for HOW Sound and AV - Your Displayed Name Must Be Your Real Full Name To Post In The Church and HOW Forums => Church Sound => Topic started by: Ken Webster on February 19, 2018, 07:17:59 am

Title: Condenser Mic fault explanation.
Post by: Ken Webster 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
Title: Re: Condenser Mic fault explanation.
Post by: Steve M Smith on February 19, 2018, 07:20:49 am
Does it have foam behind the grille?  If so, has it turned into goo?


Steve.
Title: Re: Condenser Mic fault explanation.
Post by: Ken Webster 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.
Title: Re: Condenser Mic fault explanation.
Post by: Todd Friemuth on February 19, 2018, 07:56:20 am
Have you replaced the battery with a known good one?
Title: Re: Condenser Mic fault explanation.
Post by: Ken Webster 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.
Title: Re: Condenser Mic fault explanation.
Post by: Mike Caldwell 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?
Title: Re: Condenser Mic fault explanation.
Post by: Ken Webster 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
Title: Re: Condenser Mic fault explanation.
Post by: Mike Caldwell 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.
Title: Re: Condenser Mic fault explanation.
Post by: Ken Webster 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
Title: Re: Condenser Mic fault explanation.
Post by: Scott Holtzman 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.

Title: Re: Condenser Mic fault explanation.
Post by: Ken Webster on February 20, 2018, 06:02:57 am
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.

I am obviously not the greatest at understanding electronics though I have some basics. So yes I will review the comments as you suggest.  I understand that while transformers can step down or step up AC voltage, they can't increase energy (basic entropy).  I was just repeating what I had been told by a PA trainer, though it hadn't made sense to me at the time.  No, I don't have any way to measure impedance, I am just using resistance on a very basic multimeter to check continuity etc.

I was reluctant to take the mic apart completely as that required unsoldering and I could feel resistance when unscrewing the base socket.  Really thought I'd break wires there but it came away fine and exposed the transformer.  Found some thin connections (1 strand) and a wire that had been caught in the base sockets threads.  Luckily an earth wire.   Tightly twisted wires everywhere.  I'll try rewiring the whole thing with new.  If it's component failures, some will be impossible to replace so I may come to a brick wall on this one.  Give it try anyway.

The transformer only has 3 wires so it appears there is a common tap between the 2 coils.  There is a board attached to the capsule that has a tiny black box component marked J7 I can see one leg on top connects to the capsule.  Took a while to figure out it is placed exactly between 2 large solder spots on the board so I'm assuming it's a transistor.  I drew up a schematic and can see that assumption makes sense as one leg is connected to battery + and the other to signal via a 10 uF electrolytic cap.  So it's a simple 1 stage amplifier and DC block.  Still find the transformer a bit mysterious though I can see one signal pin is direct and the other is induced at a different impedance.

In any case, I think my chances are pretty much limited to addressing possible connection issues and anything much more will see the mic go in the bin.


Ken
Title: Re: Condenser Mic fault explanation.
Post by: Mike Caldwell on February 20, 2018, 06:31:57 am
The transformer would be after the the pre-amp circuit and is used is the dual impedance output selection.

Even the slightest amount of wind hitting a microphone capsule imparts more force on the capsule than just talking into it.
Title: Re: Condenser Mic fault explanation.
Post by: Ken Webster on February 21, 2018, 03:21:14 am
The transformer would be after the the pre-amp circuit and is used is the dual impedance output selection.

Even the slightest amount of wind hitting a microphone capsule imparts more force on the capsule than just talking into it.

Yep, I thought I pretty much said that, I just had a memory of a comment suggesting it did a little more but on reading through again I don't see that now.  I have rewired the mic and it's just the same as before.  Pick up breath and pop sounds in speech but no actual sound.  The preamp is just 2 caps and 1 transformer.  I can only see a value on the electrolytic cap, so I could try replacing it.  Is that a chance or more likely a damaged capsule?

On a plus, I had success with our only other condenser mic today.  Battery case terminal had gone open circuit, so I replaced the spring's rivet with a brass screw and nut.  I have no idea what this mic is though, looks a bit like a CALREC 1050 but not quite.  I expect it's rubbish but will try it on some instruments to see if it's at all useful.

We hadn't had musicians for quite a while.  Until recently we had been merging singers with recorded music.  We have some musicians again now but only once a month or so and it's usually just a clavinova and drums.  Been surviving with SM58s but it would be nice to have some decent instrument mics for the occasional acoustic instrument, or some super cardioids when we do a carols event with a live band and choir.  However these events are so infrequent, I can't see how I can justify the expense.  We would do better upgrading the AV computers and getting some analysis software and calibrated mics to tweak sound cards and EQ.  That seem to me a bigger bang for buck.  I am just training 2 new sound people and couldn't show them a working condenser mic.  That's what prompted me to have a go at them.
Title: Re: Condenser Mic fault explanation.
Post by: Mike Caldwell on February 21, 2018, 07:49:10 am
Before you buy any analysis software buy some working mics.
You can get decent condenser mics for under a $100.

Again what are plugging these mics into, does it provide phantom power.
Title: Re: Condenser Mic fault explanation.
Post by: Ken Webster on February 21, 2018, 04:47:51 pm
Before you buy any analysis software buy some working mics.
You can get decent condenser mics for under a $100.

Again what are plugging these mics into, does it provide phantom power.

Phantom power is an option from our console, 48V from memory.  We don't have anything that requires it so it should always be off.  However I did discover it turned on a few years ago I supposed it may be possible that the mic got killed that way.  There are no obvious blackened components, its old so there are stains and detritus on the board.  Looking at it, I have a suspicion the electrolytic may have leaked but it could just be part of the general detritus.  It's likely I would have to order one the replace.  Low cost so easily done.  If it has been killed by phantom power, would the capsule definity be damaged?

I can make an argument for software to adjust the whole system spectrum as there is a clear and measurable benefit to the overall sound every day, I can't make an argument for better mics we may use maybe 3-4 times a year when we already have dynamic mics that have been doing the job.  To most, a mic is a mic and they will not see the point.  It's a small church, I have zero budget so every item has to be approved.  It often means ministry leaders purchase items themselves.  If I want misc, I'd have to purchase and donate them.  I think $100 for a condenser mic is a bit optimistic.  I have my eye on a 2nd hand stereo pair of Rode NT5s about half price.  Decent super cardioids appear to be more expensive unless you are looking at domestic video camera ones.  So for $100, I doubt I can get anything that for the audience sound substantially better than our vintage ones if working.  You know the story, you spend a heap of money and nobody notices any difference so they just think your wasting money.

Ken
Title: Re: Condenser Mic fault explanation.
Post by: Mike Caldwell on February 21, 2018, 06:01:55 pm
Phantom power is an option from our console, 48V from memory.  We don't have anything that requires it so it should always be off.  However I did discover it turned on a few years ago I supposed it may be possible that the mic got killed that way.

I can make an argument for adjusting the whole system spectrum as there is a clear benefit every day, I can't make an argument for better mics we may use maybe 3-4 times a year when we already have mics because to most, a mic is a mic. 

Ken

What is your "system" makes, models, part numbers, pictures, ect.

As far as software goes....REW is free and not too bad, SMAART is something like $900. Any software tool is not just a plug and play make a pretty picture on your computer screen and your sound system magically sounds better. It takes a bit of practice to know what your looking at and what to adjust, yes I'm still learning!
Title: Re: Condenser Mic fault explanation.
Post by: Ken Webster on February 22, 2018, 04:56:37 am
What is your "system" makes, models, part numbers, pictures, ect.

As far as software goes....REW is free and not too bad, SMAART is something like $900. Any software tool is not just a plug and play make a pretty picture on your computer screen and your sound system magically sounds better. It takes a bit of practice to know what your looking at and what to adjust, yes I'm still learning!

Video Projector

   NEC MT 1020G/820G

Video Splitter

   Quest tm VGS2

Microphones

    McCardin radio mic set (2ch) (1 head mic and transmitter)

    Shure SM58 x4

    Leem SF-600 x1

    Peavey PV Low Z Cardioid Dynamic x6

    Condenser mic of unknown brand

CD Player

    Denon DWR-840

DVD/Video Player

    LG DC593W
   
Mixing Desk

   Yamaha MR-1642

Graphic Equalizers

   Yamaha Q2031, A (FOH), B (FB)

Amplifiers

    QSC MMX1450 Power Amp (FOH)
   
    Perreaux 3000B Power Amp (FB)  (2x Line isolation units Redback A2513)

Speakers
 
    Fold Back
   
        Interlink 1201F 2 in use, 2 spare 400W 8 ohm

    FOH
        Built Up 2 of

      Enclosures:   100 L
      Tweeters:   Motorola KSN 1 142 Piezo
      Horns:      Ross KSN 1 151
      Drivers:   Selenium 12PW3C-E
      Crossovers:   Jaycar Kit CX-2612 with load resistors on HF

    Cables 4 x 7.5m 14 AWG.

PCs

    PC1 XP (Sound) backup Maxtor One Touch 3 mini

    PC2 Vista (Video presentations)
Title: Re: Condenser Mic fault explanation.
Post by: Mike Caldwell on February 23, 2018, 12:26:41 am
Your system is pretty simple and straight forward. Before investing in any software and the needed mic and IO interface I would look at upgrading some areas of your system, some of the mics, the wireless mics, a more professional amp for the monitors, that's a nice home stereo amp but that's why you needed the input interfaces.
Don't forget proper gain structure and system configuration goes a long way in
making everything play nice together.

Are your speakers two way with just a woofer the piezo tweeter or three way.
Title: Re: Condenser Mic fault explanation.
Post by: Ken Webster on February 23, 2018, 03:38:23 am
Your system is pretty simple and straight forward. Before investing in any software and the needed mic and IO interface I would look at upgrading some areas of your system, some of the mics, the wireless mics, a more professional amp for the monitors, that's a nice home stereo amp but that's why you needed the input interfaces.
Don't forget proper gain structure and system configuration goes a long way in
making everything play nice together.

Are your speakers two way with just a woofer the piezo tweeter or three way.

Agree, it is a straight forward system.  While I am not happy with the FB the Perreaux is not the problem, it's much the same power as the current FOH amp in fact, it was the FOH amp up to 2 years ago.  It developed an issue dropping the rails unevenly on power down and the previous FB amp (ETI480 kits) had lost a channel completely (cooked board).  We replaced FOH with the QSC (bought 2nd hand) and I temporarily put in a Pioneer A400X on foldback duty (did an amazing job), while Bill Crampton serviced the Perreaux which is now like brand new, possibly better than due the to cap upgrades.  Shure it isn't balanced and is devoid of features which is why it's on isolators and driving foldback.  It's way better than the speakers it's driving IMO.  So considering where we have come from, this is a considerable upgrade.

There are in fact a lot of issues you are not aware of.  We have a stage in the corner which is the bane of my PA life (someone thought it was friendlier).  Causes: echo around the stage area, FB echos muddy sound out to the audience and directly competes with and degrades FOH sound quality.  The FOH speaker position is difficult, if I put them on either end of the stage, 1 of them covers little audience and mostly just fires into the brick wall on that side  echoing interference patterns across the hall.  I have tried lots of placement options which all have problems.  Currently I have the FOH enclosures stacked vertically with the top one inverted, both aligned down the centre of the hall.  This seems to give the most even coverage and best penetration to the rear of the hall (vertical dispersion control).  Cons are, FOH source to one side of the stage and feedback as side coverage pattern runs along the front of the stage.  However,  feedback rarely happens, we are used to managing it I guess.  Even so, my advice is never ever under any circumstances put a stage in a corner, just don't do it.  There seems very little we can do acoustically with this stage position.  Any acoustic structures would adversely affect the visual design of the hall as the end wall has architectural symmetry.

Personally I think the only solution is to get an acoustic engineer consult to redesign the performance area in a more suitable location.  Pretty sure, that's not going to happen.

All I can really do is continue to keep up maintenance and gradually chip away at upgrades.
The most sub standard equipment right now is possibly the PCs.
I have just stripped down and rebuilt the sound PC just to keep it running long enough to research an upgrade.  This involved a thorough internal dedust, deoxit every plug, socket, card etc & replace battery.  This PC is the main music source for us so hopefully this will stave off further boot fails for a while.

I have tried several times over the years to EQ the system by ear.  As I am now 60, I can't hear a thing above 10kHz so have no idea how that sounds to the young ones.  The pizos are underrated so I killed the top end a bit.  Been no complaints.  I'd like to get analysis software just for some quantified evidence on the system and room response and to provide a consistent standard spectrum response.  Currently it is as good as I can do by ear but well, I don't think it's quite right.

Anyway, we have digressed from the original thread, do you think the most likely explanation for the Electret mic issue is a damaged capsule?  I thought this was the better of our 2 condensers though both are quite ancient.  I probably have a bit invested in these mics as they are the 1st things I got working after starting PA at the church all those years ago.

Ken

Title: Re: Condenser Mic fault explanation.
Post by: Mike Caldwell on February 23, 2018, 08:34:33 pm
For decent low cost condenser mics look at the Audio Technica AT2021 or the side address version the AT2020. I have a few of the AT2020's and they work well. Stepping up a little will get you  the AT Pro37, great all purpose condenser mic, I have eight of them myself.

Post a couple pictures of the stage area.
Title: Re: Condenser Mic fault explanation.
Post by: Ken Webster on February 28, 2018, 06:54:17 am
Our stage area:

Some of the things there belong to a business that leases some space during the week.  The clavinova is under that blue cover on right.  It's usually against the wall when not in use and there are some Amps on stage that don't belong to us.  The table behind the drums was a communion table but is currently hiding our Amps.  There is another window to the left of the cross that completes a symmetric set of 3 in that wall.  I could hang the speakers from the roof beam in from of the stage but then, it would be a prohibitive job to retrieve them for use in say an outdoor event.  We have 4 foldback wedges but only use 2 so in theory could use the 4  to run FOH and FB in such events but the sound is not nearly as good the our current FOH speakers on left.  I could hang the speakers on the wall above where they are and they would still be reasonably accessible there but feedback is limiting there.  That wall with the 3 windows is a short wall in a rectangular room and has a certain design symmetry to it.  This is already broken up to some extent by the screen, projector and stage.  I am reluctant to propose making this worse.  The room is rectangular and the 3 windows wall is the short wall.  The opposite wall has a kitchen servery building entry and rest rooms, so we can't put the stage that way.  The best thing I have come up with would move the stage area to the centre of the 3 windows, put heavy drapes each side of the windows so these can close over the windows, mount a speaker on a short wall on each side of the stage and run a curtain track (like hospital curtains track) from the short wall to the stage front and then along the sides of the stage to the wall behind it.  This would allow us to open up the end of the room when we needed to but deploy curtaining to deaden reflections and dissipate FOH sound from influencing the stage area and reduce foldback from being reflected forward to the house.  However I am not an acoustic engineer so I don't really know how well it may or may not work.  It would be an expensive undertaking for us with unknown outcomes.  We don't have any religious tradition issues rearranging furniture, just the cost and work for an unknown outcome.  I kind of like the speaker in short wall idea because it makes them less obtrusive and we could hide a permanent ladder, speaker lifting tackle and retracted curtaining behind the wall.  Might be good acoustically too.
  If that is understandable, how does it sound?

Ken

(https://scontent.fmel1-1.fna.fbcdn.net/v/t31.0-8/28337918_1581271828653080_6399484918020659135_o.jpg?oh=69481da14948758025e775f19c8b3c24&oe=5B4852BC)
Title: Re: Condenser Mic fault explanation.
Post by: Chrysander 'C.R.' Young on February 28, 2018, 09:59:22 am
Ken, where are you located?  We have some kind folks on here that may be willing to lend a hand.
Title: Re: Condenser Mic fault explanation.
Post by: Ken Webster on February 28, 2018, 11:59:55 pm
Ken, where are you located?  We have some kind folks on here that may be willing to lend a hand.

Bathurst NSW Australia.

I was training a new guy yesterday so we played with all our mic models including our now one and only condenser that has a permanently attached lead so looks cheap and nasty.  Tried some speech and some instruments (mine, charango, zampona & Quena in high C) ie, string, pan pipe and flute.  We found the condenser is not good for speech but is by far the best for instruments.  I guess that is a fairly normal expectation except it looks so cheap, I had doubts.  It had never worked well in my memory but rebuilding the battery + connection seems to have given it a whole new life.  As usual, most things simply come down to connectivity maintenance and conditioning.