Can I damage condenser mic by phantom power supply connected over unbalanced XLR cabl

Taylor729

New member
Hi,
I bought Chord CM05 microphone on amazon - it looked as reasonably quality mic for a good price. Since it is my first condenser mic, I just wanted to try it and bought a cheap phantom power from aliexpress.
Unfortunately I realised that the XLR cable I had (just spare one, I never used it before) is unbalanced one - only two wires, pin 1&3 interconnected. That means Chord mic got 48V on pin 2 and 0V on pin 3 and 1. I realized it soon (under one minute) after I didn't hear anything on the output.

When I obtained correct, balanced cable, I'm hearing only noise when I switch phantom power on, no other sound. I checked that there is really 48V on both pins 2 and 3 (to pin 1 of course), I measured about 10kohm between pins 2&3 on mic side of phantom power (while turned off). Also I tried a dynamic mic which passes sound through phantom power supply.

Spec of CM05 says about FET preamp built in. Can it be damaged by 48V difference between pin 2&3 ? How can I possibly berify it?

My testing setup is:

Mic - balanced XLR cable - Phantom Pwr Supply - XLRto3.5mmJack - mobile phone with recording app

This setup works with dynamic mic (with or without PhPwr). I intend to buy something better (phantom power & recorder or PC interface), but I am on budget, so I go step by step, began with mic...
 
I'm not sure about that mic, but I have used unbalanced into balanced and been fine. To my understanding, the balanced/unbalanced thing is just for noise cancellation and won't send additional current or phantom power to the mic. I could be wrong, but my answer is you're fine.

Edit: see below, you very well might not be fine.
 
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I'm not sure about that mic, but I have used unbalanced into balanced and been fine. To my understanding, the balanced/unbalanced thing is just for noise cancellation and won't send additional current or phantom power to the mic. I could be wrong, but my answer is you're fine.

Hey Nola. Never use any unbalanced equipment with phantom power enabled.
Phantom power relies entirely on balanced circuitry as it's presented equally on the +signal conductor and the -signal conductor.

Hi,
I bought Chord CM05 microphone on amazon - it looked as reasonably quality mic for a good price. Since it is my first condenser mic, I just wanted to try it and bought a cheap phantom power from aliexpress.
Unfortunately I realised that the XLR cable I had (just spare one, I never used it before) is unbalanced one - only two wires, pin 1&3 interconnected. That means Chord mic got 48V on pin 2 and 0V on pin 3 and 1. I realized it soon (under one minute) after I didn't hear anything on the output.

Hey Taylor,
Welcome to HR! :)

If you didn't let the magic smoke out that's a good sign, but it's still possible something's been damaged.
Thinking about it, though, bridging pins 1+3 (with a mic hooked up) could create 48V potential difference across 2+3 of the mic but, on the other hand, it could totally ground your 48V supply.

The former would most likely damage the mic after a minute, whereas the latter would most likely burn out something in the 48V supply.

I guess it comes down to whether the microphone circuitry presented less resistance that the circuitry in the supply, but I'm certainly no expert here.


Anyway...It's troubleshooting no matter what way you look at it. If you've tested the supply and read +48V between 1+2 and 1+3, then you've pretty much worked out that the mic is damaged.
That means it's time to open it up and see what components were in the line of fire.

There are those who would return it and play dumb.
If that's a possibility, obviously don't bother opening it. ;)
 
Balanced cable is for noise cancellation, but is also used to send phantom power to devices that require it. Using unbalanced cable where there is a phantom supply runs the risk of shorting out the 48v.

OP: When you say you are "hearing only noise when I switch phantom power on, no other sound", I assume you mean noise as in unwanted electronic sound, rather than the audio you would like to get?

Two further test you should try if you are able: (a) take your CM05 somewhere else and see if it works there. With luck you know someone with a mixer or an interface who could help, (b) try another condenser mike on your system.
 
Hey Nola. Never use any unbalanced equipment with phantom power enabled.
Phantom power relies entirely on balanced circuitry as it's presented equally on the +signal conductor and the -signal conductor.

Oh wow, sorry for giving bad advice. But at least I did tell him to listen to other opinions and I could be wrong.
I have done it by accident on my Tascam 244 (unbalanced, yet fed it 3rd party phantom power supply via balanced cable).
Same situation as the OP where I mixed up my cables. In my case, it didn't do damage. Hopefully he's alright.
 
Ha, no worries. I did exactly what the OP is describing a while back, although 1+3 weren't bridged by design...the cable was damaged and shorted.

Unfortunately that damaged the interface in a way that I still don't fully understand.
Gain is lower on the affected channel and while phantom power works, it gives a hell of a thump and 5-10 seconds of crackling when enabled.

Luckily it was only a 2channel interface that I keep around as a convenience tool. I've just accepted that it's a dynamic-only interface now.
 
A good reason to make your XLR cables or double check the ready made ones.

I know there's no law that says XLR connectors must be wired as balanced with 3-wire cable...but that's kinda the usual expectation, and I think any other wiring scheme would be a custom/special needs, and would be identified as such.
At least when you roll your own...you know what is what, and you mark it as required to avoid connection issues.

I also keep my mic XLR cables together in one pile, and they are only used for the mics.
My other XLR and combi-cables or reversed Pin and odd ground schemes...I keep separate.
Also always double check your connections/cables before you push that phantom power ON button.
 
Good point, Miroslav. I began making my own cables and have had no problems since and saved hundreds of dollars.
 
Hey Taylor,
Welcome to HR! :)

If you didn't let the magic smoke out that's a good sign, but it's still possible something's been damaged.

...

Anyway...It's troubleshooting no matter what way you look at it. If you've tested the supply and read +48V between 1+2 and 1+3, then you've pretty much worked out that the mic is damaged.
That means it's time to open it up and see what components were in the line of fire.

There are those who would return it and play dumb.
If that's a possibility, obviously don't bother opening it. ;)

Hi Steenamaroo,
Thanks for your reply. I believe that phantom power supply is resilient to short circuit by design. According to this page Tips and Tricks for Audio Engineers: Can phantom power damage your microphones?
there are two resistors that restrict current in both branches independently (pin 2 and pin 3). That's why I mentioned resistance I measured between pin 2 and 3. 10kohm / 2 is 5kohm, that means max current is 48V / 5kohm = 10mA (approx). It shouldn't fry the supply.
I'm out now, but I'll try to open the mic in the evening then. Do you thing it might be obvious that some piece is burnt out?

When you say you are "hearing only noise when I switch phantom power on, no other sound", I assume you mean noise as in unwanted electronic sound, rather than the audio you would like to get?

Two further test you should try if you are able: (a) take your CM05 somewhere else and see if it works there. With luck you know someone with a mixer or an interface who could help, (b) try another condenser mike on your system.

Only white noise. No sign of anything I say or other sounds present in the room.
Noise appears when I switch supply on and slowly disappears (as some capacitor in the supply discharged) after I turn it off.
Unfortunately I don't know anyone else nor have another condenser mic.
I will try to open the mic tonight and see if there's something obvious.
Anyway, do you think that there is no other issue with my current test recording setup as I described before?
That means cheap phantom power and unbalanced cable between the supply and recording device?

BTW I'm using this supply https://m.aliexpress.com/amp/item/32807943129.html

Thanks everyone here, it's nice to see so many answers so soon ;-)

Pavel
 
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Can you damage a DECENT capacitor microphone with a miss wired XLR cable? WERY unlikely IMO. As someone else said, XLR cables CAN be differently wired and ***t'appen. "Pro" mics are therefore likely foolproof. But..

That mic is a super cheap device. I cannot find it out but I strongly suspect it uses an electret mic capsule and 'pots down' 48V to 12V or less for the integrated pre amp (yes! I know it says 'FET' transformerless design but these people are 'economical' shall we say with the truth?) Even so, putting spook juice on pin 2, 1& 3 and shield still should not have buggered it but it all depends on how exactly they reduce the 48V.

Regarding the juice from mixer/AI XLRs. This should always be bombproof. Shorting pins 2 or 3 to 1 would produce a maximum of 7mA in the internal 6k8 resistors, about 340mW and thus a half watt MF resistor should stand that indefinitely. However the bean counters might have insisted on very wee surface mount Rs..POOOF! Same goes for inside that microphone.

Dave.
 
Hi there again,
I disassembled my Chord mic and was surprised a bit. I'll show you images.
Chord CM05 Disassembled - Overview.jpg

First I noticed when unscrewed golden capsule casing was red wire which was torn off. I'm not sure if I finished it while unscrewing or it was already torn off before. Also soldering between PCB ground and silver thing on which golden head was screwed on is a bit wobbly.

I started studying paths on PCB and noticed spot where I suspect a transistor might be missing. I marked it with red in the following picture.
Front side:
Chord CM05 Disassembled - PCB detail front (marked).jpg
Back side:
Chord CM05 Disassembled - PCB detail back (marked).jpg

What do you think about it. Is it possible that amazon distributes as much crappy thing that there are missing piece on PCB?

Anyway I'm thinking about trying to solder red wire to the capsule and also fix soldering on silver screwing and try what happens.
 
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Did the mic ever work for you?

I really doubt a component is missing. It's more likely they use the same board for several variants or different microphones.
 
No it has never worked for me.
When it arrived, I didn't have Phantom Power Supply yet. When I tired it for the first time it was with wrong (unbalanced) cable, as I mention in initial post. Then I tried it with correct cable and it produced only noise. I disassembled it and took the photos today.

Edit:
I also can't believe there's really missing part, but you can trace PCB connection on the picture from missing part to the top pin on XLR connector and it is the only connection to that pin except for diode (which I guess separates phantom power voltage from the pin.
 
Ok.
If 100% obvious where the red wires goes I'd reattach it and test, particularly if there's doubt as to whether it was already like that.
You could continuity check pin 1 to the silver threading but I doubt there'll be a problem there. Looks like the silver threaded part is screwed to the board, with the board sanded to expose the copper.
 
I would be very surprised if that is other than an electret capsule since pukha cap mic cells are not supported on bog S PCB, too 'leaky'. They are stood off on a cone of PTFE. Then there should be a VERY high value polarizing resistor like 10 GIG Ohms..DON'T TOUCH it! sweat will bugger it. But then I doubt there is one.

The 6V8 zeners sort of give it away. Why clamp the incoming 48V (or part of it) to such a low voltage UNLESS the capsule pre only needs 5V or so?

Dave.
 
Edit:
I also can't believe there's really missing part, but you can trace PCB connection on the picture from missing part to the top pin on XLR connector and it is the only connection to that pin except for diode (which I guess separates phantom power voltage from the pin.

Weird. Hopefully one of the more knowledgeable mic chaps will come back.

Edit: Oh...Dave did as I was typing!
 
I'm pretty sure that is the same pcb and housing as the Sennheiser 865 copies that were really common a couple of years ago. I had one and it sounded reasonably OK to be honest. The only issue I had was that pcb rattling about as it was a very loose fit. I used it as a talkback mic plugged into the desk, and some punter stole it one night!
 
I think Taylor may be correct about a missing transistor. If you follow the trace up from the XLR(2) connector through the resistor, it leads to a point where I believe a component should be. The diagram below is a generic Chinese mic and other than the output stage I don't know how similar this is to the mic in question, but there should be a transistor I think in that empty spot to get a proper balanced output, unless some other trickery isn't evident.

Taylor, Is it all possible you may have gotten a mic someone returned to Amazon, packaging didn't look quite right or other hints? If you don't think you broke the red wire disassembling the mic and then along with the missing component, it would make me wonder if someone may have messed with it and then returned it and it didn't get checked out by Amazon or seller. If you still have a window for a return to Amazon that's what I would suggest. Even if outside the return time contact Amazon and see if they'll make good on it. Simply state not working.
 

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Thanks for the circuit schema, very interesting.
I didn't try to repair it for now (it wouldn't help anyway due to missing transistor) and wrote to Amazon. I hope they understand and send another mic as this is not nice experience.
Thank you much for your help. I will let you know how it unfolds.

Pavel

Edit: customer support reacted quite fast. They are sending me another one and don't insist on sending the defective one back (which I'm glad for - I wouldn't want to spend even more time with this issue). I'm really looking forward for the new one and hope it will be ok. Honestly I have rather positive expectations from this mic. Its sound quality is said to be good for the price.
 
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That's great news.
If the new one works well and has no issues, you may even be able to repair or restore the original since you'll have a perfect reference model.
Nice! :)
 
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