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Hmmm, not so easy to get inside. I whipped the three tiny screws off the base of mine and successfully withdrew the preamp board to the limits of the capsule wiring - only about 2" (50mm). The PCB is covered in shrinkwrap (a good precaution against anything touching the inside of the case). So, presumably unless you're willing to remove the capsule you can't get the preamp out, and even then you have to remove and replace the shrinkwrap to see anything. I think I'll take the other approach and see if there are levels on both pins 2 and 3. I have some work on a preamp coming up - that would be a good time to answer such a question.

Terry
 

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Good grief - I seem to be right! Unheard of!

A couple of posts back, I conceded that brucek was probably right in assuming a drawing error in the ECM8000 circuit drawing shown previously.

My attempts to look inside were thwarted by the PCB being shrouded in heatshrink. I finally got around to slapping a CRO across the output from my ECM8000, and could only find a signal on pin 2 of the XLR. There was no audio at all on pin 3.

Just to prove the CRO and probes were working OK, I put both probes on pin 2, both traces showed equal signal. Then put them both on pin 3. Neither trace showed a signal. Whichever probe was put on pin 2 showed signal, the other didn't. Not much scope for doubt there.

To be sure that the signal was real, I played flute, and could see the wavelengths change as I changed note. Definitely real.

Both pins show the presence of phantom power, slightly different at 35V and 30V. That implies currents around 2mA in each lead, so there's no question of the wiring being wrong, and 4mA total sounds pretty typical.

Can't see anywhere where I'm going wrong. Always possible I guess that there's something "wrong" with my mic. Perhaps someone else with an ECM8000 and a CRO would like to check their mic?

If it's true, it's not a big deal of course, for reasons I mentioned earlier - we don't need a balanced output voltage, as long as we have a balanced output impedance, so that a balanced mic preamp will phase out any hum pickup on the cable.

So, until someone finds that they are getting signal on both pins 2 and 3, we can probably assume the circuit as originally written is correct! And that the careful duplication of the output stage is just for impedance balancing.

Terry
 

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Elite Shackster , HTS Moderator Emeritus
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Discussion Starter #103
What is a CRO? I could check mine if I knew what kind of tester that was. I have access to o-scopes, LCR's, and a really good Fluke multimeter at work.
 

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Hi Anthony

Sorry about the "CRO" - as brucek has mentioned, it stands for Cathode Ray Oscilloscope. Shows you how old I am - in my days in electronics all CRO's were based on "cathode ray tubes" - essentially a small-screen TV tube with electrostatic steering rather than the magnetic steering used on TVs. Indeed in my early days, they were all tube. So I guess I should get with the times and call it a Scope.

Now, keep in mind if you take your mic to work, you'll need to give it some phantom power to operate. And you'll need to set the Scope channels to AC to avoid the traces being pushed off screen by the phantom voltage. Be careful not to short either pin to earth (um, ground!) - the sudden spike can be very hard on the preamp input devices. (They're designed to operate on a signal around 1mV and shorting a pin to earth will give it around 30,000 times that!)

But if you can, it would be great to be able to put the matter beyond doubt!

brucek mentions the CMR, or CMRR as we used to call it. In case that's not a familiar expression to some, it's the Common Mode Rejection Ratio - the ability of the system to reject common mode signals (such as hum picked up equally on both wires) in favour of differential mode signals (such as the audio which is transmitted on only one of the wires, or which is transmitted normally on one wire and in anti-phase, or "upside down", on the other).

So the question we're investigating is which of those two options the ECM8000 uses.

Terry
 

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Hi 1st post (well besides the 5 pads) ;)
I just purchased one of these mics with a MIC-MATE USB adapter for phantom power
I wish to use it with TrueRTA to help setup some speakers
My question is - should keep the mic close to the USB adapter (with a short XLR patch cable) and run a long USB cable OR useshort USB and run a long XLR to the mic??
Thanks to any help
Regards
WopOnTour
 

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They moved my post so I did not see this previously, took me a while to figure that out was wondering why I didn't see it before! LOL!
Well, measuring the mic is the sure way to figure out how it is wired but it really doesn't make any sense since they included the phase splitter as has been already mentioned. The resistors would be the same if Ic = Ie which is close, and true for infinite beta, but in real life Ie = Ic + Ib so Ie gets some "help" from the input signal and would require a slightly smaller resistor in the emitter path. Looks like they got them backwards. Perhaps they saw a mismatch in amplitude and just decided at the last minute to ground one side. Ran out of time or money in the budget to fix it - perhaps?

Thinking a bit more, even for a beta of 100, the emitter current is only 1% higher than the collector and there is no reason with 1% value resistors to make them different. Not sure why they did it - I'd guess that they chose the values more for what they thought would be good for DC biasing. Really, they both should have been 1K and the base bias resistors chosen for a good operating point.

Pete Basel
 

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Hi,

Just a quick query regarding the ECM8000. My ECM8000 came with a response curve, provided by the manufaturer. The response curve is to within 2db from 15hz to 20khz.
I've noticed that calibration files(provided onthis sie) and response curves, taken for the calibration files, show that the mike requires up to 5db correction, above frequencies of 2khz. This somewhat makes it seem no more accurate than a bog standard spl RS meter.However, it appears accurate at lower frequencies, better than the RS spl meter using the calibration files. My questions is, is the ECM8000 useable above 2khz, even with the calibration files?

Thanks

Delphi
 

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Hi,

Just a quick query regarding the ECM8000. My ECM8000 came with a response curve, provided by the manufaturer. The response curve is to within 2db from 15hz to 20khz.
If you're talking about the curve on the box, that curve has no basis in reality. It may have at one time, but not anymore.

I've noticed that calibration files(provided onthis sie) and response curves, taken for the calibration files, show that the mike requires up to 5db correction, above frequencies of 2khz. This somewhat makes it seem no more accurate than a bog standard spl RS meter.However, it appears accurate at lower frequencies, better than the RS spl meter using the calibration files. My questions is, is the ECM8000 useable above 2khz, even with the calibration files?
It's perfectly fine as long as you're using the calibration file and you're not trying to measure very high SPL's (over ~ 115 dB).
 

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I'll third what Anechoic said. But rather than use the curve on the box, you'll be better off using our generic cal file, or having Cross Spectrum created one for you based on your particular sample.
 

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Thanks for the responses. I did a comparison between the ecm8000 and my RS meter. The RS meter is pretty good. However, there is the typical 3 to 5 db increase from 3khz up to 8khz and a quick roll off after 10khz. This would lead me to believe that the ECM mic, is flat from around 40hz up to around 9khz. Above 9khz there would appear to be a dramatic increase of a few dbs up to around 20khz. I sent a question to Beringer (see below):

"My question is have you any calibration files? I have been advised that the microphone I purchased, 2-3 years ago does not have the linear frequency response curve as seen on the box, instead there is a rise in frequency from 2khz to a peak of 5db at 10khz. I've been told that the curve may have been accurate for microphones made when the response curve was taken. Therefore, is it possible for a re-test to be done on these microphones and a calibration file, or calibration details provided?"


Thanks for writing to BEHRINGER technical support.

"No, there are no other calibration files for the ECM8000. The users manual and what is on the box is all that is available for this. There have been no changes in production to the ECM8000 since its introduction. As these mics are manufactured in China, it is not possible to be sent back to the factory for a retest. You could always have a local service center, studio, or production company test the mic for you. Honestly, for the $40 dollar price of the ECM8000, it would be less expensive to buy a new one if your current one is no longer accurate.


We hope that we have been able to help you with this information"
 

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And the bottom line is that our data on multiple ECM8000's say that some have a rise at HF and some drop off. Hence the desire to get a custom cal file generated if you're that concerned with accuracy.
 

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When creating a sound card calibration file for my MobilePre, is it okay to use an XLR (using the XLR balanced in jack) to 1/4" (using the 1/4" unbalanced out jack) cable as long as I don't turn on the phantom power? Or should I use a 1/4" to 1/4" cable (which I currently don't own). I don't want to fry my MobilePre.
 

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Elite Shackster , HTS Moderator Emeritus
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Discussion Starter #120
I did it both ways to see if there was a difference. There was nothing major that I could see. A few little changes here and there, but tough to see. The mic cal is much more important. Images below:

Top one should be the Quarter to Mic. Bottom is Quarter to Quarter.

Quarter to quarter is easier and you can get the cable at any guitar shop (or Radio Shack)
 

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