Is it possible to modify this mic preamp?

[davidgale]

I have built this electret mic preamp and it works great. However recently I have bought Behringer ECM8000 microphone which needs phantom power. Is it possible to modify the shown schematic in such a way that it is able to work with ECM800 + design the simplest possible 48V DC PSU using 4x12v batteries?

[Mooly]

According to Behringer the ECM 8000 is OK with 15 to 48 volt power.

This is a subject I know very little about... but adding a phantom PSU should be straightfoward.
This may help,
48V Phantom Feed Supply for Microphones

I see the assumption of a balanced connection is shown.

I would measure the current required and see if battery operation is feasable. Perhaps 2 or 3, 9volt packs may work well feeding both the preamp and mic. Make sure you have 63 volt caps fitted. Having lots of different battery sizes is messy.

[Corben]

By chance I've also been reading about the ECM-8000 (thinking of buying one). Like Mooly, I'm not really knowledgeable on the subject and everything that follows is just based on what I've read.

Anyways, the ECM-8000 is a bit weird in that it seems to have been designed to have a balanced output, which actually isn't. (You can find a schematic pretty easily by googling. There are some threads on diyaudio too.) I think that you might have to provide the phantom power to both signal pins. To do this, you can probably get away by duplicating the R1,R2,C2 circuit and applying that to the negative pin. Other than that, I think your circuit might work, if you increase the voltage (assuming that the preamp works with a higher voltage. I didn't check for that.).

Or, I guess you can leave JP1 open and have a separate phantom PSU as per the instructions in Mooly's link. Then you'd just connect your amp to the "Mic +" output shown in Figure 2.

Also, while the ECM-8000 might work with 15V, it's performance might be impaired if not operating at 48V, but this is just my guesswork based on the schematic I've seen.

Note that having a balanced preamp might be better to reduce noise picked up by the cable, even though the ECM8000 doesn't produce a proper balanced signal.

[tvrgeek]

Originally Posted by Corben

By chance I've also been reading about the ECM-8000 (thinking of buying one). Like Mooly, I'm not really knowledgeable on the subject and everything that follows is just based on what I've read.

Anyways, the ECM-8000 is a bit weird in that it seems to have been designed to have a balanced output, which actually isn't. (You can find a schematic pretty easily by googling. There are some threads on diyaudio too.) I think that you might have to provide the phantom power to both signal pins. To do this, you can probably get away by duplicating the R1,R2,C2 circuit and applying that to the negative pin. Other than that, I think your circuit might work, if you increase the voltage (assuming that the preamp works with a higher voltage. I didn't check for that.).


Also, while the ECM-8000 might work with 15V, it's performance might be impaired if not operating at 48V, but this is just my guesswork based on the schematic I've seen.

Note that having a balanced preamp might be better to reduce noise picked up by the cable, even though the ECM8000 doesn't produce a proper balanced signal.

Hint. Go ahead and spend the additional bucks to get one that is calibrated. You will be sorry later if you don't. Once upon a time they were pretty flat. But like all things made in China, consistency is not their forte. I have one that only has a small bump at about 10K, and rolls off above that, rolling off at 15Hz about 4dB/oct. My new one has a ragged and rising top end from 12K up, and rolls off at 16 Hz at about 5 dB. Both fine with calibration. Both inadequate without. ( knowing the rolloff of mics, makes one wonder about those eq flat to 10Hz graphs I see posted on various forums. I bet they are so over-boosted in the bass that it would drive crazy a block away!)

Yes, happier with closer to 48V. Even though the mic only uses 12V, the two driver transistors are biased with the 48V. Search the web for mic preamp circuits and you will find several you can adapt. THAT and National are good starts.

I dissagree with the "not proper balanced". Not symmetrical, no CCM rejection advantage, but the impedance is balanced. Pin 3 is not ground, it is driven from ground.

[Keith Taylor]

Sorry not to be contributing to answering the original question but my eye got stuck on an error in the circuit diagram. The second stage, U1B, has the input signs reversed. Pin 5 is non inverting and pin 6 is inverting.

Keith

[sumaudioguy]

Originally Posted by davidgale

I have built this electret mic preamp and it works great. However recently I have bought Behringer ECM8000 microphone which needs phantom power. Is it possible to modify the shown schematic in such a way that it is able to work with ECM800 + design the simplest possible 48V DC PSU using 4x12v batteries?

This is a two wire preamp and you are asking a 3 wire question. Modification would tend toward a total rebuild because a balanced input is needed for your new mic.

As a suggestion, change the 5532 for a NJM2068- every spec will improve, noise, distortion, and sound quality.