Measurement MIC preamp and level control buffer

[oneoldude]

Hi guys,

I hope I am in the right place. If not, please direct me. So, here goes.

I am sorry I am not yet allowed to post URLs so that will make this a bit more difficult.

I mess with home built speakers and measure them and I like to experiment and build projects. I thot it would be fun to try a mic system that had an internal pre at the mic and a buffer/gain stage with level control at the computer and the ability to swap out the mic capsules. Looked around and found Niant Microphones site. Check out the X-R version. It is ideal.

On that site they publish a pre that can be built in an XLR plug. It is what they call the basic circuit. It is under About/Microphone Design. Look for basic circuit. Here is a pic Pretty simple and very small with no special requirements. Nice!

Now what I need is a simple circuit that can take the balanced out from the pre, supply phantom power to the ECM, convert the mic signal to unbalanced for my computer line-in (I need to go to line-in for my analytical software) and have a level control as well. I am pretty sure that can all be done with one op amp in a bitty box near the computer.

I will not be recording, only measuring. Can anyone point me to a circuit that will do the buffer/amp/level control job? Got one handy?

And, no, I do not want to use a mixer, etc. I have one for my Behringer 8000 and want to make up a simple buffer/amp/level control as a project. Suggestions?

BTW, the Panasonic WM-64P might be an ideal ECM to experiment with. Sorry you will have to look it up. But is sure looks flat and the FR should extend flat to below 20 Hz. And they can be bot real cheap on eBay. 10 for five bucks. Cheap enough? Search for WM 64P on eBay.

I already bot some so can someone help me out?

Thanks

 

[tubegeek]

The issue with ECM's is that they don't really want PHANTOM power, but they do want POWER.

The ECM needs to see a voltage difference between pin 2 and 3 (usually it's: pin 2 positive compared to pin 3, by more than 1.5V and less than 10V, or at least, I have had a problem when supplying +15 that went away when I took the +15 and regulated it down to about +8.)

There are circuits that will convert the phantom (pins 2 and 3 both positive 48V compared to pin 1) into a polarizing voltage and - if I am reading it correctly - that is exactly what you have in your diagram. The FET will add some gain, and the Zener will put the polarizing voltage onto the electret. The two 7.5K resistors will balance your impedance to ground so you should be all set for a balanced, phantom-powered, mic-level input with the circuit you show.

If you only want to connect that mic to an unbalanced input and supply power to it externally, it can be done with a 9V battery and a couple of caps: look up "tape op mic" for a method that requires about 10 cents worth of parts and works quite well. Also look up "plug in power" for a similar type of circuit.

 

[oneoldude]

Thank you, Did the search, found nothing useful.

Kind'a looks like I am in the wrong place.

Can anyone suggest a forum better suited to design and construction of mic equipment?

Thanks

 

[Steenamaroo]

There are a few guys around here who know their stuff, but they're probably the minority.

GroupDIY has a section called 'The Drawing Board' where there's a lot of project designs and that kind of thing.

 

[oneoldude]

Thanks loads - I will try over there.