Neumann M49 noisy?

Hey there,

I think the M49 in our studio is getting a little noisy, but I'm not sure. If you happen to have one... Would anyone on here be kind enough to measure the self noise of your M49?

We're thinking about getting a Flea power supply to try and reduce the noise. Currently we are still using the original. When we were at Air Studios the other day, we noticed they had replaced all their old vintage power supplies.

Real M49 or clone?  Have a scope?  Look for noise and hum on the DC outputs going to the mic...be careful on the HT...use ac (capacitor blocking) so dc voltage isn't on front end of scope preamp...Make certain the heater voltage for the tube is correct...especially if the mic uses a AC701...the HT is a little more forgiving but the heater voltage MUST be correct at 4.00 volts for a AC701.

Selenium rectifiers go bad...electrolytic caps go bad...the stabilytes go bad...I use AA size rechargeables for the stabilytes (with low ohm series resistor)... Spend a little time with the scope and you should find the noise problem (if it is the power supply).  Some of the supplies used a 150B2 tube regulator for the HT.  If you don't mind a wiring change on the 150B2 socket, the American OA2 works fine.  (150B2 tubes can still be obtained if you want to keep the supply original.)

For a real M49, Peter Drafahl in Germany makes a nice power supply if you don't want to fix the originals... I have one of his supplies on a Schoeps M221 and it works fine...

Will investigate all this! Thank you!

Would you be able to send me the contact detail for Peter Drafahl too please?

A real M49 by the way...

bobober said:

Will investigate all this! Thank you!

Would you be able to send me the contact detail for Peter Drafahl too please?

Click to expand...

Contact Peter Drefahl at www.drefahlaudio.com or www.mikrofonservice.de..
I have one of his D221 supplies for a Scheops M221 mic using the AC701.
You will want his D221-R supply that has the remote pattern switching.

His power supply uses a toroidal transformer, clean regulated HT, and the LV is brought up slowly for the AC701 heater...  The toroidal transformer can be strapped either for 110 or 220 v primary..

Check with Peter and make certain the dual voltage primary is still available on his supplies...  I recall his instructions were to unsolder one wire at the fuse holder and tape the end, and solder the other wire to the fuse holder for US 110 v operation...and MARK the supply for 110 volts so it doesn't accidentally get plugged into 220 volt European by mistake...