input level not stable with ecm 8000

[neal]

I’m wondering if anyone else has had this condition when using the ECM 8000 mic and the eurorack ub802 mixer. I can set up the input level to an acceptable level for Rew to work with, and calibrate the sound level to that input level.
This input level will only stay stable for about 2 minutes, and then it will start to spike up the input level enough to change the sound level meter in Rew about 5 db. After the spike the input level will continue to fall all the way off.
Increasing the signal output on the mixer will bring the input level back up but only for a short time again.
If I unplug the mixer unit and let it sit for 10 minutes the input level to Rew will be back to normal only to fall off after a couple of minutes.
The thing is if I loop it with in and out cables the input level to Rew stays stable, so it only varies when the mic is in the circuit.
To try to prove the mic is not the problem I have disconnected the mic from the mixer when the input level falls, but I leave the mixer turned on, I let the mic sit for 10 minutes and plug it back into the mixer and the input level is still not right.
I have taken the cover off the mixer to look for anything obviously wrong and have not found anything.
The mixer acts the same way with the mic in either of the two locations, and the mixer is set up the way Brucek shows in his one post.
I can get repeatable measurements in Rew until the input level falls so I think the mic is working properly.
So this long question is can the mixer be bad even when it is stable when looped with cables?

[brucek]

You've eliminated just about everything. The only thing left might be the +48 volt phantom voltage to run the mic which is common to both mic inputs. Have you jiggled the switch or measured the voltage when the problem occurs.

When you put a meter between pin 1 (ground) and pin 2 (+ve) without the mic plugged in, there would be +48vDC. It will rise slowly when the switch is turned on and drop slowly when the switch is turned off.

brucek

[neal]

Thanks brucek,
I’ll check the voltage tonight, looks like I’ll be buying a new mixer.