noisy mic pre

[slackdaddy]

Hey All, New guy here,

I have just gotten a UA LA-610 channel strip and when I hook up my condenser mic (AT4040), I get very bad white noise/static. If I turn the phantom power off to the mic, the strip by itself is very quite. I can also leave the phantom power on and disconnect the mic and it is quite. If I turn the phantom power off and use a sm58, there is no noise and it works great. I checked the phantom power with a voltmeter and it was 47.8.

I can use the condenser straight into the recorder and it is fine. I also have a cheap presonus preamp that works fine with the mic. I have tried 3 different cables and moved the mike away from any power sources.

Anyone have a clue? Thanks

[rufus13]

Unplug the UA power from the wall: don't trust switches.

Notice how noise-free the preamp is without power. Silence is not always good.

With a test oscillator or a diode checker (tone) test for continuity from the power ground pin (the round one that goes into the wall) to the shell of the mic input connector (or pin 1 on xlr). Wiggle to hear discontinuity. If it is not continuous, open the box and look at the back of the connector: is the ground lead soldered to the shell/pin1? Is anything else loose? Look and sniff for loose and burned parts.

Is your UA under warrantee? Yes: Clean the connectors with Qtips and alcohol. Get another capacitor mic to verify malfunction. Carefully reinstall panels without damaging screws or gouging panels. Call UA for RMA instructions. Return to UA.

Not under warrantee: Clean the connectors with Qtips and alcohol. Get another capacitor mic to verify malfunction. Call your buddy who graduated from Navy ET school or USAF Ground Radio/PMEL school. Call UA for shipping instructions and cost estimate.

Dynamic mic doesn't care if ground opens sometimes- no P48 to worry about.
P48 capacitor mic's care very much if ground is intermittent.

[slackdaddy]

Hey Rufus,
Thanks for the reply. Since I don't currently own a oscillator or diode checker, can I use a voltmeter on the resistance setting? I don't know how many ohms it should read for good continuity but a zero reading would show a break I assume. Thanks

[carival]

good continuity would be 0 ohms, or very close to it. no or very little resistance.