Audio noise when using AC adapter

[Rob Wilson]

Anyone experience significant AC hum when using the AC adapter instead of a battery on your GL2? I was using it to record some track with a Rode K2 mic though a XLR adapter. Tried the ground lift switch on the adapter and it was MUCH worse. Just my camera/setup or???

[Ales Marlin]

Hi,

I noticed similar problem with my GL1. If it is powered via AC adapter, hum appears in sound if a person holds the mic ih his/her hand. If mic is mounted on boom or placed on table, there is no audio noise. But as soon as one directly touches the mic, hum appears. I tested with two different mics, an "el cheapo" Sony and an AT ATR55 Shotgun mic. However, these are not XLR mics.

[Tom Elliott]

Originally Posted by Ales Marlin

Hi,

I noticed similar problem with my GL1. If it is powered via AC adapter, hum appears in sound if a person holds the mic ih his/her hand. If mic is mounted on boom or placed on table, there is no audio noise. But as soon as one directly touches the mic, hum appears. I tested with two different mics, an "el cheapo" Sony and an AT ATR55 Shotgun mic. However, these are not XLR mics.

From what I understand all 60cycle hum is produced when a "ground loop" is created.
I just got a new sound board, new mikes, xlr balanced cabels AND 10 gauge extstension cords, three prong MOULDED plugs, am carefull not to have mike cables cross, run paralell or loop which causes more problems. THUS I got really clean sound NO with no hum. Now if I eventually do get a hum, I will get a seperate battery, the big ones one uses for storm outages etc, that will last 8 or more hours.
Upgrading to balanced xlrs, 10 gage extensions seem to solve the problem.
Tom

[Rob Wilson]

Tom,

Agree, I've found and isolated ground loops in the past as well as hum from mic cables laying over 120VAC cords. In this case, all the cables were kept away from each other ( and I tryed moving them closer to see if it increased the noise. No effect). I used the ground/lift switch on both the xlr adapter and the mic pre in all possible configurations. Anything but ground on both made it worse. Also made sure the mic pre and the GL2 AC adpater were plugged into the same circuit. Guess I'll just stick with the battery.

[Greg Boston]

Originally Posted by Rob Wilson

Tom,

Agree, I've found and isolated ground loops in the past as well as hum from mic cables laying over 120VAC cords. In this case, all the cables were kept away from each other ( and I tryed moving them closer to see if it increased the noise. No effect). I used the ground/lift switch on both the xlr adapter and the mic pre in all possible configurations. Anything but ground on both made it worse. Also made sure the mic pre and the GL2 AC adpater were plugged into the same circuit. Guess I'll just stick with the battery.

60 cycle hum can be the result of a ground loop or by induction (cables close together, poor shielding). However Rob you might also have a faulty AC adaptor with an open capacitor so you're not getting as pure DC as you should. If you have the opportunity to try another adaptor, do so. All the other steps you've taken should have eliminated the hum if it was ground loop or induction. The only thing left is poor filtering of the power supply.

-gb-

[Tom Elliott]

100% battery AND/OR shielded cables both in mikes and power. Much more expensive, but not as expensive as a reshoot or lost clients. Notice just how thick the power cables and support cables are used by any of the national broadcasting companies and film companies use when they are on location?? Some are as big around as your wrist!!
My new board (Soundcraft 8), shielded mike xlr cables and new mikes, and new 10 gauge power cable cost me about $1200 USD, but it sure was worth it.
Tom