Double Bass Ischell, Headway, powered MAS-16 hum problem

[Jim Dombrowski]

I am getting 60 cycle hum with this set-up:
An Ischell contact mic plugged into channel 2 of the Headway EDB-2 mic input with a standard mic cable, and with 18v phantom power to the mic.

I then have a 1/4" patch cable from the Line Out of the Headway into the input of a powered MAS 16.

The Headway is powered by a 18v regulated DC wall-wart.

The hum sometimes goes away if I touch the metal case of the Headway. It does not go away by changing the ground lift switch on the Headway, or by plugging the Headway or powered cab into different outlets.

The hum does not occur if I unplug the mic, or if I plug my Full Circle into channel 1.

Any thoughts or questions would be appreciated

Jim

 

[Ric Vice]

I am getting 60 cycle hum with this set-up:
An Ischell contact mic plugged into channel 2 of the Headway EDB-2 mic input with a standard mic cable, and with 18v phantom power to the mic.

I then have a 1/4" patch cable from the Line Out of the Headway into the input of a powered MAS 16.

The Headway is powered by a 18v regulated DC wall-wart.

The hum sometimes goes away if I touch the metal case of the Headway. It does not go away by changing the ground lift switch on the Headway, or by plugging the Headway or powered cab into different outlets.

The hum does not occur if I unplug the mic, or if I plug my Full Circle into channel 1.

Any thoughts or questions would be appreciated

Jim

Jim,
Have you tried powering up the Headway EDB-2 with batteries to see if the Power Supply is the issue? Probably something to try
Headway had a power supply with a drop in plug. I've had issues with that one disconneting completely.

 

[BobKay]

If the hum stops when you touch something, doesn't that mean there is a faulty ground?

 

[s0707]

I'd suggest trying different cables. It is probably electro-magnetic (EM) noise picked up by the mic cable or the cable from the preamp to the powered cab. The behavior is common in electric bass or electric guitars with poor shielding in the pickup or control cavities. The hum goes away when you touch the metal part because your body grounds the induced signal; voltage is low enough that we don't feel a shock.

EM noise sources are TV's, computer monitors, tube lights, dimmers, wal-wart power supplies.

Here's a video that shows how a Canare star quad cable can shield better with even lower sources of EM noise. My understanding is Mogami cables are also rated very good for this.

 

[Ric Vice]

While I personally use Asterope and Zolla cables, I've never used Canare Star-Quad. Some will say
that their is a break over price point where the more expensive cable isn't necessarialy any better
than standard sheilded cable. Just my take. I guess the jury's out until someone does a blinfold
test conparing the two.