Hum Problem

Lee Baucum · From: McAllen, Texas (Extreme South) The Final Frontier

At church, I play a Martin acoustic guitar, which has a McIntyre Feather pickup installed inside. From the guitar I go to a Baggs pre-amp and from that, out to a Crate acoustic guitar amp. The amp has a low-z output on the back, which is connected to the p.a. system. This rig produces a low frequency hum in the p.a. I don't hear it in the amp, though. I can touch a metal jacket on either of the two cords, or even touch the metal case on the Baggs pre-amp, and the hum goes away. Sounds like a ground problem, right? How do I get rid of it? And why is the hum in the p.a. and not in the amp?

Since this isn't steel guitar related, perhaps it would be best to respond by e-mail.

Thanks.

Lee, from South Texas

Michael Hartz · From: Decorah, Iowa, USA

You can try a hum eliminator box. You can get these through Musician's Friend or American Music Supply. There are a couple of different brands.

John Daugherty · From: Rolla, Missouri, USA

Are you sure the Lo-Z output is actually Lo-Z ? If it is Lo-Z it will use two wires and a shield and must be wired properly. With a Lo-Z cable run to the PA, there should be no hum unless the hum is also in your amp.
If the output from the amp is a Lo-Z output and you are using the proper cable, try a 3-prong adaptor on the power cord of the preamp and/or the amp, to eliminate ground loops. The amp chassis would still be grounded through the PA.
Also, eliminate the guitar as the hum source by unplugging it from the preamp to see if the hum is still there.

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Ron Randall · From: Dallas, Texas, USA

Lee

I know that Furman has several products that will help. One of their new products is a rack rider that solves all ground lifting problems. There are simpler and more elegant solutions, too.

Ron

Ken Fox · From: Nashville GA USA

I ran into a simliar problem with a commericial installation a few year back. It was a TOA Wireless transmitter. Low-Z output but it was unbalanced! I used a Radio Shack 1:1 audio transformer to to balance the signal and thus eliminate the hum when it was connected to the main PA rack. I used a two wire-mike cable with the shield lifted at the source end but connected at the rack to eliminate ground loop hum.

Lee Baucum · From: McAllen, Texas (Extreme South) The Final Frontier

The amp that I use is a Crate CA60. It has two outputs on the back.

High Z Bal - Use this jack to connect a high impedance, line level signal to a house sound board, by means of a 1/4" stereo plug-terminated cable.

Low Z Bal - Use this jack to connect a low impedance, line level signal to a house sound board by means of an XLR-terminated cable.

I'm using the Low Z Bal output to the board.

This evening, at practice, I tried using a 3 to 2 prong adapter (on the power cord), to see if that would help any. It didn't.

Lee

[This message was edited by Lee Baucum on 20 April 2006 at 08:17 PM.]

Jack Stoner · From: Kansas City, MO

I wonder if it's the XLR cable that you are using? Some have the internal ground jumpered to the XLR connector's ground lug and some do not. My friend Blake Hawkins, who is an Electronics/Broadcast Engineer, told me if the cable ground is connected to the connector it can be a source of hum.

I bought some cheap Musician's Friend XLR cables a while back and all of them had the ground in the cable jumpered to the connectors. I removed that from all of them to avoid any potential problems.

Lee Baucum · From: McAllen, Texas (Extreme South) The Final Frontier

Thanks, Jack. I'll try a new cable and see if that helps.

By the way. When the amp is turned off, there is a HUGE hum produced through the mains. Do you think that is indicative of the same problem?

Lee

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