Hum in bass amp when line out to Digi 001

justinmc · Post by **justinmc** » Mon Jun 25, 2007 8:21 am

My late 70's Ampeg V4B has a couple of "Ext Amp" jacks on it, which are line outs for feeds to other amps, DI, etc. When I plug it into my Digi 001, I get a loud hum out of my bass amp. If I send the line to a mixer instead, no hum. Any ideas?

Thanks!

Johnny B · Post by **Johnny B** » Mon Jun 25, 2007 6:12 pm

Where's everything plugged in?

justinmc · Post by **justinmc** » Mon Jun 25, 2007 6:31 pm

Front of Digi 001, channel 2, no phantom power on

thanks...

apropos of nothing · Post by **apropos of nothing** » Mon Jun 25, 2007 8:25 pm

Are they on the same electrical circuit?

justinmc · Post by **justinmc** » Mon Jun 25, 2007 8:32 pm

yep, same circuit; the electrical is all updated and three-wire grounded.

I just tried it with another amp's line out and got the exact same thing: loud buzz. So it's not the ampeg's fault...

Haven't had any other problems with this digi 001

I should note that the buzz volume is independent of the amps' volume setting, and only occurs when the amps are off standby (of course)

Johnny B · Post by **Johnny B** » Tue Jun 26, 2007 11:06 am

What's the mixer? Are you plugging into an unbalanced input on the mixer? The 001 are balanced, correct? Are you using TS or TRS cables? I'm thinking it could be a balanced/unbalanced issue, but if the mixer inputs are balanced as well, then it's probably something else... You've tried flipping the ground switch on the amps? Have the outlets been tested?

Also, if it's ok going into the mixer, couldn't you just run it through the mixer?

justinmc · Post by **justinmc** » Tue Jun 26, 2007 11:18 am

I'm using 1/4" plug guitar cables for all these connections.
As I understand it, the digi 001 should be able to take unbalanced connections in the front two inputs.

If I go amp>mixer>digi, I get the hum in the amp - whatever it is, travels right through the mixer.
If I go amp>mixer, there's no hum.

Both digi front inputs act the same in this way

Thanks!

Brett Siler · Post by **Brett Siler** » Tue Jun 26, 2007 5:11 pm

This happened with me before with a Mesa head once. I was in the middle of a session and couldn't figure it out quickly so we just used a Marshall head with a line out and it did not hum...

justinmc · Post by **justinmc** » Wed Jun 27, 2007 9:18 am

Thanks for the 101 lessons y'all; It's a polarity issue. Neither amp has a polarity switch, so I flipped a 3>2 adapter over yesterday and tried it out - works, no hum.
Now I just need to find some polarity reversing 3 prong adapters.

Ampeg had the polarity switch in earlier '70's V4-B models, but not mine; I wonder why.

justinmc · Post by **justinmc** » Wed Jun 27, 2007 11:02 pm

EDIT: I'm going to try out the Ebtech Hum X and Hum Eliminator... I'll post results

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Actually, I'm not sure what to do about this! I don't think that I want to flip the polarity on the whole amp, because as it stands I don't have other problems with the PA & amp, this amp & other amps, etc, and I don't want to worry about mixing that up.

What I think I need to do is flip the polarity in the 1/4" going from the amp to the digi 001. I've searched around a bit but can't figure out the simplest way to do this. The most exotic thing I have in my quiver is have five(!) XLR/Lo-Z to 1/4"/Hi-Z adapters...

Thanks for any help!

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Hum in bass amp when line out to Digi 001

Hum in bass amp when line out to Digi 001

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