The Steel Guitar Forum

I run my CD player, laptop w/Biab, to a small Radio Shack mixer and then out thru NV 400. This set up worked fine until I got a new laptop and now I get a loud hum when the computer is plugged in. The CD player still works fine. My amp set up is actually transtubefex to power in on the back of NV 400 (thus by passing pre amp on NV 400).

Sonny,
What you have is a ground loop. This often occurs when you have more than one device with a grounded (3-wire) plug in your signal chain. For example, using 2 amplifiers can cause this problem.

There are two solutions:
1. Get an EBTech Hum Eliminator (an isolation transformer -- costs about $50 for the 2-channel version from Musician's Friend). Plug it into the last point in the chain before the amplifier (output to amp; input from the mixer). There is no risk of electrical shock or damage with this solution.
2. Lift the ground on one or more of the components using a '3 to 2' connector that removes the ground on some (but not ALL) of the components. There MAY BE a risk of electrical shock or component damage with this solution, but it is MUCH CHEAPER.

Hope this helps.

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<small>Larry Bell - email: larry@larrybell.org - gigs - Home Page
2003 Fessenden S/D-12 8x8, 1969 Emmons S-12 6x6, 1971 Dobro, Standel and Peavey Amps

Larry is right on the money. I have practically the same setup. I had a similar problem with hum and ended up using a '3 to 2' power adapter on my Carvin amp. The hum went away.

I use a Eurorack 602A mixer and it seems to induce "hiss" into the system, probably due to the gain it provides. Anyone have a solution for removing hiss?

John,
Tips for reducing hiss:
1. Make sure all unused inputs are turned all the way down. This applies to Aux returns, two track returns, etc.
2. Make sure all of your gain structures are set to maximum S/N ratio....input gain trims are only set high enough to get best signal-in other words, make sure all inputs are set to their maximum output available before hitting the inputs of the mixer.
3. "Reverse" set the gain....set your master output faders at 0dB, then set each input channel fader of the channels being used to 0 dB, THEN set the input trim. Remember step 1 in this step...
4. Always start with all EQ centered, the high boost EQ will add substantial hiss to a track...along the same lines, make sure you're not boosting highs on an instrument containing no highs-like base, etc. Remember-cutting is ALWAYS better than boosting...cut all freq's EXCEPT the ones you want to emphasize.
5. Make sure that the output from the mixer is the right level for the power amp (-10dB or +4 dB)
6. If a turntable is connected to the mixer, make sure the ground wire is connected to a ground point on the mixer.

I hope this helps

Jay

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<font size="1"><img align=right src="http://www.scaryoak.com/images/SOP_Tree1.GIF" width="200 height="240"><B>
J.L. Fagerlie</B> - email: jayster@scaryoak.com - website -
1963 Fender 1000, 1955 Magnatone Maestro T-8, 1947 National Grand Console D-8 ,1948 Gibson BR-9,‘60’s Melobar Acoustic

Hi Sonny….

I am also using my lap top to mix a BiaB file with steel and plugging into a Nash 400. I also experienced a 60 cycle hum, even with head phones plugged into the lap top. What I did to remedy this problem was to go into the computers master volume audio and balance settings. Check the mute button under CD audio. This will stop the interference.

Rob ...

make sure all devices are plugged into SAME outlet, my hum went away

IS THIS FORUM GREAT OR WHAT,,,,,,,Thanks Larry and all you guys!!! I got a Ground Loop isolator from Radio Shack and plugged everything into the same surge protector power strip and it all works great! Thanks a million.