huming

dana Murphy · Post by **dana Murphy** » 21 Jan 2000 3:29 pm

I am useing a evans preamp & a lexicon mpx 100. It is in a 4 space rack case I can,t seem to find a place to put the wall wart with out eny hum is there tricks i could use? How do you have yours setuo thanks dana

Jack Stoner · Post by **Jack Stoner** » 21 Jan 2000 3:55 pm

You probably have what is called a "ground loop" hum. It could be the Evans preamp causing it or it could be the Lexicon. Try lifting the AC ground on the Evans preamp, using an AC ground lifting adapter.

That may take care of it. If it doesn't then you'll have to isolate the rack units, using "humfrees" mounting insulators. They're available from Musician's Friend and some music stores.

Kenneth Kotsay · Post by **Kenneth Kotsay** » 21 Jan 2000 5:16 pm

Had the same hum/noise problem with my rack unit,(MACKIE POWER AMP 1400i,PEAVEY PROFEX II, TRANS/TUBEFEX & FURMAN POWER STRIP) I purchased a bag of "HUM FREES" at Mars Music store in Ft. Lauderdale, Florida. These plastic folding tabs isolate all the metal on each unit from the frame of the rack unit. After I installed them, presto no more hum.

Blake Hawkins · Post by **Blake Hawkins** » 23 Jan 2000 2:38 am

Dana, Are you putting the "wall wart" inside the rack case with the equipment?
Is the rig Ok with the wart outside of the rack case?
If so, then the problem is the magnetic field from the wart. The only remedy is to
leave the wart outside the case and to extend
the low voltage cable from it if it is too short.
If it hums with the wart away from the case, then you have a ground loop hum and the previous comments will correct that.
Blake

Jerry Roller · Post by **Jerry Roller** » 24 Jan 2000 7:01 pm

Dana, you need to make certain that the hum is not due to speaker wires coming in close contact with as AC line. Make sure you speaker wires are coming out from the rack in an area opposite where the AC line or lines are coming out.