Hum when used with profexII

JOZEF SMITH · Post by **JOZEF SMITH** » 19 Apr 2000 10:32 pm

I am using a profexII and Peavey Nashville 400 amp and I can't get rid of the hum unless I turn the volume way down. I tried using seperate outlets, various in and output levels of the ProfexII, using 2 prong plugs instead of 3 prongs, moving the Profex away from the amp but none of them works.
It does not make any difference what amp I use.But there is no hum when used with battery operated e.g delay etc. Do those hum eliminators work? Recommendations anybody?
Thanks,
Joe
jsmith1378@aol.com

Joseph Barcus · Post by **Joseph Barcus** » 20 Apr 2000 2:31 am

if your hooking it to the front of the amp the trouble is there, u need to hook it to the back of the amp. joe

Jack Stoner · Post by **Jack Stoner** » 20 Apr 2000 2:40 am

You're problem, as described, is typical of a "ground loop hum" problem. Make sure all of your guitar cords are good and then try the ground lifting plug (3 to to 2 prong adapter) again on the amplifier.

You're description of working fine with battery operated effects but not with the AC powered unit also goes along with symptoms of a ground loop hum problem.

Is the Profex II in a rack by itself (or not in a rack)? or is it in a rack with some other equipment?? Many times the hum is caused by more than one piece of AC power operated equipment in a rack.

Sam Marshall · Post by **Sam Marshall** » 20 Apr 2000 4:21 am

The front panel effects send on the Nashville 400 is not a balanced differential feed. It is the wiper (unbuffered) of the first gain pot. This is the cause of your hum as there is too high an effective output impedance and no means to buck the hum out on the send side. I have found ground lifting your effects unit is the best way to go.

By the way, using a transformer (another common method) to break the ground loop is useless when applied to the Nashvilee 400. The high effective output impedance really screws up your tone!

Sam in AZ

Kenny Forbess · Post by **Kenny Forbess** » 20 Apr 2000 4:56 am

Might try moving the profex away from the p/u as to the other end of the guitar, helped mine alots.
mine sounded like a ground loop hum also.
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Kenny pf
Derby D-10 8&6
66 Emmons D-10 8&7

[This message was edited by KENNY FORBESS on 20 April 2000 at 05:57 AM.]

Tony Palmer · Post by **Tony Palmer** » 20 Apr 2000 6:59 am

Mine was in a case with the wall wart transformer plugged in a power strip.
I found the proximity of the transformer to the ProFex caused a hum and was reduced when I moved it away.

Sam Marshall · Post by **Sam Marshall** » 20 Apr 2000 3:52 pm

Sounds like the wall wort was magnetically coupling into the profex. Was it coupling into the input?? Power Transformer?? The wall-wort was probably some switching-type supply.

Anybody else looked at a copy of Yamaha's "Sound Reinforcement Handbook?" It has stuff about the use of differential amplifiers and audio signal transformers and how they break ground loops.

Sam in AZ

[This message was edited by Sam Marshall on 20 April 2000 at 04:58 PM.]

JOZEF SMITH · Post by **JOZEF SMITH** » 20 Apr 2000 10:38 pm

Thanks gents for all the input.
My Profex and Korg DTR-2 tuner are on a rack and they are plug into the same outlet box. I do know that when I turn on my Tuner that the hum gets louder, but I turn off the tuner
after tuning the PSG. I will try all the suggestions that you all have given me.
How about those hum eliminators that I have seen advertise, are they any good?
Thanks again.
Joe.

Jack Stoner · Post by **Jack Stoner** » 21 Apr 2000 2:37 am

Now we get to the bottom of this. Several people that have reported hum problems here on the forum had a rack with a Korg tuner in it. That's probably the culprit. The "humfrees" isolation tabs will work to minimize the ground loop hum problems between units in a rack.

Keith Hilton · Post by **Keith Hilton** » 25 Apr 2000 2:57 pm

Jack you are correct as usual. When the different cases in a rack touch, each has a different ground potential. The reason each has a different ground potential is because each has it's own power supply. Manufacturers must ground the case to prevent noise coming in. The problem occurs when one case touches the other case. Each case has a different ground potential.

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JOZEF SMITH · Post by **JOZEF SMITH** » 25 Apr 2000 11:39 pm

The rack I have, is made out of wood and the Profex and tuner cases do not touch each other. I made a real nice plywood case for these 2 units with a 115 VAC outlet and 1/4"
jack going to the amp. The cover in the open position will also function as a tray for your bar, picks etc. It measures 20"x15"x5"
with reinforced aluminum corners and brass locks and handle. I think that having the transformer and the AC connection inside the case is causing the problem. It hums with and without the tuner connected or on.
Again Thanks for your input gents.
Regards,
Joe.

Dag Wolf · Post by **Dag Wolf** » 26 Apr 2000 1:30 am

Jozef, I think you`ve solved the problem. I need to take the powersupply for the profex out of my flight case to avoid hum. I can not have it mounted inside my 3 units flight case.

Dag

Jack Stoner · Post by **Jack Stoner** » 26 Apr 2000 1:52 am

How about the rails? How do you have them mounted (screwed in) to the case??

Keith Hilton · Post by **Keith Hilton** » 26 Apr 2000 7:02 am

If the transformers were inside the case, that can cause trouble sometimes. Another thing, keep the Pro-Fex and all other units away from your pickups. Good luck!

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JOZEF SMITH · Post by **JOZEF SMITH** » 26 Apr 2000 9:50 pm

Jack,
Yes, the rails are screwed onto the case with wood screws. I have made some pictures of it and I'll show them to you as soon as I know how to attach them to my message.
Joe.

Kenneth Kotsay · Post by **Kenneth Kotsay** » 30 Apr 2000 1:32 pm

I had the same problem with my rack unit lots of hum: PROFEX II, TRANSTUBEFEX, KORG DT-1, FURMAN POWER OUTLET. I went out & purchased "HUM FREES" little black plastic folding tabs that mount between the metal part of the rack unit (rail) and each of the above units ( 4 for each effects unit). When I got finished, presto, no more hum.Most music stores carry these plastic tabs.

WWJD