[paba]

Hi all,

I just connected a Equi=Tech ET1R (1000VA) that is about ~10 years old. It seems to hum. The hum doesn't travel into the signal chain but I can hear it from the unit. It seems to dissapear in the 1-2 sec current inrush when I first turn on my amps but once the current settles it hums. It hums with nothing connected or with everything powered up and running.

Is this the famous DC on the line issue or is it because I'm just not loading the unit enough with my gear?
I looked inside and it is a Piltron transformer, didn't see an capacitors or other parts that could need replacement.

thanks
Paba

[Speedskater]

Have you tried using it in a friends home?
Have you checked for loose nuts and bolts?

Piltron transformers are not supposed to be bothered by a little DC offset.

See:
http://www.idc-online.com/technical_references/pdfs/electrical_engineering/MEASURING_ACOUSTIC_NOISE_EMITTED_BY_POWER.pdf

[satfrat]

From what I'm reading, this humming was an issue with the older transformers used in the early Equitech's and there's not much you're gonna do about it except either live withit or sell it. Equitech eventually changed to their new "Q" series transformer to solve this issue. I really wonder if Equitech was even using Plitron transformers (BPT has always used them) at the time.
 
My suggestion would be to give Equitech a call or email and see what suggestions (if any) they might have or options they might offer you. It's obviously a transformer quality issue for which a transformer replacement would seem to be the only solution.    The fact that you bought it used doesn't really give you much wiggle room with Equitech but it never hurts to explore all your options, especially if you like what the Equitech has to offer your system. 
 
Cheers,
Robin

[Quiet Earth]

Hi paba,

I own two Equitechs, a Q and son of Q. The Q is a 15 amp unit and I can hear it hum in a quiet room when I'm about three feet away from it. Once a whisper of music begins I can't hear it hum anymore.

How close are you sitting to the ET1R? How loud is the hum?

How much AC wattage does your system draw? Are you approaching the 1000 watt limit?

Have you tried to place the ET1R on some footers. Those cheap rubber cork footers can help reduce the hum a little bit. So do Herbies Iso-Cup feet.

[BPT]

Only Equitech "Q" version products use Plitron LONO (low noise) transformers. There other versions do not.
Chris H.

[paba]

Thanks guys,

yeah, it is a Plitron but an older unit before the LONO technology. The sticker is on it.
I tried rubber feet and adding weight to the top but it isn't the case. It hums just the same with the top off. The only thing I didn't try was to add a rubber washer between the bolts holding down the doughnut on both sides.

I agree that I can't hear the hum once the music starts, but the fact that it is so obvious with no music tells my head that it is there even with the music playing.

I'm tempted to build a DC Blocker (diodes and caps) like shown here:
http://sound.westhost.com/articles/xfmr-dc.htm

I sent Equi=Tech an email before my first post, let's see what comes back.

/paba

[jtwrace]

Only Equitech "Q" version products use Plitron LONO (low noise) transformers. There other versions do not.
Chris H.

Do all of your units use the LONO transformer?

[BPT]

Yes.
Chris H.

[paba]

update...

I kept the unit plug to the same wall outlet and instead of my audio system, removed all that, I plugged my 50" plasma and PS3 and watched a few minutes of a movie. Guess what hum is gone or comes and goes depending it seems on the current draw based on how the screen is lit... where as my class A amps always draw the same steading current regardless of volume. Anyway that;s my theory. Turn off the TV and hum comes back.
So , I am thinking this isn't DC offset on the line, it would always be there regardless of current or would it?

/paba

[Speedskater]

I think that  a DC offset would come and go.
The most likely causes are:
a] Home appliances with heating elements when operating at less than full power.
b] Large machines in nearby buildings.  I read about a broken welding machine and it had a circuit to compensate for the defective parts, so the welder didn't know it was broken. In a mountain town center, they installed a ski lift to take people up to the ski area.  The lifts new DC motor drive messed up electricity for the entire town.
c] SMPS (Switch Mode Power Supply) that are in PC's and now many other types of equipment.  But each unit marches to a different drummer, so they add or subtract from each other minute by minute.

Most of the above don't operate 24 hours a day 7 days a week,  so the DC offset should very.

Did you read the Piltron white paper?  They suggest other  transformer problems than DC offset.