Ground Loop Isolator

[Graham Doggett]

Like many guys, my hifi set up is a compromise of home theatre and stereo.
I have a Denon AVR and Denon DVD providing home theatre duties, and my Thorens TD160 and Project Phonobox SE providing amazingly good stereo through my modified Jaycar Hybrid Amp. I simply connect either system to my speakers using jackplugs. Crude but effective !!
The other day I decided to also feed the DVD/CD to my Jaycar amp from the RCA outputs as an option when listening to CDs, but discovered it produced a ground loop hum.
Investigations proved the loop was via the RBG ground shields into the TV and to ground via the TV earth in the power plug.
Bugger !!!!
Googling suggested using a Ground Loop Isolator in the leads from the DVD/CD to the amp to break this loop circuit but warned that it could compromise or degrade the sound.
I discovered Surplustronics had a simple unit for $15 so I figure what the hell give it a go.
Well, either my ears are totally stuffed or this predicted degrading of sound was a load of bollocks.
It works a treat with sound quality just as before and not a hint of hum.
So what I'm eventually getting around to saying is, if you have a ground loop hum that can't be cured by repositioning interconect leads etc,don't hesitate to use one of these isolators.
Another urban myth busted.
Graham.:)

[Owen Young]

That's good Graham.
Traditionally, these devices are transformers, which break signal & ground legs of the connection, but not sure if these Jaycar ones are transformers (heavy?). If so, then signal bandwidth is limited by the TX. Signal transformers within systems, like TVCs, preamp output transformers, etc, effectively do the same...isolate Ground lines.
I see that they are a popular offering for HT systems in USA....hum/noise must be a common problem in these setups.

[Graham Doggett]

Damn, don't you hate it when the pundits were right after all !!!!!
While the isolator certainly completely eliminates the hum, it does slightly attenuate the extreme high and low frequencies.
It's a bit like listening to the mid range speaker with no tweeter or woofer.
A bit more googling indicates that to retain full 20 - 20k range requires quality audio transformers in the isolator with 1 - 10k ohm resistance.
At least the experiment has confirmed that the hum is a ground loop.
Back to the drawing board !!
Graham.:)

[Owen Young]

Actually that may be odd, Graham... those Denon AVR & DVDPs usually have only 2pin plugs with no mains earth. So your hum loop is not going through the mains, right?
This suggest that you have (i)a local hum/ground loop located say in one of your cable connections/connectors...or (ii)picking up hum from a nearby EMF source, eg. transformer.
May have to get on hands & knees & investigate, Sherlock ;)

[moby]

Audio tansformers are very much a "you get what you pay for" issue. Teeny weenie cheapies are subject to core saturation at low frequencies. Other issues are the resonance peak at high frequencies and susceptability to induced magnetic fields (hum) due to poor/no shielding.
A good quality studio grade Jensen transformer can cost well in excess of $200 apiece.

[Graham Doggett]

Hi Owen.
The AVR and DVD player may only have 2 pin power plugs but my Sony TV and the Jaycar amp have 3 pin.
The hum stops if I unplug the RCA leads from DVD player to Jaycar amp, or the 3 RBG leads from DVD player to the TV, so thats where the loop is.
The blurb claimed that the Ground Loop Isolator had 20 - 20k frequency response, but this is clearly not correct. What do you expect for $15 :rolleyes:
The hum is actually only audible if I turn the volume up way past normal listening level ( ie 3 oclock instead of 11oclock) but I find it annoying that it is there.
Makes for an interesting little challenge on a wet and miserable Sunday afternoon.
Graham.:)

[Owen Young]

Try putting the isolator thingie on the red/white audio leads betw DVD & TV (rather than betw DVD & amp). Or unplugging the TV audio cables when playing the DVD/CD (if only to see if that solves the problem).

It doesn't sound too serious as far as hum problems go :)

BTW there should be 3 pin plugs on every device for safety, except for those manuf as 'dble-insulated' products with no Earth pin.

Moby is right, no such thing as a cheap & good audio transformer!