ccrse@ucdavis.UUCP (Steve Ehrhardt) (07/22/85)
In a previous article, someone indicated that the arrows on some high-end interconnect cables may be related to a wiring scheme designed to reduce problems with ground loops. Can anyone tell me for certain if this is true? If it is true, how exactly are they wired to achieve this goal? My reason for asking is that I have a Hafler 200 amp with what I *believe* to be a ground loop problem. The amp is completely quiet as long as only one input channel is connected to a source, but starts to hum slightly as soon as both are connected to the same source. This seems to happen regardless of the source (or cables) used. This problem has been getting on my nerves for some time, and I would appreciate any advice on how to solve it. If the aforementioned cable scheme exists, it might be an ideal (cheap) solution, but I'm open to other suggestions. appreciate any advice on how to solve it. (Please don't recommend that I take it to a shop to be repaired - if I could afford that, I wouldn't be asking this now!) If the aforementioned cable scheme exists, that
ark@alice.UUCP (Andrew Koenig) (07/24/85)
> My reason for asking is that I have a Hafler 200 amp with what I *believe* > to be a ground loop problem. The amp is completely quiet as long as only > one input channel is connected to a source, but starts to hum slightly > as soon as both are connected to the same source. This seems to happen > regardless of the source (or cables) used. Try disconnecting the shield of one, but not both, of your connecting cables. If this makes the problem go away, it was a ground loop and you have fixed it. If not, it's probably something else.
rfg@hound.UUCP (R.GRANTGES) (07/24/85)
[]
It's very easy to do it yourself and all you risk is one audio patch
cord (even I can afford that). To see if this is your problem, take one
of the interconnecting shielded cables (the one which when you connect
it, the amp hums). Examine the area where the connector joins the cable
at the end away from the amp (the other end, the preamp end). With a razor
or other sharp object carefully cut away the outside cover <and> the shield
wire, leaving unsisturbed the inner conductor and the insulating material aroundit. You may wish to wrap the operation site with some insulating tape to keep
the shield from unraveling further and provide some more mechanical
protection. Now plug the cable back in. If the hum stops you have your
answer. I will try to draw the cable as it should look when you are finished:
- -----------------------------------------
/ \
ooooo--------------------------------------------oooooo
\ /
- -----------------------------------------
^
Shield
interrupted
here
Preamp end of cable Amp end of cable
What perhaps you should do is treat both cables from amp to preamp
this way and provide a seperate ground wire return path via a fairly
heavy wire. Real purists will make all interconnects this way - single
ground wire. Big danger is that if that ground wire should come loose,
you have one fine lot of hum from your speakers (just before they
vaporize).
Good luck!
Dick Grantges hound!rfg
--
"It's the thought, if any, that counts!" Dick Grantges hound!rfgsjc@angband.UUCP (Steve Correll) (07/26/85)
> My reason for asking is that I have a Hafler 200 amp with what I *believe* > to be a ground loop problem. The amp is completely quiet as long as only > one input channel is connected to a source, but starts to hum slightly > as soon as both are connected to the same source. This seems to happen > regardless of the source (or cables) used. This does sound like a classic ground-loop problem. If you're willing to sacrifice one cable to try to fix it, cut off the connector from one end of the cable, then solder it back--but connect only the center lead, not the concentric outer shield. (It's often reasonable to disconnect one end of the shield of an ordinary unbalanced two conductor audio cable--that is, a cable which has an inner signal wire plus an outer, concentric shield. Since we normally connect two audio cables--one for the left channel and the other for the right--between each pair of components, we are actually providing a superfluous ground. My old AR turntable is designed this way; only one cable has its shield connected to the phono plug at the preamp end, but both have their shields connected to the turntable's ground.) -- --Steve Correll sjc@s1-b.ARPA, ...!decvax!decwrl!mordor!sjc, or ...!ucbvax!dual!mordor!sjc