Mistake on DIY phono cables lead to ground loop with interesting observations... (long!)

Cable Asylum

Interconnects, speaker wire, power cords. Ask the Cable Guys.

Yesterday I made up a continuous wire cartride clips to RCA jacks phono cable (4 foot). I used small gauge teflon insulated silver wire (an unknown now, purchased of eBay about a year ago, about 28 AWG IIRC so not the smallest for the task). From the RCA jack the wires were twisted (lots of twists per inch given the small wire) until the last 16 inches (to the cartridge). The twisted section was covered with plumbers white teflon tape (talk about labor intensive, what a pain!) and then covered with braid shield (salvaged from a piece of coaxial cable... the shield give good coverage when stretched to the small size of the wires. The shield was connected to the RCA ground (i.e. signal ground).
When I first put all together (wire runs external to the arm tube... I like it that way!) I had a pretty bad ground loop hum. Oddly when I separated the two cables physically the hum increased considerably. I decided to twist the two cables together to ensure as much shield to shield contact, which helped, but I still had hum.
Then I recalled that near the exit of the turntable the ground wire was soldered (it had broken in the past) and that when I bundled everything together I must have made (ground cable) contact to the shields! Sure enough I had as I hadn't bothered to cover the fix point with tape.
Consequently I had the turntable ground connected to both signal ground *and* chassis ground. That explain the ground loop. However I still find (with things the way they were) the increase in hum with the two cables separated to be somewhat mysterious. The hun was still present when the chassis ground was disconnected as well.
Anyway, the gound loop is gone, and the cable shields remain twisted... don't know it this is necessary but guess it can't hurt.
Few pics:
One channel completed as an interconnect to allow burn-in. Surprisingly it didn't appear to need much, in fact when put on the tuner I discovered the Blue Jeans/Belden 89259 I had been using was causing some exaggeration of a mildly annoying sibilance problem (on DJ voice)
It wasn't a match for my normal Ear to Ear interconnect, the DIY while not bad flattened the soundstage a little, less rich tonally, and a tad aggresive.
I did about 12 hour burn-in just to be safe.

Finished with the two sides twisted.

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Topic - Mistake on DIY phono cables lead to ground loop with interesting observations... (long!) - bjh 13:57:31 03/04/07 (2)

Two things - Jon Risch 10:07:10 03/05/07 (1)

Re: Two things - bjh 14:22:40 03/05/07 (0)

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