Well, seems I am not so inept at my new hobby as I am cheap. The
problem was a shorting RCA cable that I pulled out of the junk
drawer. Should have known better. I will make up an nice new one
out of shielded cable tomorrow and move on with this.

Thanks all.

--- In diy_audio_tweaks@yahoogroups.com, "sssisskokid"
<alovesupreme@...> wrote:
>
>
>
> Thanks, Larry. But nope. That didn't work. Still a great hum
that
> increases if I place my hand anywhere on the stereo amp metal
cabinet
> or controls etc. etc. I think I will forego the switches and wire
> every decoder to one of six separate output jacks, and physically
> change plugs as needed.
>
> --- In diy_audio_tweaks@yahoogroups.com, Larry Owens <larryo@>
> wrote:
> >
> > Only the unasked question is a poor one.
> >
> > Try eliminating the (6) audio transformers from where they are
> wired
> > in - reconnecting the wires where the transformers used to be.
> Then
> > insert one of the transformers into the lines between the
> aggregating
> > terminal strip and the audio output jack on the left side.
> >
> > Cheers,
> > LarryO
> >
> >
> > At 05:34 PM 5/25/2008, you wrote:
> >
> > >I am not sure if I should be bothering you folks in this group
with
> > >my amateurish audio problems...also, because it is actually part
of
> > >my HO train hobby audio circuitry.
> > >
> > >But if anyone would care to throw in his or her two cents worth.
> > >
> >
>
><http://i168.photobucket.com/albums/u172/dcrane_2007/C.jpg>http://i16
> 8.photobucket.com/albums/u172/dcrane_2007/C.jpg
> > >
> > >What I have made here is a box containing six audio circuits to
> play
> > >the audio out of six HO train sound decoders. These are little 1
W
> > >amplifiers that can be passed through small audio transformers if
> > >desired, to jack into a stereo amp, for example, to provide room
> > >filling audio of the locomotives. (These decoders are used
normally
> > >with up to 4 " speakers as stationary sound devices, or mounted
in
> > >model rail cars.)
> > >
> > >Now, every time I connect an individual decoder via a
transformer
> to
> > >the stereo, things work great.
> > >
> > >However, when I get ambitious and wire them all up as shown in
> > >the sketch, with the DPDT switches to allow me to alternate
> between a
> > >8 ohm internal test speaker and the audio out jack, I get
terrific
> > >hum....which as an amateur I take to be horrible ground loop.
> > >
> > >Note, this hum has nothing to do with the power circuit (not
shown
> in
> > >the sketch) because I didn't even get ot the point of switching
the
> > >track power on.
> > >
> > >I'm sure this will seem like a dunderhead's bit of wiring. But
just
> > >for the record, the hum rises and falls with my placing a hand
on
> the
> > >surface of the DPDT switches, and/or on the metal case of the
> stereo
> > >amplifier.
> > >
> > >Disconnecting the internal speaker from the terminal strips
solved
> > >nothing.
> > >
> > >I imagine I have created a ridiculous bit of circuitry. Back to
the
> > >drawing board.
> > >
> > >I may just have to create six individual little boxes and jack
them
> > >in and out as needed instead of trying have all the decoders in
one
> > >locaction "ganged" up on the terminal strips.
> > >
> > >I thought I had isolated everything. Did I use the wrong
switches
> or
> > >wire them incorrectly? They are center off. I have the decoder
> > >audio leads to the center tabs. Connections to the internal
speaker
> > >via a terminal block on two bottom tabs, and connections to the
> input
> > >of the audio transformers on the top two tabs.
> > >
> > >You see, this post is in a way, one about improving home audio.
> >
>