[isw]

In article ,
(Don Pearce) wrote:

On Sun, 05 May 2013 23:04:35 -0700, isw wrote:

In article ,
(Don Pearce) wrote:

On Sun, 5 May 2013 10:26:13 -0700, "Bob F"
wrote:

Don Pearce wrote:
On Sun, 5 May 2013 09:44:40 -0700, "Bob F"
wrote:

The schematic here seems completely wrong to me.
http://www.mcmelectronics.com/conten...Sheets/50-7725
.pd
f

http://canada.newark.com/mcm-custom-...alun-rca-plug-
rj4
5-shield/dp/96K0889

Looks OK to me. It's configured as a series common mode stopper.
What's the problem?

Will this design eliminate ground loop problems? My concept of baluns was
that
they isolated the two ends by placing them on opposite windings of a
transformer. I am no expert, which is why I asked.


That is a different thing. You need a transformer to kill a ground
loop entirely, but yes, provided there is enough inductance in the
coils this will still make a good job of getting rid of hum from a
ground loop.

If there's enough inductance to attenuate 60 (or 50) Hz from the power
line, why won't it do the same for similar frequencies in the desired
signal?


No, because of the way the windings are arranged their inductances
cancel each other out for the audio signal, but not for the induced
hum.

I'd sure like to see (and measure) those inductors. My "spidey sense"
(combined with the fact that they don't bother to spec the CMRR at 50 or
60 Hz.) tells me that they're probably way too physically small for that
to be the case.

The downside of the transformer method is that lower bass response is
usually somewhat compromised.

For any sort of well-designed and properly terminated transformer, the
lower 3dB point will be well below the frequency of any "musical note"
you'll ever want to pass through it. So, no, bass response won't be
compromised at all.

Effects strat becoming apparent well before you hit the 3dB point.

Know anybody who can hear the difference *on actual program material*
between flat to 5 Hz and -3dB at 5 Hz? Because the little thumb-sized
not-at-all-special transformers I use in a homebrew groundloop killer
have that measured characteristic. It's just not hard to find decent
transformers for audio.

Isaac