[1000mp] isolation transformers and SuperCable

[Tom Rauch]

> Bill, typical audio isolation transformers (e.g. Stancor TTPC) have
> less than 2dB of loss.  I've never noticed any loss in level when
> using Stancor or Radio Shack transformers between the MP's rear audio
> connectors and various SoundBlaster cards.

My station is full of isolation transformers on the headphone lines, 
since I have multiple receivers and transceivers and an audio buss 
that ties any audio output to any listening position. Even a 4 inch 
wide thick copper flashing is NOT low enough ground resistance to 
prevent audio hum from ground loops. Without the audio transformers I 
can even hear the hum from my tower lights blinking in the 
headphones, and see it on the computer spectrum display or hear it 
when I play back digital recordings. All of this in spite of the fact 
my station is very well grounded.     

Because of that, my sound card has additional isolation transformers. 
They are mounted on a PC board hanging from the soundcard aux input 
plug on the computer. That way I NEVER need to ground a shield at 
both ends. As someone else pointed out, grounding the shield of an 
audio line at both ends is just begging for problems.

I use transformers from Mouser, and loss in them is negligible. 

By the way, some symptoms that appear to be RF ingress are really not 
due to RF. They are actually from power supply currents that vary at 
an audio rate as the current in the PA stages changes, as that 
current causes a drop across audio cables that are grounded at both 
ends.73, Tom W8JI
W8JI@contesting.com