[Date Prev][Date Next] [Thread Prev][Thread Next] [Date Index] [Thread Index]

RE: OT question about sound cards/chip-sets and high-end musicsystems

Paul E Condon wrote:

> long adapter cable (>~100ft). The cable would be carrying analog

Unbalanced signals, such as might be found on computer sound card 1/8"
TRS jacks and audio equipment RCA jacks, are susceptible to common-mode
noise and ground loops.  If your computer sound card line out jack and
your pre-amplifier/ receiver line input jacks are grounded to your
electrical power distribution system, directly or indirectly (e.g.
3-prong power cable to anything connected to either), connecting your
computer to your audio gear will create a large single-turn transformer
with your equipment and house as the core.  Induced currents would
result in common-mode noise; you might hear your electrical appliances
through your audio system.  (I was able to hear my refrigerator
switching on and off in one apartment; I can see my garbage disposal
operating in my current house.)  Electrical system ground faults, arc
welding, etc., could damage your audio gear and/or computer.

Balanced signals are designed to reject common-mode noise.  I've sent
line-level public address signals from a mixer to a series of amplified
loudspeakers using ~800 ft. of XLR cables with no perceived loss in

Isolation transformers can connect balanced and/or unbalanced systems,
and break ground loops.  (Good direct boxes incorporate a transformer
and include a "ground lift" switch.)

The fast, cheap answer is to buy 100+ ft. of twisted, shielded pair
(TSP) cable, run it, make up the ends, and take a listen.  Adding load
resistors at the audio end might reduce common-mode noise (observe sound
card line out load impedance specifications).  If it sounds okay, tape/
staple down the cable and you're done.

Two 100+ ft. cables would give you less cross talk.

Two isolation transformers/ direct boxes and two cables would be a
reasonable best effort.

That said, I still think you'd be better off with an HTPC (with wireless



Reply to: