FWIW, I've had trouble in the past with noise on the line-outs, on
both a desktop and a laptop, and in both cases it was cured (to an
acceptable degree) by wiring a common mode choke in series with the
line out - I used a 4-winding 4.7mH unit (50c from a disposals shop).
Split into separate left and right pairs, then immediately take all 4
wires through the choke, then through unbalanced shielded cable to the
amp. Of course that won't help if the noise is actually inside the PC,
but don't assume it just because it's a compact PC - the proximity can
equally well cause ground issues that DO respond to a common mode
choke.

I also had one case where a serial out from the PC to an external Midi
synth (in "Host" mode, where it accepts serial data at 38.4kb/s)
caused noise in the audio system even when nothing was happening. this
was cured by a similar common mode choke in the serial port cable.

On Mon, 29 Nov 2004 09:52:28 -0500, "Arny Krueger"
wrote:

"Anthony James" wrote in message
. com
"james" wrote in message
...
OK, I asked a previous question earlier about whether I can connect
3.5mm minijack output on my PC soundcard to my hi-fi speaker.

There's nothing to stop you taking the audio line-out from a sound
card and putting it into one of the inputs on your hi-fi amplifier.

However, PCs tend to be very 'noisy' inside and you may notice a lot
of pops and whistles as other activity in the PC interferes with the
sound outputs.

It is true that activity inside a PC can cause noises in the sound, but its
not always true that using an external interface makes those noises go away.
For example, noise due to video card bus domination can affect external
audio interfaces just as easily as internal ones.

History shows that one of the first external digital audio interfaces, the
Zefiro was highly susceptable to noises due to PC operation and design.

Some people seem to think that the digital noise inside a PC is exceptional.
In fact virtually every hi fi DAC and CD player has the same noise running
around inside it. Particularly the CD player has at least one motor and a
3-D actuator mechanism. Most have a motorized tray. They almost all are full
of TTL signals with fast rise and fall times. Some even have switching power
supplies. What makes the CD player quiet sonically is not the absence of
sources of interference, but rather the care taken to avoid contamination of
its audio outputs.

It is the care taken to avoid contamination of audio outputs that makes a PC
quiet or noisy, sonically. One way to obtain this care is to upgrade to a
better audio interface, whether internal or external.

It is a false claim that putting common line-level audio circuitry inside or
outside the PC case necessarily makes an audible difference.

I'm just about to move to an external USB sound card
to get rid of this.

Depending, depending this might make things better or worse. Choose your
interface carefully, but don't choose it for sound quality based on where
the circuitry is mounted.

Tony (remove the "_" to reply by email)