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Noise (buzz) problem.

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Last response: in Home Audio
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May 17, 2005 1:50:07 AM

Archived from groups: rec.audio.tech (More info?)

For the first time in about thirty years, I was running the music at a party
for a medium size group. It was pretty hard to take the Rap but being able
to introduce some blues, jazz and classic rock to a largely younger group
took most of the sting out of playing boom boom er, ah, music. Last time,
many years ago, it was a 10 inch reel to reel, 3 head, 3 motor deck.

Today I am using a Dell laptop computer to run MP3 files into a Peavy
mixer/amplifier. Guys, I know that this combination is not audiophile grade
but the sound is reasonably good except for some noise almost down in the
grass. None of the guests complained but it drove me batty because it
shouldn't be there. Originally, I was using just the standard headphone
output of the Dell into a line input. By the way this functions quite nicely
with my home stereo regardless of power source. The noise disappears when
the Dell is removed from AC power. I figured OK some sort of
interaction/leakage from the Dell's switching supply. To eliminate the
problem I purchased an external Audigy2 NX USB sound card. This card has a
completely separate power supply. No difference, the same noise at the same
relative level.

Precis:

Source: Laptop computer, headphone or external sound card line out

Amp: Peavy mixer/amp line input.

Problem: Low buzz audible when laptop is on AC supply. Buzz can only be
heard in silent or quiet passages. Sounds about 400Hz so I'm assuming it is
the switcher supply. Yes, I could get a big linear supply if I had the
special connector but would like to try to stick with the stock supply if
another solution is possible.

Note: Buzz only occurs when used with the Peavy and not my home receiver
regardless of laptop's pwr source.

Thanks in advance for any suggestions.

Bob H

More about : noise buzz problem

Anonymous
May 17, 2005 7:46:06 AM

Archived from groups: rec.audio.tech (More info?)

In <118itvv8mchr7f5@corp.supernews.com>, on 05/16/05
at 09:50 PM, "Bob_H" <deltad2@yahoo.com> said:

[ ... ]

>Problem: Low buzz audible when laptop is on AC supply. Buzz can only
>be heard in silent or quiet passages. Sounds about 400Hz so I'm
>assuming it is the switcher supply. Yes, I could get a big linear
>supply if I had the special connector but would like to try to stick
>with the stock supply if another solution is possible.

>Note: Buzz only occurs when used with the Peavy and not my home
>receiver regardless of laptop's pwr source.

Computers generally have not so friendly (to audio) grounding. There is
some sort of interaction between the Peavy, the Dell, and the power and
grounding on location.

A "ground isolator" inserted in the signal cable between the Dell and
the Peavy will cure your problem. While the official store bought
breakers are the best idea, sometimes you can push the hum down under
the grass and into the mud by inserting a 10 Ohm resistor into the
shields on the signal cable tying the Dell to the Peavy.

Sometimes those switching power supplies will couple directly into
nearby audio equipment or interconnections. Make sure the power supply
is as far away as possible from anything audio (cables too).

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