loud hum :o(

Mad Hamez

unread,

Jan 2, 2003, 6:09:20 AM1/2/03

to

hi
i've got an old seck 12:2 mixer, i use it in my small home studio with
the master outs sent to the line input of a soundblaster live 5.1 card
on my pc.
the desk gives off a low booming hum if i turn the output up the hum
increases until it reaches feedback level and then kills any other
sound :o(
when using headphones to monitor the desk the hum is also present,
however if i use the chanel and master solo buttons the hum vanishes
completly from the monitor headphones output.
i mentioned this to someone and they said something about needing to
replace the capacitors.
please can somone help me asap with any ideas at all.

there is no connection between the pcb and the outer casing if the
desk if that's significant ?

cheers

rich

--
Mad Hamez

"I know I believe in nothing but it is my nothing" -
(Edwards/Wire/Bradfield/Moore)

Jerry G.

unread,

Jan 2, 2003, 11:48:15 AM1/2/03

to

If there is no input in to the unit, and the hum is present, then there
are no external influences on its performance. The only thing it can be
are most likely defective main capacitors, or main decoupler capacitors
in the power supply. Nobody would be able to easily tell you specifics
unless they know your unit by heart and had the exact same symptoms. It
is more expensive to guess and replace defective parts, than to properly
identify them. If you cannot figure this out, and have no experience
with this, you would be safer and best off to take the unit to most any
electronics service centre. The tech should be able to troubleshoot it
to determine the exact defective parts and replace them for you.

--

Greetings,

Jerry Greenberg GLG Technologies GLG
==============================================
WebPage http://www.zoom-one.com
Electronics http://www.zoom-one.com/electron.htm
Instruments http://www.zoom-one.com/glgtech.htm
==============================================
"Mad Hamez" <madh...@blueyonder.co.uk> wrote in message
news:Xns92F7720C717A2ma...@194.117.133.134...

Erik Squires

unread,

Jan 13, 2003, 1:00:10 PM1/13/03

to

Try disconnecting your PC. This is usually (90%) a major source of ground
loop problems for people.

Radio Shack sells a ground loop isolator for cars that will work, and Jensen
Transformers sells the expensive versions.

Good luck,

Erik

"Mad Hamez" <madh...@blueyonder.co.uk> wrote in message
news:Xns92F7720C717A2ma...@194.117.133.134...

Michael R. Kesti

unread,

Jan 13, 2003, 1:09:09 PM1/13/03

to

Erik Squires wrote:

>Try disconnecting your PC. This is usually (90%) a major source of ground
>loop problems for people.
>
>Radio Shack sells a ground loop isolator for cars that will work, and Jensen
>Transformers sells the expensive versions.

Under what conditions do ground loops occur in cars?

--
========================================================================
Michael Kesti | "And like, one and one don't make
| two, one and one make one."
mke...@gv.net | - The Who, Bargain

CJT

unread,

Jan 13, 2003, 1:27:50 PM1/13/03

to

Michael R. Kesti wrote:
> Erik Squires wrote:
>
>
>>Try disconnecting your PC. This is usually (90%) a major source of ground
>>loop problems for people.
>>
>>Radio Shack sells a ground loop isolator for cars that will work, and Jensen
>>Transformers sells the expensive versions.
>
>
> Under what conditions do ground loops occur in cars?
>

DC on a ground loop won't produce hum, so look for something that
impresses AC on the loop -- perhaps an alternating load.

Richard D Pierce

unread,

Jan 13, 2003, 1:49:45 PM1/13/03

to

Yeah, like someone plugging and unplugging a desk lamp, 120
times a second :-)

CJT

unread,

Jan 13, 2003, 7:13:17 PM1/13/03

to

Richard D Pierce wrote:
> In article <3E230528...@prodigy.net>, CJT <chel...@prodigy.net> wrote:
>
>>Michael R. Kesti wrote:
>>
>>>Erik Squires wrote:
>>>
>>>
>>>
>>>>Try disconnecting your PC. This is usually (90%) a major source of ground
>>>>loop problems for people.
>>>>
>>>>Radio Shack sells a ground loop isolator for cars that will work, and Jensen
>>>>Transformers sells the expensive versions.
>>>
>>>
>>>Under what conditions do ground loops occur in cars?
>>>
>>
>>DC on a ground loop won't produce hum, so look for something that
>>impresses AC on the loop -- perhaps an alternating load.
>
>
> Yeah, like someone plugging and unplugging a desk lamp, 120
> times a second :-)
>

I don't have a desk in my car, nor a desk lamp. But if I had, e.g., a
power inverter, I might expect that to present a load with some AC
characteristics.

Todd H.

unread,

Jan 16, 2003, 2:36:04 PM1/16/03

to

"Michael R. Kesti" <mke...@gv.net> writes:
> Erik Squires wrote:
>
> >Try disconnecting your PC. This is usually (90%) a major source of ground
> >loop problems for people.
> >
> >Radio Shack sells a ground loop isolator for cars that will work, and Jensen
> >Transformers sells the expensive versions.
>
> Under what conditions do ground loops occur in cars?

Ground loops can occur in cars because of the common practice of
grounding a device to a body ground that's physically adjacent to
device, yet distant (electrically and physically) from the negative
battery terminal.

Alternator whine can show up in your system because of ground loops,
and it can be a real PITA to eliminate.

--
Todd H.
http://www.toddh.net/