Hum in the sound card, when turned off, (help needed)

[Over G]

bought a new Sound card
(tascam Us144.)

When I turn the computer off I get this annoying endless hum from the
sound card,
no matter what I do.


(since there is no power off swtich in the card the only way to turn
it off is to unplug it.)


how can I remove that sound.???


when I turn o the computer every thing is fine.


it looks like something is stuck in card buffer.

[Richard Amirault]

"Over G" wrote ...
> bought a new Sound card
> (tascam Us144.)

Doesn't look like a "card" to me.

>
> When I turn the computer off I get this annoying endless hum from the
> sound card,

Is the sound (hum) coming from the *card* or coming from your speakers?

> no matter what I do.
> (since there is no power off swtich in the card the only way to turn
> it off is to unplug it.)
> how can I remove that sound.???
> when I turn o the computer every thing is fine.
> it looks like something is stuck in card buffer.

Plug the computer and the "card" into a switched power strip and use the
switch on the power strip to shut down the "card"
--
Richard Amirault, Boston, MA, USA
http://n1jdu.org
http://n1jdu.org/Fandom/science.htm

[Mike Rivers]

On Apr 1, 7:38 pm, "Richard Amirault" > wrote:

> Plug the computer and the "card" into a switched power strip and use the
> switch on the power strip to shut down the "card"

The US-144 is powered from the Firewire bus so it goes on and off with
the computer. There may be some sort of active ground on the USB port
that leaves the ground floating when the computer is turned off. I've
heard of this before but I've never experienced it first hand so I've
never really been able to figure out what's happening.

Basically, there's a ground loop or a shield being lifted somewhere
when the computer is powered off. It needs the help of someone who can
dig into it with a little test equipment and isn't afraid to start
cutting wires (ground wires in the connecting cables, that is). This
isn't likely to be a problem that will be solved by forum discussion,
but we'll have a ball going off topic in about a day.

[Meindert Sprang]

"Mike Rivers" > wrote in message
oups.com...
> On Apr 1, 7:38 pm, "Richard Amirault" > wrote:
>
> > Plug the computer and the "card" into a switched power strip and use the
> > switch on the power strip to shut down the "card"
>
> The US-144 is powered from the Firewire bus so it goes on and off with
> the computer. There may be some sort of active ground on the USB port
> that leaves the ground floating when the computer is turned off. I've
> heard of this before but I've never experienced it first hand so I've
> never really been able to figure out what's happening.

Doesn't necessarily have to be the ground that starts floating. A line
output of a sound interface has a low impedance, but only when it's powered.
The moment you power down any amplifier, the output stage becomes high
impedant. So you end up with a monitor chain input that is plugged into the
sound interface but is not driven, aka an open input. It just depends on
whether there are other passive, low impedant components between signal and
ground or not, how "open" the input becomes.

Meindert

[Meindert Sprang]

"Meindert Sprang" > wrote in message
ll.nl...
> Doesn't necessarily have to be the ground that starts floating. A line
> output of a sound interface has a low impedance, but only when it's
powered.
> The moment you power down any amplifier, the output stage becomes high
> impedant. So you end up with a monitor chain input that is plugged into
the
> sound interface but is not driven, aka an open input. It just depends on
> whether there are other passive, low impedant components between signal
and
> ground or not, how "open" the input becomes.

So a possible solution could be to mount a 1kOhm resistor between each
line-out and ground or, in case of a balanced output, between the hot and
cold signals.

Meindert

[Over G]

On Apr 2, 2:38 am, "Richard Amirault" > wrote:
> "Over G" wrote ...
>
> > bought a new Sound card
> > (tascam Us144.)
>
> Doesn't look like a "card" to me.
>
>
>
> > When I turn the computer off I get this annoying endless hum from the
> > sound card,
>
> Is the sound (hum) coming from the *card* or coming from your speakers?
>
> > no matter what I do.
> > (since there is no power off swtich in the card the only way to turn
> > it off is to unplug it.)
> > how can I remove that sound.???
> > when I turn o the computer every thing is fine.
> > it looks like something is stuck in card buffer.
>
> Plug the computer and the "card" into a switched power strip and use the
> switch on the power strip to shut down the "card"
> --
> Richard Amirault, Boston, MA, USAhttp://n1jdu.orghttp://n1jdu.org/Fandom/science.htm

the hum comes from the speakers.
when I unplug the USB from the card,
the sound is turned off,
(because the electricity is turned off in the Tascam)

it look liks a sound was stuck in the Tascam card (buffer maybe ?),

and there should be a way to clean it somehow,..

[Mike Rivers]

On Apr 2, 1:58 am, "Meindert Sprang" >
wrote:

> Doesn't necessarily have to be the ground that starts floating. A line
> output of a sound interface has a low impedance, but only when it's powered.

Good thought. So the solution is that if it hums with no input, you're
not going to be listening to anything playing out of the interfface
anyway, so turn off the power amplifier or turn down the volume.

[Over G]

On Apr 2, 2:56 pm, "Mike Rivers" > wrote:
> On Apr 2, 1:58 am, "Meindert Sprang" >
> wrote:
>
> > Doesn't necessarily have to be the ground that starts floating. A line
> > output of a sound interface has a low impedance, but only when it's powered.
>
> Good thought. So the solution is that if it hums with no input, you're
> not going to be listening to anything playing out of the interfface
> anyway, so turn off the power amplifier or turn down the volume.

that what wierd!
turning down the volume doesn't help!

[Mike Rivers]

On Apr 2, 7:19 am, "Over G" > wrote:
> On Apr 2, 2:38 am, "Richard Amirault" > wrote:

> the hum comes from the speakers.
> when I unplug the USB from the card,
> the sound is turned off,
> (because the electricity is turned off in the Tascam)

Let's get this straight:

1. Computer turned on, USB cable connected to the computer - no hum
2. Computer turned off, USB cable connected to the computer - hum
3. USB cable disconnected - hum

Is that correct? This would be consistent with Meindert's suggestion
that the output impedance of the US-144 is high when it's not powered
up. This would be like connecting an "antenna" to the cable that's
going to your powered speakers.

Unplug the speakers from the US-144, and touch the tip of that plug
with your finger. You won't get a shock. Do you hear the same kind of
hum as with it connected and with the US-144 unpowered? That would
confirm the diagnosis.

> it look liks a sound was stuck in the Tascam card (buffer maybe ?),
> and there should be a way to clean it somehow,..

Nope, when it's unpowered, there are no buffers to supply audio.

[Over G]

> 1. Computer turned on, USB cable connected to the computer - no hum
correct.

> 2. Computer turned off, USB cable connected to the computer - hum
correct
> 3. USB cable disconnected - hum
no,
USB out, no power to the card thus = no hum.

so what can that be?
(the impedance thing?)

[Mike Rivers]

On Apr 2, 7:02 pm, "Over G" > wrote:

> USB out, no power to the card thus = no hum.
>
> so what can that be?
> (the impedance thing?)

Ground thing. You're screwed. Maybe an isolation transformer between
the US144 and the speakers. Ebtech makes a pair in a box for a
rational price.