[Boris Lau]

Hi there,

I've bought a Behringer Powerplay Pro-XL HA-4700, and I'm not very happy
with it. There is some clearly audible whit(ish) noise, even with all
volume pots turned down. It is that loud that if I turn the pots up, it
gets only a bit louder. Annoying, but I could live with that.

What I don't like: as soon as I connect a source to the main inputs
(balanced or unbalanced, with all cables), there is a bit of hum (like
broken ground). When I connect the same source to a direct in, the hum
is pretty loud.
My source seems to be ok, I don't have this problem if I hook it up to
my small Behringer mixer.

Do you think that headphone amp unit is broken, and I should get a
replacement? Is that noise something I have to expect with that class of
equipment? Is the hum something I have to live with?

Thanks,

Boris

[Kevin McMurtrie]

In article ,
Boris Lau wrote:

Hi there,

I've bought a Behringer Powerplay Pro-XL HA-4700, and I'm not very happy
with it. There is some clearly audible whit(ish) noise, even with all
volume pots turned down. It is that loud that if I turn the pots up, it
gets only a bit louder. Annoying, but I could live with that.

What I don't like: as soon as I connect a source to the main inputs
(balanced or unbalanced, with all cables), there is a bit of hum (like
broken ground). When I connect the same source to a direct in, the hum
is pretty loud.
My source seems to be ok, I don't have this problem if I hook it up to
my small Behringer mixer.

Do you think that headphone amp unit is broken, and I should get a
replacement? Is that noise something I have to expect with that class of
equipment? Is the hum something I have to live with?

Thanks,

Boris

I see that only its main inputs are balanced. The individual inputs are
unbalanced. That's kind of missing the point

So just a single balanced input to the main connector hums? That sounds
broken.

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[Boris Lau]

Kevin McMurtrie wrote:
So just a single balanced input to the main connector hums?
That sounds broken.

Thanks Kevin,
I think so too. I've sent it in and asked for a replacement unit. I hope
that will solve the problem...

Boris

[Boris Lau]

Boris Lau wrote:
Thanks Kevin,
I think so too. I've sent it in and asked for a replacement unit. I hope
that will solve the problem...

Ok, I've got a replacement. The hum is much better, but the high-pitched
periodic noise is still there, if I use the unbalanced Aux-ins (there is
one per channel). I packed out my scope and looked at the grounds - and
tataa - there is some nasty electrical rubbish sitting on the GND of the
firewire cable coming from my PC, and on the GND of its power supply as
well.
So I guess this reduces my available options. "Grounding" the ground of
the firewire cable did not help unfortunately. I guess an optical
firewire decoupler would help. Are there any for reasonable prices?
Should I expect problems with the firewire protocol of my units and a
decoupler not supporting them, or is that standardized?

Thanks,

Boris

[Norbert Hahn[_2_]]

Boris Lau wrote:

Ok, I've got a replacement. The hum is much better, but the high-pitched
periodic noise is still there, if I use the unbalanced Aux-ins (there is
one per channel). I packed out my scope and looked at the grounds - and
tataa - there is some nasty electrical rubbish sitting on the GND of the
firewire cable coming from my PC, and on the GND of its power supply as
well.

What did you use a reference point (ground) for your scope?
If you see rubbish on the ground of your FW card and you see rubbish
on the GND of the power supply you *may* have use the wrong point for
GND of the scope. Of course, you may have a faulty power suppy.
You may even have a ground loop which does not exhibit hum but high
pitched rubbish.

Norbert