Problem with Behringer headphone amp

[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 <fp3vt1$beq$1...@inn-newsserver.rz.tu-ilmenau.de>,
Boris Lau <bori...@stud.tu-ilmenau.de> wrote:

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]

Boris Lau <bori...@stud.tu-ilmenau.de> 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