Trouble Buzz from Behringer MVX1000 dj mixer

[Harry Putnam]

Setup:
OS = Winxp pro sp/2
Receiver/amp = Panasonic SA-XR25
DJ Mixer = Behringer vmx1000
Speakers = Industrial strength Yamaha
500Watts Program/1000watts Max Power

Summary:

When I connect the Behringer mixer listed above into the system it
also introduces a low freq hum or buzz.

Anyone wanting to see the front panel and connections panel of the
mixer can look here:

http://www.jtan.com/~reader/exp/web_ready/dispimg.cgi
(Note: The images are large for clarity so may load slowly)

When I attach a direct ground from one of the mixers RCA in channels
by way of a chassis screw for that purpose, to a dead ground in the
actual wall electric panel, the buzz increases.

How can I trouble shoot/eliminate the buzz?

Further info is that if I bypass the mixer the buzz is eliminated.

I don't know anywhere near enough about this to come up with a step by
step proceedure to reveal the source of this buzz, but I was quite
surprised to notice that it increases when a direct ground is
connected. I had hoped the ground would eliminate it.

[Ron Hardin]

Does the MVX series have the wall wart (good) or the switching power
supply (bad)? They recently switched to switching supplies, which
produces all sorts of RF hash picked up by suitable receivers.

Another possibility is a ground loop, which is fixed by removing grounds
rather than adding them. The Radio Shack ground loop isolator 270-054
(basically a stereo audio transformer) ($15) is good for experimentation
even if you don't want the permanent effect on fidelity it introduces.

Or put everything on the same AC circuit, if it isn't already.
--
Ron Hardin


On the internet, nobody knows you're a jerk.

[Arny Krueger]

Harry Putnam wrote:
> Setup:


> OS = Winxp pro sp/2

PC with a grounding plug. Ground #1

> Receiver/amp = Panasonic SA-XR25

2 prong power cord, no doubt.

> DJ Mixer = Behringer vmx1000

According to the Behringer web site, this device is powered
via a standard IEC cord with ground pin.

Mixer with a grounding plug. Ground #2

> Speakers = Industrial strength Yamaha
> 500Watts Program/1000watts Max Power

Floating with respect to ground.

> Summary:
>
> When I connect the Behringer mixer listed above into the
system it
> also introduces a low freq hum or buzz.

Ground loop due to presence of two seperate grounds

> When I attach a direct ground from one of the mixers RCA
in channels
> by way of a chassis screw for that purpose, to a dead
ground in the
> actual wall electric panel, the buzz increases.

That would probably be ground #3. You've just increased the
number of ground loops.

> How can I trouble shoot/eliminate the buzz?

> Further info is that if I bypass the mixer the buzz is
eliminated.

That eliminates ground #2.

> I don't know anywhere near enough about this to come up
with a step by
> step proceedure to reveal the source of this buzz, but I
was quite
> surprised to notice that it increases when a direct ground
is
> connected. I had hoped the ground would eliminate it.

Try adding a Radio Shack ground isolator (about $15) into
the audio line coming out of the PC.

[Harry Putnam]

Ron Hardin > writes:

> Does the MVX series have the wall wart (good) or the switching power
> supply (bad)? They recently switched to switching supplies, which
> produces all sorts of RF hash picked up by suitable receivers.

Not sure what you mean here. But the mvx1000 has a three prong ac
powercord and an on/off switch.

[Harry Putnam]

Ron Hardin > writes:

> Another possibility is a ground loop, which is fixed by removing grounds
> rather than adding them. The Radio Shack ground loop isolator 270-054
> (basically a stereo audio transformer) ($15) is good for experimentation
> even if you don't want the permanent effect on fidelity it introduces.

What effect is that?

> Or put everything on the same AC circuit, if it isn't already.

It is now.


"Arny Krueger" > writes:

[...] snipped handy analytic steps

> Try adding a Radio Shack ground isolator (about $15) into
> the audio line coming out of the PC.

Thanks posters... that is something I can try and will shortly.

[Ron Hardin]

Harry Putnam wrote:
>
> Ron Hardin > writes:
>
> > Does the MVX series have the wall wart (good) or the switching power
> > supply (bad)? They recently switched to switching supplies, which
> > produces all sorts of RF hash picked up by suitable receivers.
>
> Not sure what you mean here. But the mvx1000 has a three prong ac
> powercord and an on/off switch.

I get all sorts of hash generated by my Behringer UB1204 that's RF
radiated by the thing and picked up by the radio that I'm trying to
run through it; it's a result of a badly engineered switching power
supply. The former models eg. MX1604 had a wall wart power supply
that is not switching and works fine (though it generates more heat).

If everything is at audio frequencies, you do fine, but radios can
unfortunately pick up the RF harmonics from the switching supplies.

It sounds like you have a switching supply, though it may not be the
cause of your particular problem. It's just another misfeature
that can be a failure mode. If an AM radio near the mixer picks up
hash, it's a switching supply.

I like the ground loop alternative better however.
--
Ron Hardin


On the internet, nobody knows you're a jerk.

[Harry Putnam]

> Ron Hardin > writes:
>
>> Another possibility is a ground loop, which is fixed by removing grounds
>> rather than adding them. The Radio Shack ground loop isolator 270-054
>> (basically a stereo audio transformer) ($15) is good for experimentation
>> even if you don't want the permanent effect on fidelity it introduces.

[...]

> "Arny Krueger" > writes:
>
> [...] snipped handy analytic steps
>
>> Try adding a Radio Shack ground isolator (about $15) into
>> the audio line coming out of the PC.

[...]

I'm glad to report back that inserting the groud isolator thing at pc
to Mixer stopped the hum dead.

Thanks