Mathias Lenz wrote:
Has anyone experience with Furman Power Conditioners. They claim to have RFI
filtering.
I'm working in a theater and dimmer-buzz is introduced trough the power line
to my BSS FDS 360 Crossovers. I'ts not much but enough to disturb the
audience during silent scenes. Would this thing fix the problem?

If the problem is RF trash coming into the power cord, yes. If the problem
is RF trash just radiating through the air, no.

You will almost certainly get better results putting the low-pass on the
dimmer packs rather than on the audio gear. But it still won't solve the
problem of RF trash radiating from the cables from the packs to the lights.
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."

The audio gear is located 8 meters away from the stage lights and 30 meter
away from the dimmer packs, all lines are balanced. So the RF trash in the
air shouldn't be the problem, should it?

On the other hand I had the experience that the BSS FDS 360 are quite
sensitive to such trash. (I once mounted a FDS 360 4 U above a Crown amp
and the result was a terrible hum at 50 Hz)

You will almost certainly get better results putting the low-pass on the
dimmer packs rather than on the audio gear.

Too expensive for the theatre.

Another problem is a small electric elevator in the scenery. Every once in a
while the motor causes a plopp when turned on or off.

Thanks for your help scott,

Mathias

Sounds like you need to do a little troubleshooting here. You may need to
supply a clean ground to your crossovers. The building ground you are using
may be contaminated by the dimmer, and that would not give a good ground for
the power conditioner either. Also, make sure your cable shield is
disconnected at one end. It may like the ground from one side and not the
other.

Jim


"Mathias Lenz" wrote in message
...
The audio gear is located 8 meters away from the stage lights and 30 meter
away from the dimmer packs, all lines are balanced. So the RF trash in the
air shouldn't be the problem, should it?

On the other hand I had the experience that the BSS FDS 360 are quite
sensitive to such trash. (I once mounted a FDS 360 4 U above a Crown amp
and the result was a terrible hum at 50 Hz)

You will almost certainly get better results putting the low-pass on the
dimmer packs rather than on the audio gear.

Too expensive for the theatre.

Another problem is a small electric elevator in the scenery. Every once in
a
while the motor causes a plopp when turned on or off.

Thanks for your help scott,

Mathias

Mathias Lenz wrote:
Has anyone experience with Furman Power Conditioners. They claim to have RFI
filtering.
I'm working in a theater and dimmer-buzz is introduced trough the power line
to my BSS FDS 360 Crossovers. I'ts not much but enough to disturb the
audience during silent scenes. Would this thing fix the problem?

My experience (mainly in theatre) has been that dimmer buzz is almost
always down to a problem with sound system grounding rather then problems
with the racks, RF or power line noise. Try unplugging everything from the
crossovers (except the amps) and see if the buzz is still there, if so fix
the problem then work on the desk-crossover link, then add the outboard,
then the mic ties...

I often find that a better fix then disconnecting the screen is to add an
additional low impeadence ground path with a bit of 10mm earth cable
running in parallel with the signal cables and tied to case ground at both
ends.
In particular if you have impulsive noise (contactors, motor switching),
this can work much better then approaches based on telescoping sheilds.

This sort of thing can be a real bear to track down and lots of
experimentation is really the only way.

If the humm is low level, it can be worth experementing with gain
structure (if the amp clips at 1V input with gain at max, and the
crossovers clip at say +22dbV, then you can turn the amp gain down 22db
and still have enougth drive available to get full output. Obviously
this depends on the desk being able to drive the crossovers hard enougth
(should be a given, but....). Not a real fix, but sometimes it does
enougth.

Regards, Dan.
--
** The email address *IS* valid, do NOT remove the spamblock
And on the evening of the first day the lord said...........
..... LX 1, GO!; and there was light.

wrote:
Mathias Lenz wrote:
Has anyone experience with Furman Power Conditioners. They claim to have RFI
filtering.
I'm working in a theater and dimmer-buzz is introduced trough the power line
to my BSS FDS 360 Crossovers. I'ts not much but enough to disturb the
audience during silent scenes. Would this thing fix the problem?

My experience (mainly in theatre) has been that dimmer buzz is almost
always down to a problem with sound system grounding rather then problems
with the racks, RF or power line noise. Try unplugging everything from the
crossovers (except the amps) and see if the buzz is still there, if so fix
the problem then work on the desk-crossover link, then add the outboard,
then the mic ties...

Ground loops pick up RFI from the air; that's why you want to avoid them.
In a perfectly silent place with no ground currents circulating in the
power lines and no RFI, ground loops would not be a problem. Such places
don't exist.

I often find that a better fix then disconnecting the screen is to add an
additional low impeadence ground path with a bit of 10mm earth cable
running in parallel with the signal cables and tied to case ground at both
ends.
In particular if you have impulsive noise (contactors, motor switching),
this can work much better then approaches based on telescoping sheilds.

Sometimes. Sometimes ferrite beads are a good solution, and sometimes you
just can't get away without a transformer.

This sort of thing can be a real bear to track down and lots of
experimentation is really the only way.

The key is to find out what the noise is and where it's coming in. If it
it coming in without anything plugged into the box, it's not RFI and it's
not the result of a ground loop. If it comes in with one thing plugged into
the box and the ground lifted, it's the result of RFI but not a ground loop.
If it appears only with the signal ground and power ground both in place,
it's a ground loop.

You can go about this slowly and systematically, and plugging a pair of
headphones into an output and listening to what is going on without anything
else attached can be very helpful.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

Given the elevator noise he mentioned, it sounds like audio is on the same
service as the rest of the building. It won't be cheap but the real fix should
be a separate service with its own isolated ground for audio only.
Scott Fraser

ScotFraser wrote:
Given the elevator noise he mentioned, it sounds like audio is on the same
service as the rest of the building. It won't be cheap but the real fix
should be a separate service with its own isolated ground for audio only.
Scott Fraser

My experience has been slightly different in this regard as I routinely
run sound systems in a venue where the sound power and the feeds for
6 variable frequency drives (Effects winches), and a large air compressor
are all fed from the same distro board. Everything works fine (and it is
quiet). It took a lot of work to get the system to this point, but it was
all local grounding work within the system, we did not need a clean
ground connection (A practice I am dubious about in a TN-C-S (PME)
installation anyway).

The power is *NOISY*, but with decent kit and good wiring practice
this noise stays out of the audio. Would I have liked to have had a
seperate transformer from 11KV? Of course, but even with really nasty
power supplies a quiet setup can be contrived and this is usaually much
cheaper then pulling in a new feed from the transformers.

Regards, Dan.
--
** The email address *IS* valid, do NOT remove the spamblock
And on the evening of the first day the lord said...........
..... LX 1, GO!; and there was light.