balanced help

[Theo]

Agree with Magnus here, go ballanced.
Guess there will be stage lights around = lot's o' polution from triac
switching.
Needless to say, keep those dimmer packs away from the audio stuf.
Same thing for the cables.

Only two notes on the cable channels.
1) If your friens means some protective strips to run his and alone his
cables throug, it's a good thing.
Beats gaffa anytime, realy protects your cables and is cheaper than tape.
Return of investment only about 10  to 15 preformances.
2) If he means exsisting cable channels with other cabels in it, please
don't.
BTW the direct dutch translation would be cable gutter, says it all doesn't
it?

Cheers Theo.

----- Original Message -----
From: Magnus Danielson <cfmd at swipnet.se>
To: <czech at Micronas.Com>
Cc: <synth-diy at node12b53.a2000.nl>
Sent: Friday, June 09, 2000 10:15 PM
Subject: Re: balanced help


> From: Martin Czech <czech at Micronas.Com>
> Subject: balanced help
> Date: Fri, 9 Jun 2000 10:19:30 +0200 (MET DST)
>
> > I have a friend who is preparing an electronic music performance (16.
July
> > 2000 - ) in Friedrichhafen, Germany. (btw. this is where Graf Zeppelin
> > build his famous "silver cigars"). He wrote me that he installed four
> > active speakers in the corners of the room and that he put the audio
> > cables in "cable channels". Now, all unbalanced, you might know what's
> > happening: hum and radio interference all the way.
> >
> > The hum may be due to magnetic coupling (no galvanic ground loop here,
> > no protective earth plugs), and the radio should be capacitive coupling
> > on the shield which is unfortunately the audio "return" path. The word
> > cable channel makes me sick!  I think the cure would be to use one
> > transformer per line, thus balancing using balanced shielded cable.
> >
> > Or may be the transformer is not neccessary (no ground loop), just
twisted pair
> > shielded cable.
> >
> > The "real thing" would be certainly two transformers, one at each side,
fully
> > balanced, but there is short money ...
> >
> > Now there are two possible positions the trafo may have: at the signal
> > source or the drain. I'd say that it should be at the drain. I.e. a
> > balanced cable comes from the unbalanced source all the way to the
trafo,
> > there the secondary winding is fed into the unbalanced speaker input.
Now ,
> > where do we connect the cable shield. If the enclosures are plastic, I
guess I
> > have to propose protective earth.
> >
> > I have only one attempt to make it work, a couple of hours before the
event
> > starts. I'm 170 km away till then.
> >
> > So any suggestions for achieving a "first hit" solution would be very
much
> > appreciated!
>
> OK. My first attempt would be:
>
> Trafos in the reciever ends, no earth connection from primary to
> secondary side. The cable shield should be connected in the source
> end. If you have a shield in the trafo, hook it to the shield. If you
> have a double shield, hook the one closest to the primary side to the
> shield and hook the other one (closest to the secondary) to the earth
> end at the secondary side.
>
> If you have the time, throw together a balanced drive using
> buffers/inverters using standard op-amps. You could veroboard them
> quickly and they would most probably be worth the effort I think.
> Just don't forget the caps ;)
>
> Just running unbalanced from one end into a transformer is not as
> efficient as running balanced since electrostatically the shield is
> roughtly at the same level as one of the signals in the unbalanced
> case where as in the balanced case it is rougthly inbetween.
>
> If you spend the money on the trafos, do go ahead and spend some small
> amount more on the balanced drivers.
>
> Cheers,
> Magnus