Conference napalm::commusic_v1

    Gack!  Aren't dimmer switches one of the main culprits when it comes to
    noise in the audio lines?  I should think that if possible you would
    either go with a low-wattage system that doesn't need adjustment or rig
    up a DC system that is low voltage and that you can just use pots to
    modulate.  Just my uneducated opinion ...
    
    Steve

    
    
    Unless you want varilite-like action, or want to do disco light shows,
    you can probably get by with X-10 stuff.  Steve was right, though:
    just about every dimmer setup I've heard introduces a lot of noise on
    the AC lines.
    
    If you're in the UK, the X-10 stuff won't do you any good.  I believe
    they have equivalent units known as "red boxes".
    
    Press KP7 to add the X-10 conference to your notebook.
    

	If you want a cheap, noiseless dimmer, I have an inexpensive
	solution (I've been using ths set up for the last 9 years, with
	no problems), the only limitation is that there are only 3 modes
	of light - Off, Half-bright and Full-bright. Here is the ASCII
	representation of the schematic:

	 light
         on-off    dim-bright
           /          /
	--0 0---+----0 0-----+-----------
		|            |
	120V	|            |       To Light 
	AC In	+----->|-----+         Bulb  (2 to 4 flood lights are fine)

	---------------------------------


	The diode is a 400 volt, 10 amp, stud mounted power diode, and
	the swich causes current to flow thru it, or be ignored. As
	you know, diodes only let current flow one way, and an AC signal
	is 50% posative, and 50% negative - the diode throws 50% of the
	signal away. The best part is that it adds no noise to the AC line
	like a regular dimmer does. It does get warm, however, and I would
	suggest mounting it on a steel of aluminum plate (it doesn't have
	to be large) - I have 4 such diodes mounted to a 1 1/2 in aluminum
	angle, about 6 inches long. The stud commons all connect to the
	same plate (aluminum angle), and this is screwed to one of the wooden
	sided of the box that holds my on/off dim/bright switches. 
								Jens

Here's another twist on this topic: my church already has *several* dimmer
switches controlling its overhead lights, and there is a substantial amount of
noise on the PA system which seems to be a direct result.

Not being an EE type, I'm not clear on what kind of noise this is, or how (if
at all) it can be reduced or removed. Is this RFI? Fluctuation in the line
voltage? Will an RFI filter plug, a line voltage controller, or some short
of shielding around the PA system help? Will putting the PA system on a separate
circuit have any effect or is it a waste of time? (Will this paragraph set a
Guiness world record for continuous questions? Tune in and find out the answers
to these questions and more on next week's episode...)

Maudlin aside:

It looks like my DEC contract will most likely be ending up on or around the
end of September (though another extension *may* squeeze in under the wire).
I find myself missing my many "notable" friends in advance, and this conference
in particular. Sigh... (No, I'm *not* going to do "Thanks for the Memories!")

Anyway, back to the present: any and all tips appreciated.

Cheers,
	Bob

	The noise comes from clipping the AC waveform with I think triacs.
	Hey, I'm a s/w guy now. ;-).  Some kind of SCR (silicon controlled
	rectifier.  A cheap potentiometer is used to set a trigger voltage on
	the triac; when the AC 110V 60Hz power line reaches the trigger
	voltage, it turns on and heavy current can flow through the triac.  
	It doesn't turn off until the waveform
	crosses zero.  This makes a clipped waveform (flat on the side)
	with lots of harmonics creating conducted inference (back into
	the power lines.).
	So yeah seperate lines can help and so can filtering above the dimmers.
	I'm assuming filters aren't one-way.  I can't imagine how they 
	would be one way.
	
	This  is a great way to control motors and lights and is used
	everywhere, including your living room dimmer.
	If you want a circuit diagram, I have an old RCA book with that
	kind of thing.
Tom

    re .3
    
    I've used it several times to a moderate degree of satisfaction. What
    you may not like about it is some noticeable flickering. With normal
    wiring, the brightness of a lamp is varying with double the frequency of
    the mains voltage (similar to full wave rectification) which is too
    fast for human eyes, so it's unnoticeable.
    
    The diode reduces it to just the frequency of the mains voltage
    (half wave rectification) which may be visible.
    
    Besides this, it has lots of advantages.
    
    Ueli

>                    <<< Note 2714.6 by MINNY::WALDISPUEHL >>>
>                        -< .3 is nice, but not perfect >-

	But is sure is cheap & I've never noticed any flickering on floodlights.
	This may not be the case on other types of lighting.

								Jens