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Conference napalm::commusic_v1

Title:* * Computer Music, MIDI, and Related Topics * *
Notice:Conference has been write-locked. Use new version.
Moderator:DYPSS1::SCHAFER
Created:Thu Feb 20 1986
Last Modified:Mon Aug 29 1994
Last Successful Update:Fri Jun 06 1997
Number of topics:2852
Total number of notes:33157

2144.0. "Shield components in rack?" by FGVAXX::LAING (Soft-Core Cuddler*Jim Laing*282-1476) Fri Oct 20 1989 17:12

Thought some of you in this notes file might be able to help ...

Is there a simple way to "shield" one component from another in a 19" rack?

My problem is this: I have a 3-space rack, with the following components:

	Carver PM-100 power amp
	Furman 4-ch stereo mixer
	Rane 2x15 stereo EQ

I was getting more "hum" than I'm used to (I had just assembled this rack)
from the amp.  After alot of checking, re-cabling, ground-lifting, etc.,
etc. I thought of an experiment: is it the physical proximity of these
components that's causing the problem?  Sure enough, when I removed the
mixer from the rack, set it down 12" away, the "hum" disappeared!  When
I moved the mixer closer to the amp, the hum began to re-appear.

I *must* have these 3 components together in this rack; is there a simple
way for me to "shield" the amp from the other components?  Is there some
material I can place between components, etc?

	Thanks for any suggestions/advice!

		-Jim
T.RTitleUserPersonal
Name		DateLines
2144.1Ground plane?TALK::HARRIMANDr. Science's younger brotherFri Oct 20 1989 17:437

	Can you make a ground plane? Or have you got an insufficient ground
	connection between the amp and mixer?

	A ground plane would look like a shelf between the components. Is this	
	a metal rack or a non-metal one?
2144.2Read the front panel: "Magnetic Field"KALLON::EIRIKURCDA Product ManagerFri Oct 20 1989 17:508
I think you don't have a general problem.  Get that mixer away from the Carver
"Magnetic Field" power amp.  The Carver amp uses some radical power supply
design that I would suspect of radiating more stray 60 Hz. than a standard
rackmount amp or SGU.

	Eirikur
2144.3Shields ShmieldsMILKWY::JANZENcf. ANT::CIRCUITS,ANT::UWAVESSun Oct 22 1989 20:3014
    Ordinary conducting shields don't work all that well at low audio
    frequencies, at least not without mu metal.    I think your stuck
    having to keep them apart.  Perhaps it would help to put them in the
    rack ina different order, that is, put the offender on top or bottom
    whatever is opposite from what it is.
    You could try a shield, though.  Shields work because the changing
    magnetic
    field induces electric currents in the shield, which then produce
    opposing magnetic fields, but the strength of that current falls as
    frequency falls because the magnetic field isn't changing as fast.
    Gee that's opaque.  Maybe I shouldn't try to finish an article for a
    dec house organ tonight after all...
    TOm
    8-)
2144.4Just watch out for the vent holes...GUESS::YERAZUNISOooh, that must be hexadecimalWed Oct 25 1989 18:446
    
    Try wrapping the mag-field power amp in a laminate of copper and
    soft iron. (copper for the RF generated by the switching power supply
    and soft iron for the magnetic field).
             
    	-Bill