Conference napalm::commusic_v1

"If they write to the FCC, you're shut down."

Not necessarily. Depends on the TV and at what freqeuncy your stuff is
radiating.

Some TV designers, to save money, leave out filters on the antenna leads.
This allows nearby signals OFF THE TV FREQUENCY to get into the
receiver and screw things up.  Hams know a lot about this.  As long
as the ham operator is staying in his band, IT ISN'T HIS FAULT if
his neighbor's TV sees interference.  To be a good neighbor, the
ham often will build the required trap filter and give it to the
neighbor.

But if your stuff is emitting in the TV band, it is YOUR fault, Unless your
stuff is emitting where it should not, or at greater levels than the FCC
allows. Remember when the FCC swooped down on a computer show where a bunch
of cheap PC clones were on display?  The clones had not bothered getting FCC
certification and they were emitting all over the place.

    I thought it was the vendor, rather than the owner, who was responsible
    for EMC compliance.  In particular, devices intended for use in
    the home are subject to more stringent constraints than industrial
    gear.  There should be a plate or label somewhere on the device
    certifying FCC EMC compliance.  If you bought something without
    a label, or from pre-compliance eras, I don't know what your
    responsibility is.

    len.
    

    I have a somewhat tangential problem with my modem at home receiving
    radio signals.  It's all DEC stuff and the system manager who gave
    it to me doesn't know anything about it and hasn't heard of any
    similar problems.  Should I post a description of the problem here
    or is there a more appropriate forum?  (It seems some of you gentlemen
    know a bit about interference problems.)
    
    Richard

    
    	I took my tv into my studio last night.  Turned things on/off
    to learn who the major RFI emitters were.
    
    	As expected, the MIDIverb is public enemy No. 1.  Even a
    (ungrounded) box with many layers of alunimum foil failed to
    provide any relief.  I'll try grounding it tonight.
    
    	The Mac and the KX88 tied for second place.  Curiously, the
    TX816 seemed to have no noticeable effect.
    
							- km

    Karl,
       Try the Mac without external cables.  I have a digitizer
    hooked up to my Mac, and when it's on, I hear loud cursing
    emanating from houses all up and down the block.
    
    David
    

I mentioned this in another note.  The midiverb is the noisiest thing
I own by far.  It literally wipes out my TV reception.  Of course at 
my house, electronic music has a much higher priority than television...

Perhaps there is some way to shield the midiverb with foil on the *inside*
of the plastic box and bring a ground out.  I havn't tried disconnecting
the audio cables from the midiverb - I'll have to try that next.  I wonder
if Len's SRVs are noisy.?

Todd.

    Hmm...the SRVs are in metal-cased rack mountable units.  I don't
    have an operable TV, and I don't often use my FM tuner at the same
    time I've got all the high-clock-rate-devices in the other room
    running, and none of my neighbors have complained, but maybe they
    don't know I'm responsible *if* I'm generating any EMI.  My most
    susceptible-to-EMI device, the Scholz Rockman (another damn plastic
    case) isn't any noisier in my studio than it is anyplace else, but
    I don't know if it's a representative receiver.
    
    The way we used to solve the "can't get my fingers through the Faraday
    cage" syndrome back in a research/testing lab I used to work in
    was to make a really BIG Faraday cage - so big it had a door and
    you worked inside it.  It was called, affectionately, the "Scween
    Womb".  Depending on the frequencies you're working with, the "walls"
    of the cage can actually be screen rather than solid, which helps
    solve some of the temperature, lighting and claustrophobia problems.
    
    len.

                                    
    As I read .0 I remembered reading a handbook on studio construction
    discussing the sheilding of the control room in a faraday cage 
    made by lining the walls, ceiling, etc, with metal screen underneath
    the paneling, wallboard, etc.  Wish I could find that book.
    
    By the way, I have a MicroVAX II workstation in my office.  I also
    have a stereo which is enclosed in my steel desk (faraday desk),
    except for the line cord (which is also used as the antenna).
    
    When the screen scrolls while displaying, say, a directory listing,
    I hear white noise, like a machine gun sound as the characters 
    get fired up on the screen.
                                                  
    Fredric
    

    'Progress' report -
    
    Tried some more experiments.  Grounding the aluminum foil box to
    the back of the receiver (the phono ground) did not improve things.
    
    However, yes, the cables are part of the problem.  I called Tweeter
    and talked with a (seemingly knowledgeable) guy there.  He said
    that, depending on length, high quality shielded cables could run
    as high as $90 a pair!!  Of course, this includes gold tips!
    
    He did, however, add that he had some 1 1/2 ft. cable that he could
    sell for $12 a pair.
    
    Ok, wizards - how about some Rube Goldberg ingenious solutions?
    Lead (that's 'LED', not 'LEED') sheets wrapped around for the cables?  
    Patio screen?  Can a techie modify the MIDIverb?  Buy cable for the 
    neighbors? 
    
    Hmmm, just looked at the MIDIverb manual.  Not a word about FCC
    compliance.  How is Alesis able to sell this?
    							- Karl

    
    Because no ones filed a complaint yet?
        
    Have you confirmed that you are only radiating via air,
    and not power lines?
    
    If your setup would allow, why not try stuffing the 
    m-verb AND the cables in the box with just the phono
    plugs extending out. Ground the box AND the plugs. 
    
    You could always buy your neighbors a midiverb to get
    back at you.
    
    ron
    
    

    You don't want density (it's not radioactivity), you want conductivity.
    Also, those pricey cables you looked at are probably no better shielded
    than the stuff you're already using - you'll be paying for low
    capacitance (not much help for radiated EMI) and exotic conductors
    (for the signal, not the shield).  Don't waste your money.  Also
    I doubt that your signal cables are radiating EMI; if they were,
    you'd hear it in your own signals.  MIDI cables may be at fault
    (although they're only carrying 32 kbps signals, not nearly RF).
    The source is multiMHz clocks and logic INSIDE the boxes, leaking
    out through the case or via the power cable.
    
    len (who admits to no expertise in this area).
    

    
    	Audio cables are definetely part of the problem.  
    
    	Turn on TV.  Plug in MIDIverb.  TV goes nuts.
    
    	Pull out input cables. TV gets better.  Pull out output cables.
    	TV gets even better.
    
    	Is there some way to ground the MIDIverb?  Since there are
    	only 2 plugs on the power cord, I assume it isn't.
								- km
    
p.s. I'd give it all up and become a conceptual artist, but some
telepath down the hall would probably complain.

    Thanks, Tom, I needed to be put in my place.  You forgot to mention
    that you learned all this when you were 11.
    
    len the charlatan.
    

    So, I called Zak at Alesis.  I think he's the designer.  I said
    'Maybe you can help me with my neighbors' television reception.'
    He said, 'Uh-oh'.
    
    Said to send him the unit and he would do something or other that
    would fix things.  Said he had done this for someone else.  I'll
    give that a try.
    
    Otherwise, I just checked the unit, the manual (with the warranty)
    and the packing and box.  Not a mention of passing Class B  FCC
    requirements.  Could they really be trying to pull a fast one?
    Aren't they taking a huge risk?
						,km

    
    	Oops, line noise got me.  The last reply's title should have
    been 'MIDIverbalizations'.  That way you would have some idea that
    I was talking about the MIDIverb.
    
    						sorry, Karl

I wonder what Zak would say if we posted this on the usenet and he were to
recieve 100 MIDIverbs, all with a letter requesting that he shield them ;)

Seriously tho, if the cables are a huge culprit, it's my guess that they are
acting as antennas for the HF digital signals (clock, etc.) inside the box.
If this is true, then it may explain why the MIDIverb's audio output is
noisy.  THERE IS NO ISOLATION BETWEEN THE DIGITAL NOISE AND THE AUDIO SIGNAL
THAT THE BOX IS PRODUCING!  Sounds like it would be best not to shield the 
entire MIDIverb box, but to shield the clock/cpu chips right up thru the A/D 
and D/A chips.  Of course, how is this gonna be done if everything is on
a single board?

Todd who_can't_believe_Alesis_didn't_put_in_a_few_extra_bucks_to_clean_up_the_
	audio_signals_and_also_relieve_EMI_problems.

    wait wait wait. Theres a way to decide if it's the
    midi cables/transmission and/or the audio 'antennas'.
    
    Unplug the audio out and in cables. Send midi info to unit.
    If the TV 'display' changes while youre sending, 
    theres a component of midi involved (it still may be
    the internal processor reacting to midi, NOT the midi
    signal edges themselves.)  

    It's a start....    

    rr
    

    re;-1
    
    	Good idea, but I haven't been using it with MIDI.  Gee, that's
    something else for me to worry about.
    
    						,km

I doubt that the MIDI cables would cause a problem because there is a fair
amount of capacitance on the cable itself (depending on its length).  This
capacitance will introduce delays in the changes of the digital signal being
sent over the MIDI cable, and thus smooth out the edges - and we all know
that the smoother the edges are, the less harmonic garbage will be generated.

I'll bet the mortgage that it's the high speed logic with low capacitance
lines (READ: clock) that is generating the garbage.

Todd.