Emu XL-7 & MP-7 User's Group

Just one more thing to add...

MIDI can sometimes cause noise to be added to a synth, especially so-called
clock noise.  My spec a MIDI connector should only have its shield pin
connected to ground if it is a MIDI output jack (MIDI itself is a current
loop interface that is optically coupled so it does not need ground
connected between sender device and receiver device).  Unfortunately this
requirement is violated more times in my experience then it should be.  Some
computer interfaces are particularly prone to this mistake.

So if you have noise in your outputs be sure you try to disconnect all the
MIDI connections to the device (XX7 for example) and see if that causes the
noise to be eliminated.  If the MIDI cable connected to your device's output
is the cause then you have a MIDI device it is driving that has incorrect
wiring.  If the MIDI input on the device eliminates the noise then your
instrument is incorrectly wired.

How do you fix this?  Make a MIDI cable that does not have the middle pin
connected nor any shield wiring.  or if you have some flexibility in your
setup try different connection schemes.  Sometimes a THRU box can fix this
too.


drk

www.delora.com/music
www.mp3.com/zdrk
drk.iuma.com



On 11/4/02 1:14 PM, "Aaron Eppolito" <synthesis77@...> wrote:

> Before this gets too out of hand, I figured I'd offer some insights
> into what causes hum.  The answer?  Just about everything.  =)  See the
> last paragraph for an issue specific to the XL-7.
> 
> As with all gear, ground loops can be a problem.  If two devices are
> plugged in to each other via audio cables and have different ground
> references (i.e. plugged into different AC circuits), some of the AC
> power "leaks" through the audio cables, causing 60 cycle (and possibly
> harmonics) hum.  To solve this problem, search around the web for tips
> on reducing ground loops.  I'm sure there are many more comprehensive
> sites out there than what I can offer.
> 
> Second, most analog gear (especially mixers) is sensitive to
> electromagnetic interference.  Particularly nasty culprits are computer
> monitors, halogen lamps, computer cases, refrigerators, etc.  The only
> solution here is to try and physically rearrange the interfering
> devices.
> 
> Finally, the XL-7 has a requirement that the front panel be grounded to
> the main chassis.  The symptom of this is buzzing from the HEADPHONE
> JACK ONLY.  If you also have hum out of the mains or subs, go back and
> reread the previous two paragraphs, because this is not your issue.  If
> you must open up your unit (eeek, that didn't sound good) make sure to
> check that all ribbon cables are snug, as they have a tendency to come
> loose when you pull the two pieces apart.  Also, make sure to put all
> the screws back in when you put it together again.  This should ensure
> that grounding comes from the chassis rather than the headphone ribbon
> cable (the littlest one).
> 
> Hope this helps,
> -Aaron
>