Yamaha MLC100 (was Hum in System)

[Guest]

Archived from groups: rec.audio.tech (More info?)

I had a chance last night to check the cables and guess what - you guys were
right (not that I ever doubted you).

I was doing this based on memory and my memory told me that those
connections were all MIDI cables and connectors - I remembered not really
looking at the pins and just turning the connectors until the indent fit, so
I just assumed they were MIDI cables, and, truth be told, if you had quizzed
me before this I wouldn't have been able to tell you how many pins are on a
MIDI cable - I was going on exterior appearance alone.

They are in fact 8 pin (or is it 8 din?) cables, the ones Yamaha provides
with the unit.

Nonetheless, it still confirms what I've been saying - that the Clavs are
connected to the Teacher's console with an Audio signal only - From the clav
HP out, to the MLA100 box, through the 8 pin cable to the teacher's console
(and HPs).

The ONLY MIDI connection is from the USB port of the Mac to the Clav (MIDI
In/Out via MidiSport USB interface).

I have not yet checked the ideas that Tim (IIRC) gave me (I was busy last
night and only had time to check the cables). But now this is cleared up
maybe it will eliminate some of the guesswork I've unfortunately presented
you guys with.

Thanks,
Steve

 

[Guest]

Archived from groups: rec.audio.tech (More info?)

Steve,
I hope by now you've found a solution but if not my experiences may
help.

We had exactly the same problem at the music lab at my daughter's
school.

Turned out to be two causes.
(1) The first and lesser problem was that the audio cables between the
student's interface box and the teacher's console were run across the
floor and were very close to the transformers powering the keyboards.
It was a simple matter to re-route the cables and remove this effect.


(2) The other, and more serious problem, was with the MIDI cables
connecting the keyboards to the PCs. (Yes, I saw there was some
confusion in earlier postings about how the units were connected but
I do mean the MIDI cables.) The fix for this is a bit more
complicated.

The second problem is caused by the fact that the standard MIDI cable
includes an earth as well as the data connections. Each of the
computers is earthed through the power plug and by connecting the
computers to the keyboards by the MIDI cables and in turn connecting
all the keyboards to together via the MLC100 you create massive earth
loops.

The solution in our case was to make some very short extenders for the
MIDI cables which connected the data signals but did not connect the
earth. (It was only necessary to modify one of the cables but I
forget now whether it was the OUT or IN cable - if you're interested
let me know and I'll check which it was).

This was a definite fix and the hum was removed entirely, but you have
to apply it all the computers - even one or two exceptions will bring
the hum back.