Again with my questions to fix my dear guitarrist issues with his
rack. I think I already have a clear picture on how to proceed, but if you mind take a
look into the novel I am about to write, and give me your opinions, I will greatly
appreciate the learning experience.
1) The gear part.
First part: The electrical instalation.
distribution starts with a mains transformer to get 110v (Argentina is 220V and my friend
got most of his gear in the US. Earth is OK (connects straight from the wall to the earth
terminal on the 110V side). This goes to the rack (an SKB unit) to a Furman power
conditioner. All rack units connect to the rack with 110V three terminal male plugs
(except one unit, more about this later)
I checked with a continuity tester and
all external housings show good continuity to the earth terminal on the 220V side of the
transformer (even the unit that does not have the earth connection). I did this test with
all the audio and midi cables connected... must recheck with all cables removed...
Second part: The modules.
The rack contains the following items:
PSA-1, Digitech IPS 33-B, Korg A2, Lexicon LXP-15 II, Behringer Denoiser NSR 2000 and
Behringer Ultrafex PRO EX 3200. To control all this gear he has a ground control
pedalboard "fueled" by a wall-wart transformer (that also goes to the Furman Unit) and
MIDI cables all over chaining everything.
Regarding the MIDI chain, despite
jumping from module to module instead of going through a MIDI patch bay, it is working
The Korg A2 still has the original 110v plug without earth... do you think
it worth changing the cable (or plug) to include an earth terminal on the "furman side"?
What if the cable does NOT have a third cable on it? Should I ask a technician to open up
the unit and fit a ground line? or just connecting the housing to any other rack unit will
be enough to be "safe"?
2) The audio connections.
The effect chain is linked like this:
From SansAmp Send output, mono unbalanced cable to the Digitech
Digitech, stereo unbalanced cables to Korg
From Korg, Stereo unbalanced cables to
From Lexicon, Stereo unbalanced cables back to the effect return on the
From SansAmp, stereo BALANCED cables to Denoiser
From Denoiser, stereo
BALANCED cables to Enhancer
From Enhancer.... lots of HUMMMMmmmMMMmmmm
Also we have the chain of MIDI cables that (I think) will add more to the ground loop
My approach to the solution and questions.
First: Should I worry about the KORG unit
not being Earthed (as already mentioned up there). Suggestions to solve it
Should I worry about the units being bolted to the Rack housing hence creating a common
earth parallell to the cables?
Third: I could not find any info on the Digitech and
Korg connections being Balanced or Unbalanced. I found an A2 service manual on the net,
and the schematic looks like both inputs and outputs are unbalanced. Lexicon outputs, no
clue (input says "unbalanced" on the manual!!). Is there an easy way to tell if an output
or input is balanced or unbalanced?
Fourth: How can I check if the inputs and outputs
have "ground lifts"... I remember reading an article in SOS, but was unable to find it
again!!!! shame on me.
Fifth: Can MIDI cables help in creating ground loops on the
audio side of the business? This MIDI cables are quite long and "looped" inside the rack
(nobody manufactures patch-length MIDI cables in Argentina!!!!)
to the problems are all the unbalanced cable connections, and my idea was to strip all the
rack out, separate the parts and start installing one rack unit at a time, connect, check,
and move on adding the next module to the rack... Once detecting the "offending
connection" just cut the sleeve connection out and move on with my life. Just purchased a
sensible amount of good quality connectors and cable to do this.
And this leads
me to the final question. I have microphone cable... when soldering for unbalanced
connections, I do not know if soldering BOTH center cables to the tip makes a difference
vs connecting just one and leave the other "floating"....
THANKS A LOT!!!!
Please,as usual, I GREATLY appreciate your thoughts and opinions.