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Guitar effect rack, ground loops and advise required!

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Guitar effect rack, ground loops and advise required!

Postby SMV_Argentina » Mon Oct 29, 2012 9:30 pm

Hi chaps.

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.

Chapter 1) The gear part.
First part: The electrical instalation.
The electricity 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:
SansAmp 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 OK.

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"?

Chapter 2) The audio connections.
The effect chain is linked like this:
Guitar to SansAmp
From SansAmp Send output, mono unbalanced cable to the Digitech
From Digitech, stereo unbalanced cables to Korg
From Korg, Stereo unbalanced cables to lexicon.
From Lexicon, Stereo unbalanced cables back to the effect return on the SansAmp
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 potential!!

Chapter 3) 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
Second: 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!!!!)

My candidates 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.
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Re: Guitar effect rack, ground loops and advise required!

Postby zenguitar » Tue Oct 30, 2012 12:46 am

I'll start with some more straightforward information and leave the hard work for others

The MIDI side should be the least of your problems. The MIDI spec requires all MIDI inputs to be opto-isolated which goes a long way towards preventing ground loops with MIDI cables. You might find this Hinton Instruments MIDI guide very useful as it gives you a lot of detailed info in a very digestible form.

However, it might be worth checking each of the MIDI devices to confirm which of the ins/outs/thrus are connected to the chassis ground as that might come in useful later.

And while you are checking the MIDI chassis grounds, you should also check the audio ins and outs to see which of those are connected to the chassis as well.

Unfortunately, a lot of rackmount guitar equipment is designed and built by companies that don't generally make rack equipment. They test their gear in isolation but don't always consider whether it will play nicely with other rack gear from other manufacturers. So if all audio ins & outs and MIDI connectors are grounded through the chassis there is a lot of scope for ground loops once you bolt them all together in a steel rack with steel bolts.

My starting point would be to remove everything from the racks, lay it out so none of the cases have any physical contact (side by side but not touching if you can, if not, stack them with cardboard, wood, plastic sheet, or anything else non-conducting between them) and then connect everything up so that the cables are the only connections. If you still get hum, you have to use a process of elimination to work out where the problems lie and eliminate them. Once you've done that start rebuilding the racks piece by piece and regularly testing. If the hum returns when you rack the gear you might have to invest in nylon washers/nuts&bolts to isolate some of the rack units from the rack case.

Andy
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Re: Guitar effect rack, ground loops and advise required!

Postby Goddard » Tue Oct 30, 2012 1:58 am

SMV_Argentina wrote:Hi chaps.

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.

Chapter 1) The gear part.
First part: The electrical instalation.
The electricity 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).

Be careful using a Furman power conditioner with that "mains transformer" (from your description, sounds as if it's really an autotransformer, not a true step-down isolation trans):

http://www.gson.org/stepdown/
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Re: Guitar effect rack, ground loops and advise required!

Postby SMV_Argentina » Tue Oct 30, 2012 4:46 pm

Thanks for the input (a very cheap pun on words... but you know what I mean).

Regarding the transformer... YOU ARE RIGHT!! it is an autotransformer indeed. Before plugging the transformer, I checked the wirings and had continuity across primary and secondary windings, so before plugging the rack, I checked "polarity" on the 110V side and the plug orientation was OK, so every rack unit received neutral through neutral, and viceversa. Thanks for the advise!

Best
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Re: Guitar effect rack, ground loops and advise required!

Postby Gadget13769 » Thu Nov 01, 2012 4:18 pm

You might find these Humfrees useful...

Image
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Re: Guitar effect rack, ground loops and advise required!

Postby SMV_Argentina » Thu Nov 01, 2012 7:37 pm

Gadget13769 wrote:You might find these Humfrees useful...

Image

Not sure if I will be able to get those here in argentina... but I am thinking on how to "clone" them.... lovely!

Thanks.
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Re: Guitar effect rack, ground loops and advise required!

Postby zenguitar » Fri Nov 02, 2012 1:11 am

SMV_Argentina wrote:
Gadget13769 wrote:You might find these Humfrees useful...

Image

Not sure if I will be able to get those here in argentina... but I am thinking on how to "clone" them.... lovely!

Thanks.

They are exactly what I had in mind when I suggested nylon nuts, bolts, and washers. But as I wasn't sure whether or not you could easily get them in Argentina I decided to avoid mentioning a specific product.

Andy
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Re: Guitar effect rack, ground loops and advise required!

Postby Gadget13769 » Fri Nov 02, 2012 4:07 pm

Part of the isolation is easy to replicate in a variety of ways (using the aforementioned nylon washers front and back, or cutting your own strips of plastic to fold around, etc.) but the crucial bit is the sleeving on the head end of the bolt, which has to be just the right length to insulate the bolt from the rack without fouling the captive nut and strong enough to not wear-through with the weight of equipment / vibration.

Plus, you may need to add more insulation if either the faceplates or back the rack equipment is likely to touch when installed. I find self adhesive neoprene tape or cut-up mousemat foam to work well.

I agree with previous comments though - first layout all your gear in an isolated fashion and then connect / add / remove pieces to establish where the problem is coming from.
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Re: Guitar effect rack, ground loops and advise required!

Postby ef37a » Sat Nov 03, 2012 7:45 pm

If you cannot get Humfrees you might be able to find these..

http://www.cmsplc.com/hellermanntyton-rack-snaps-4.html

Dave.
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Re: Guitar effect rack, ground loops and advise required!

Postby SMV_Argentina » Sun Nov 04, 2012 10:52 pm

Thanks for all the good info.

Yesterday night we had our first gig (as this band) and everything went OK. The Sound Lady gave us a hand to take the noise out (without cutting earth wires!) with DI boxes and some patch cables (seems that they cross with this kind of issues all the time with amateur bands).

Now, the in-famous rack will have a pit-stop in my home for a full diagnostic run and solving all earthing, looping and stuff...

Regarding the rack isolation, I was thinking in line with the self adhesive neoprene but with rubber (I have a rubber wholesaler not far from home) and find out how to isolate the "exposed thread" part of the bolts (have an idea...).

Thanks again chaps!

Best!
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