Old 01-21-2019, 05:48 PM   #1
Coachz
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Default Isolate midi cables?

Anyone know of a connector/box to isolate midi from my computer midi cable to my midi guitar effect? I get a lot of CPU noise with the 5 pin DIN cables connected.
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Old 01-21-2019, 05:59 PM   #2
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Anyone know of a connector/box to isolate midi from my computer midi cable to my midi guitar effect? I get a lot of CPU noise with the 5 pin DIN cables connected.
Midi is opti-isolated as part of the design spec., so there is no physical connection wire-wise.

https://en.wikipedia.org/wiki/Opto-isolator
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Old 01-21-2019, 06:47 PM   #3
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Midi is opti-isolated as part of the design spec., so there is no physical connection wire-wise.

https://en.wikipedia.org/wiki/Opto-isolator
Unfortunately the reality is even though it's opto isolated there is a transistor that is amplifying the signal Down The Wire that then connects to another transistor at the end of The Wire where it connects back to the destination unit. And that's where the ground Loop is created. it is a physical wire and there is no light going down the copper. It's electrons. electrical engineer here
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Old 01-21-2019, 10:21 PM   #4
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If Midi connects the ground, IMHO something is wrong with the plugs. The information is transferred via pin 4 and 5 (5-pin) or 2 and 3 (XLR) and does not need ground & shield (pin 3 (5-pin) or 1 (XLR), optionally case on both) to be connected in the plugs, If the cable connects more pins, it should not harm.

Most likely the socket case is connected with the housing of some equipment, it should be possible to isolate this in the plugs. Breaking the cable shield with that should not harm.

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Old 01-22-2019, 02:59 AM   #5
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I have some kind of loops which I try to eliminate since years, unsuccessfully till now:

Kawai DP -> (MIDI) -> TC GTX -> (XLR) -> mixer/interface
Generate noise if MIDI cable is connected AND
TC is connected with XLR to something else. So:
* no problem if I use headphone output to the same equipment.
* no problem if MIDI is not connected
* no problem if I connect MIDI from another equipment to GTX

The noise is also present when Kawai is connected with USB to computer and line output to something else, but that I can (almost) eliminate using isolating DI box on analog outputs.
That USB connection also trigger noise from Behringer mixer or Roland TD (when they are also USB connected).

While it is clear Kawai has some bad internal design, I am also interested how to decouple MIDI. It something like Motu MIDI box proper isolate things? Too pricey for me to just test, but if I can keep everything connected throw it, that can be a good investment (also from latency perspective, USB from Kawai has bad MIDI latency and even Roland is far from perfect. At least after comparison with MIDI->RME. I guess Motu has also implemented it right).
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Old 01-22-2019, 03:11 AM   #6
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You getting a ground loop. Midi cables, usb cables, etc have outer ring grounded so you're connecting grownd from one device to another via another route, not only via the power lead ground cable. I used to have a lot of hassle with that.
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Old 01-22-2019, 08:49 AM   #7
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Not all cables have the rings connected to ground but lots of older ones do. Had the exact issue with a Digitech Whammy pedal i was controlling from my computer. I tested my cables and found that only one had the ground connected to the outer ring. I chucked it and got a new cable. Problem was solved.
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Old 01-22-2019, 08:55 AM   #8
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I wish I knew how to buy a pair online that don't have the grounds connected
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Old 01-22-2019, 01:06 PM   #9
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I'm electronics designer by trade and I know my way around MIDI hardware specification, and yes, it definitely should be optically isolated, meaning there's no electrical connection between two units that are connected with a MIDI-cable.

that being said, if manufacturer of the devices connected by MIDI-cable have botched their hardware (could happen... lot's of crap around these days) it might be that the shield is connected from both ends on accident (it shouldn't be connected but from one end).

Also, it's possible to cause a ground loop if you accidentally connect midi output to midi output since the shield should be connected to ground only from the output side of the cable and this wrong connection could cause problems.

All that said, it's more probable that the ground loop is coming from somewhere else from your system and MIDI has nothing to do with it.

See how MIDI is supposed to be connected from this picture and notice if the shield is for any reason connected at the receiving side, there's a possibility of a ground loop. also all MIDI-cables are supposed to be the same and non directional (unlike XLR) so the proper grounding scheme should be followed by the device manufacturers:

https://en.wikipedia.org/wiki/MIDI#/..._schematic.svg
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Old 01-22-2019, 01:20 PM   #10
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Quote:
Originally Posted by Coachz View Post
I wish I knew how to buy a pair online that don't have the grounds connected
If you want a cable that has one end of the cable ground lifted and marked, you can order a proper MIDI-cable from (for example) Thomann with Neutrik/rean plugs (so you can open them easily) and modify it as such that it lifts the ground from other end. After that you simply mark out which is the ground lifted end and always put that as the input side.
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Old 01-22-2019, 01:32 PM   #11
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thanks, great idea :-)
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Old 01-22-2019, 02:08 PM   #12
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thanks, great idea :-)
Just make sure you follow the schematic I linked... You need the two wires, but the SHIELD should be connected to ground only from one end of the connection and the signal ground shouldn't be connected with the receiving devices ground at all.


You could use a basic multimeter with basic continuity measurement mode to check if the devices you're using are at least properly designed or not. Then you know if you can fix the issue with custom cable. It could be that even signal grounds are improperly connected together and then you can't really do that... hmmh :/
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Old 01-22-2019, 04:03 PM   #13
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Biggest problem with an embarrasingly large number of commercially-available "MIDI din cables is that they are often actually old DIN convention Audio cables, which DO give problems for the reason outlined here by others. I bought a bunch of supposedly proper MIDI cables a couple of years back for 8 GB pounds each - not cheap - boxed and labeled as MIDI cables. All 5 pins connected, so I had to takw the buggers apart and fix them. Original supplier - a smallish electronics company local to me - refused to accept that they werent actually suitable for MIDI. Grr!
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Old 01-22-2019, 11:48 PM   #14
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In fact having a 1:1 cable transfer additional pins is not supposed to create any problems. It's the Midi Gear sockets that are faulty, if they connect more than two pins (no ground !!!!) or do not isolate the socket case at the "Midi In" site.

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Old 01-23-2019, 09:34 PM   #15
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Test your cable and see if it has ground connected on both sides. All my midi cables have it but generally only need one because one of the pins takes care of that anyway.

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Old 01-24-2019, 08:20 PM   #16
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I believe the last batch I bought was from Monoprice. Cheap as dirt but wired correctly and decently made.
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Old 01-25-2019, 04:40 AM   #17
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Originally Posted by ivansc View Post
Biggest problem with an embarrasingly large number of commercially-available "MIDI din cables is that they are often actually old DIN convention Audio cables, which DO give problems for the reason outlined here by others. I bought a bunch of supposedly proper MIDI cables a couple of years back for 8 GB pounds each - not cheap - boxed and labeled as MIDI cables. All 5 pins connected, so I had to takw the buggers apart and fix them. Original supplier - a smallish electronics company local to me - refused to accept that they werent actually suitable for MIDI. Grr!
Why didn't you just say you changed your mind and don't want the cables.
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Old 01-25-2019, 05:05 AM   #18
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Originally Posted by gvanbrunt View Post
I believe the last batch I bought was from Monoprice. Cheap as dirt but wired correctly and decently made.
The last review and questions says full 5 pin implementation. Odd.

https://www.monoprice.com/product?p_id=8536
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Old 01-25-2019, 03:31 PM   #19
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you need a pair of good cables with good (golden) jacks
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Old 01-25-2019, 05:51 PM   #20
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you need a pair of good cables with good (golden) jacks
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Old 01-26-2019, 02:18 AM   #21
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Why didn't you just say you changed your mind and don't want the cables.
You had to be there. Seller was a mate or so I thought & it was easier just to mod them rather than starting a fight over it. FWIW, at least it was pretty easy to disconnect the other 3 pins and then do a direct shield connection between just the case shells.
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Old 01-26-2019, 02:19 AM   #22
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Quote:
Originally Posted by producerspot View Post
you need a pair of good cables with good (golden) jacks
Ha Ha! REALLY????!!! Labelled "Monster" as well?
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Old 01-26-2019, 06:12 AM   #23
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I have not checked if there is some improvement, but I can confirm that cutting the wire to the pin 2 (in the output connector) does not prevent MIDI to work

PS. where can I buy something to upgrade my head? I have tried hard, but I can not hear the difference in sound when connecting monitors with Kimber Kable Hero (I have got by accident). Or is that possible only once I use platinum based USB cable to my audio interface?
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Old 01-26-2019, 08:01 AM   #24
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Sorry but you are SO last year! everyone knows all the pros now use sintered gold/iridium alloy now.
Get with the program!


(muffled titter)
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Old 01-26-2019, 08:04 AM   #25
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Quote:
Originally Posted by ivansc View Post
Sorry but you are SO last year! everyone knows all the pros now use sintered gold/iridium alloy now.
Get with the program!


(muffled titter)
And you have to buy it with bitcoin.
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Old 01-26-2019, 08:13 AM   #26
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Quote:
Originally Posted by ivansc View Post
Sorry but you are SO last year! everyone knows all the pros now use sintered gold/iridium alloy now.
Get with the program!


(muffled titter)
Oh no... I hoped this one can do the trick:
https://www.highend-audiokabel.de/ca...usb-kabel.html
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Old 01-26-2019, 08:16 AM   #27
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Originally Posted by azslow3 View Post
Oh no... I hoped this one can do the trick:
https://www.highend-audiokabel.de/ca...usb-kabel.html
The homemade shrink tubing is what makes it special.
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Old 01-27-2019, 04:13 AM   #28
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Cant find it at present but my brother Bry has a hilarious site featuring HiFi nerds bullshit..

I will go look or if it comes to it email him for a link.
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Old 02-01-2019, 10:03 AM   #29
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Originally Posted by ivansc View Post
Biggest problem with an embarrasingly large number of commercially-available "MIDI din cables is that... All 5 pins [are] connected, so I had to take the buggers apart and fix them.
mschnell is right though, a proper MIDI cable has all 5 pins connected straight through and if there is an issue with grounding etc. it's because the MIDI-device manufacturer screwed up with their schematics.

It's the same thing when people blame the XLR-cables when the equipment manufacturer messed up their grounding scheme on a mixer/amplifier or what not etc..

One can fix these issues with custom cables, ground lifting etc. but they shouldn't have to.
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Old 02-01-2019, 10:14 AM   #30
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I put everything on the same ground, computer, amplifier, converter, guitar effects processor. There's still too much noise as soon as the MIDI cables are connected. It's like at 10 DB increase in noise floor and it's not a pretty noise either. It's like all digital noise.
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Old 02-01-2019, 10:35 AM   #31
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I know it sounds crazy but I always keep a few various types of inline hum isolators/filters and the AC adapter isolators on hand - never seen a problem they couldn't solve.

Can be pricey but you buy once, you cry once. I bought some over a decade ago, no hum since...

https://www.amazon.com/TASCAM-DTI-Tr.../dp/B0009GUOQA

https://www.amazon.com/Audio-iDefend.../dp/B01N3XKOLG

https://www.amazon.com/Ebtech-Hum-Gr.../dp/B0002E4YI8

https://www.amazon.com/EBTECH-HE-2-E.../dp/B0002E4YH4
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Old 02-01-2019, 10:52 AM   #32
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Quote:
Originally Posted by karbomusic View Post
I know it sounds crazy but I always keep a few various types of inline hum isolators/filters and the AC adapter isolators on hand - never seen a problem they couldn't solve.

Can be pricey but you buy once, you cry once. I bought some over a decade ago, no hum since...

https://www.amazon.com/TASCAM-DTI-Tr.../dp/B0009GUOQA

https://www.amazon.com/Audio-iDefend.../dp/B01N3XKOLG

https://www.amazon.com/Ebtech-Hum-Gr.../dp/B0002E4YI8

https://www.amazon.com/EBTECH-HE-2-E.../dp/B0002E4YH4
thanks. I have a tonelab le connecting to the effects Loop of a marshall amp and so the tonelab has tow midi cables, two audio cables and a power supply cable connected so what do you isolate?
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Old 02-01-2019, 12:36 PM   #33
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Quote:
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thanks. I have a tonelab le connecting to the effects Loop of a marshall amp and so the tonelab has tow midi cables, two audio cables and a power supply cable connected so what do you isolate?
I just look for places a loop can occur and try there, anything you have connected that has a ground wire. That USB one was assuming someone using a USB connection (MIDI keyboard whathave you), the ART one, I'd use for in/out (one, other or both) in that effects loop and so on. At minimum send the FX loop send or return through one of the channels on the ART.

I often have ground loop issues when I split and use two amps and on one of those I go through the ART and it breaks the loop. I also always end up with a loop between my computer, rack and powered monitors so I use an ART for L/R going to my monitors and it kills the noise DEAD.
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