Ground lift question

[Dr88s]

I have no background in any kind of electronics. This is all a mystery to me.

 

I splurged and bought a Key Largo. I tried to use it last night, but it seemed to fail with whatever set up I had at my practice space. My question is actually unrelated.

 

Being my first time using it, I started to troubleshoot at home with a more basic setup. Something came up that I don't understand, and I'm wondering if it's normal.

 

The KL has paired outputs, a set of stereo 1/4 inch for a monitor(s), and a pair of XLR for FOH.

 

I tested each side of each channel with my Nord, outputting to my EV-ZLX12 which has combo jacks that except both 1/4" and XLR.

 

When I ran the monitor output into the EV through a 1/4" TS, there was a pronounced hum in the 'lift' position which disappeared in the down position. Even in the down position, if I was physically touching the top of the box, there was a quiet hum. Interestingly, when outputting to the exact same monitor using XLRs (MAIN output), there was no hum at all.

 

What gives? Does this have anything to do with the cable I was using, based on this description?

 

I did not want to hijack the KL thread.

 

 

[MIDI2XS]

[...] When I ran the monitor output into the EV through a 1/4" TS, there was a pronounced hum in the 'lift' position which disappeared in the down position. Even in the down position, if I was physically touching the top of the box, there was a quiet hum. Interestingly, when outputting to the exact same monitor using XLRs (MAIN output), there was no hum at all.

 

What gives? Does this have anything to do with the cable I was using, based on this description?

I don't have any personal experience with the Key Largo, but according to this...

http://www.prosoundweb.com/channels/live-sound/radial-engineering-releases-key-largo-keyboard-mixer/

...the monitor outs are balanced TRS, and the main (XLR) outs are transformer isolated.

 

Since using unbalanced cables on a balanced output can have various outcomes, depending on circuit design, you might try TRS cables rather than TS and see if that helps.

 

[The Real MC]

What gives? Does this have anything to do with the cable I was using, based on this description?

 

The 1/4" TS plug connects the chassis grounds at both ends. That's causing your hum, it created a ground loop.

 

XLR cables - when wired correctly in your case - don't connect chassis ground of both devices. The shell of the XLR connector connects to chassis ground, and only one shell of the cable should be connected to the shield in the cable. This isolates chassis grounds between two devices while providing a shield for the wires carrying audio. Pin 1 of both XLR plugs are supposed to be connected to CIRCUIT GROUND, which is different from chassis ground. That's the ideal grounding scheme and the 1/4" plugs can't provide that.

[Raymb1]

Try one of these: https://www.amazon.com/Ebtech-Hum-Voltage-Filter/dp/B0002E4YI8

 

Sweetwater carries them also.

[Dr88s]

Thanks to all 3 respondents, addressed below.

[Dr88s]

The 1/4" TS plug connects the chassis grounds at both ends. That's causing your hum, it created a ground loop.

 

XLR cables - when wired correctly in your case - don't connect chassis ground of both devices. The shell of the XLR connector connects to chassis ground, and only one shell of the cable should be connected to the shield in the cable. This isolates chassis grounds between two devices while providing a shield for the wires carrying audio. Pin 1 of both XLR plugs are supposed to be connected to CIRCUIT GROUND, which is different from chassis ground. That's the ideal grounding scheme and the 1/4" plugs can't provide that.

 

Thanks for the detailed explanation. Seems like this is an inherent problem with TS/TRS design.

[Markyboard]

Try one of these: https://www.amazon.com/Ebtech-Hum-Voltage-Filter/dp/B0002E4YI8

 

Also prevents pregnancy and the common cold.

[Dr88s]

Try one of these: https://www.amazon.com/Ebtech-Hum-Voltage-Filter/dp/B0002E4YI8

 

Sweetwater carries them also.

 

For now it's not a major problem for me as monitoring is from my FOH feed, and I can silence the hum with the appropriate side of the ground lift switch even if I do need to do my own monitoring... Good to keep one of these handy, though.

[Dr88s]

I don't have any personal experience with the Key Largo, but according to this...

http://www.prosoundweb.com/channels/live-sound/radial-engineering-releases-key-largo-keyboard-mixer/

...the monitor outs are balanced TRS, and the main (XLR) outs are transformer isolated.

 

Since using unbalanced cables on a balanced output can have various outcomes, depending on circuit design, you might try TRS cables rather than TS and see if that helps.

 

I will report back later. I'll troubleshoot more tonight.

[Markyboard]

This has been posted at least once before but it's the bible of audio grounding/ ground loops and proper connections between balanced, unbalanced and everything in between:

 

Ground Loops etc.

[MIDI2XS]

This has been posted at least once before but it's the bible of audio grounding/ ground loops and proper connections between balanced, unbalanced and everything in between:

 

Ground Loops etc.

Yes...

https://forums.musicplayer.com/ubbthreads.php/topics/2673740/Re_Grounded_keyboards_synthesi

 

[U.Honey]

The 1/4" TS plug connects the chassis grounds at both ends. That's causing your hum, it created a ground loop.

 

XLR cables - when wired correctly in your case - don't connect chassis ground of both devices. The shell of the XLR connector connects to chassis ground, and only one shell of the cable should be connected to the shield in the cable. This isolates chassis grounds between two devices while providing a shield for the wires carrying audio. Pin 1 of both XLR plugs are supposed to be connected to CIRCUIT GROUND, which is different from chassis ground. That's the ideal grounding scheme and the 1/4" plugs can't provide that.

 

Thank you for the explanation! All these years I've been making my own cables and soldering them wrong. I've always connected the shield to pin 1 of the XLR on both ends :-o

[Throbert]

SOS has an article by Hugh Robjohns: Q. Is there a better balanced-to-unbalanced cabling solution?,

but it's actually about an unbalanced signal to a balanced input the solution is in the last 2 paragraphs.

You can check it out here. I'm having Redco build and retrofit some cables based on this.

[MIDI2XS]

[...] All these years I've been making my own cables and soldering them wrong. I've always connected the shield to pin 1 of the XLR on both ends :-o

Connecting the shield to pin 1 of the XLR at both ends is "best practice" - it minimizes the chances of RFI (Radio Frequency Interference). I suggest you continue to do so unless there's a specific situation that merits otherwise. If you make some cables with the shield lifted at one end, you should mark them so that they're easily identified.

 

Note that the connector "shell" and the cable "shield" aren't the same thing, physically or electrically with reference to ground in most cases. Read the Rane info linked to, if interested in a better understanding.

 

[U.Honey]

[...] All these years I've been making my own cables and soldering them wrong. I've always connected the shield to pin 1 of the XLR on both ends :-o

Connecting the shield to pin 1 of the XLR at both ends is "best practice" - it minimizes the chances of RFI (Radio Frequency Interference). I suggest you continue to do so unless there's a specific situation that merits otherwise. If you make some cables with the shield lifted at one end, you should mark them so that they're easily identified.

 

Note that the connector "shell" and the cable "shield" aren't the same thing, physically or electrically with reference to ground in most cases. Read the Rane info linked to, if interested in a better understanding.

 

Well here is a picture from Rane website:

 

http://www.rane.com/png/n110fig4a.png

 

The first cabling is XLR to XLR and it suggests leaving pin 1 open on the input side, doesn't it?

 

Here is the whole webpage: http://www.rane.com/note110.html

 

[MIDI2XS]

Connecting the shield to pin 1 of the XLR at both ends is "best practice" - it minimizes the chances of RFI (Radio Frequency Interference). I suggest you continue to do so unless there's a specific situation that merits otherwise. If you make some cables with the shield lifted at one end, you should mark them so that they're easily identified.

 

Note that the connector "shell" and the cable "shield" aren't the same thing, physically or electrically with reference to ground in most cases. Read the Rane info linked to, if interested in a better understanding.

 

Well here is a picture from Rane website:

 

http://www.rane.com/png/n110fig4a.png

 

The first cabling is XLR to XLR and it suggests leaving pin 1 open on the input side, doesn't it?

It certainly shows that configuration. However, Figure 4 is under the heading "The Last Best Right Way To Do It" - in other words, those diagrams represent compromises to be used if there's a hum problem that can't be dealt with otherwise.

 

Earlier in the Rane article, under "The Absolute Best Right Way To Do It", is this:

http://www.rane.com/png/n110fig1a.png

 

But please feel free to do whatever you think is appropriate.

 

[Throbert]

SOS has an article by Hugh Robjohns: Q. Is there a better balanced-to-unbalanced cabling solution?,

but it's actually about an unbalanced signal to a balanced input the solution is in the last 2 paragraphs.

You can check it out here. I'm having Redco build and retrofit some cables based on this.

[U.Honey]

Earlier in the Rane article, under "The Absolute Best Right Way To Do It", is this:

http://www.rane.com/png/n110fig1a.png

 

You're right. Sounds like I've assembled my cables the right way after all.

[Markyboard]

SOS has an article by Hugh Robjohns: Q. Is there a better balanced-to-unbalanced cabling solution?,

but it's actually about an unbalanced signal to a balanced input the solution is in the last 2 paragraphs.

You can check it out here. I'm having Redco build and retrofit some cables based on this.

 

 

I wonder if Redco or someone has a little smt module for the cap/resistor? No way would I mess with building this myself out of standard parts and hope it fits (and doesn't short). I'm going to change out all my mono cables soon as part of my on-going noise reduction. I'm leaving the shield unconnected at the balanced input end since Rfi is not a big concern for me on a home studio. Thus no need for the cap/resistor but I believe the shield will provide some degree of rfi supression.

 

Thoughts?

[The Real MC]

This has been posted at least once before but it's the bible of audio grounding/ ground loops and proper connections between balanced, unbalanced and everything in between:

 

Ground Loops etc.

 

I've seen many of the Rane notes, but not that one. That's a good read.

[MoodyBluesKeys]

In places like radio or TV studios where there transmitters also exist, even the Standard XLR cable idea of shield only connected at console end doesn't always get rid of the grunge.

 

RCA, in the days when they made a lot of broadcast equipment made special cable for studio microphones. It was four conductors (three inside and a shield). The three inside ones were connected to the XLR in a 1-2-3 pattern on both ends, and the shield was connected only at the audio console end.

 

According to RCA Engineers, this provided a "Faraday shield" on the cable.

(Reason I know about this: while I was C.E. of a TV station, we had a lot of problems with 60hz sync buzz on the studio microphones. All original wiring had been done with standard Belden audio cable (2 wires and aluminum foil shield with an added copper uninsulated wire for the length of the cable).

 

The new owner of the station was upset about this, and informed me one night that I had better get it fixed before his next visit. I called RCA, and they recommended their cable. Did I mention that this stuff cost about ten times what the Belfoil cable cost?

Two weeks later, owner comes back, and wants to know why I didn't have the problem fixed. All I knew was I made the order, then someone cancelled it before shipment. I informed the owner that some stupid idiot, probably a bean counter in Accounting, had cancelled my order.

 

Owner turned out to be the idiot that cancelled it. I held my ground and finally he agreed to buy the cable, with the admonition that, if it didn't fix the problem, I was fired.

Considering how much money I was not making at the time I didn't get real upset.

 

Two weeks later, when owner returned, all the studio mics were quiet as a churchmouse (not sure of the exact level of a churchmouse, think it is about -140dbm or so). I was still C.E. a couple of years later, when I quit for a better paying position elsewhere.

 

[Markyboard]

I held my ground ...

 

[Throbert]

I wonder if Redco or someone has a little smt module for the cap/resistor? No way would I mess with building this myself out of standard parts and hope it fits (and doesn't short). I'm going to change out all my mono cables soon as part of my on-going noise reduction. I'm leaving the shield unconnected at the balanced input end since Rfi is not a big concern for me on a home studio. Thus no need for the cap/resistor but I believe the shield will provide some degree of rfi suppression.

 

Thoughts?

I'm thinking they're using SMT as well. Maybe soldering the chips directly to the ts shield with the cold and bridging the other ends to the line shield.

If your going from signal-ts-trs input Id connect the shield at the trs or XLR, gives noise a place to ground out.

[I-missRichardTee]

May a slow to grasp electronics musician ask a few questions?

 

I just come out of my keyboards with L and R outputs. I am not aware of the nature of my $50 cables

I just go straight into powered speakers and that's it.

IS there something I am missing out on?

 

and what does TS stand for?

[Michael Wright]

and what does TS stand for?

Tip sleeve, unbalanced.

[Markyboard]

If your going from signal-ts-trs input Id connect the shield at the trs or XLR, gives noise a place to ground out.

 

Thanks - that is a bit easier to solder up as well.

[MIDI2XS]

I just come out of my keyboards with L and R outputs. I am not aware of the nature of my $50 cables

I just go straight into powered speakers and that's it.

IS there something I am missing out on?

Probably not, if everything seems to be working properly.

 

 

and what does TS stand for?

See https://ehomerecordingstudio.com/wp-content/uploads/2014/09/trs-and-ts-connectors-e1417633858352.png