Add ground lift to (natively without it) amp

[EmpInfNed]

Hi, I wanted to buy this:
Hosa GLT-255 XLR Female to XLR Male Ground Lifter

but in this video it's said it doesn't work and it is a placebo-product only:


My goal is to find some way to add to my Ashdown Bass head DI ground lift feature considering it doesn't have it.

Can you suggest me any working solution or working product?
I found this:
Behringer | Product | DI100
Producer says "you can even plug your guitar or bass amp’s speaker output into the DI100" so it seems me a connection: AMP XLR > Behringer Ultra-di 100 > MIXER XLR can be done. Am I right?

Thank you very much

 

[agedhorse]

If it’s truly a ground loop, that adapter will work, it does exactly the same thing as the switch.

Note that ground lift switches only work about 90% of the time, there are other causes of between components that can result from either circuit design, or things outside of your control.

The video is looking at galvanic isolation which is different yet related, and show video examples which are also different.

 

[EmpInfNed]

If it’s truly a ground loop, that adapter will work, it does exactly the same thing as the switch.
Note that ground lift switches only work about 90% of the time, there are other causes of between components that can result from either circuit design, or things outside of your control.

Thank you a lot: I will also investigate the "other possible causes" too!

A question about the Berhinger adapter, if you know: to connect the amp-XLR-output to the adapter-XLR-input is required a male/female XLR cable unbalanced or balanced?

Thank you very much again

 

[Redbrangus]

If you use the Hosa adaptor, do open it up and clip the wires connecting Pin 1 on the XLRs to the case ground, as the presenter describes in the video.

With the Behringer DI box, if you use an XLR cable to connect it to your amp's output, that cable should be balanced. Although it's not unheard of, you aren't likely to encounter an XLR-to-XLR cable that's not a balanced cable.

 

[Old Garage-Bander]

Hi, I wanted to buy this:
Hosa GLT-255 XLR Female to XLR Male Ground Lifter

but in this video it's said it doesn't work and it is a placebo-product only:


My goal is to find some way to add to my Ashdown Bass head DI ground lift feature considering it doesn't have it.

Can you suggest me any working solution or working product?

Thank you very much

The video was all over the map, pro audio, consumer, computer. So I won't address any of that here.
I am (was, now retired) a broadcast technician of nearly 50 years. My duties included the audio broadcast chain from the DJ's microphone all the way through to the transmitter's antenna. This included analog and digital audio, recording and live remote broadcasts. I spend a lot of time interfacing between pro, prosumer, consumer and computers. I will discuss the Hosa device in question, and touch on other aspects to hopefully address ground loop issues and solutions. And BTW, not all hum is caused by ground loops.

The Hosa device is listed as a ground lifter. It should work if Pin 1 is not passed through. If both sides have pin one also tied to the shell then it will pass ground through. But ground also must be carried through on the shells of the other cables it is connected to, which they shouldn't be normally.

I don't recall ever trying one of these for lifting a ground so can't speak to the internal wiring for that purpose. It does have value as a straight thru adapter when you run into the occasional instance where you do need to mate connectors of the same gender. I kept a couple of these in my tool box for that purpose. For ground lifts I usually rolled my own because I know how. Likewise for audio transformer adapters which can also solve hum problems. But I also purchased audio transformer adapters. My go to was usually someone like Whirlwind.

What does a ground lift do? It disconnects pin 1 on an XLR connector, aka the round jobs with three pins used most often in pro audio. Pin 1 carries the shield of a balanced audio cable. No audio signal is carried on the shield, only on pins 2 and 3. You can create a lifted ground cable by disconnecting pin 1 on one of the connectors. I'd make short cables with two XLR connectors (one of each sex) and just not connect pin 1 on one of the connectors. BTW, in pro audio, it is standard practice to NOT connect pin 1 (ground/shield) to the outer metal shell of the XLR, as was claimed in the video that Hosa did. There is a connection tab to do this, but it is not common practice in audio for the very reason raised in question of the Hosa adapter. Which end to lift can also be a consideration. But that's another discussion.

What is a ground loop? If you have two (or more) pieces of equipment powered from an A.C. wall outlet and that equipment uses a three prong A.C. plug (aka grounded plug) and then connect the equipment using XLR cables as is normally done in pro audio, like an amp D.I. output to a mixing console. You can get a ground loop hum, due to multiple grounds at slightly different voltage potentials. (Grounds aren't perfect) To keep the A.C. safety ground on the power cord operating you don't want to break ground there. Rather you employ some method to disconnect the audio shield/ground at one end of the cable. This is safe, effective, and relatively inexpensive. The other method is to use an audio isolation transformer.

This acts by placing an audio transformer on pins 2 and 3 between one device and another. These get relatively expensive and and you definitely get what you pay for here. Again, I like Whirlwind for these if I don't make my own, using a quality transformer. My use for something like this was more to convert unbalanced audio (2 conductor like phono or phone connectors) to the balanced, 3 conductor XLR for most pro use. Many store bought transformers, as well as the all the ones I built into a small box include a ground lift switch. That should be a clue that transformers and switches might be used for different purposes to solve different problems. A non- transformer ground lift switch won't degrade the audio as can happen with lower quality transformers.

All of this like so many other subjects will fill volumes and shelves. I spent a career working with it and only feel like I've scratched the surface. Lot of guys with lots more education and diplomas to prove it can take you on a dive, much deeper than you can ever imagine.

Note several re-edits. FYI.

 

[beans-on-toast]

Whirlwind makes a popular XLR barrel ground lifter. I make them with Neutrik connectors and a short cable.

 

[Redbrangus]

The Behringer DI referenced is an ACTIVE direct box that needs a battery or phantom power from a mixer. I'd recommend getting a passive, transformer-based one. As has been noted, Whirlwind makes some good ones, but there are others. What you are looking for is more of an isolation transformer than a direct box, since you're wanting to use it to isolate the balanced XLR output of your amp. If you go the direct box route, be sure it has an XLR on the input side -- not all of them do.

 

[Old Garage-Bander]

If you use the Hosa adaptor, do open it up and clip the wires connecting Pin 1 on the XLRs to the case ground, as the presenter describes in the video.

With the Behringer DI box, if you use an XLR cable to connect it to your amp's output, that cable should be balanced. Although it's not unheard of, you aren't likely to encounter an XLR-to-XLR cable that's not a balanced cable.

If you have to do balanced to unbalanced, keep the unbalanced part as short as possible. XLR type balanced cables/systems have several noise reduction advantages over unbalanced audio. They are designed for long runs even at mic level.
Unbalanced systems can pick up noise and hum on the shield. That shield also carries your audio in an unbalanced system.

 

[Lostgallifreyan]

I have no need to add anything here other than the obligatory nudge to prompt a search for the Rane documents "Sound System Interconnection" and "Grounding and Shielding Audio Devices". Both can be found as good quality PDF files. One has examples of passive methods, the other goes into useful detail about the 'Pin 1 problem' etc..

Between those and OGB's main post above (and the one about short lengths on the unbalanced end), you'll probably get all you need to make and test a passive answer to this, at low cost. It's worth trying this before you consider active devices of any kind.

 

[agedhorse]

The way to achieve true galvanic isolation from an XLR output is to use a 1:1 audio isolation transformer. Most of these lift pin 1 or contain a switch for lifting pin 1.

I actually stock these for touring players that need a bulletproof solution.

 

[Lostgallifreyan]

The way to achieve true galvanic isolation from an XLR output is to use a 1:1 audio isolation transformer. Most of these lift pin 1 or contain a switch for lifting pin 1.

I actually stock these for touring players that need a bulletproof solution.

I second this, before trying any active device. It's hard to see how a passive transformer method could fail in a way an active device could fix, with the exception being AC magnetic fields from powered coils of some kind if the isolation transformer doesn't have magnetic shielding, and these days there won't be many devices that use mains transformers so the main risk is gone.

 

[Old Garage-Bander]

I have no need to add anything here other than the obligatory nudge to prompt a search for the Rane documents "Sound System Interconnection" and "Grounding and Shielding Audio Devices". Both can be found as good quality PDF files. One has examples of passive methods, the other goes into useful detail about the 'Pin 1 problem' etc..

Between those and OGB's main post above (and the one about short lengths on the unbalanced end), you'll probably get all you need to make and test a passive answer to this, at low cost. It's worth trying this before you consider active devices of any kind.

Off I go to read the Rane stuff. Thanks for posting that.

Bias, Oscillator

 

[Lostgallifreyan]

Off I go to read the Rane stuff. Thanks for posting that.

Bias, Oscillator

With your history, mentioned earlier, I'd begun to wonder if you'd helped to write it.

 

[Old Garage-Bander]

I second this, before trying any active device. It's hard to see how a passive transformer method could fail in a way an active device could fix, with the exception being AC magnetic fields from powered coils of some kind if the isolation transformer doesn't have magnetic shielding, and these days there won't be many devices that use mains transformers so the main risk is gone.

I also dislike actives where passive solutions work. Es the multiple failure mode reasons. I've used them and if done right it can be an effective solution for converting unbalanced line level to balanced line level. Be aware that line level is not the same in balanced as it is in unbalanced. Unbalanced line level signals usually requires a significant boost to get up to balanced line levels. That requires an amp, aka active. Balanced and unbalanced line levels also run into impedance incompatibilities. The active circuit can resolve this as well. So they do have their place in the larger scheme of things.

We must remember that all of this originated when tubes were the only option. The tube's output transformer not only did impedance conversion but acted as an isolation transformer. This applied to gear intended to connect audio signals at line levels. Not so much the case in power amplification, though it can, and is used in systems, and even some instrument amps that we might use. So best to be very careful around it all with things that drive speakers. Grounding something there that shouldn't could let the smoke out.

With the move to solid state balanced line interconnects, we were able to do it electronically, not because it was just as good, (I don't think so) but it was a lot cheaper than a 1:1 isolation transformer, especially when putting it after an electrically balanced line output.

As @agedhorse said, his transformer coupled with a ground lift is bulletproof. It could very well be the best gadget in your tool box. And it is literally plug-and-play.

 

[Engle]

The video was all over the map, pro audio, consumer, computer. So I won't address any of that here.
I am (was, now retired) a broadcast technician of nearly 50 years. My duties included the audio broadcast chain from the DJ's microphone all the way through to the transmitter's antenna. This included analog and digital audio, recording and live remote broadcasts. I spend a lot of time interfacing between pro, prosumer, consumer and computers. I will discuss the Hosa device in question, and touch on other aspects to hopefully address ground loop issues and solutions. And BTW, not all hum is caused by ground loops.

The Hosa device is listed as a ground lifter. It should work if Pin 1 is not passed through. If both sides have pin one also tied to the shell then it will pass ground through. But ground also must be carried through on the shells of the other cables it is connected to, which they shouldn't be normally.

I don't recall ever trying one of these for lifting a ground so can't speak to the internal wiring for that purpose. It does have value as a straight thru adapter when you run into the occasional instance where you do need to mate connectors of the same gender. I kept a couple of these in my tool box for that purpose. For ground lifts I usually rolled my own because I know how. Likewise for audio transformer adapters which can also solve hum problems. But I also purchased audio transformer adapters. My go to was usually someone like Whirlwind.

What does a ground lift do? It disconnects pin 1 on an XLR connector, aka the round jobs with three pins used most often in pro audio. Pin 1 carries the shield of a balanced audio cable. No audio signal is carried on the shield, only on pins 2 and 3. You can create a lifted ground cable by disconnecting pin 1 on one of the connectors. I'd make short cables with two XLR connectors (one of each sex) and just not connect pin 1 on one of the connectors. BTW, in pro audio, it is standard practice to NOT connect pin 1 (ground/shield) to the outer metal shell of the XLR, as was claimed in the video that Hosa did. There is a connection tab to do this, but it is not common practice in audio for the very reason raised in question of the Hosa adapter. Which end to lift can also be a consideration. But that's another discussion.

What is a ground loop? If you have two (or more) pieces of equipment powered from an A.C. wall outlet and that equipment uses a three prong A.C. plug (aka grounded plug) and then connect the equipment using XLR cables as is normally done in pro audio, like an amp D.I. output to a mixing console. You can get a ground loop hum, due to multiple grounds at slightly different voltage potentials. (Grounds aren't perfect) To keep the A.C. safety ground on the power cord operating you don't want to break ground there. Rather you employ some method to disconnect the audio shield/ground at one end of the cable. This is safe, effective, and relatively inexpensive. The other method is to use an audio isolation transformer.

This acts by placing an audio transformer on pins 2 and 3 between one device and another. These get relatively expensive and and you definitely get what you pay for here. Again, I like Whirlwind for these if I don't make my own, using a quality transformer. My use for something like this was more to convert unbalanced audio (2 conductor like phono or phone connectors) to the balanced, 3 conductor XLR for most pro use. Many store bought transformers, as well as the all the ones I built into a small box include a ground lift switch. That should be a clue that transformers and switches might be used for different purposes to solve different problems. A non- transformer ground lift switch won't degrade the audio as can happen with lower quality transformers.

All of this like so many other subjects will fill volumes and shelves. I spent a career working with it and only feel like I've scratched the surface. Lot of guys with lots more education and diplomas to prove it can take you on a dive, much deeper than you can ever imagine.

Note several re-edits. FYI.

Just want to say well done on taking the time to write a concise explanation

 

[Lostgallifreyan]

I also dislike actives where passive solutions work. Es the multiple failure mode reasons. I've used them and if done right it can be an effective solution for converting unbalanced line level to balanced line level. Be aware that line level is not the same in balanced as it is in unbalanced. Unbalanced line level signals usually requires a significant boost to get up to balanced line levels. That requires an amp, aka active. Balanced and unbalanced line levels also run into impedance incompatibilities. The active circuit can resolve this as well. So they do have their place in the larger scheme of things.

I have to admit I really like a simple voltage follower, one of the simplest things to build with an op-amp and they can solve hugely diverse problems where a tenuous high-resistance source must be passed to something that expects a good solid source, or where feeding a long signal cable that might otherwise act like a capacitor microphone.. With nothing but a wire for feedback, there is no 'design' short of choosing an amp that is unconditionally stable at unity gain. It's probably easily in the scope of the kind of DIY that many people here do with a bass, and if they do this at all, adding two resistors for gain control is also easy..

As @agedhorse said, his transformer coupled with a ground lift is bulletproof. It could very well be the best gadget in your tool box. And it is literally plug-and-play.

He's in the US, I'm in the UK and have terrible access to the webz on my systems (Paypal is utterly unusable for me), but I'm contemplating buying some of his. Maybe a bank transfer...

 

[Old Garage-Bander]

With your history, mentioned earlier, I'd begun to wonder if you'd helped to write it.

Naw. I had a lot of help getting started in this from guys much smarter than me. And I also made, and sometimes (maybe) learned from a whole heck of a lot of mistakes.

I do recall now having seen the Rane Interconnect paper. I recognized the how to connect this to that drawings. The Grounding one got by me, but what I did learn was by the same methods when cutting my teeth on audio. Maybe a bit scarier. But before that, I remember having a very tattered copy of some of the audio/transformer info published by Western Electric. Yup... Ma Bell, when it was Ma Bell.

The (Thee) phone company pretty much pioneered this stuff. Not only did the old analog dial up phone, rotary or pushbutton, operate over balanced lines for audio, they ran some highish AC and DC voltages on the same pair of wires to provide dial tone and ringing, and audio signaling and other stuff they were less reluctant to tell us about. No individual shields used either. Just a big metal jacket around up to 500 pairs in a cable. It was almost like magic.

And if you wanted to pony-up for special lines to get you around 30 Hz to 15 kHz, +/- 3 ish db, they could do that too. And did it over very long distances. My first transmitter site used a pair of these to deliver stereo audio from our studio site to the transmitter. I also would use this for remote broadcast in stereo for FM stations. Those did include some active gear at points along the way, but it was all set up ahead of time by telco, you just needed to connect at the ends.

But a lot of this especially on the engineering level of it still eludes my capacity to absorb it.

 

[Old Garage-Bander]

Off I go to read the Rane stuff. Thanks for posting that.

Bias, Oscillator

Rane makes a very good case for keeping the shield continuous through the entire cable. You can get away with it most of the time with line level signals, but not when used for microphone cables. This also answers someone's question about why they don't sell lifted cables. Because they have no control over how it is used. So all the conductors, get passed through on everything that you buy.

In my experience, I never ran into issues with RF getting in on a lifted balanced line level cable. Even at transmitter sites. But again it was all line (not mic) level and the cable runs were often very short. And I put a lot into grounding everything very well.

 

[Lostgallifreyan]

Naw. I had a lot of help getting started in this from guys much smarter than me. And I also made, and sometimes (maybe) learned from a whole heck of a lot of mistakes.

Me too. My single biggest (if inconsequential) mistake was at a practise, setting up recording of a punk band called the Seers in the mid 80's. So many things to think about, I miked a hi-hat beside the thing, failing to consider what happens when the air rushes out of the closing hat! Mortifying... That one moment made me very cautious about trying to minimise errors when I dare to commit any kind of opinion. I already knew some electronics, even then, but that mistake was a doozy, plain and simple.

About the phone lines, that's interesting, I was aware a lot was pioneered by them, but never of how much. I did learn fairly recently that RF engineers have only reluctantly come to see balanced lines as better in many cases than coax, again, without any shielding! I think in this case it is the highly precise making of twisted pairs in 'CAT5' cabling that has led to this discovery for antenna wiring.

EDIT. I just saw your second post that appeared right after posting this, ans we separately had the same sort of thought about RF and low level signals. As well as the precision in modern twisted pairs, a shield grounded at one end for the same line has been advocated in some RF antennas, for signals up to 30 KHz, as received by modest vertical whips with a local ground right underneath them. Coupled back to the receiver by an isolation transformer too. Nice combination.

 

[agedhorse]

I have to admit I really like a simple voltage follower, one of the simplest things to build with an op-amp and they can solve hugely diverse problems where a tenuous high-resistance source must be passed to something that expects a good solid source, or where feeding a long signal cable that might otherwise act like a capacitor microphone.. With nothing but a wire for feedback, there is no 'design' short of choosing an amp that is unconditionally stable at unity gain. It's probably easily in the scope of the kind of DIY that many people here do with a bass, and if they do this at all, adding two resistors for gain control is also easy..



He's in the US, I'm in the UK and have terrible access to the webz on my systems (Paypal is utterly unusable for me), but I'm contemplating buying some of his. Maybe a bank transfer...

I might be able to help you find a source in the UK