Help Design an unbalanced consumer Line level to Balanced interface

[Newmarket]

Because the guitar is unbalanced with a high inductance coil (which is usually poorly shielded) exposed to EMI along with all of the metal bits which includes the strings of course. So if 0V didn't have some relation earth, you would get noise from being bombarded with EMI all around us. The metal bits could charge up relative to earth and cause popping noises as you touch and release the strings.



But there is also a safety reason in that there are many opportunities for an uncontrolled voltage to contact that 0V, such as through a guitar amp or any of the other unbalanced guitar gear, in which case it might be good if there was a better path to earth than through your body and into the shield of a mic or some other bit of earthed metal you happen to touch.

Yeah - I understand that a passive guitar pickup is a hi-Z transducer and this inherently susceptible to noise. But there is nothing 'special' about the planet Earth in relation to this if it is not part of the connectivity. The basic requirement is that the conductive parts - strings, bridge etc are connected to a low impedance reference voltage. Typically this is the return of the power supply. Eg think about a street busker running their kit from a car battery. No actual Earth connection. The metal parts are connected to the battery negative.
And you do get noises if you lose contact with the metallic parts then remake contact. Because you are acting as a noise source then not doing so when you remake contact.
I see safety related comment. But on a train atm and the bumpiness is making the touch keyboard on phone a bit too much of a challenge now
Cheers.

 

[Bo Deadly]

Yeah - I understand that a passive guitar pickup is a hi-Z transducer and this inherently susceptible to noise. But there is nothing 'special' about the planet Earth in relation to this if it is not part of the connectivity.

If an SMPS was used without an earth ground connection, then 0V is totally floating. The guitar uses 0V as a signal conductor and it's exposed to EMI through all of the metal parts and strings. I actually don't know if the pickup matters as that would be an entirely differential signal. But the noise induced on 0V from EMI would be common mode which could find it's way through things (high frequency common mode will go right through a transformer). Granted, these induced currents are tiny. So just a little bit of resistance to ground through the players body would be enough to shunt it. THis is why I think that touching and releasing the strings would make noise.

Although in practice, a guitar rig almost always connects 0V to earth ground somewhere. If it's going to an amp, the amp is going to have earth ground. And you only need one earth ground connection (only one is ideal actually).

On interesting test might be to play the guitar directly into the DI of a USB audio interface connected to a laptop running on battery and watch the FFT. Does the noise floor go up / down depending on how well you're grounded, touching the strings, etc?

 

[Whoops]

Hi Guys,
great discussion you're having of really important and relevant topics.
It's so important and interesting that it deserves it's own thread.

I'm afraid not only this great info will be lost in this thread, but also that the subject matter and purpose of this thread will get lost also. It's a Lose Lose situation.
So I please ask you to start another thread to continue that discussion

I would just like to build a really simple circuit to convert the signal from Synths, Drum Machines, Samplers, etc to a Balanced signal for live sound duties (without having to use a DI box), a lot of nice ideas were brought here and it was going in a good direction...

Thank you so much

 

[Newmarket]

Hi Guys,
great discussion you're having of really important and relevant topics.
It's so important and interesting that it deserves it's own thread.

I'm afraid not only this great info will be lost in this thread, but also that the subject matter and purpose of this thread will get lost also. It's a Lose Lose situation.
So I please ask you to start another thread to continue that discussion

I would just like to build a really simple circuit to convert the signal from Synths, Drum Machines, Samplers, etc to a Balanced signal for live sound duties (without having to use a DI box), a lot of nice ideas were brought here and it was going in a good direction...

Thank you so much

Fair enough. We often veer of course. I don't want to start a new thread esp as I don't think there's a lot more to post on it at this point.
So I will reply to a few of Bo's points that I think best not left hanging.
Then if the subject requires more after that I'll start a new thread on Guitar / Hi-Z Noise and Grounding.

 

[Newmarket]

If an SMPS was used without an earth ground connection, then 0V is totally floating. The guitar uses 0V as a signal conductor and it's exposed to EMI through all of the metal parts and strings. I actually don't know if the pickup matters as that would be an entirely differential signal.

The pickup does matter. The high impedance and orientation of the pickup influence the magnitude of the noise pickup. This becomes clear if you wave a guitar around in front of a noise source - try a PC or similar.
The pickup coil itself produces a voltage across its output - just like a dynamic microphone except high impedance.
But depending on the pickup construction this signal might be brought out floating or with one end connected to 0V making it a single ended signal.

But the noise induced on 0V from EMI would be common mode which could find it's way through things (high frequency common mode will go right through a transformer).

HF noise coupling across transformer - yes though very dependent on transformer construction / internal shielding.

Granted, these induced currents are tiny. So just a little bit of resistance to ground through the players body would be enough to shunt it. THis is why I think that touching and releasing the strings would make noise.

But in general there is no guaranteed path to either 0V or "Earth" through the players body.

Although in practice, a guitar rig almost always connects 0V to earth ground somewhere. If it's going to an amp, the amp is going to have earth ground. And you only need one earth ground connection (only one is ideal actually).

It's usual yes. Although there is now often no big amp rig. eg guitar to "Modelling Box" to DI to PC / FOH / IEM.

On interesting test might be to play the guitar directly into the DI of a USB audio interface connected to a laptop running on battery and watch the FFT. Does the noise floor go up / down depending on how well you're grounded, touching the strings, etc?

I can't easily do that as my stuff runs on a big old full size 3 wire PC and the Audio 0V has continuity to the PE.
Although I guess I could if I used the built in interface on my laptop.
But I would expect it to be much the same. The reference is the 0V (rather than "Earth") and you are contacting / not contacting with that when you make/break with the conductive parts. When you are near but not touching the guitar you act as a antenna for noise. When you make contact with the conductive parts then you fix yourself at the reference potential and stop being a source of noise (assuming you have the usula wire from bridge to 0V, typically to the back of a potentiometer in the control cavity.

 

[MidnightArrakis]

I was thinking of doing maybe 3 Boxes, 2 boxes with 4 circuits/channels and one box with 6 channels. The goal is to make them as small as possible, so the XLR connectors size will dictate how big it is. But for the size of one normal DI box, I want to have at least 4 circuits/channels.
I need to same space in my Trolley while traveling.

I was thinking in using one of this options and choose it after I have all the measurements (still a bit early):

View attachment 103000
View attachment 103001




I might also do some circuits in these barrels, the end is the exact size for a chassis XLR:

View attachment 103002







I was going to design the PCB myself, I'm able to do it but I'm really slow working with Eagle or KiCAD, so I accept your help for sure. Thanks mate.
As for the mechanical part, maybe that's not needed because I'm going to use an already made box but maybe if you help with front panels design in case needed that would be awesome.



For Sure mate, and thank you so much for your offer.
Just give me some time to build and test out circuits and when i have the final decision of what I'm going to do I let you know and we go from there.
Thanks

Whoops: I came across this information tucked down inside one of my "forgotten" audio folders and it looks as though this is what you are looking for!!! Not only that, but sometime this past Autumn I had also downloaded the 3D CAD-files from NEUTRIK, so with that kind of data in-hand.....I could easily either design a PCB and/or CAD-Model your PCB and place it within my CAD-Model of the NEUTRIK enclosure. See included images and attached PDF files. Whaddya think???




While my examples shown down below have XLR connectors on both ends,
it is certainly way more than easy enough to replace one of the XLR's with
either a female TRS-jack or a cable-grommet with an audio cable going
through it and a male 1/4" TS or TRS connector terminated at its end.

-- FEMALE XLR CONNECTOR --


-- MALE XLR CONNECTOR --


Just let me know what you need and/or what you want to have done, OK??? Or.....you can let me know that you simply want to do and take care of this entire little project all by yourself!!! NO OUTSIDE ASSISTANCE NEEDED!!!

/

 

[MidnightArrakis]

Hi Guys,
great discussion you're having of really important and relevant topics.
It's so important and interesting that it deserves it's own thread.

I'm afraid not only this great info will be lost in this thread, but also that the subject matter and purpose of this thread will get lost also. It's a Lose Lose situation.
So I please ask you to start another thread to continue that discussion

I would just like to build a really simple circuit to convert the signal from Synths, Drum Machines, Samplers, etc to a Balanced signal for live sound duties (without having to use a DI box), a lot of nice ideas were brought here and it was going in a good direction...

Thank you so much

Here's a start (for a PCB):



"Standing By....." for "shredding" comments!!!

/

 

[nille]

https://www.thomann.de/intl/pro_snake_tpa_mp.htm?

 

[Whoops]

I could easily either design a PCB and/or CAD-Model your PCB and place it within my CAD-Model of the NEUTRIK enclosure. See included images and attached PDF files. Whaddya think???

View attachment 103363

Hi mate, for sure,
if you see my last reply to you on the topic of enclosure I put there a photo of a barrel just like the Neutrik one. I have 2 of them in stock at the moment, they're not Neutrik, they're from Aliexpress but are great and are the same as the Neutrik ones.
This could be used for single boxes with just one circuit for sure. I even tough that I could screw quite a few of these barrels together side by side and make it mode channels, they're small enough, which is something I really need.

This is the photo I posted earlier, if you want the aliexpress link I can send it to you

Just let me know what you need and/or what you want to have done, OK??? Or.....you can let me know that you simply want to do and take care of this entire little project all by yourself!!! NO OUTSIDE ASSISTANCE NEEDED!!!

Oh mate, for sure I prefer help and accept help gladly. Actually is a privilege to be in a forum like this were people help eachother. Thank you so much.
I just still didn't build any of the circuits here yet because I was waiting for a reply from Bill about the attenuation level (which is already answered) and also because I had to finish mastering 4 records last week, and now I have 2 songs to mix to today, and tomorrow I have a new Master to do from a really important artist. I was nominated for a Grammy last year for my mastering work, and now it's the new album of the same artist, so it's Top priority.
I do electronics as a side thing to my Engineering Work (it's what pays me the bills), so in weeks I'm really busy with music I don't have much time for electronics, but changes a bit every week, it's not always busy and not always free time.

If you want to do a pcb of Bill's passive circuit to fit inside those Neutrik XLR barrels/enclosures, please do, that would be awesome, I would put it in use very fast.
Thank you so much

 

[Whoops]

View attachment 103370

The schematic needs to be changed a tiny bit,
the input jack it's an TS jack (and not TRS),
so C2 minus leg has to connect to the Sleeve of the Jack

 

[Whoops]

https://www.thomann.de/intl/pro_snake_tpa_mp.htm?

Wow,
that's even cheaper than the ones I got from Aliexpress.
The ones I got are 3,5€ (with shipping) but without XLR and JACK connector.





I will order those ones from Thomann to try them out,
the XLR and Jack connector's are cheap connectors for sure, but for the price it's unbeatable.
And maybe the writings on the case can be removed with Acetone or Benzine.

Thank you so much for the link

 

[Newmarket]

Here's a start (for a PCB):

View attachment 103370

"Standing By....." for "shredding" comments!!!

/

Standard convention the T signal should go to XLR pin 2 (L).

 

[Whoops]

Standard convention the T signal should go to XLR pin 2 (L).

Oh yeah, I didn’t see that at first look

 

[MidnightArrakis]

Standard convention the T signal should go to XLR pin 2 (L).

[standard convention the T signal should go to XLR pin 2 (L)] -- OOPS!!! MY BAD!!! I'm old enough to have come from the time when it used to be "Pin-3 HOT", so many times I automatically and subconsciously wire things up as they were when I grew up.

One time, back in the 1970s, I was doing a "LIVE" sound gig that combined the PA power-amplifiers and speakers from a local sound reinforcement company (in Indiana) and the mixing console and signal-processing gear from a "guest" sound company that was touring with a "famous" artist from the UK. Once all of the equipment was setup and turned-on for the sound-check, everyone was amazed that.....> NOTHING < came out of the PA at all!!! Immediately, both my sound crew and the UK sound crew began to scurry around trying to find out why > NOTHING < was coming out of the PA speakers!!!

Long story short.....it was finally discovered that the two different sets of sound equipment were "cancelling" each other out because all of our U.S. designed and built equipment was wired as "Pin-3 HOT" and all of the UK-based equipment was wired as "Pin-2 HOT". Back then, even though there was a so-called "Wiring Standard", the U.S., the UK and even Japan each had their own standard. So.....it wasn't yet a "universal" wiring standard yet at that time.

Because the UK-based equipment was being provided by the "famous" artist, I was forced to "cave-in" and re-wire all of my sound systems' "Input/Output" XLR connector panels to "Pin-2 HOT" in order to get the audio signals to pass-thru and make the concert PA system actually work!!! When all of the equipment got back to the shop, I then had to again go and re-wire everything back to "Pin-3 HOT" because that's how it was in the U.S. at that point in time.

So.....I sincerely apologize for the wiring error I made in the schematic. Sometimes "old habits die hard", ya know???

One question that I do have is.....based upon the hand-made drawing of this circuit that uses an audio cable, should the R and S terminals be connected together at the PHONEJACK? I can understand them being connected for use with a cable, but I am not sure about them being connected together when being used on a PCB. Any comments/ideas/suggestions? THANKS!!!





/

 

[Whoops]

One question that I do have is.....based upon the hand-made drawing of this circuit that uses an audio cable, should the R and S terminals be connected together at the PHONEJACK? I can understand them being connected for use with a cable, but I am not sure about them being connected together when being used on a PCB. Any comments/ideas/suggestions? THANKS!!!

View attachment 103414

View attachment 103415

That's another thing I can see now that I missed in your schematic, the input female Jack doesn't need to be TRS, it can be a TS jack (like Bill's drawing).
The signal that goes to PIN 3 and the ground connection (PIN 1) are derived from the same point, so they have to be connected, as sooner as possible in the circuit.
A TRS jack can be used like the one in the schematic and that way when you insert a male TS Jack in the TRS female the Ring will make contact to the Sleeve through the male jack TS connector, yielding the same result

 

[Newmarket]

[standard convention the T signal should go to XLR pin 2 (L)] -- OOPS!!! MY BAD!!! I'm old enough to have come from the time when it used to be "Pin-3 HOT", so many times I automatically and subconsciously wire things up as they were when I grew up.

One time, back in the 1970s, I was doing a "LIVE" sound gig that combined the PA power-amplifiers and speakers from a local sound reinforcement company (in Indiana) and the mixing console and signal-processing gear from a "guest" sound company that was touring with a "famous" artist from the UK. Once all of the equipment was setup and turned-on for the sound-check, everyone was amazed that.....> NOTHING < came out of the PA at all!!! Immediately, both my sound crew and the UK sound crew began to scurry around trying to find out why > NOTHING < was coming out of the PA speakers!!!

Long story short.....it was finally discovered that the two different sets of sound equipment were "cancelling" each other out because all of our U.S. designed and built equipment was wired as "Pin-3 HOT" and all of the UK-based equipment was wired as "Pin-2 HOT". Back then, even though there was a so-called "Wiring Standard", the U.S., the UK and even Japan each had their own standard. So.....it wasn't yet a "universal" wiring standard yet at that time.

Because the UK-based equipment was being provided by the "famous" artist, I was forced to "cave-in" and re-wire all of my sound systems' "Input/Output" XLR connector panels to "Pin-2 HOT" in order to get the audio signals to pass-thru and make the concert PA system actually work!!! When all of the equipment got back to the shop, I then had to again go and re-wire everything back to "Pin-3 HOT" because that's how it was in the U.S. at that point in time.

So.....I sincerely apologize for the wiring error I made in the schematic. Sometimes "old habits die hard", ya know???

One question that I do have is.....based upon the hand-made drawing of this circuit that uses an audio cable, should the R and S terminals be connected together at the PHONEJACK? I can understand them being connected for use with a cable, but I am not sure about them being connected together when being used on a PCB. Any comments/ideas/suggestions? THANKS!!!

View attachment 103414

View attachment 103415

/

No apologies needed. It's just two wires / tracks swapped. If that was the biggest mistake I made in a design I'd be laughing
But yeah - standards are great - that's why we have variations
IIRC Shure used the opposite convention wrt + / - on earlier XLR connections ?
And (again from an old memory so don't quote me) but a South east Asian (Singapore ?) state broadcaster used to have the male (output) / female (input) convention reversed on their kit.
I tend to think of it as X = Pin 1 / L = Live / R = Return. No, It's not accurate but it did the job when I needed it.
For an explanation of why it's actually termed XLR (courtesy of SHURE) see link below.

https://service.shure.com/s/article/history-of-the-term-xlr?language=en_US

wrt the "PhoneJack" question : I don't see that it matters since with a TS plug the R and S connections will be commoned by the plug.
I'd keep it as a TRS connector (rather than TS) since it would then allow proper connection of a balanced signal and the output would be a padded down version of the input.

 

[MidnightArrakis]

[ A) the input female Jack doesn't need to be TRS, B) with a TS plug the R and S connections will be commoned by the plug, C) I'd keep it as a TRS connector (rather than TS)] -- Since this is Whoops' project, I would tend to defer to whatever it is that he would rather have and use. But, for me personally, I would tend to go with Newmarket's suggestion, as I believe that by doing so, this little circuit would then be more "universal" in its use. But.....it is ultimately Whoops' call and decision to make.

[I would just like to build a really simple circuit] -- YOU pick out whatever schematic that you wish to use, OK? All I did was take a hand-drawn "sort of" schematic and created a CAD schematic out of it. It doesn't mean that you have to use my version if there is something else that you would much rather use.

>> STILL OUTSTANDING -- One question that I do have is.....based upon the hand-made drawing of this circuit that uses an audio cable, should the R and S terminals be connected together at the PHONEJACK? I can understand them being connected for use with a cable, but I am not sure about them being connected together when being used on a PCB. Any comments/ideas/suggestions?

[For an explanation of why it's actually termed XLR] -- That was interesting, but.....I had always heard and read that "way back in the oldies days".....when "stereo" was first being introduced into the radio and television broadcast markets and they were running two-channels of unbalanced audio around the studios, that the 3-Pin connectors got their name from being used as -- X = GND, L = Left and, R = Right). How much water this old story holds, I don't know!!! But, that's what I have always heard.

/

 

[Whoops]

[ A) the input female Jack doesn't need to be TRS, B) with a TS plug the R and S connections will be commoned by the plug, C) I'd keep it as a TRS connector (rather than TS)] -- Since this is Whoops' project, I would tend to defer to whatever it is that he would rather have and use. But, for me personally, I would tend to go with Newmarket's suggestion, as I believe that by doing so, this little circuit would then be more "universal" in its use. But.....it is ultimately Whoops' call and decision to make.

I personally will only use it with unbalanced signals at it's input.
But let's go with Jack TRS, it doesn't hurt and it's more "universal"

>> STILL OUTSTANDING -- One question that I do have is.....based upon the hand-made drawing of this circuit that uses an audio cable, should the R and S terminals be connected together at the PHONEJACK? I can understand them being connected for use with a cable, but I am not sure about them being connected together when being used on a PCB. Any comments/ideas/suggestions?

Mate, I already explained that in my last post.
On Bill's drawing a TS jack is used (there's no ring), The signal for pin 3 is taken from the sleeve, as also the signal for ground Pin 1.
And yes they both need to be connected at the jack

On your schematic you are using a TRS jack for the input.
When a male Jack TS is inserted in the female TRS jack, the ring will short with the sleeve, so making the exact same connection as in Bill's drawing and circuit, so it's all fine the way it is in the schematic you drawn

 

[abbey road d enfer]

Note that there is not much room left in these boxes when standard connectors are fitted. Just enough for a (very) small PCB, a small xfmr or a few flying components.
I use these boxes in my MicBooster, and I have to use specific protruding connectors that are only available at Neutrik, AFAIK.
https://www.neutrik.com/en/product/nm3md-bhttps://www.neutrik.com/en/product/nm3fd-bNo option for 1/4", though.

 

[Newmarket]

Note that there is not much room left in these boxes when standard connectors are fitted. Just enough for a (very) small PCB, a small xfmr or a few flying components.
I use these boxes in my MicBooster, and I have to use specific protruding connectors that are only available at Neutrik, AFAIK.
https://www.neutrik.com/en/product/nm3md-bhttps://www.neutrik.com/en/product/nm3fd-bNo option for 1/4", though.

Thanks for that info.
Wasn't aware of those previously.