Proper wiring to avoid ground loops

[Riley Casey]

If Edison won "the war of currents" the 60 Hz hum would not be an issue.

Topic shift warning. It occurs to me that when / if rooftop solar becomes ubiquitous if perhaps DC powered everything might not come back into fashion. Certainly eliminate the 60hz pedal note of the built universe ( or 50hz if you're so inclined ).

 

[Rob Flinn]

This is always easier to understand when people use Earth to describe chassis Earth connected to the Earth on you mains as opposed to Audio Common i.e zero volts on the power supply. Unfortunately "Earth" or "ground" is commonly used to describe both.....

 

[Newmarket]

no they don't and lifting pin one can defeat a safety ground path.

+1

 

[moamps]

Topic shift warning. It occurs to me that when / if rooftop solar becomes ubiquitous if perhaps DC powered everything might not come back into fashion. Certainly eliminate the 60hz pedal note of the built universe ( or 50hz if you're so inclined ).

Absolutely correct. Already at this moment, a lot of devices that we use in our lives could be powered directly with DC voltage (all those devices that have a universal power supply of 100-240V). I was discussing this with a few colleagues recently. Even power transmission with existing power lines at voltages of 200 to 400kV could be somewhat more efficient (after all, there is no skin effect for DC). The switching inverters used in solar plants now already have an efficiency above 95%... One of the major problems that needs to be solved is the switching/interruption of DC currents (the problem of electric arcs, but that could also be solved). All in all, I think it's an interesting idea.

 

[Voyager10]

(...) the only one manufactured lately that has engineering issues is the Golden Age 1073 preamp because they didn't engineer the grounding scheme correct for its power supply.

There's a recent thread here about this: Golden Age Projects Pre-73 PSU Schematic and Mods

Basically, it's a disaster caused by not understanding where the return currents from those voltage doublers were ending up.

 

[JohnRoberts]

what does an optional cable shield on the xlr twisted pair wiring circuit have to do with chassis earth ground? Especially when most the time now they are 3 prong earth ground bonded individually because no one runs double insulated two prong stuff ?

if labelled as ground UL tests at 50A

Put down the bong and return to reality.

how about you return to civility. https://groupdiy.com/threads/groupdiy-rules-read-before-posting-in-any-of-the-forums.6650/

you are a new guy so might not be aware of the rules, specifically see #4 (link above) and leave your gratuitous insults over at that other forum.

JR

 

[Brian Roth]

Hmmmm...I was thinking you might be OK....and was trying to have a few conversations....yet you seem "off kilter" now. shrug.

https://www.dictionary.com/browse/douchebag
At least spell it correctly. If you don't like us, just move along. I was actually liking some of our random conversations. Dunno why you are so .....???....hateful/negative.

I assume you will attack me next. Go buy some tampons and F off and go away.

I suspect some folks here don't want your BS comments.


Bri

 

[Brian Roth]

At least some of us do not hide behind a BS screen name, but stand behind our documented lifetime of work.

Bri

 

[Brian Roth]

My apologies to the sane folks here for my "explosion" earlier.

I try to be a quieter person.

Bri

 

[Brian Roth]

OK....so why do you seem to always insult other people here???

John and I've been here for years and try to be civil.

dr.whatever.your. name. is....I liked our other conversations....

I ASSume you have a reason to hide with a screen name vs showing any creds that demonstrate anything you have done besides spewing vitrol. BTW I do check spelling.

Dammit...I hate fighting....

Too bad we don't seem to get along....some threads were semi-interesting......

Bri

 

[Brian Roth]

OK dr...when you have a beef with an assertion, then back it up with actual fact-checked papers.

Bri

 

[Brian Roth]

I've been working with pro audio systems for 50 years and I understand the entire balanced concept.

I also know to lift a shield at one end....IF REQUIRED...and often add a 0.1 uF cap from pin 1 to chassis at the destination chassis to quell RFI intrusion.

I also have built several audio systems in a high RF environment.....say near a 50000 Watt AM TX (In those situations, large copper straps or thick copper braids were required.)

I learned much by trial and error decades ago when fighting CB radio interference into a church sound system. "Breaker Breaker 19....where can I find a blow job?" did NOT go well over well at the 1st Baptist Church via their new PA system....lol.

Bri

 

[Brian Roth]

Hey....for "bullet proofing" use a transformer....lol!

YEARS before I moved here and I still drove through the region doing studio service calls....two Stories in one!

1. New client complained of lotsa hum in the headphone cue system. Trident 80B desk into a Crown DC-300A (passive distro into cue boxes). I was instantly a hero when I dug into my "traveling stash" and with some adapters and stuck a Radio Shack "car stereo" xfmr at the Crown input.

2. You hadda been here for this one..lol!.....I was told several channels on the Trident "came and went" when tracking into his Studer A80. When duplicating the signal path, I used the side of my fist and "banged" on the Trident desk. New client thought I was batsh!t...until I made the errant audio come on and off by doing "percussion therapy". Rickety edge connectors and Schadow switches. Now lifetime friends here in Salina as we do "sensible" (no side fists) gear refurb.

Bri

 

[nsalis]

Hi, thanks for the reply, but by balanced power do you just mean using a 3 prong power cord? I have that on everything piece of equipment in my signal chain except the audio interface at the end.

 

[nsalis]

No. Balanced Power is a concept by Martin Glasband

https://equitech.com/about-equitech/
in which an isolation transformer is connected between the power supply into the house and the sockets in the studio, with neither secondary connection connected to the building earth, as is normally the case.

The solution and, above all, its implementation is complex and achieves relatively little. It is better to stick with the standard power distribution and instead ensure that the devices used do not have a pin 1 problem. Then you can achieve high signal-to-noise ratios at low cost. If you are interested in the subject, you should read everything you can get your hands on by Bill Whitlock (Bill Whitlock especially - he has made infinitely great contributions to the education of the audio community), Neil Muncy, Jim Brown, Ray Rayburn and Dale Shirk. I have built systems based on their recommendations for decades that have not had any hum or buzz problems.

 

[Newmarket]

Mackie Big knob is 400 ohms impedance balanced, so every monitor device has to be 400 ohms input impedance or adapted to it or suffer from noise and hum people misunderstand as a ground loop or unbalanced power.

No.

 

[JohnRoberts]

I don't try to be insulting, but I find it interesting the stuff I know is contradictory to the so called experts here.

Any public forum will have a mix of novices and self described "experts" like you.

The moderators here have decades of experience designing commercial products so have a good grasp of modern technology

I find our transformer expert here interesting because the basic theories he should have known is apparent that he doesn't know or understand the circuit it was in because that would be covered by knowledge he should already know.

?

There are others that mislead people in a build and I interrupted their insanity, but went on to change things after I provided a basic design because I felt sorry for the guy that started the thread and got misled

As I already shared we have rules about forum decorum. If you disagree with some technical issue feel free to disagree but do so using civil language.

Equipment manufacturers in the past and present use balanced line drivers to achieve balanced connection across a wide range of impedance.
So for a monitor controller, to be truly a universally applied across different monitors, and amps, it should have this driver.
However, the budget ones use "impedance balanced" connections and people get hum city and wonder why. Mackie Big knob is 400 ohms impedance balanced, so every monitor device has to be 400 ohms input impedance or adapted to it or suffer from noise and hum people misunderstand as a ground loop or unbalanced power.

Mackie advertised the hell out of "impedance balanced" output (I joke it was their most valuable $0.02 resistors). I'd love to dis Mackie, but can't because of this. Impedance balanced is fully functional and sufficient to preserve signal integrity feeding properly balanced interfaces.

JR

PS @ Brian : do not respond in kind...

 

[Khron]

they used the wrong op amp that is designed for 400 ohm operation.

You ARE aware that these opamps and circuits are not meant to work into a short-circuit to their (ground) reference, right? You get no signal at the other end, if that's the case.

And how often (nowadays) is impedance matching (as opposed to bridging) a thing, when dealing with line-level audio (as opposed to RF stuff, or historical pieces of audio gear)?

True, that NJM4565 is "only" rated to drive down to 400 ohms, but... Aren't the outputs of that Big Knob meant to plug into the line input (5-10-20k input impedance, whatever it may be) of active monitors? Don't think i've ever heard of active monitors with 150 ohm or 400 ohm input impedance, but what do i know?

 

[Khron]

There is several line driver style op amps that can go as low as 50 ohms that would work better.

"Better", how? And also, why???

I was under the impression that opamps, for the most part, had output impedances in the milliohm range, so for all intents and purposes (of line-level audio driving), negligible. The series 47-150 ohm resistors added to the output are for isolating the opamp from the capacitance of the unknown-length cables it may be asked to drive.

I could be wrong, but i thought line-level audio and welding were two very different applications of electricity...

But as going to a higher input impedance, it defeats the intended balance operation by definition.

Once again, how (does it defeat "the intended balance operation")?

The worst case was a studio monitor that was 47K input impedance that was fixed by putting a 150 ohm resistor across 2&3.

What sort of problem was that supposed to solve? And how and why was 150 ohm the "magic bullet" value, as opposed to, i dunno, 10k, 4.7k, 1k?

I'm all for "if it's stupid and it works, it ain't stupid", but the "why" behind it all can be useful to know for later - the method may need adapting to a new problem, where the initial (empirical?) solution may no longer be suitable.

 

[Brian Roth]

@drtechno ..So you are saying a THAT 1646 is worthless for a balanced (and essentially universal) output?

Damn I need to redesign my aftermarket Otari module with multiple vacuum tubes and a transformer....

Bri