Balanced ground loops

[Ardacer]

Apparently making a small connection between amp and pc chassis should do it too, but all the metql is black ionized, and I'd rather not scrape it :/

 

[Sal1950]

BTW, the AV7701 has a two pin power cord (that looks like a three pin) and only has two pins where it plugs into the chassis. I was surprised to see that in a relatively modern AV device.

Same for new 7703, and neither does the Emo DAC as Amir revealed in his tests that caused the hum? Adcom Amps are 2 pronged cords. Can always go back to Toslink though don't believe its a big issue short of some internal failure

 

[sergeauckland]

Apparently making a small connection between amp and pc chassis should do it too, but all the metql is black ionized, and I'd rather not scrape it :/

That can also work, as it removes the potential difference between PC and amp chassis, which is what's causing the hum. Anodised finishes are insulating, but you may find a screw with a star washer that has perforated the anodising. It does mean running another wire, and with active loudspeakers that wire can be quite long and it can also pick up hum and RF, so may or may not be a solution. It's certainly cheap to try, and definitely safer than removing a safety earth.

My preference would still be to remove the screen connection from one end of the cable to the 'speakers.

S.

 

[Speedskater]

Getting back to balanced interconnect systems.
Balanced interconnect systems do not require a shield or a circuit ground to to function correctly. Many pro are now using unshielded Cat5 cable for multiple interconnects. Transformer coupled interconnects have no circuit ground reference. Pros have been using interconnects with the shield connected at the send end for a long time.
Why back in 1994/95 Neil Muncy (RIP) wrote an AES paper about this problem, it became known as the "pin 1 problem". Then John Windt wrote a paper about the "Hummer Test" to see if a hi-fi component's shields are correctly connected. A DIY "Hummer Tester" costs about $20. The basic idea became AES48 standard. It took about a decade for pro equipment manufactures to get up to speed and after two decades some hi-fi manufactures still get it wrong.

 

[RayDunzl]

BTW, the AV7701 has a two pin power cord (that looks like a three pin) and only has two pins where it plugs into the chassis. I was surprised to see that in a relatively modern AV device.

I have at least one of those myself.

Tascam CD200 or Oppo 93 (?), can't remember which right now.

So.

From where does it establish its ground reference?

 

[Speedskater]

Many modern products (including hi-fi components) have double insulated enclosures. They have a square within a square safety symbol. Only two wire cords are permitted. They should not be modified for a three wire cord because their chassis may not be at Safety Ground potential.

 

[Blumlein 88]

I have at least one of those myself.

Tascam CD200 or Oppo 93 (?), can't remember which right now.

So.

From where does it establish its ground reference?

Going by the convention of Live, Neutral and Earth with Earth being the 3rd safety ground wire, it would have to use Neutral as the ground reference.

BTW, as well as being double insulated products can earn the double insulated rating if the casing is made so no components or wiring were it to come loose could contact the outer casing even if that casing is metal. I assume that is what is happening with metal cased hifi components with the double insulated rating.

 

[Sal1950]

Ya never really know till you open them up! My Emotiva DC-1 DAC

 

[Blumlein 88]

Ya never really know till you open them up! My Emotiva DC-1 DAC

I wouldn't worry. Call it double insulated since it has remote control. You need never touch the unit. GFCI outlet might be smart imo.

I'd be more worried about this soldering job here. That's carrying the digital audio signal:

 

[RayDunzl]

Going by the convention of Live, Neutral and Earth with Earth being the 3rd safety ground wire, it would have to use Neutral as the ground reference.

Neutral is not even close to Earth in potential here.

With a 'scope on Hot and Neutral (from distant memory), I see something like this when referencing to Earth, due to voltage drop in the lines to the outlet, at least 80 wire feet to the breaker box:

If something Audio used Neutral as reference, I'd think it would be hummmm city.

Voltage drop on Neutral = I x R of the Romex.

---

Then to confound that a little more, there's my use of "Balanced Power" which puts a 60Vrms sine on Neutral to the gear...

 

[Sal1950]

I'd be more worried about this soldering job here.

That's not solder, Amir had run out of Red Man and was chewin some stainless mesh when he drooled a bit the day he did my measurements.

 

[DonH56]

The common-mode voltage (Vcm) of the signal is Vcm = (Sp + Sm)/2 and will be established by the transmitting and receiving circuits. Both could be capacitively coupled so the voltage may actually "float" on the wires.

HTH - Don

 

[Wombat]

FYI

Double insulation: https://en.wikipedia.org/wiki/Appliance_classes

Osha view: https://www.osha.gov/laws-regs/standardinterpretations/1985-11-08-0

 

[Speedskater]

f something Audio used Neutral as reference, I'd think it would be hummmm city.

Why would an audio component use Neutral or Safety Ground/Protective Earth as a reference?
True the audio circuit common is often connected to the chassis and the Safety Ground/Protective Earth is also connected to the chassis, but as a reference?
It's more a source of Common Impedance Coupling noise currents.

 

[Ardacer]

Solved it by optical. I made a cable that's shield is connected only to the speaker. Still loops. Silly that balanced trs output earths the gnd wire :/

 

[sergeauckland]

Solved it by optical. I made a cable that's shield is connected only to the speaker. Still loops. Silly that balanced trs output earths the gnd wire :/

Yes it is silly, and shouldn't happen. What should happen is that the chassis is permanently connected to safety earth, and the audio ground should be separate, with the option of a connection between safety earth and audio ground through a switch, or better still, a strap that can't be inadvertently connected. a 10 ohm or thereabouts resistor between safety earth and audio ground is sometimes incorporated, but there's no excuse for safety earth and audio ground to be permanently connected, even worse for safety earth to be optional!!

S.

 

[Sal1950]

A great bit of info I came across on grounding and loops.
http://sound.whsites.net/earthing.htm
http://sound.whsites.net/index2.html

 

[Ardacer]

I've studied everything mr. Elliot had to say years ago. Very nice site, lots of superb info. I'd kinda not use his loop breakers if I don't have to, though.