understanding star grounding

[Tripmaster]

Maybe just a couple of words

'The schematic calls for a 100R resistor with a 0.22nf cap wired in parallel between the power ground star and the main chassis earth point'

What is this used for?

Thanks

[AndrewT]

to lower the impedance of the Safety Earth to Audio Ground connection at frequencies other than mains 50/60Hz.

[fjhuerta]

This thread may have saved a couple of lives (no kidding) including mine! THANK YOU very much to all, I now understand how grounds and earths work, and how to correctly wire an amp!

[Pancakes]

Originally Posted by digi01

the attached is another idea.
it is useful when you build an integrated amp with pieces single channel pcbs.
connecting all pcb's ground track via a strong wire.i use 4mm diameter copper wire.this wire is your amp's common ground.then connecting all RCA plate together to this common ground.

again,
assemblied the amp units as compact as possible.

Zang

Can I confirm why there is the resistor lifting the signal ground from chaasis/power ground?

[alevans51]

I've read a lot of this stuff about grounding to remove hum, and found myself creating the star by natural instinct. But what I believe is happening in that star is similar to a balanced antenna or resonant cavity which oscillates against itself, thus canceling a good deal of the 60 cycles.

Another take from all this is that there is little I can do about a computer audio card whose connector goes to a computer power supply with a 3-prong plug. Indeed, I have no intention of cutting the chassis safety PE ground on the computer. So the net resuslt is use a pull-up resistor from the ground of the chassis to the signal ground input from the RCA plugs coming in.

Do I sound like an amateur, or what?

[Mooly]

Originally Posted by alevans51

I've read a lot of this stuff about grounding to remove hum, and found myself creating the star by natural instinct. But what I believe is happening in that star is similar to a balanced antenna or resonant cavity which oscillates against itself, thus canceling a good deal of the 60 cycles.

It's much simpler than that
You have to think in terms of "volt drops across conductors" and whether your method of connection will cause a portion of that "volt drop" to find it's way into an audio circuit. It's nothing more than ohms law really.

Second to that is when a "loop" exists that can have current induced into it from say a transformer magnetic field.

It helps to just think in terms of DC currents. If you imagine supplying 10 amps into 10 ohms as a load for an amplifier, then put in values for all the wiring to and from the PSU (Use 1 ohm say) and then "make the wiring "disappear" through good layout and routing.

[digi01]

Originally Posted by Pancakes

Can I confirm why there is the resistor lifting the signal ground from chaasis/power ground?

there are three 'ground' in a decent designed amp.number one is safe ground from the chassis to the outlet protected field (E),number two is power ground from the regulated power ground to the chassis.number three is signal ground.if connect the signal ground directly to the power ground,then it will share the safe ground too.the protected field is not clean.
the resistor was set up between the signal ground and power ground to avoid safe ground noise.

zang

[alevans51]

I got a pair of these TK2050 Class D amplifiers of Ebay from Sure Electronics. They are connected to a 7.1 channel computer audio card - the Asus Xonar D2X.
I have a single switched power supply too. I am observing the hot neutral and earth ground on it using a 3-prong power plug. Its a 27volt 37A Meanwell PS.

I got most of the hum out, but why can't I get it all? I ran separate power lines - 16ga wire - from the PS terminals to each amp. For signal grounding, there is connector wire soldered to the the RCA shields of 8 recepticals. They are joined only to themselves.

One thing I did that may seem peculiar is mount each amp and the PS in separate cookie tins. I did this for cham, but I cannot believe that would be the cause of this humming problem.

Speaker out terminals are not allowed to connect to ground on this amp. Speakers are Koss and are magnetically shielded. Maybe I need shielded speaker wire?

Pictures:

[matt09]

Don't mean to resurrect an old thread but is this correct?

The B1 buffer creates the star ground by commoning the channels.

If i were to use the star ground throughout it would mean I couldn't use ground output terminals on the ref_c boards.

Thanks

[alevans51]

You are at a higher level now, and the ground is a return.