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Old 15th June 2006, 11:46 PM   #11
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Default Ground

I'm no expert.

But I have two ground points
1. Power ground: central point for all power grounds inluding, supply from mains, chassy ground(on boards), output grounds.

2. Signal grounds: This is for all signal source grounding. Signal ground(on boards) grounds on volume pot(if used), grounds on input signals.

3 Then there is the joining of the two. From what I gather you want to make it slightly more difficult for power ground to travel through the system and contaminate the signal. So you keep the two seperate for as long as possible the at the last stage join them up. I place a 1ohm resistor between the two so theres slightly more resistance and hopefully the power ground would not rather go through the signal ground but to it's own one.

I hope that somehow explains it.........sorry, like I said I'm no guru,

Yes i know its not a 1ohm in the picture, but any small resistor is better than nothing IMHO

Brett
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File Type: jpg signal earth to power earth.jpg (86.1 KB, 354 views)
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Old 16th June 2006, 12:47 AM   #12
kvholio is offline kvholio  Netherlands
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If you look carefully at the pcb you will see that the star-ground of the amplifier-circuit is on the pcb. joining signal-gnd and power-gnd and output-gnd in taj's configuration is done on the pcb.
One step at a time pls

With kind regards,

Klaas
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Old 16th June 2006, 12:49 AM   #13
preiter is offline preiter  United States
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I am also somewhat confused and not only do there seem to be many opinions on how to wire things together, they are usually described poorly adding to the confusion.

To break it down some, here is a list of the grounds in a gainclone...

Input signal ground (left and right)
Output ground (left and right)
Power Supply ground
Amplifier board power ground (sometimes separated left and right)
Chassis Ground
AC input ground (the green wire from the power cord)

So, which of these grounds are wired together?
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Old 16th June 2006, 03:15 AM   #14
taj is offline taj
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Quote:
Originally posted by kvholio
If you look carefully at the pcb you will see that the star-ground of the amplifier-circuit is on the pcb. joining signal-gnd and power-gnd and output-gnd in taj's configuration is done on the pcb.
One step at a time pls

With kind regards,

Klaas

Thanks Klaas. If I understand you correctly, in my case, I will only need to connect the AMP board's 'CHG' connection to the chassis (through a resistor) and I'm done. Is that correct?

And what about input/output ground? Isolated from chassis or not?

..Todd
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Old 16th June 2006, 03:35 AM   #15
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I'm not nearly qualified enough to answer this question, but IMHO, the resistor is totally unnecessary.
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Old 16th June 2006, 01:20 PM   #16
kvholio is offline kvholio  Netherlands
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Todd, input/output-gnd's isolated from chassis.
Safety-gnd (from ac mains) connected to chassis.

Briangt advises in his pdf to connect both channels to this point.
(chg at pcb).
In general, i find this connection in amplifiers not needed and undesirable.
Normally you want to keep secondary ps-gnd isolated from the chassis and safety-gnd.
Also connecting gnd's from both channels will, in almost any case, cause a big gnd-loop.
In most audio-sources (preamp, cd/dvd-player) both channels share a common gnd.This common gnd gets separated at the rca-outs.If you hook these gnd's up at the chassis/safety-gnd, you will create a big gnd-loop .Thats why some people are using resistors here, to break the groundloop.

I'm no expert on gainclones however, so this amp might benefit from this connection. If so, someone might step up to explain WHY.
Referring to this point as being "star gnd" is confusing imo.
Star-gnd is at the pcb. In a gainclone most of the hard work is done for you already

With kind regards,

Klaas
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Old 16th June 2006, 10:20 PM   #17
taj is offline taj
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Again, thanks Klaas.

..Todd
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Old 16th June 2006, 10:55 PM   #18
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Taj,

Pleae, please, please, post an updated skecth of the correct star ground configuration to help the rest of us out. Some pics to clarify wuld also be great.

Thanks
Neil
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Old 17th June 2006, 06:43 AM   #19
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Quote:
Originally posted by neil_kaye
Taj,

Pleae, please, please, post an updated skecth of the correct star ground configuration to help the rest of us out. Some pics to clarify wuld also be great.

Thanks
Neil

Okay, here's my updated sketch. I've drawn in all the wiring with a wire-colour legend. This is for AudioSector/Stereo/Parallel LM4780 configuration only. Note that according the the advice offered above, both the ground wire named CHG and the resistor are optional/controversial. I'd probably leave it off unless you get a hum/buzz, then try adding it.

Klaas, does this look right?

..Todd
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File Type: gif chassis.gif (42.5 KB, 399 views)
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Old 17th June 2006, 02:20 PM   #20
kvholio is offline kvholio  Netherlands
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Todd, apart from the chg to ac-safety gnd connection with resistor, yes.

If possible, you might also extend the shaft for the stepped attenuator to make the input-signal wires as short as possible and keep them away from the noisy parts of the circuit: ac mains, transformers, rectifier diodes.

With kind regards,

Klaas
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