Need grounding advice

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taj

diyAudio Member
Joined 2005
I'm almost ready to start wiring my AudioSector module chipamp but I'm a little (a lot) unclear on how best to ground everything for minimum hum/buzz.

Here's a drawing of what I've come up with based on my chassis layout. Am I close?

..Todd
 

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Three things:

1: The Star Ground should be the AC Ground Primary
2: (Correct me if I'm Wrong, but doesn't the ground output need to be connected to V-?:xeye: You might have problems getting any sound...
EDIT: 3: Just the case should be AC Primary Ground. The rest of the stuff like the smoothing caps (if they're 2 in serial) and other "GND" things should be connected to the transformer's ground! Don't let those grounds get mixed up.
 

taj

diyAudio Member
Joined 2005
DJ Exprice said:
Three things:

1: The Star Ground should be the AC Ground Primary

Yes, and connected to the chassis, correct?


2: (Correct me if I'm Wrong, but doesn't the ground output need to be connected to V-?:xeye: You might have problems getting any sound...

You lost me here. Is your "ground output" the black speaker terminal? In most amplifier schematics I've looked at, it's tied to earth/AC/chassis ground. I don't think I understand what you're saying.



EDIT: 3: Just the case should be AC Primary Ground. The rest of the stuff like the smoothing caps (if they're 2 in serial) and other "GND" things should be connected to the transformer's ground! Don't let those grounds get mixed up.

I think you're referring to 'signal ground' versus 'chassis/AC/earth ground' right? But I don't understand what you mean regarding transformer ground. Do you mean the center tap of the secondaries should NOT be tied to AC ground?

Thanks DJ.

..Todd
 
Yes, and connected to the chassis, correct?

Good.

You lost me here. Is your "ground output" the black speaker terminal? In most amplifier schematics I've looked at, it's tied to earth/AC/chassis ground. I don't think I understand what you're saying.

Yes - I was talking about signal ground. I'm not sure about the black terminal needing to be what, but maybe somebody else knows...


I think you're referring to 'signal ground' versus 'chassis/AC/earth ground' right? But I don't understand what you mean regarding transformer ground. Do you mean the center tap of the secondaries should NOT be tied to AC ground?


Center tap and AC Primary ground shouldn't touch unless the 0v one the transformer is PERFECTLY 0v. I wouldn't connect them.
 
Thanks Todd. You can connect one secondary winding to rectifier-pcb at 2 points both marked "ac1", and the other secondary winding to points marked "ac2".(so you DONT connect the secondary windings to eachother).

Connect pg- from rectifier-board to pg- on amplifier-board, and of course pg+ from rectifier-board to pg+ on amplifier-board.It's also a good idea to twist those wires.
Please get back and tell if this makes sense to you - i know there's more connections to be made, like to take it one step at a time.

With kind regards,

Klaas
 

taj

diyAudio Member
Joined 2005
kvholio said:
Thanks Todd. You can connect one secondary winding to rectifier-pcb at 2 points both marked "ac1", and the other secondary winding to points marked "ac2".(so you DONT connect the secondary windings to eachother).

Connect pg- from rectifier-board to pg- on amplifier-board, and of course pg+ from rectifier-board to pg+ on amplifier-board.It's also a good idea to twist those wires.
Please get back and tell if this makes sense to you - i know there's more connections to be made, like to take it one step at a time.

With kind regards,

Klaas

Yes, of course you are right. I wasn't thinking properly when I drew that picture. I would have discovered that as soon as I began connecting it together. I'm more confused about which items need to be connected to the star ground. Especially regarding input and output jack grounds.

And Daniel mentioned using resistors between signal ground and AC ground. I assume this is done on the AMP board where it is marked CH gnd. From there to resistors to star?

..Todd
 
I have noticed a lot of confusion on these forums as to how to ground the GainClone. Myself included.

I've seen plenty of different ways of doing it, none labeled as "correct". The PDF on chipamp.com for the LM3875 kit instructs the user to connect both CHG (chassis ground) wires from the amplifier boards to the AC earth ground pin on the IEC connector, and to the chassis. Physical details on this are vague.

Then I've seen all kinds of other configurations. Including using the chassis as ground for the negative binding post and negative signal input. Then there are people using 10R resistors to chassis ground. This doesn't make sense to me.

What we need is Peter Daniel or BrianGT to step up and explain the correct way to do it, WITHOUT options.

I also made the mistake of using ONE toroid and TWO rectifier boards, only to find out later that that is not true dual mono and will most likely introduce hum. If my right channel hadn't blown up I would be able to confirm that.
 

taj

diyAudio Member
Joined 2005
phorensic said:
I have noticed a lot of confusion on these forums as to how to ground the GainClone. Myself included.

I've seen plenty of different ways of doing it, none labeled as "correct". The PDF on chipamp.com for the LM3875 kit instructs the user to connect both CHG (chassis ground) wires from the amplifier boards to the AC earth ground pin on the IEC connector, and to the chassis. Physical details on this are vague.

Then I've seen all kinds of other configurations. Including using the chassis as ground for the negative binding post and negative signal input. Then there are people using 10R resistors to chassis ground. This doesn't make sense to me.

What we need is Peter Daniel or BrianGT to step up and explain the correct way to do it, WITHOUT options.

I also made the mistake of using ONE toroid and TWO rectifier boards, only to find out later that that is not true dual mono and will most likely introduce hum. If my right channel hadn't blown up I would be able to confirm that.

I'm sure you're right; there are plenty of ways to accomplish a good quiet ground system. "Correct" will probably have many variations.

I suspect the ChipAmp forum (if I am at all typical) is where amp builder's begin their hobby, rather than dive straight into a Nelson Pass design, for example. For that reason, I think it's normal to expect more confusion in this area.

You are also right that it would be nice to see Daniel or Brian chip in (no pun intended) with some advice. As Daniel well knows, I'll be happy to document/illustrate any schemes deemed "correct". They are not, however, the only ones able to offer advice in this area, and the other helpful souls that reside here can straighten us newbies out just as well methinks.

..Todd
 
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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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?
 

taj

diyAudio Member
Joined 2005
kvholio said:
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
 
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
 

taj

diyAudio Member
Joined 2005
neil_kaye said:
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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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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