Ok...i am a newby and i am building my first dual channel lm3886 amplifier.
On each pcb i have the signal in ground(sgn-in-gnd),the speaker out ground(spk-out-gnd) and the power ground(pwr-gnd).
other grounds that also exist(not on the pcb!) are the main power ground(main-gnd) and the pot ground(pot-gnd).
1)I connect (main-gnd) on the chassis
2) points (sgn-in-gnd) and (pot-gnd) into a single point,lets say point1
3)point (pwr-gnd) goes on another point,lets say point2.
Then i connect point1 with point2.
Is that correct?
Where should i connect th spk-out-gnd?point1 or point2?
Please answer with the names used above cause im really confused..
Thnks!
On each pcb i have the signal in ground(sgn-in-gnd),the speaker out ground(spk-out-gnd) and the power ground(pwr-gnd).
other grounds that also exist(not on the pcb!) are the main power ground(main-gnd) and the pot ground(pot-gnd).
1)I connect (main-gnd) on the chassis
2) points (sgn-in-gnd) and (pot-gnd) into a single point,lets say point1
3)point (pwr-gnd) goes on another point,lets say point2.
Then i connect point1 with point2.
Is that correct?
Where should i connect th spk-out-gnd?point1 or point2?
Please answer with the names used above cause im really confused..
Thnks!
For safety the chassis should connect to safety earth if it is metal, the exception is if the unit is powered from an external double insulated power supply.
You should join the grounds to the chassis, join it at the power ground point (point 2) and ensure this is a good connection as it too acts as a safety earth route should the transformer insulation fail (a possibility in a toroid). Joining the metal chassis to circuit ground does effectively shield the electronics which is nice.
However, the consequence of all this is that the ground is tied to earth potential, which becomes an issue if the amplifier is used with other earthed equipment, such as a desktop PC. You may then experience a ground loop. Most CD players will not cause issue if connected to an earthed amplifier. Look here for more details on this:
Earthing (Grounding) Your Hi-Fi - Tricks and Techniques
You should join the grounds to the chassis, join it at the power ground point (point 2) and ensure this is a good connection as it too acts as a safety earth route should the transformer insulation fail (a possibility in a toroid). Joining the metal chassis to circuit ground does effectively shield the electronics which is nice.
However, the consequence of all this is that the ground is tied to earth potential, which becomes an issue if the amplifier is used with other earthed equipment, such as a desktop PC. You may then experience a ground loop. Most CD players will not cause issue if connected to an earthed amplifier. Look here for more details on this:
Earthing (Grounding) Your Hi-Fi - Tricks and Techniques
Hi - I posted up an answer to another thread you started with the same question here:
http://www.diyaudio.com/forums/chip-amps/169563-lm3886-grounding-made-easy.html#post2231853
http://www.diyaudio.com/forums/chip-amps/169563-lm3886-grounding-made-easy.html#post2231853
The answer to that depends on whether those grounds on the pcb were already connected or not. Did you find out for sure?
Single point grounding sequence
Well the way I'd do it (bearing in mind there are dissenting views here) is have a bolt (say M3) for the chassis connection which is mechanically fixed to the chassis. That takes care of your safety earth because the first tag to go over the bolt is the earth wire from the mains inlet. The next tag is the highest current one - to the power (main-gnd) ground - that's the centre point of your main rail caps. Over that tag goes the speaker ground (spk-out-gnd). Next up is the decoupling ground from your pcb, which I take to be pwr-gnd in your nomenclature. After this I'd have a tag which goes direct to the screen of your input cable - don't bring the screen connection onto the PCB as this ground is noisy with RF. The last ones on are the quietest signal grounds - i.e. pot-gnd and sig-in-gnd. These last two could even be combined together, no real need for separate connections. Then fit an M3 nut and tighten them all down nicely so they lead out in the form of a star.
Well the way I'd do it (bearing in mind there are dissenting views here) is have a bolt (say M3) for the chassis connection which is mechanically fixed to the chassis. That takes care of your safety earth because the first tag to go over the bolt is the earth wire from the mains inlet. The next tag is the highest current one - to the power (main-gnd) ground - that's the centre point of your main rail caps. Over that tag goes the speaker ground (spk-out-gnd). Next up is the decoupling ground from your pcb, which I take to be pwr-gnd in your nomenclature. After this I'd have a tag which goes direct to the screen of your input cable - don't bring the screen connection onto the PCB as this ground is noisy with RF. The last ones on are the quietest signal grounds - i.e. pot-gnd and sig-in-gnd. These last two could even be combined together, no real need for separate connections. Then fit an M3 nut and tighten them all down nicely so they lead out in the form of a star.
I cant understand what you mean with the bold sentence. Which is the screen of input cable?
Correct me if i am wrong: the rca-ground goes to the pcb signal-in-ground. The pot ground goes also to the pcb signal-in-ground.then a wire must start from pcb signal-in-ground and then joined with the M3 bolt? Which is the screen of input cable?
a coaxial cable has an inner and an outer.
The outer is the screen.
The inner is the core.
It is usual to send the signal through the core and bring back the return through the screen.
I see Andrew has replied to clarify this point.
According to the way I do things, this is wrong. The rca-ground is the same as the screen of the input cable. Don't bring this onto the pcb if you want the best transparency of your amplifier. It carries RF because the cable to your CD player (or whatever source you're using) is an antenna. It also carries hash from the mains back to safety earth because many source components are not grounded nowadays, they tend to be double insulated. So for both of those reasons its sub-optimal to feed all that noise onto your amp pcb.
Yes, you may do it this way - I offered that as an option in my earlier post. The pot ground may be combined with the pcb signal-in-ground and the two of them only need one wire back to the M3 bolt.
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