hi guys excuse me i'm kinda not well experienced... Should we connect the input signal ground to the power ground and speaker return or shouldn't ? i see it in some schematics such as that of APEX separated by marking (SGND) and (PGND). meanwhile at the wiring it's all connected to the power STAR Ground.
i'm a little confused😕.
i'm a little confused😕.
Hi Guys
Electrically ground is ground. The important thing to avoid hum and oscillation is the physical orientation of those connections. Fortunately, it is not voodoo but simple science.
The detail to consider is the path of any given current. Current moves in loops. Some of these loops are very noisey; some are very quiet. We have to keep the noisiest currents separated from the quietest ones so that the amp will be quiet overall.
The noisiest current is the rectifier charging pulses into the main filter caps. These are in fact pulses, so very short duration but comprised of horrific noise harmonics. This current circulates through the PT secondary, the rectifier and the filter cap.
The next current loop is from the filter cap to the output stage. Idle currents are flat DC but signal currents in a typical power amp are like half-wave DC. These latter currents are again noisy and must be kept away from quiet currents. Again, we orient the physical connections so that these currents are isolated as much as possible from the rectifier current.
Physically, rectifier current loop wiring must be kept floating and confined. The fitler caps have their ground ends tied together and then brough out as a single lead. This lead carries a mix of send and return currents but is nominally "quiet", at least compared to the rectifier current loop. We can take a line from this output to the chassis. Most people use this point as the star but there are reasons not to, which I won't go into here.
The half-wave DC currents in the output stage must be summed and brought out on a single wire before being connected to the feedback loop or to the output network and jack. The speaker jack carries the heavy AC speaker current that is nominally quiet, and because of its magnitude, usually has its own wire to the star. The power leads to the output stage should be twisted together but NOT with the output stage ground. If there are local filter caps, the grounds for these should be brought to the star on their own wire.
The front end of the amp has fairly steady quiet currents, so its power feed and ground should be separate as well.
The input signal has its own circulating current through the signal lead and the ground connection at the input.The input jack can be tied directly to chassis or be insulated - arguments both ways as to which is best. The coax bringing the signal to the front-end is an extension of the shield between the preamp and the power amp. In many cases, a 10R is placed between the input signal ground referencing and the higher-current grounds of the amp. This small R isolates the ground currents allowing the input device to establish the input reference. The 10R also breaks a potential loop between left and right channels.
With a low-impedance signal source, there are sins one can get away with even with sloppy wiring and ground loops everywhere. Partly it will depend on how fussy you are. One approach is to simply get everything working to begin with, then re-arrange wiring and such as required to alleviate noise.
Have fun
Electrically ground is ground. The important thing to avoid hum and oscillation is the physical orientation of those connections. Fortunately, it is not voodoo but simple science.
The detail to consider is the path of any given current. Current moves in loops. Some of these loops are very noisey; some are very quiet. We have to keep the noisiest currents separated from the quietest ones so that the amp will be quiet overall.
The noisiest current is the rectifier charging pulses into the main filter caps. These are in fact pulses, so very short duration but comprised of horrific noise harmonics. This current circulates through the PT secondary, the rectifier and the filter cap.
The next current loop is from the filter cap to the output stage. Idle currents are flat DC but signal currents in a typical power amp are like half-wave DC. These latter currents are again noisy and must be kept away from quiet currents. Again, we orient the physical connections so that these currents are isolated as much as possible from the rectifier current.
Physically, rectifier current loop wiring must be kept floating and confined. The fitler caps have their ground ends tied together and then brough out as a single lead. This lead carries a mix of send and return currents but is nominally "quiet", at least compared to the rectifier current loop. We can take a line from this output to the chassis. Most people use this point as the star but there are reasons not to, which I won't go into here.
The half-wave DC currents in the output stage must be summed and brought out on a single wire before being connected to the feedback loop or to the output network and jack. The speaker jack carries the heavy AC speaker current that is nominally quiet, and because of its magnitude, usually has its own wire to the star. The power leads to the output stage should be twisted together but NOT with the output stage ground. If there are local filter caps, the grounds for these should be brought to the star on their own wire.
The front end of the amp has fairly steady quiet currents, so its power feed and ground should be separate as well.
The input signal has its own circulating current through the signal lead and the ground connection at the input.The input jack can be tied directly to chassis or be insulated - arguments both ways as to which is best. The coax bringing the signal to the front-end is an extension of the shield between the preamp and the power amp. In many cases, a 10R is placed between the input signal ground referencing and the higher-current grounds of the amp. This small R isolates the ground currents allowing the input device to establish the input reference. The 10R also breaks a potential loop between left and right channels.
With a low-impedance signal source, there are sins one can get away with even with sloppy wiring and ground loops everywhere. Partly it will depend on how fussy you are. One approach is to simply get everything working to begin with, then re-arrange wiring and such as required to alleviate noise.
Have fun
Well..thats a rich info STRUTH thank you this is gonna be very usefull to me in designing PCB too.... i will just tell you the result of my understanding to your rich info to make sure i got it right....i should wire all ground together with a star ground but because of the current loops i should isolate the input ground (Signal ground) from the power ground with a 10R resistor and the output ground (Speaker return) is connected directly to the power ground after filter caps..am i right?
Hi Guys
The concept of circulating currents is the essence of the galactic ground system I've used for decades. It applies to any technology of circuit.
When laying out linear PCBs, NEVER use the auto-router.
I do not use the ground symbol in Eagle as I want to control the routing of the ground connections - which you can always do anyway (even if you have to remove a fly-trace that got you to the starting point you wanted to use rather than the one the layout editor wants you to use). If you keep the current loop paths in mind, the board will be laid out correctly. There will be some redundant looking traces, but they do the isolating for you.
overall, if you have a sensibly laid out schematic and then lay the physical circuit out similarly, the circuit should be stable and quiet.
Have fun
The concept of circulating currents is the essence of the galactic ground system I've used for decades. It applies to any technology of circuit.
When laying out linear PCBs, NEVER use the auto-router.
I do not use the ground symbol in Eagle as I want to control the routing of the ground connections - which you can always do anyway (even if you have to remove a fly-trace that got you to the starting point you wanted to use rather than the one the layout editor wants you to use). If you keep the current loop paths in mind, the board will be laid out correctly. There will be some redundant looking traces, but they do the isolating for you.
overall, if you have a sensibly laid out schematic and then lay the physical circuit out similarly, the circuit should be stable and quiet.
Have fun
I auto-routed a mixer with a power supply on the same pcb.
When I built it up and tested it I had 1 volt hum on the output.
I had a look around the charging impulses into the power supply smoothing capacitors was modulating the ground line and was being amplified.
I reworked the pcb keeping the power supply separate and the hum went away.
Look up "star grounding" and you will find volumes written on it.
Connect all grounds to a single point.
The return from the speakers should always go to junction of smoothing capacitors.
When I built it up and tested it I had 1 volt hum on the output.
I had a look around the charging impulses into the power supply smoothing capacitors was modulating the ground line and was being amplified.
I reworked the pcb keeping the power supply separate and the hum went away.
Look up "star grounding" and you will find volumes written on it.
Connect all grounds to a single point.
The return from the speakers should always go to junction of smoothing capacitors.
Hi Guys
Nigel - you experienced what an auto-router can do to audio performance. Better to do it by hand.
A star ground is the most easily understood organised grounding scheme, but it is not the best choice for most things. A star ground should not be confused with the fact that there should only be one tie point between the signal ground buss and the chassis ground.
Chassis should only be used as a shield - not as a conductor of signal currents between circuits.
The safety ground ties the mains ground to the chassis at its own independent point.
Have fun
Nigel - you experienced what an auto-router can do to audio performance. Better to do it by hand.
A star ground is the most easily understood organised grounding scheme, but it is not the best choice for most things. A star ground should not be confused with the fact that there should only be one tie point between the signal ground buss and the chassis ground.
Chassis should only be used as a shield - not as a conductor of signal currents between circuits.
The safety ground ties the mains ground to the chassis at its own independent point.
Have fun
Just about the most succinct grounding description I have read, particularly as it gives the reasons, not just the practice. This one is a 'keeper'. Many thanks.
- Status
- Not open for further replies.