Hi, I'm busy drawing a schematic for a 6 channel amplifier using the LM4780 chips. This will be controlled with a ATMEGA163 MCU and some PGA2310 chips.
The problem I've got is that on the 4780's eval board there is a resistor between power Gnd and signal Gnd.
Do I need to keep each amps signal ground Isolated?
I'll end up with Digital ground(for +5v), Ground for +-15v(PGA2310), Ground for the power amplifier V supply AND then Each chips signal ground.
This is 6 different grounds.
The problem I've got is that on the 4780's eval board there is a resistor between power Gnd and signal Gnd.
Do I need to keep each amps signal ground Isolated?
I'll end up with Digital ground(for +5v), Ground for +-15v(PGA2310), Ground for the power amplifier V supply AND then Each chips signal ground.
This is 6 different grounds.
Hi Wynand, lekker dag vandag nè.
Sorry I don't have an answer, but would like to add a question to your list for when the smart people wake up... if you'd be so kind.
Anyway on basic inverted GC the signal ground and power ground are to be connected, could I use a 1 ohm resistor between these 2 points, I don't have any suitable thin wire left...
Sorry I don't have an answer, but would like to add a question to your list for when the smart people wake up... if you'd be so kind.
Anyway on basic inverted GC the signal ground and power ground are to be connected, could I use a 1 ohm resistor between these 2 points, I don't have any suitable thin wire left...
Hi,
my basic grounding philosophy is simple.
Design your system with three separate grounds (for Wynand you need four).
Safety ground (chassis), Power ground (dirty), Digital power ground (spiky?), Signal ground (clean).
Keep these three/four grounds completely separate throughout the design and construction. Keep in mind that PCB decoupling is considered as dirty ground and so too are the Speaker return and Zobel/Thiel network at the output of Power Amps. The input connector ground is Signal ground and should be isolated from chassis.
Decision time;-
option A, connect all the grounds to a central star ground (CSG).
option B, connect Safety to network then to CSG. Connect P, S & D to CSG.
option C, connect Safety, D & P together, then network and then to CSG. S to CSG.
In B & C there is a network between Safety and S. This usually keeps hum and buzzing out of the output.
The Network can be any single or combination of the following:- resistor//capacitor//diode bridge//snubber//shorting switch. Closing the switch converts B & C to A. Opening the switch is the equivalent to lifting the ground (commonly referred to in commercial amps). You can experiment with other combinations but as Pinkmouse said keep the different grounds separate until they reach CSG.
The PSU common (on bipolar supplies) should connect 0Volts to smoothing capacitor common to transformer centre tap. Make a wired connection from 0V to CSG. Do not use the cap common as a CSG.
Really important safety rule. Always connect the Safety ground permanently to chassis. NEVER switch this connection and NEVER run the equipment from the mains with this connection temporarily disconnected.
The safest way to achieve this is welding the mains safety earth to chassis, next best is bolt this connection directly to chassis with it's own nut then add the other grounds/connecting wire above this first nut and use a second nut for experimenting with different grounding arrangements.
my basic grounding philosophy is simple.
Design your system with three separate grounds (for Wynand you need four).
Safety ground (chassis), Power ground (dirty), Digital power ground (spiky?), Signal ground (clean).
Keep these three/four grounds completely separate throughout the design and construction. Keep in mind that PCB decoupling is considered as dirty ground and so too are the Speaker return and Zobel/Thiel network at the output of Power Amps. The input connector ground is Signal ground and should be isolated from chassis.
Decision time;-
option A, connect all the grounds to a central star ground (CSG).
option B, connect Safety to network then to CSG. Connect P, S & D to CSG.
option C, connect Safety, D & P together, then network and then to CSG. S to CSG.
In B & C there is a network between Safety and S. This usually keeps hum and buzzing out of the output.
The Network can be any single or combination of the following:- resistor//capacitor//diode bridge//snubber//shorting switch. Closing the switch converts B & C to A. Opening the switch is the equivalent to lifting the ground (commonly referred to in commercial amps). You can experiment with other combinations but as Pinkmouse said keep the different grounds separate until they reach CSG.
The PSU common (on bipolar supplies) should connect 0Volts to smoothing capacitor common to transformer centre tap. Make a wired connection from 0V to CSG. Do not use the cap common as a CSG.
Really important safety rule. Always connect the Safety ground permanently to chassis. NEVER switch this connection and NEVER run the equipment from the mains with this connection temporarily disconnected.
The safest way to achieve this is welding the mains safety earth to chassis, next best is bolt this connection directly to chassis with it's own nut then add the other grounds/connecting wire above this first nut and use a second nut for experimenting with different grounding arrangements.
Bit of a ghetto project, with oll the odds and ends left over from other tests.... the wires I used so far is pretty thin, I like using a thinner wire between PGS and SGS than the rest of the wires, which with the dental floss thin stuff I used anyway, would mean I need a hair or something made of copper... PSU and 2 channels all on one recyled piece of veroboard... one benifit of being poor is, you learn to build things so you can reuse as mutch of it as possible... even veroboard...
thats why I thought a one ohm would do the job, to connect the PGS and SGS but still be more "resistive" than the rest of the connections from PGS, keeping the noise frome there, away from the signal ground, yet still allowing a grounding path for the signal ground.
Milnerton hier
thats why I thought a one ohm would do the job, to connect the PGS and SGS but still be more "resistive" than the rest of the connections from PGS, keeping the noise frome there, away from the signal ground, yet still allowing a grounding path for the signal ground.
Milnerton hier
Hi,
although I called it simple, it always seems longwinded by the time I get through all the important points.
I'm glad you had the patience to read it through.
The main thing is keep the different grounds separate until the CSG then you have the flexibility to experiment if an obscure problem crops up.
although I called it simple, it always seems longwinded by the time I get through all the important points.
I'm glad you had the patience to read it through.
The main thing is keep the different grounds separate until the CSG then you have the flexibility to experiment if an obscure problem crops up.
Have a look at this page (scroll down a bit), where I show a schematic of the grounding scheme I used for a chipamp with separate PSU. It is absolutely silent.
Mick
Mick
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