Hello,
I am planning on building two 4-way active speaker boxes. 4 chipamp-based amplifiers , Linkwitz-Riley filters , and switched PSU. Most materials are available already.
I have read tons on correct grounding of chip-amp modules and how to correct and improve that when not optimal.
My big doubt and question is how to correctly design the grounding for four chip-amps on one power-supply and one active 4-way-filter .
Anyone can help me there ? Thanks
I am planning on building two 4-way active speaker boxes. 4 chipamp-based amplifiers , Linkwitz-Riley filters , and switched PSU. Most materials are available already.
I have read tons on correct grounding of chip-amp modules and how to correct and improve that when not optimal.
My big doubt and question is how to correctly design the grounding for four chip-amps on one power-supply and one active 4-way-filter .
Anyone can help me there ? Thanks
Basic principle: do not connect the signal screens (assuming RCA) to power ground or chassis. Move each signal through the system by dragging its screen along, grounding the screen at the input right at each stage, like the input resistor ground at an (op)amp input, taking the screen from output ground point like the (op)amp output load resistor ground point, in going to the next stage.
Ground all speaker returns at a central ground point for each amp but NOT at the common power ground.
The central idea is to avoid running signal ground, speaker ground or power ground through a common wire at any point; they each should have different wiring until the very last point.
Jan
Ground all speaker returns at a central ground point for each amp but NOT at the common power ground.
The central idea is to avoid running signal ground, speaker ground or power ground through a common wire at any point; they each should have different wiring until the very last point.
Jan
Hello Jan thanks for your answer.
that pecisely where I have myu biggest doubts.
Lets see if I can explain myself.
I have 4 pcbs each an amplifier so from all four there is a ground wire to the central point of the power supply capacitors and a second wire from the pcbs ground to the speaker it serves.
Now the bass amp reproduces some heavy signals . This causes a voltage drop in the wire from the capacitors to the ground of the bass pcb because the current returning from the speaker goes through that wire which has a resistance and an inductance. So the ground of the bass pcb is at a sligjtly different voltage from the other amps which are not reproducing anything at this time.
at the same time the ground of that bass pcb is connected to its own input ground and through that to the active filter ground which in turn is connected to the input grounds of the other three amp pcbs. The signal through these grounds will be a very small amplitude but it is an error signal which is outside of any feedback-loop of the amps and therefore will remain uncorrected and amplified? Am I right and if so how can this be avoided? Can I connect the shielding of the interconnecting cables at one side only , either the four amp-pcbs or the four-way-filter and avoid these internal ground loops in this way or is there any other correction I can and must apply?
Thanks Michael
that pecisely where I have myu biggest doubts.
Lets see if I can explain myself.
I have 4 pcbs each an amplifier so from all four there is a ground wire to the central point of the power supply capacitors and a second wire from the pcbs ground to the speaker it serves.
Now the bass amp reproduces some heavy signals . This causes a voltage drop in the wire from the capacitors to the ground of the bass pcb because the current returning from the speaker goes through that wire which has a resistance and an inductance. So the ground of the bass pcb is at a sligjtly different voltage from the other amps which are not reproducing anything at this time.
at the same time the ground of that bass pcb is connected to its own input ground and through that to the active filter ground which in turn is connected to the input grounds of the other three amp pcbs. The signal through these grounds will be a very small amplitude but it is an error signal which is outside of any feedback-loop of the amps and therefore will remain uncorrected and amplified? Am I right and if so how can this be avoided? Can I connect the shielding of the interconnecting cables at one side only , either the four amp-pcbs or the four-way-filter and avoid these internal ground loops in this way or is there any other correction I can and must apply?
Thanks Michael
An open source layout for the lm3886 ? At post #103 there is a beginning of a design for an onboard filter and how the HBR (hum breaking resistor) between signal and power ground) works can be found at post #55 and beyond.
Or, you could use signal transformers between each board.
Or, you could use signal transformers between each board.
I will only have to get the grounding within each speaker-box right. They will be connected through a Wifi-network and the signal to them will be streaming at 1440mbit/sec that is cd quality. No ground problem there. BUT
Each box is comparable to an amp with four channels although in this case these are used for different frequencies.
The input grounds of these 4 amps have to go to the frequency-filter , so that is a 4 way ground loop. But the I have the ground from the power supply to the 4 pcbs as well. If I take these last ones directly to the union between the power caps it is four wires to there . If I take them to a starpoint which then is taken to the caps I still have a 4 way loop to that point where they join.
The speaker ground going to each amp will cause voltages in the ground from the pcb to the starpoint which will affect the other three amps
If instead the speaker return goes to the starpoint and from there to its pcb I avoid the return currents in the ground to the pcb but I do not know how that will affect the feedback and with it the distortion. And what about the return currents from the amps themselves?
I do not understand how to avoid that or how to cancel the effects
Each box is comparable to an amp with four channels although in this case these are used for different frequencies.
The input grounds of these 4 amps have to go to the frequency-filter , so that is a 4 way ground loop. But the I have the ground from the power supply to the 4 pcbs as well. If I take these last ones directly to the union between the power caps it is four wires to there . If I take them to a starpoint which then is taken to the caps I still have a 4 way loop to that point where they join.
The speaker ground going to each amp will cause voltages in the ground from the pcb to the starpoint which will affect the other three amps
If instead the speaker return goes to the starpoint and from there to its pcb I avoid the return currents in the ground to the pcb but I do not know how that will affect the feedback and with it the distortion. And what about the return currents from the amps themselves?
I do not understand how to avoid that or how to cancel the effects
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I've done it with three way actives. It isn't as big a problem as you are worrying about. Put it all together and it is likely there won't be a problem; there wasn't with mine.
Even if there is, it won't take much to fix.
I found the bigger problem was hum and interference with using unbalanced (RCA) leads to the speakers. That is why I use balanced feeds now, with XLR connectors.
I wont have problems with the feeds as they will be by WLAN at high streaming bitrate. bandwidth more than 10 megabits necesary only about 1,5
What I am worried about is hum caused internally and mutual interference between the 4 amps which can easily boost distortion through voltage differences in the grounding. Any voltage at an input because of grounding will be amplified by the gain factor appearing at the output. Now 15KHz at the bass wont be a problem because the bass wont even react to that but 50 Hz at the Tweeter will be . The speakers are all coupled directly to the amps!!!!
What I am worried about is hum caused internally and mutual interference between the 4 amps which can easily boost distortion through voltage differences in the grounding. Any voltage at an input because of grounding will be amplified by the gain factor appearing at the output. Now 15KHz at the bass wont be a problem because the bass wont even react to that but 50 Hz at the Tweeter will be . The speakers are all coupled directly to the amps!!!!
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I think you are overthinking it. I have four 3886 amps closely spaced at the bottom of the box against a 300mm long heatsink and don't have a problem. Cross distortion between amps isn't even worth worrying about.
The ground point is a ground, so any potential differences are between it and the individual amp modules. Mine work, so will yours.
The ground point is a ground, so any potential differences are between it and the individual amp modules. Mine work, so will yours.
Hello Mark ,
what I do know is how to do the grounding for a single amp and how to optimize it. What I am not so sure about is what happens when its 4 amps on a common powersupply each with a ground to that and a ground to an also common Linkwitz-Riley Filter. I am a good repair technician but I am not an engineer so I have my limitations. Knowing this its better to ask those who know better than I do.
I want to make sure I do tyhings right and the best way possible
Greetings Michael
what I do know is how to do the grounding for a single amp and how to optimize it. What I am not so sure about is what happens when its 4 amps on a common powersupply each with a ground to that and a ground to an also common Linkwitz-Riley Filter. I am a good repair technician but I am not an engineer so I have my limitations. Knowing this its better to ask those who know better than I do.
I want to make sure I do tyhings right and the best way possible
Greetings Michael
A solution can be found on the thread I linked to before.
The problem is really the inputs and not the power ground connections. Just make the PSU to amp connections as short as possible and away from the transformer.
http://www.updatemydynaco.com/documents/GroundingProblemsRev1p4.pdf Here is shown how to simulate a ground loop (Figure 4-5). A transformer with primary and secondary plus two extra secondaries placed in inputs/ground loop of both amps. To fix this a resistor is strategically placed to break the loop. In the open source lm3886 thread you can see some simulations done.
There are other solutions possible. This one is the cheapest.
The problem is really the inputs and not the power ground connections. Just make the PSU to amp connections as short as possible and away from the transformer.
http://www.updatemydynaco.com/documents/GroundingProblemsRev1p4.pdf Here is shown how to simulate a ground loop (Figure 4-5). A transformer with primary and secondary plus two extra secondaries placed in inputs/ground loop of both amps. To fix this a resistor is strategically placed to break the loop. In the open source lm3886 thread you can see some simulations done.
There are other solutions possible. This one is the cheapest.
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