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2.1 channel LM3886 star ground questions
2.1 channel LM3886 star ground questions
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Old 7th November 2019, 08:28 PM   #1
lost eden is offline lost eden  United Kingdom
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Default 2.1 channel LM3886 star ground questions

I'm making very slow progress on my 2.1 channel LM3886 & have reached the point where I need to work out the grounding. My previous 2.0 channel LM3886 was essentially permanently ground lifted so I didn't go through this process.

Following the diagram & explanation toward the bottom of this page I think what I need to do is shown in the attached images of my build so far.

Am I on the right track? If so, what is the best physical way to achieve this? Trying to stack 11 crimp connectors onto a single bolt is going to end up a mess, but presumably I can double/triple up wires to crimps?

Also, if I am using shielded cables for the line level inputs to the amps, what should I connect the shield to (if anything)?
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Old 8th November 2019, 01:06 PM   #2
pitbul is offline pitbul
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I think that your 2.1 system will have subwoofer amp bridged, so tehre is no speaker ground for it.
A I correct, if Yes, then you should have only 2 speaker grounds for L & R speaker and for sub you will have wires directly from LM3886 modules (one positive output as +speaker terminal and the other one from positive output as -speaker terminal).
In general your star point is correct.
Maybe in future you will lift your star point with ground lifter (many times suggested in this forum). Mains earth will stay on the metal part of the chassis and star point for all the modules will be on ground lifter side.
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Old 8th November 2019, 01:24 PM   #3
Michael Bean is offline Michael Bean  United States
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Daisy-chaining the power connections like that is a bad idea...each amp needs to to be connected to the power supply separately. All wires have resistance, and the amps down stream from the others will be prone to voltage modulation of the power due to the amps up stream drawing power ahead of them in the circuit. So in effect, what you have there is one amp connected directly to the power supply, the next amp is connected to a power draw through a small value resistor, that amp's power will be affected by the first amp, the third amp will connect through the second amp and the first amp through yet another resistor and will be affected by amps one and two...and even worse for amp number four.
As for your original question...I suggest you read this:
Taming the LM3886 Chip Amplifier – Neurochrome
Tom Christiansen (DIY member) has a very informative and comprehensive article that should help you out.

Mike
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Last edited by Michael Bean; 8th November 2019 at 01:26 PM.
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Old 8th November 2019, 01:49 PM   #4
pitbul is offline pitbul
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I think that your 2.1 system will have subwoofer amp bridged, so thre is no speaker ground for it.
Am I correct, if Yes, then you should have only 2 speaker grounds for L & R speaker and for sub you will have wires directly from LM3886 modules (one positive output as +speaker terminal and the other one from positive output as -speaker terminal).
In general your star point is correct.
Maybe in future you will lift your star point with ground lifter (many times suggested in this forum). Mains earth will stay on the metal part of the chassis and star point for all the modules will be on ground lifter side.
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Old 8th November 2019, 03:44 PM   #5
scottjoplin is offline scottjoplin  Wales
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It's best to keep all flow and returns close coupled to reduce loop areas and minimise hum pick up, that includes power as well as inputs and outputs. http://hifisonix.com/wordpress/wp-co...ound-Loops.pdf
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Old 9th November 2019, 10:02 PM   #6
00940 is offline 00940  Belgium
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I would second both Michael Bean and scottjoplin suggestions.

1. Do not daisy chain power. Bring the power to each amp pcb by a twisted triplet (v+, gnd, v-). Same for the crossover board.
2. Twist the output wires together (speaker out and gnd out) and connect them to the amp pcbs.
3. On the input side, use insulated rca jacks, twist signal and gnd together and bring together to the crossover board. Also use twisted pair between each amp pcb and the crossover board.
4. Ideally, I would use two ground loop breakers. One between the gnd of the amps power supply and the chassis (earth) and one between the crossover power supply gnd and the chassis.

I'm not quite clear on what you're doing with the two amps for the sub. Are you using them paralleled (with a 4ohms driver) or bridged (with a 8ohms driver) ? In the first case, you'll need an inverter before one of the board. In the second case, you'll need high wattage, low value sharing resistors at their outputs. It would also be good to use well matched gain setting resistors.
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