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P3A PCB Layout
P3A PCB Layout
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Old 10th February 2019, 10:56 PM   #1
vivek1052 is offline vivek1052
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Default P3A PCB Layout

Hi,

I have been working on Elliot's P3A PCB. I am stuck with the confusion whether to go for star ground on the PCB itself or star ground on the Power supply ground bus.
Any other comments on PCB are welcome.
PCB_NEW-PCB_20190209232547.jpg

new.jpg
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Old 11th February 2019, 12:45 AM   #2
Tromperie is offline Tromperie  Australia
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Are you aware that the circuits shown on the project pages are likely to be slightly incomplete? This is so that the circuits are not stolen, but are.
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Old 11th February 2019, 01:07 AM   #3
Ian Finch is offline Ian Finch  Australia
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The DIY tradition of arranging the power supply leads separately around the sides of the amplifier PCB might look neat and symmetrical but it's actually a bad idea. Most P3a DIY threads and many other old favourites here, all start with that same layout error. It presents the largest possible loop area for the high currents and hence the low level signal levels within that loop are more prone to hum and noise from EMI, radiated by the rails. Every cm. of length and sq cm of area matters here.

Instead, minimise the current loop area by maintaining the power conductors together, direct to the output stage and as close together and short as safety permits. It would also be better to remove the fuses to the power supply and don't forget to twist those leads and the speaker leads tightly together all the way.

All these measures are intended to reduce the power flow loop area and path length, which is often more important inside the case, than the choice of design when you perhaps don't realise what really matters for good sound quality.
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Old 11th February 2019, 08:16 AM   #4
vivek1052 is offline vivek1052
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Ohk. I can fix the power traces but i didn't get answer to my original question. Which star ground is better? The PCB one or the one which is located on the power supply
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Old 11th February 2019, 01:09 PM   #5
Mark Whitney is offline Mark Whitney  Netherlands
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If a star ground resembles an octopus then it is bad.
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Old 11th February 2019, 03:23 PM   #6
jacques antoine is offline jacques antoine  France
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P3A PCB Layout
Quote:
Originally Posted by Mark Whitney View Post
If a star ground resembles an octopus then it is bad.
Hexapus OK?
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Old 11th February 2019, 08:28 PM   #7
nigelwright7557 is offline nigelwright7557  United Kingdom
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Quote:
Originally Posted by vivek1052 View Post
Ohk. I can fix the power traces but i didn't get answer to my original question. Which star ground is better? The PCB one or the one which is located on the power supply
Definitely a star ground on the pcb.
Same for wiring.
One pin with zero volts on the pcb that is starred.

If you are unsure about the pcb layout given design your own from scratch using a star ground.
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Old 12th February 2019, 03:44 AM   #8
jaycee is offline jaycee  United Kingdom
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Power ground should be kept separate to signal ground. Your main star point should be at your power supply board - this includes the speaker ground return. The second layout is the better of the two.

As others have said, dont have the power supply tracks like that. Keep them short and close together.

As for transistors, use MJE350 for Q4, and MJE243/253 for Q5/Q6. If you can get better transistors instead of the TIP35C/TIP36C do so.
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Old 12th February 2019, 03:52 AM   #9
vivek1052 is offline vivek1052
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Thanks for you replies. I am clear now on what needs to be done
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Old 12th February 2019, 03:57 AM   #10
vivek1052 is offline vivek1052
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Regarding the output transistors, is there an audible difference using the Motorola transistors? I meam if we are going to run this amp on +-35v, how is the tip one not good.
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