Help with power supply

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Hello everyone. Recently I finalized the assembly and installation of my amplifier based on the chip LM3886 with design of power supply and amplifier taken from the internet (from here DIY HiFi Gainclone Power Amplifier (2x68w, Class AB-A, LM3886)). It is a stereo amplifier with a 24v/5A center-tap laminated core transformer.

I've used the amp a few times (it's currently connected to 4ohms speakers) but I've never been completely happy with its performance due to noise, especially when the amplifier is turned on and now during uses.

This was my first experience with a DIY amplifier and considering that I certainly made some mistakes in the assembly (mainly related to grounding), I decided to redo everything, including new pcbs (power supply and amplifier).

After many searches in the forum and the internet I found many layouts. What I liked the most and that apparently was very well built is this: A Complete Guide to Design and Build a Hi-Fi LM3886 Amplifier - Circuit Basics
However, in relation to power supply, the author used a transformer with dual secondary outputs, while mine is center cap. So, based on the above link design (which seems to me to be inspired by carlosfm's design), I "drew" the schematic below with the respective pcb.

As I've never "drawn" a board before, I do not know if it's correct and so I would like your views.

Thank you very much in advance.

Regards,

Felipe

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Hi Felipe,

Whether you use a transformer with two separate windings or a transformer with a center-tap should make no difference.

Am I wrong in that your center-tap (P8 / Chassis star ground) is not connected to the midpoint of the capacitors?
For all those symmetrical supplies I have made it is connected, and my impression is that your power supply midpoint may be floating. That will create noise.

Check with an Ohm-meter (no power) if the transformer center-tap is connected to the midpoint between the capacitors (P3 Earth etc.).
 
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Hi Felipe,

Whether you use a transformer with two separate windings or a transformer with a center-tap should make no difference.

Am I wrong in that your center-tap (P8 / Chassis star ground) is not connected to the midpoint of the capacitors?
For all those symmetrical supplies I have made it is connected, and my impression is that your power supply midpoint may be floating. That will create noise.

Check with an Ohm-meter (no power) if the transformer center-tap is connected to the midpoint between the capacitors (P3 Earth etc.).


Hi, FauxFrench, thanks for the contribution.

In fact I removed the interconnection of the P8 connector with the board. According to the articles and documents I read about grounding there were mentions to make the star ground in a single point on the chassis so that all landings were made in one place, preferably with wires of the same length and that was the which is why I thought about connecting the center cap of the transformer directly to the point of the star ground instead of connecting it to P8.
That being said, what would be the best way to link the center cap? On the board P8 or star ground point of the chassis?

About the layout of the board and the components used do you have any other considerations?

Regards.
 
My first worry is if there is no connection at all. There must be a connection. The midpoint of the capacitors cannot just be left floating as a virtual ground.
Scott mentioned an article about grounding. I am absolutely no expert.
Intuitively, I would use a star connection but from a point of the ground track after the large storage capacitors. There are important current surges running from the transformer windings and into the storage capacitors. I see no advantage of having these current surges pass the star point. I would not connect the center tap to the star point.

For your layout that would mean the center tap terminal goes directly to your ground-plane on the PCB. I would use wider tracks between the transformer terminals and the + and - terminals of the storage capacitors. All the way to the output terminals. Your current surges may approach 10A, why use narrow PCB tracks? The star point I would find between the output terminals. Once more, this is my intuitive feeling and I am no expert.
 
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