noise, ground plane, amp PAM8304, best practices ?


Well-known member

I have been using pam8304 class D amp for many of my projects. This amp delivers a lot of power from 5V.
But it is a pain to reject noise. Digital noise tends to leak in power rails (I think).

I would like to know what are the best practices to limit digital "leaks". I need advices for :
- PCB ground planes design
- power rails design
- decoupling
- and also advices to avoid ground loops

I join the schematic of a little synth project. It works "as is" pretty well, but I would like to improve noise rejection.
I would appreciate comments about this schematic, and advices to get a well designed PCB. I use a Teensy 4.0, an i2s dac (uda1334) and a pam8302.

The red dots on the schematic are capacitive pads, for notes triggering.
I use a resistive ladder to add a lot of switches with only 1 input. It is working well, no problem on this side.
Pots readings are noisy. Digital noise leaks again. Some analog inputs are almost free of noise, others are very noisy (+- 10 on 1024). But it is ok with basic filtering.

Thank you,
View attachment Schematic_MiniTouch.pdf
Have a look at this schematic:

View attachment Schematic.pdf

Notice the (noise )bypass capacitors at every IC on the board. Also notice that all the analog stuff on the left is fed through a low pass filter (usually referred to as a Pi filter), this keeps the digital noise out of the analog circuits. The ground planes for analog and digital circuits are completely separated, and are tied together at one point which has a jumper to connect them together, some people connect the two planes together with an inductor. All power traces should be as large as possible to fit on the board, most people use a separate layer altogether for their power planes which keeps the impedance to a very low level therefore reducing I2R losses.
Remember to put in as much distributed capacitance on the board as possible, this helps to keep the digital noise as low as possible.

Most people would probably think that I am being way to conservative in my designs, but since I have been doing this since 1963 and many of my mentors and experiences are from the Aerospace world from the 1970's to the 2000's this is the way we were required to design our circuits.
One of my good friends and mentor designed the electronics package on the Voyager space probes. It is still working after some 40 years and its original design life was supposed to be only 7 years, not bad Huh!

I would recommend sitting through this 2 hour long Rick Hartley video for both hobbyist and professional PCB designers: It is the some of the best advice on grounding (an essential feature of a PCB) and covers multi-layer boards too. I also like Phil Salmony, and Robert Feranec's channels, which cover lots of schematic and PCB aspects:,

If you design a PCB for your project, a four-layer board with both inner layers as ground planes is considered the best approach. I'm using this for a current synth project and it's made a significant difference to digital noise from the display feeding into the analogue audio.
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