Each chip should have it's own 100nF//1000uF supply decoupling caps.

Move the input coupling caps close to the respective inputs on the chips. You need to put components where they need to be not where it is convenient or looks pretty: Please read (2.2) in (2) in: [https://easyeda.com/forum/topic/How-to-ask-for-help-and-get-an-answer-71b17a40d15442349eaecbfae083e46a](https://easyeda.com/forum/topic/How-to-ask-for-help-and-get-an-answer-71b17a40d15442349eaecbfae083e46a)

@andyfierman Thank you. As each chip has two VCC inputs, should I do a pair of the mentioned capacitors on each pin for each chip, making it a total of 4 coupling capacitors per chip?

@hitbyatruck, Follow the advice in the device datasheet: [https://www.st.com/resource/en/datasheet/sta540.pdf](https://www.st.com/resource/en/datasheet/sta540.pdf) Also make your positive supplie tracks as wide as possible. Put the GND plane on the top layer and a VCC supply plane on the bottom. With careful routing you can maintain good continuity in both even though you will have tracks routed across them..

@andyfierman Thank you so much for the tips. I believe I have improved it somehow with your feedback. I moved all the components in order to have the coupling capacitors as close to the chips as possible and the input capacitors closer to the input connectors. I also added the GND plane to the top layer and a VCC plane to the bottom one and made the VCC net as wide as 1mm with a 0.3mm clearance.

"... the input capacitors closer to the input connectors..." They are better placed close to the chip inputs too. Basically any components connected directly to a pin on a chip should be close to that chip.

@andyfierman I figured that as well, I tried to get them as close as possible to the chip, but as the pins are a bit to close to each other, I got them in between the input connectors and the chip as close as possible as it seemed feasible without compromising the capacitors placement having them too clustered. I think I'm gonna do a prototype and measure the input and output signals to see if the any degradation occurs. Thank you so much for all your feedback. I'm still strugling a bit with the software in order to understand how to edit and manipulate specific pcb wires and how to add pins or pads in the circuit schematic in order to reflect themselves on the pcb layout. I'll keep looking at the documentation and tutorials and see if I can get a better grasp of the full functionalities of EasyEDA, which so far seems a very nice experience to design PCB's.

"I think I'm gonna do a prototype and measure the input and output signals to see if the any degradation occurs." It's not so much a question of how the component placement might degrade the signal, it's more to do with reducing track lengths that might be susceptible to RFI or maybe static damage. For a simple audio amp like this it is not so critical but even at this low frequency range, attention to ground return paths and minimising the loop area enclosed by conductors can make a big difference in hum pickup and stability. It's a pity that there are no apps notes for the STA540...but the datasheet for a couple of earlier versions, the STA540SAN and STA541SA, might be helpful: [https://www.st.com/resource/en/datasheet/sta540san.pdf](https://www.st.com/resource/en/datasheet/sta540san.pdf) [https://www.st.com/resource/en/datasheet/sta541sa.pdf](https://www.st.com/resource/en/datasheet/sta541sa.pdf) "...in order to understand how to edit and manipulate specific pcb wires and how to add pins or pads in the circuit schematic in order to reflect themselves on the pcb layout." The appendix in (2.2) and the document (2.3) might help with that. The Essential Checklists (4) and (6) too. :) To help with understanding EasyEDA I recommend that people start off with a very simple project and just play with the software to get the hang of the various features. If you do that and then try things out on it as you go through the documentation that is a much easier way of making sense of it than waiting until you get stuck with an issue and then trying to find a solution in the documentation and the forums. The appendix in (2.2) and the document (2.3) might help with that

@andyfierman Thank you so much for all the feedback given. I don't do PCB designs and layouts for a long time. Last time I did, I used SPICE and ORCAD and have been several years ago. This is a way to refurbish an old Logitech Z506 kit that I had lying around with a malfunctioning main board. Since the speakers are alright and I only have a problem of crackling and noise on the front left channel, which I can't figure out what's causing it, I decided to build this in order to be able to use the speakers again. The Z506 have a PT2325 for volume control, which I don't actually need, and several opamps for what I believe to  be line level amplifiers for the inputs on the STA540. Since I'll be using line level signals as the source I thought I may as well get back to the "electronics lab" and develop just the amplification stage of the circuit in order to be able to use the speakers on a small home cinema just for the fun of it.

@hitbyatruck, Are you not going to need volume controls of some sort somewhere in the chain? There's something to be said for recycling the box that the original kit came in with new innards! I once build a 3W + 3W stereo amp using some very early power amplifier chips in an upside down valve radio chassis... Have fun.   :) I have built a lot of the in-house models for EasyEDA and recently I've been toying with the idea of making very crude device models that whilst not necessarily giving anything near the datasheet performance of the target device, at least give the basic functionality in a Spice schematic Symbol with the right pinout and the right PCB footprint so that they can just be dropped into a schematic to run a quick simulation to check that the connectivity of the schematic and hence that of the PCB are correct. It's not the way simulation is used normally but it makes a lot of sense in EasyEDA because the three tool of schematic capture, simulation and PCB design are more closely knit than most EDA tools (at least the free ones!). Unfortunately there's no spice model of the STA540 and I have got the time to build more models at the moment.

@andyfierman Actually I don't need volume control on this specific application since I have all lines independently controlled by a mixer. If this one works out, I'll probably go over the schematic and implement a Pt2325 ic to handle the 6 inputs volume, or I'll check a way to implement 6 individual control volumes so anyone can adjust each channel volume independently.

Hi! I took this saturday to cleanup your schematic. Hopefully you can use this to improve your design: [https://easyeda.com/markus_jidoka/main-board-sta540](https://easyeda.com/markus_jidoka/main-board-sta540) or [https://oshwlab.com/markus_jidoka/main-board-sta540](https://oshwlab.com/markus_jidoka/main-board-sta540) Regards, Markus Virtanen HW / Electronics Designer

Hi! I took this sunday morning to update the layout for you. You can download the schematic and layout to yourself. I might delete this project from my own personal folder once you have copied these to yourself. Regards, Markus Virtanen HW / Electronics Designer

@hitbyatruck If there is new/additional functionalities needed to this project, let me know, I might help if I got time. -Markus

@markus_jidoka sorry for the delay on the response, but have been away on work and couldn't get back to this board for some time. Thank you so much for the clean up and changes on the schematic and PCB. In the meantime I was struggling with the standby function of the ship which couldn't trully understand from the datasheet, but with the prototype I needed to get pin 7 HIGh, so I stuck a 10K or 100K resistor between pin 3 and 7 in order for the IC's to get off standby mode. The fuse and diode were a nice addition, just to avoid bad connections to the board. One other thing I may add up in the future will be a volume control for the inputs or at least get the board ready with the adequate pins in order to insert 2 x double 10K audio taper pots and 2 x normal 10k audio taper pots, so anyone can control the front stereo, surround stereo, center and sub individually. I don't believe there's much to gain in adding some form of processing to achieve these functions. One thing it may make sense is to add the Mute function for the STA540 as well, but for my specific purpose, I don't consider it to be a need. Thank you so much, once again, for the interest shown and the help. I gladly implement and improve this circuit further with you, if you're into it.

@markus_jidoka Updated the schematic and PCB to version 1.2 with the added 100K resistors to enable operation of the IC. Added you as well as a developer to the project. [https://oshwlab.com/hitbyatruck/main-board-sta540-updated](https://oshwlab.com/hitbyatruck/main-board-sta540-updated)<br> <br> [https://easyeda.com/editor#id=ea0e35a39d1f42b0a3c7564bbd99a1fc](https://easyeda.com/editor#id=ea0e35a39d1f42b0a3c7564bbd99a1fc)<br> <br> Once again, thank you so much for all the help.

Hi! Thanks, I'll try to help with the project now and then when I don't have my own projects under way. -Markus

Hello All! I got some time today to update the project. I revisioned it to v1.2a, go check it out! [https://easyeda.com/hitbyatruck/main-board-sta540-updated](https://easyeda.com/hitbyatruck/main-board-sta540-updated)<br> <br> Regards, Markus Virtanen HW / Electronics Designer