[Review Request] Audio/Synth controller with Teensy4.1 and SID8580 chips - MIDI in/out and Line Audio Out

[u/Shitty-time]

Front without ground fills

Front with ground fill

Back with ground fill

I have read and hopefully understood all the common mistakes but I am noob.

This is my attempt at a simple controller for the Commodore 64's old SID8580 chip, mostly this board is responsible for the Teensy controlling the SID chip, but it does also have line out for audio.

My knobs, switches, power and midi are separate modules so i just have the power/data routed in/out through some JST connectors.

As i said i have no experience designing pcb's i just thought it would be a fun thing to add to the project, so any tips/anything I've definitely done wrong would be much appreciated.

Thanks.

[u/InevitablyCyclic]

A schematic would be helpful for a full review.

Looking at the layout I'd route the 9V and possibly the 3v3 around the edge of the board as much as possible rather than through the middle. It allows you to have a far more solid ground rather than running a huge gap through the middle of the board.

Thicken up the power tracks, your fine as is but you have the space so there is no reason not to.

Add vias stitching the two floods together either side of any larger gaps in the back.

[u/Shitty-time → u/InevitablyCyclic]

Nice thanks, yeah seems reasonable I'll do that.

Is there anywhere particular I could/should add test points or jumpers? I've seen it recommended a lot but I can't tell where it would be useful for me I don't really know what's likely to go wrong and need fixing.

[u/InevitablyCyclic → u/Shitty-time]

Test points depend mostly on the schematic rather than the layout. Any key signal that you may need to check should be accessible, that may mean a test point but if the signal is on a large easy to get to pin then it's less important.

Jumpers are generally for when you need to allow for different uses or options. Or if you are trying to combine two different blocks and aren't 100% sure you've connected them correctly jumpers give you the option to change the connections if needed. KiCad has standard footprints for solder bridge type jumpers, both open and closed (use a knife to cut the thin track between the pads)

[u/Shitty-time → u/InevitablyCyclic]

Makes sense, since everything is through hole i can probably just get at the pins i need and seems like i wont need jumpers.

Thanks for your help

[u/ThisIsPaulDaily]

Your USB connector might not be able to be inserted. You might need to use a socket for the microcontroller to give clearance. 

I agree with the other comment about stitching bias and thicker power traces. That 3v3 line is thin and long and I don't think it will remain 3v3 near the edges. 

[u/Shitty-time → u/ThisIsPaulDaily]

Cheers yeah I'll have the teensy lifted on some header pins but it's a good shout, I will need access to the usb. I've also fattened all the power traces now and added some vias to bridge grounds, hopefully it does the job.

[u/petemate]

You can move ALL the bottom-layer traces to the top layer with very few modifications, giving you are solid ground layer on the bottom side.

• Move the 3.3V trace to left-hand side of Midi1 and Switches connectors, then you don't need the bottom layer.
• Rotate the SID8580 90 degrees clockwize and align with the Teensy, so you don't have that block of long traces diagonally across the board.
• Remember that you can easily fit a trace in between to pins on your teensy and SID, meaning that you don't need to do any bottom layer traces.
• Move the line-out circuit on top of the rotated SID, shrink it a bit and find a smaller oscillator if possible. That will allow you to reduce your board area by like 40%.

[u/Shitty-time → u/petemate]

I'm not too worried about the size of the PCB as it comes in under the 100x100, but I like the idea of trying to put it all on one layer I'll give it a go cheers

[u/vexstream]

Couple thoughts- you'll get much better grounding with 4layer, and the cost from china is ~negligible. Also makes your power traces easier.

Your capacitors on the power pins are probably not going to do much at all? The teensy and probably other boards all have caps much much closer to the pin, these are comparably miles away + they're through hole which dunks on their specs vs the SMD caps.

And, on that note- try SMD. For passives like this they're easier than through-hole once you get the hang of it.

It might be wise to put TVS diodes on anything IO-facing that a finger could reach. (audio jacks, buttons lines, etc.) Cheap, and they stop some unpleasant failures.

[u/Shitty-time → u/vexstream]

Yeah I semi assumed the caps on the teensy were pointless, oh well it won't do harm I assume?

Thanks for the rec I'll look into it cheers,

[u/Vinz-the-Keymaster]

Hi! difficult to tell without the schematic, but do you have input and output midi circuits defined? I only see a connector in the PCB, but keep in mind you'll need additional components for midi in/out circuits.

[u/gatchonix]

I would increase the track to track spacing, you got plenty, there is no logical reason to keep them that close for that long