pcb design review - my first project

[hummusdude]

This is my first board so I'm sure it has some issues. It's an audio pre-amp with active 2-band tone. I made this to go with a power amp design I found online. I intend to put it in the case with the power amp. The power supply for the power amp is beefy and puts out +- 25VDC so I'm using that to supply this pre-amp board. For fun I added some different controls to trigger the microcontroller. The Nano is used just to control the dpot that controls the gain of the pre-amp, and to drive the shift registers that control the two 7-segment displays.

Some questions I have...

Is the 5VDC linear regulator too close to the analog section?

I tried to keep all of the signal lines on top but there a couple of places where I had to use the bottom. I kept them as short as possible and at right angles. Is that okay?

Does it make a difference in the overall power dissipation if I supply the 5V linear regulator from 15VDC or 25VDC? I understand the power loss issue but not sure if it matters in this case.

The treble/bass controls are potentiometers that I will panel mount on the front of the case. Is it okay to twist all three wires for the run from the front panel to the board connections to help with emi?

 

[KlausST]

Hi,

Not that bad. Well done.

I see no problem with the linear regulator.

what 5V current do you expect? Mind a lot of generated heat in the voltage regualtors.
It makes no difference of total power dissipation. when connected in series (only marginal). I guess the 5V current is much bigger than the 15V analog current.. Thus serializing helps to spread the heat to two regualtors. You will need a heatsink in any case.
Mechanically a benefit if all are mounted inline at the PCB edge to use a simple aluminum sheet (or metal case).

The volume pot is linear, thi is not ideal for audio signals. There are "logarithmic" ones or dedicated audio volume control ICs. Some even have tone control inside.

If you are interested in high channel separation (low cross talk) then rearrange in/out as R|GND|L. Also you might route some dummy GND traces besides the audio signal lines.

The tone control pots are instsalled externally with wires? Then use shielded cables. One common shield for the three wires should be sufficient.
You need a "GND PAD" for the shields. Also connect the pot´s metal case to the shield.

I recommend to add bigger bulk capacitors. There is no "too much".

Klaus

 

[andre_luis]

In addition to Klaus's remark concerning regulator issues, I would also suggest to move/rotate it a little so that a heatsink could be mounted with no obstacles if needed. The place where it is, there are high profile components nearby.