DIY Desk Audio Amplifier With Tone Control & Dual Input

I was frustrated when switching speaker input between my pc and my piano keyboard because I had to move my pc off my desk just to unplug the audio cable from the chassis and plug it back in after my piano practice multiple times a day. That time, I was using my PAM8403 module with the audio cable directly soldered onboard. So, the audio cable cannot be unplugged on the module end.

A while after that, I decided to make another amplifier board upgraded with removable audio jack connector onboard to make my life easier. However, just as I thought it would finally be over, the module came faulty.. Total waste of time.

This is why I came up with this over-engineered audio amplifier that lets me switch 2 audio sources with just a switch and lets me control EQ without software.

This is a desk audio amplifier I designed and built to quickly switch between 2 audio sources and apply custom analogue Baxandall EQ to audio without software dependency. It is capable of delivering a maximum of 2x5W output compatible with 4 ohm and 8 ohm speakers.

You can find the full firmware, custom PCB Gerbers, and 3D design files all in my Github Repository

These are the materials you will need to build this:

Components

1. Custom PCB (Gerber files included in repository)
2. HT8696 10W Module - AliExpress
3. 6 Pin Type-C Connector - AliExpress
4. MTS-102 Toggle Switch - AliExpress
5. 2x MTS-202 Toggle Switch - AliExpress
6. 2x SMT PJ320D 3.5mm Jack - AliExpress
7. 2x 2 Pin KF301 Screw Terminal - AliExpress
8. 4x B100K, 75mm Length, 15mm Lever Slide Potentiometer - AliExpress
9. 2x 5.1K 0805 Resistor - AliExpress
10. 6x 10K 0805 Resistor - AliExpress
11. 6x 510 0805 Resistor - AliExpress
12. 2x 2.2nF 0805 Capacitor - AliExpress
13. 4x 22nF 0805 Capacitor - AliExpress
14. 2x 220nF 0805 Capacitor - AliExpress
15. 6x Warm White 0805 LED - AliExpress

Tools

1. Soldering station (any will do!) - AliExpress (<= here is the one I use)
2. Tweezers
3. 3D Printer

The PCB is designed in EasyEDA Pro with these kept in mind:

1. 5.1kΩ pull down resistor on Type-C CC lines (R1, R2) for compatibility with PD chargers. Power delivery is controlled via a SPDT switch (SW1).
2. Audio jack (U2, U3) input are switched with DPDT switch (SW2) to isolate sources. The signal then enter a toggleable passive Baxadall tone control network (R3 - R8, C1 - C8, VR1 - VR4) with dedicated Left/Right bass (fc = ~72 Hz) and treble (fc = ~7.2 kHz), with an insertion loss of roughly 20dB.

The Gerber file is then sent to JLCPCB for manufacturing with 1.2 mm PCB thickness.

Once the PCB arrives from JLCPCB, it is ready to be soldered! This is how I soldered them:

1. Start with SMD components first (R1 - R14, C1 - C8, LED1 - LED 6).
2. Connectors second (Type-C - U4, 3.5mm jacks - U2, U3).
3. Through hole last (slide potentiometer - VR1 - VR4, toggle switch - SW1 - SW3, screw terminals - U5, U6, HT8696 module - U1).

Ensure there is no short circuit or cold joints that can affect the circuitry!

I chose a bare-board look rather than a full enclosure. The only thing that needs CAD and printing is the slide potentiometer sliders. I chose a clean and simple look for it. Since I don't have a 3D printer, I outsourced it to JLC3DP alongside with my PCB. The model is compatible with any 3D printer too.

Once everything is ready, combine the soldered PCB, 3D-printed sliders and your speakers!

1. Insert the sliders into the slider potentiometer levers.
2. Connect a 4 ohm or 8 ohm speaker wire into the screw terminals.
3. Power on!

Now enjoy!

Thank you for following along with this build. I hope you enjoyed the building process as much as I did! Bye for now!

Future Revision

1. Adding a built in voltage booster can supply the HT8696 Module with 8.5V, which unlock up to 9.5W per channel. A 4.5W increasement.
2. Isolating the speaker ground and audio jack ground can fully eliminate speaker buzzing noise.

You can find the full firmware, custom PCB Gerbers, and 3D design files all in my Github Repository