#+TITLE: Portable stereo speaker
#+AUTHOR: Svjatoslav Agejenko
#+LANGUAGE: en

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* General
+ DISCLAIMER: I DO ELECTRONICS AND 3D DESIGN SOLELY AS A HOBBY. THERE
  COULD BE ERRORS THAT CAN RESULT IN ALL KINDS OF DAMAGE. USE THESE
  DESIGNS AT YOUR OWN RISK.

+ This design is released under Creative Commons Zero (CC0) license.

+ Author:
  - Svjatoslav Agejenko
  - Homepage: https://svjatoslav.eu
  - Email: [[mailto://svjatoslav@svjatoslav.eu][svjatoslav@svjatoslav.eu]]

+ See also:
  - [[../../index.html][Other physical projects in this repository]]
  - [[https://www.svjatoslav.eu/projects/][Other projects hosted at svjatoslav.eu]]

* Project description
I had pair of good compact stereo speakers lying uselessly around as
well as secondhand TDA2030 Chinese knockoff audio amplifier chips.
Also I wanted to test modular construction approach: motherboard with
shared bus and functionality realized via pluggable modules. So I
built stereo speaker:

[[file:make.png]]

Indicator on the front panel shows available power within the
system. Ideally it should be at the maximum. It drops when batteries
run empty or when consumed power (too loud music) is greater than
onboard power supply or batteries can handle. It has on/off switch and
stereo audio input. Audio input impedance is about 100 ohms.

[[file:make,%20side.png]]

Idea for the holes on the top and smaller ones on the bottom back is
to enable air flow for passive cooling.

[[file:make,%20back.png]]

Entire construction is made of parts, no larger than
120x120x120mm. Maximum for my printer.

* Battery holder
Device is powered by 4 times AA NiMH batteries (1.2V each).

[[file:battery%20holder/schematic.png]]

I happened to have AA battery adapters lying around with different
bottom hole configurations. Therefore this weird hole design:

[[file:battery%20holder/battery%20holder.png]]

Download:
+ [[file:battery%20holder/battery%20holder.FCStd][FreeCAD file]]
+ [[file:battery%20holder/battery%20holder.stl][STL file]]

Result:
[[file:battery%20holder/make.png]]

Attaches to the back of the body:
[[file:battery%20holder/mounted%20on%20the%20back.png]]

* 20V up-step module
Battery pack voltage is routed through main on/off switch on the front
panel, and then it goes to the 20V up-step module.

[[file:20V%20upstep%20module/schematic.png]]

It uses ready made upstep module, but adds extra voltage filtering via
inductor and capacitors.

[[file:20V%20upstep%20module/make.png]]

* Main board

Voltage upstep above sits on top of main board (motherboard). It has
uniform central bus that spans all connectors.

[[file:main%20board/internal%20bus.png]]

[[file:main%20board/bus%20on%20the%20bottom,%202.png]]

First row of the main board is special IO terminal (for connecting
speakers, front panel, etc..)

[[file:main%20board/IO%20terminal.png]]

Remaining rows are for connecting boards:

[[file:main%20board/1.png]]

To provide structural support, main board is attached to frame:

[[file:main%20board/board%20fixator%20body.png]]

Download:
+ [[file:main%20board/board%20fixator%20body.FCStd][FreeCAD file]]
+ [[file:main%20board/board%20fixator%20body.stl][STL file]]

And boards plugged into main board are fixed at the top, using clip:

[[file:main%20board/board%20fixator%20top%20clip.png]]

Download:
+ [[file:main%20board/board%20fixator%20top%20clip.FCStd][FreeCAD file]]
+ [[file:main%20board/board%20fixator%20top%20clip.stl][STL file]]

Result:

[[file:main%20board/bus%20on%20the%20bottom,%201.png]]

[[file:main%20board/board%20fixator.png]]

* Mono audio amplifier module

Design uses scavenged secondhand Chinese TDA2030 audio amp
clones. Each chip is mono audio amplifier. Therefore 2 almost
identical audio amp modules had to be built, one for left speaker, one
for right.

[[file:mono%20audio%20amp%20module/schematic.png]]

I like to build on top of prototype PCBs. Gives results much faster
for one-off projects. Before soldering, I solve component layout on
paper:

[[file:mono%20audio%20amp%20module/PCB%20layout.png]]

Result - front:

[[file:mono%20audio%20amp%20module/assembled%20front.png]]

Result - back:

[[file:mono%20audio%20amp%20module/assembled%20back.png]]

Here copper tape is used as improvised heatsink.

* Speakers

High frequency small speaker and medium frequency bigger speaker are
combined.

[[file:speakers/schematic.png]]

Capacitor acts as high-pass filter on top of tiny PCB:

[[file:speakers/PCB%20layout.png]]

Speaker enclosure:

[[file:speakers/speaker%20enclosure.png]]

Download:
+ [[file:speakers/speaker%20enclosure.FCStd][FreeCAD file]]
+ [[file:speakers/speaker%20enclosure.stl][STL file]]

Speaker enclosure cover:

[[file:speakers/speaker%20enclosure%20cover.png]]

Download:
+ [[file:speakers/speaker%20enclosure%20cover.FCStd][FreeCAD file]]
+ [[file:speakers/speaker%20enclosure%20cover.stl][STL file]]

Result:

[[file:speakers/make.png]]

* Front panel

Initial idea was really simple panel:
+ on/off switch
+ system power indicator
+ stereo audio input

But, since I'm using "agile" approach, during load-testing, it become
clear that active fan based cooling would be nice (when playing loud
music). I found tiny cooler fan that needs 5 volts to operate. Also I
need to power backlight for power indicator. For both of these cases,
I decided to add another voltage up-step module (target voltage output
set to 6V). This time directly on the front panel.

[[file:front%20panel/schematic.png]]

Front panel case:

[[file:front%20panel/front%20panel,%20front.png]]

[[file:front%20panel/front%20panel,%20back.png]]

Electronics fits inside:

[[file:front%20panel/front%20panel,%20back,%20make.png]]

Front view:

[[file:front%20panel/front%20panel,%20front,%20make.png]]

And attaches to the remaining components:

[[file:front%20panel/attachment.png]]


* Extra capacitors
Another thing that become clear during load-testing: output
power/volume can be further enhanced by adding high power capacitors
to even out load on primary 20V up-step module.

[[file:extra%20capacitors/extra%20caps.png]]

Download:
+ [[file:extra%20capacitors/extra%20caps.FCStd][FreeCAD project]]
+ [[file:extra%20capacitors/extra%20caps.stl][STL file]]

Extra caps are mounted on top of the speaker and electrically attached
to the main board.

[[file:extra%20capacitors/make.png]]

* Center box

Last physical part, to attach it all together: central body.

Front:
[[file:center%20box/front.png]]

Back:
[[file:center%20box/back.png]]

Download:
+ [[file:center%20box/center%20box.FCStd][FreeCAD file]]
+ [[file:center%20box/center%20box.stl][STL file]]


* Conclusions / TODO

These things could be done better:

+ Instead of using undersized heatsinks on the audio amplifiers and
  need for active cooling as a consequence, it would be better to try
  to mount audio amplifier chip on top of speaker metallic body. It
  would provide plenty of cooling and reduces power losses within
  cable, since amplifier would be as close to the speaker as possible.

+ I used agile design. That is, implemented functionality ad-hoc. If I
  had done design in advance, then I could have had smarter connector
  layout between main board and front panel. That is: Instead of
  multiple smaller cables, one wide (multi connector) cable.

+ Screw holes are too close to the edges on the front panel.

+ It would be better if screw heads were slightly buried within
  construction body.


Overall, it was good learning experience and I was able to test
various ideas on it. Will add cooler later :)


Photo of initial PSU + audio amp test:

[[file:initial%20test.png]]