My Version of the Dinas Boombox - Guitar Amp Style
As probably most of you, I had to find me a distraction during the last “do not leave the house” winter. Since I just setup my small hobbyist electronics lab and also was eager to learn more about woodworking, I did what most average guys would do in this situation - build a boombox 😉. I decided to use Nick's Dinas Boombox design as a starting point and see where it will lead me to.
Everything started with a stack of boards, a couple of fullrange speakers from Dayton Audio (4"), a subwoofer from TangBand (6") and a passive radiator* (8.5").
(* The original design uses a port instead of a radiator. I will describe this and other deviations later.)
The woodworking part was not that complicated - glueing the sides together and covering them with brown structured Tolex, routing holes in front and back for speakers, radiator, and control panel, veneering front and back in Mahogany, and adding a handle, some rubber feet, and cabinet corners to give it a vintage “guitar amp”-ish look. Afterwards, the shell looked like this:
For the "inner values" I used the Arylic Up2Stream Amp 2.1 board. Unfortunately, I had the “glorious” idea to unsolder the volume encoder from the Arylic board (to use it in my own control panel) - and failed miserably. I add the following picture for educational purposes only (and your entertainment 😆).
My kudos to the Arylic engineers for the robust design - the board still worked perfectly with the little flaw that the volume could only be controlled via App or remote control now - since I destroyed the encoder (and some part of the PCB) 😩.
Only afterwards I learned that the board has a very handy 9pin breakout connector that allows, beside other things, to connect an external volume control. At least, if you can teach your volume control to provide a voltage impulse of intensity A for “volume down” and intensity B for “volume up”. Unfortunately, none of the volume encoders I know will do this, instead they just return a noisy 2-bit Gray code and let you figure out what they want to tell you. To solve this problem, I used a small microcontroller (ATtiny 85) to decipher the encoder response and convert it to the voltage impulses requested by the Arylic board. I put the encoder (a new one since I broke the original one during my desoldering failure), the microcontroller, and some more electronic components on a small piece of PCB, connected it to the Arylic board and - it worked 😲.
This success encouraged me to design a small control panel for the volume control, the mode switch, the mode LEDs (Line In, USB, WiFi, Bluetooth), the power/WPS switch, the Play/Pause and Next buttons, and the infrared sensor. All of these functionalities (and more) are provided by the 9pin breakout connector mentioned. One tip if you also want to use this connector: The Arylic manual just says “PH2.0-9P” but the correct name of the needed female connector is “JST XH 9pin” (pitch 2.54mm). Since crimping these small connectors can be a nightmare I suggest to buy the connector with pre-installed wires.
Here’s the control panel (goes to the front of the boombox), the audio in/out panel, and the power supply panel (later two go to the back). I didn’t find a better (while still affordable) solution than using a two-layer approach. The inner layer is hand-made from 2mm aluminium, the outer layer is laser-cut from 1.5mm acrylic. Unfortunately, the acrylic was not stable enough to use it as the only layer.
Now, everything was ready for final assembly. Here’s a picture of the interior of the boombox (with speakers not mounted yet):
In the upper left corner, there is the Arylic Up2Stream Amp 2.1 board. In the lower left corner, there is a DIY relay-based speaker control board. In the upper right corner, there is a Dayton lithium battery board holding five 18650 batteries (not visible because mounted underneath the board). In the lower right corner, there is a DIY power supply distribution board.
After mounting the speakers and screwing on the back, the boombox was finished. Voila 😀:
Until now, I only did some initial adjustments of the sound, experimenting with extra weight on the passive radiator and the programmable Arylic board (using REW and ACPWorkbench). I did not manage to get down to 35Hz (only to about 43Hz) but want to wait until the speakers are broken in and I have learned more about acoustic tuning before I fine-tune it.
Finally, here are the main deviations from the original Dinas Boombox design:
- As already mentioned, I did not use a port but a passive radiator (Dayton Audio DS215-PR, 8").
- I slightly changed the dimensions of the box. Instead of 18" x 10" x 5.5", my box is 16" x 10" x 8" (40x26x20cm) but has about the same net volume as the Dinas boombox. One reason to change dimensions was the depth of the passive radiator, another was a more aesthetic one (to have a Golden Ratio of the front face).
- To cover the box, I used brown Tolex as well as cabinet corners to give it a kind of vintage rugged guitar amplifier look.
- Both the front and back side (0.5" birch plywood) are veneered in Mahogany and then oiled. This was quite challenging since I had to try several ways to get a clean result without cracks.
- I started with the TPS3116D2 Class D 2.1 amplifier board suggested in the original design but it didn't sound that great (or I got a bad copy) with some noise on the subwoofer channel that I was not able to eliminate. Therefore, I decided to go for more quality (and price) and chose an Arylic Up2stream Amp 2.1 board. Beside the fact that it has more input interfaces (of which I use Bluetooth, WiFi, USB, and Line-in), can be controlled by an IR remote control, has multi-room capabilities, and can be programmed, it provides a 9-pin breakout connector for volume control, play/pause/etc., IR control, and indicator lights. This allowed me to create my own control panel.
- I did not use any physical crossovers but just the programmable EQ of the Arylic board.
- To use the speakers also in a passive way (without the internal amplifier) there is a backplate for driving them directly from external sources. This feature is a bit special but I want to use the boombox also in my electronics lab for acoustic experiments and design tests.
Hope you enjoyed the presentation. Please let me know if you have any questions.
Cool project and design 🙂
Working one something similar based on the Dina sub/boombox