A boombox project

Phuncz

Lord of the Boards
Original poster
SFFn Staff
Gold Supporter
May 9, 2015
5,523
4,762
So I've been mulling a while what to do with my car audio I have left over from previous cars. It's quite expensive stuff, being quality components and in good shape. I thought of a portable speaker. Nah not exactly, but similar.

I have a small love for old-school Hip Hop and boomboxes were a big thing in those days. As it seems these are quite in demand yet again but I'm not paying a few thousand dollars to destroy an iconic boombox. I'd much rather try to make my own. Especially because I want to use the combined 500W of nominal power with my four speakers. There weren't many boomboxes back in the day with four 6.25" woofers but one of the most iconic, the Sharp GF-777, did. So I want to base my project on that one as much as I can.

So let's start off with my sketch which I made on a 9mm thick piece of MDF cut to the size of the aformentioned Sharp boombox:



Measuring 750x380mm, this boombox was certainly not SFF.

I already had the speakers, amplifier and Raspberry Pi, but I needed much more. To begin, I needed a proper DAC since the stock Raspberry Pi is just inadequate. Next I would need some way to use the RPi, so a 7" touchscreen IPS LCD screen was added. The RPi isn't able to power both itself, the DAC, the LCD screen and a possible USB device all through the MicroUSB so I got a surface mount LogiLink USB 3.0 Hub with 3.5A of current (default USB 2.0/3.0 = 2.0A).

I also needed a stable power source that was able to handle the max demand of the amplifier (factory-tested at over 175W per channel !) which was able to output around 12V. I'll get around to that in a bit. But the 12V is not the correct voltage for the USB hub, so I had to use a step-down converter (above most-right speaker).



As most car amplifiers require a "remote" signal to trigger it's ampiflier circuits (to not drain battery), I used a cheap rocker switch. I also added a volt and am-meter (for measuring current) so I could get an idea of how much power was going through the system.

It's about 1.05A at 12.8V for a noise level loud enough that you can hear it easily through a closed door.



This is the power supply: an HP 700W Server PSU. The model number is "HP DPS-700GB", it's a hot-swappable power supply for an old HP DL360 G5 rackserver, but it's cheap as dirt. Most server power supplies are just plain 12V output meaning no cross-load crap where I'd have to put X amount of load on the 5V rail and it's also quite compact. An issue is the forced cooling, which is absent in this model, but that was on purpose, since most server power supplies use Delta 40mm fans that are 10k or 15k rpm screamers. Hence the Noctua 80mm fan which fitted nicely with some modding of the PSU case.



The problem with these hot-swappable PSUs is that they use card-edge connectors to easily and securely swap out. Not easy to solder 20mm² or 4 AWG gauge wiring onto. Yes, I've used quite the oversized cable for this, it's the recommended size for the amplifier and I want to be sure it makes a proper connection.

Anyway, back to the power supply. The card-edge connector, I figured out was Amphenol 10035388-500LF, which is quite difficult to find. So I ordered a DL360 G5 motherboard for €10 instead. The pads for the 12V and GND each have 10 pins per pad and at two pads for 12V and two pads for GND, with 7A rating per pin, I should be well in the safe zone with 8 wires even if I was looking at reaching the 56A current of the power supply, but I'd have to test it out in long sessions to find out.

I later found these but apparently none (that I found) had been made for the 700W HP PSU. Also there needed to be some pins jumpered to ground to switch the power supply on. I found this here.



This is a picture of the rear, with the amplifier and it's finger-thick 20mm² power cables and 4mm² speaker cable. Snug ! I propped it up with a cardboard box because for easy of accessibility but also because I'm probably going to mount it at a 45° angle.



In this final image you see one of the 2-way speaker crossover (thin wires are the stock tweeter ones) and a Raspberry Pi 3 to the right.

Next up is the most enterprising part of all: design the case. This will be made out of 18mm thick MDF and for the subwoofers I need atleast to have a 5 liter (sealed) enclosure each, so I'll have to figure that out as well. Also it has to be made sturdy enough to be able to be carried around.
 

Phuncz

Lord of the Boards
Original poster
SFFn Staff
Gold Supporter
May 9, 2015
5,523
4,762
I forgot the list the audio components I used, should anyone care:
- Focal PolyGlass 165VR composite set (mid-range woofer and tweeters)
- Kicker CompRT 672 subwoofers (shallow depth and small size)
- Alpine PDR-F50 amplifier (built like a tank)

The 7" touchscreen LCD is a Waveshare 7" screen with SKU 11199, it has an IPS panel with 1024x600 resolution and capacitive touch.

The DAC on the Raspberry Pi is the HiFiberry DAC+ Pro.
 
Last edited:

CC Ricers

Shrink Ray Wielder
Nov 1, 2015
2,211
2,511
Really cool project! Looks like a proper step up from a DIY Bluetooth speaker in that you are integrating the music source with it.
 

Phuncz

Lord of the Boards
Original poster
SFFn Staff
Gold Supporter
May 9, 2015
5,523
4,762
Which DAC did you get for the RPi ? Interesting project :thumb:
Good question, added it in the post above too ! It's the HiFiBerry DAC+ Pro: https://www.hifiberry.com/products/dacplus/
I have good experience with a simpler HiFiBerry DAC, for my previous vintage radio project I made for my mom.

Really cool project! Looks like a proper step up from a DIY Bluetooth speaker in that you are integrating the music source with it.
Thanks ! The Volumio software is really good for this kind of "all in one" solution. I can use the Raspberry Pi's WiFi and BlueTooth for AirPlay and DLNA, along with directly attached iPods, MP3 on USB, Shoutcast, locally stored music, etc etc.

It's mainly developed for web-interface use, but I wanted a screen on there to be able to have on-device controls. I'd like to use a hardware volume knob, but I'm not sure I'll be able to without learning to program.