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Portable, loud, and fashionable. Take a vintage suitcase and install a set of speakers, passive crossovers, an amplifier, and a couple of rechargeable batteries. Now, you have a portable, albeit heavy, stereo that will make your ears bleed.

Inspiration

I got the idea from a handful of Internet vendors that make custom, build-to-order jamboxes. They sell them for stupefying amounts of money, often around $800+ (U.S.). In some extreme cases the product costs over $2,000. I liked the idea and the sense of profit! I also had the know-how and decided to build one for half the cost.

Construction

The Critical Case

It was clear from the outset that the look of the suitcase was almost as important as how it sounded. After striking out at several thrift shops, I found that the best place to shop for vintage and unusual suitcases was online. I purchased a striped tweed suitcase from the 1940s that was to my liking and reasonably priced.

The Electronics

As an application engineer, I have access to the full catalog of Maxim Integrated parts and evaluation (EV) kits. I picked the highest wattage Class D amp, the MAX98400A. This part was appealing because it could be configured to work as a stereo amp with 20W per channel, or with minimal tweaking, it could be configured to work as a mono 40W amp. I really liked that the EV kit (Figure 1) had two amps on it with shared power rails.

Figure 1. The MAX98400A started the whole project. The EV kit board has two 40W amps on it and I was ready to build something that could be loud.

This EV kit demonstrates that filtering the output of a Class D amplifier is not necessary because the speaker that it drives acts as a filter. So one amp on the EV kit is specified for filterless evaluation and the other has an on-board passive Class D filter. At first I thought that I would build a 2.1 system with one amp outputting stereo and one amp driving all of its power into a single woofer. After careful consideration I decided to go with a bi-amped design driving eight speakers. One stereo amp powered the two woofers. The other stereo amp went to a crossover and then to a midrange driver with two tweeters per channel (Figure 2).

Figure 2. Schematic of the speaker elements in the case using the two MAX98400A amps. One amp is dedicated to powering the big 8in drivers; the other amp goes through a crossover to power two 2in tweeters and a 3in full-range speaker.

The Audio Setup

Having rebuilt home audio speakers before, I selected drivers with two design considerations: size/geometry and look. I made paper templates to ensure that they would fit in my desired layout. Once the speakers were installed, I noticed that the walls of the suitcase could not support the weight of all the drivers. I then cut out the lining and glued in plywood to improve rigidity and support for the speakers. Next, I selected the passive crossover that made sense with the speakers’ frequency response.

I originally planned to lowpass filter the woofers as well, but listening tests indicated that filtering for the woofers was not really needed. I later confirmed this decision by the improved loudness of the unfiltered design. While a filtered scheme would have produced more balanced audio, I was not really targeting a “balanced” sound. I wanted loudness!

During assembly, I used 12-gauge speaker wire and banana jacks to connect the speakers and crossovers to the EV kit. Then I glued the crossovers to the suitcase walls (Figure 3). I soldered wires to the pins of the headphone jack connector, then heat shrunk the solder joint, and did the same to the terminals of my gigantic power switch. Don’t skimp on build quality!

Figure 3. I used 12-gauge speaker wire (overkill, I know) and banana jacks to connect the speakers to the board. I also glued the crossovers to the suitcase walls.

Figure 3. I used 12-gauge speaker wire (overkill, I know) and banana jacks to connect the speakers to the board. I also glued the crossovers to the suitcase walls.

The Power System

Each amp has an absolute maximum supply voltage of 28V, and 24V is within the operating range. I picked two UPS, lead-acid batteries for their high-energy density. Yes, they are heavy, but they are contained in a suitcase built to carry a modest load — weight is not a problem. With this much power the boombox will run at maximum volume for about five hours and much longer at more reasonable volumes.

The battery holster is made from plywood and pipe strap (Figure 4A). To manage the weight distribution, I placed the holster at the bottom and back of the case to counter balance the weight of the speakers. I cut out some suitcase lining to glue in the battery holster (Figure 4B). I also used an XLR port on the side to connect to a 24V battery charger and an on/off switch with indicator LED. Finally, I stuffed the case with polyfill which helps deepen the bass and reduce rattling (Figure 5).

Figure 4. Batteries in the holster (4A). Some of the suitcase lining was removed to accommodate the battery holster, which was placed in the bottom and back of the case to counterbalance the weight of the speakers (4B).

Figure 5. Stuffing the case with polyfill helps deepen the bass and reduce rattling.

Figure 5. Stuffing the case with polyfill helps deepen the bass and reduce rattling.

Enjoying the Sound

From the beginning I had decided that the audio source from this boombox would be a 3.5mm jack. This way it could play music from smartphones and other portable devices. Then I ran into an interesting problem when using my phone which uses a jack-detect circuit. The first time I plugged my phone into the boombox, it was barely audible. I added a 32Ω resistor to ground on the amplifier’s input to the amplifier (Figure 2) to trick the jack detection circuit. Now when the smart phone checks the impedance during its jack detection, it thinks that it is powering headphones and puts out a larger signal level.

The boombox is loud and was really fun to build. And it sounds as good as it looks (Figure 6). But, I am not done. I want to try to create a better seal between the suitcase and the lid. Currently if you play “bassy” music at loud volumes you can hear what sounds like port noise. For now, the plan is to use something like thin foam strips, similar to weather stripping, and line where the two parts of the case meet. I also plan to add Bluetooth connectivity. The boombox already has style for miles, but ditching the headphone wire would really put it over the top.

Figure 6. The completed boombox.

Figure 6. The completed boombox.

Bill of Materials (BOM)
Item Qty Description
MAX98400AEVKIT 1 Evaluation kit with board for the MAX98400A Class D amplifier
WKA12-5F2 2 Werker 12V UPS batteries
260-198 2 2-way 8Ω 5,000Hz, 150W crossover, Partsexpress.com
264-809 2 3in full-range driver, Tang Band
264-805 4 2in tweeters ,Tang Band
295-332 2 8in aluminum cone woofer, Dayton Audio
2404SX 1 24V, 2A battery charger, Soneil
F3FSTF 1 Female XLR connector, Switchcraft
GRB292A201BBNA2 1 Rocker switch, CW Industries
30-711 1 .5mm female jack receptacle, Markertek.com
Builder’s choice 1 “Sweet-looking case”

The Bluetooth word mark and logos are registered trademarks owned by Bluetooth SIG, Inc. and any use of such marks by Maxim is under license.

I’d like to thank Dominic Odbert for inspiring this design. To check out some of his great work, click here.

This piece was originally published on Imgur.

About the Author:

Patrick Gallagher received a B.S. in Electrical Engineering from Texas A&M University and joined the audio division of Maxim Integrated immediately after graduation, as a member of the technical staff. His work includes precision amplifiers, video amplifiers, audio amplifiers, codecs, and gamma references.


Related

Comments

  1. David Colburn says:

    Would this board be suitable for a guitar amp (different speaker setup) or would you recommend another?

    What about in-setting the guitar amp speaker(s) and adding a somewhat flush protective grille?

    Thanks for the idea!

    1. davydka says:

      A small battery powered preamp would be enough to convert a guitar signal into something that would work well with a boombox like this. Something similar to this would work:
      http://www.musiciansfriend.com/pro-audio/art-powermix-iii–3-channel-personal-mixer

  2. I heartily endorse this big noisy thing.

  3. Patrick Gallagher says:

    @ David C
    Plugging a guitar directly in is barely audible. I’ve tried hooking up a guitar through a pedal (to buffer the signal) then to the Boomcase. Which is a little better, but it isn’t loud enough to be any fun. To make that work right I’d need pre-amp which could live in the case, or it could be its stand alone box, much like a pedal.

    The flush mounting would certainly be a little tricky as you’d have to build some sort of support inside the case rather than using the case itself. I didn’t explore the options of grills too much, but they would be sweet especially if you were making it a guitar amp.

  4. Goli Mohammadi says:

    Yes please! All kinds of awesome!

  5. docpop says:

    Maybe not what you want to hear but I know Dom from Boomcase and he’s a swell dude. I bought a custom case from him 4 or 5 years ago and still use it all the time. I think it’s awesome that your sharing how to make stuff, but it seems like you could have done it without stepping all over his trademark. Or, at the absolute very least, give him a link and some credit. You credited “Bluetooth” after all.

  6. Patrick Gallagher says:

    @docpop
    Is Dom that Mr Simo? If then yes, he does deserve credit (http://www.mrsimo.com/). I’m certainly not trying to step on anyone’s trademarks. I just wanted to share the story of a fun project.

    I’m not the first nor will i be the last to build my own version of a Boomcase. There is an instructable and a handful of similar blog posts if you google around form them.

    As for crediting Bluetooth… All I can say is editors will be editors.

    1. docpop says:

      Yep, that’s him. BoomCase is his registered trademark and http://theboomcase.com/ is the site that should be linked. I believe MrSimo.com is for his personal stuff.

  7. bmisenstein says:

    Do you have any problems with rattle / vibration in your design. I have built a similar system with a completely sealed Aluminium briefcase and it seems like many speaker designs have a air port or passive speaker to help mitigate this problem.

    1. Patrick Gallagher says:

      Only at very loud volumes is it a problem. But yes the handle as well as the locks will rattle. The music will overcome these vibrations as you get farther away from the case.

  8. That is wonderful!!! It was so artistic of you to have thought of using that suitcase and made it a boombox. I hope you can share a video while using that. I’d be so happy to see it. Thanks!

  9. Jon Anderson says:

    This isn’t an easy DIY project, as I ran into a few problems with cutting the cases etc. Also, set aside a full day to work on this, or maybe a week depending on how savvy you are. So all-in-all, it costs about $400 to do this. Ironically, I recently visited New York and stayed at the Gansevoort Hotel. They have vintage suitcase boomboxes inside their rooms! I decided to make a purchase from the maker, Curious Provisions, and have to say, great work! Save yourself the time. They have 200 watt amps with lithium batteries. Amazing quality. Anyways, my 2 cents.

  10. Vincent says:

    YOU DA MAN.

  11. Joe Register says:

    We built one and liked it so much that we created a company to build them just look up the “Sharkbox Pulse”

  12. David says:

    Really professional build. Great job. I silicon seal all my bags to solve your issue. Also I dont want customers rummaging around inthere.

  13. Patrick Gallagher says:

    I was about to build this box for just under $400 bucks. If you cared less about the look of the box you could build it for cheaper. The speaker drivers were the most expensive part of the project.

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