Bluetooth Speaker Upcycle Project 1
Introduction
I had a Harman/Kardon HK395 2.1 computer speaker system sitting on my garage workbench for years.  One day I looked at it and thought, "Man, I need more room on my workbench. What am I gonna do with that bulky, old speaker system?"  It occurred to me that I could probably turn it into a nice, Bluetooth enabled speaker that the family could use again.
[The Harman/Kardon HK395 2.1 computer speaker system. 2 satellites and a subwoofer.]
Deconstruction
The first order of business was to disassemble the speakers and take a look around.  The speakers seemed to be of decent quality: a couple of 2" full range drivers and a 5 1/4" subwoofer.  The amp and power supply construction looked pretty straightforward as well.  The only issue that presented a challenge was the multi-pin umbilical cord that went to the speaker on the left in the photo below.  The wiring for power on/off, volume control, left and right speaker connection, line in, and power LED were all contained in that cord.  Since I wanted to eliminate as many unnecessary connections as possible, I needed to figure out how to get rid of the umbilical.
I set about drawing a wiring diagram of the umbilical and the components it served.  The original volume potentiometer was mounted in such a way as to be unusable in my new design. So I took some resistance measurements of the pot and purchased a new one.
[Wiring diagram of the volume pot, line in, satellite speaker connections, and power LED.]
Construction
I had some scrap 1/2" bamboo plywood lurking around my workbench for several years and I thought that the look of bamboo would compliment the new enclosure nicely.  Also, bamboo ply machines cleanly to fairly tight tolerances so the material was a good fit for the project.  However, I did not have enough material to build an enclosure identical in volume to the original Harman design.  Knowing that a difference in enclosure volume would affect the low frequency response, I went over to The12Volt.com to calculate a new enclosure port length.
[Enclosure panels cut to size and machined for construction. The enclosure port tube is shown at the top of the photo.]
[Front panel machined for full range speakers, volume pot, power LED, line in jack, and power switch.]
[The face side of the front panel. The power LED hole is a 1/16" hole with a 3/16" hole machined in the back to accommodate a standard size LED but only allow a pinpoint of light through the front panel. It's a nice effect.]
Adding Bluetooth
It turns out that adding Bluetooth capability to an audio project is pretty simple.  I headed over to PartsExpress and found the Bluetooth module shown below for about $20.00.  
+5V power and signal in are the only connections needed to make the module work.  Since the module draws very little power, I just tapped the +12V, filtered DC from the Harman power supply, added a 7805 5V voltage regulator with some 100uf decoupling caps and presto ... we have 5V to power the module.
[Everything wired up to make sure it still works before final assembly.  Notice the Bluetooth module in the lower-right and the +5V regulator at the top of the photo.]
[Close up of the voltage regulator circuit for the Bluetooth module.  LM7805 voltage regulator with 2 100uf decoupling capacitors.  Everything can be picked up at Radio Shack for a couple of bucks.]
[All components secured inside the case.  It's a tight fit.  The yellow wire temporarily replaced the power supply fuse that had blown somewhere along the way.  I ultimately put in a panel mount fuse holder in the back of the case.]
Completion
The finished project turned out well; it sounds pretty good and the Bluetooth connection is reliable.  Its low-end response is a bit weak but I believe that's an artifact of the smaller enclosure size.  The case is finished in tung oil and wax and the enclosure fits nicely on a bookshelf.  I love the fact that I can stream Pandora to this system and still carry my phone in my pocket!  Oh, and the cool, chrome volume control knob can be found at PartsExpress too.
Bluetooth Speaker Upcycle Project 1
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Bluetooth Speaker Upcycle Project 1

Bluetooth enabled, bamboo speaker enclosure upcycled from a Harman/Kardon computer speaker system.
32
1828
0
Published: