Intro: DIY Audio Sound Station
Hi, Just wanted to share what I've made, I was looking through some others, listed as "boombox" and decided mine was worthy of a share on here.
I decided I wasn't going to simply call mine a boombox as typically they consist of an enclosure, and amp, a couple of speakers and an audio source... mine is a little bit more than that.
...if you're interested, read on:
Step 1: The Reason and the Parts.
At the bottom left of the photo grid is a Bluetooth/SD/USB audio player. This was for sale on eBay at £8.88, I bought it with no purpose in mind. When it arrived it came with no cables, which I brought to the attention of the seller, who refunded part of the sale price. Looking at the board it was very easy to work out what pins did what.
Once I had this powered up I then decided, because of how nice it sounded, that I was going to create an enclosure for it.
I did not like the look of the front panel, however, so I sanded it down and sprayed it silver.
The unit itself came with a remote control and that's the only way to change the volume (which is preset at maximum, unfortunately) so I knew I'd have to fit an outboard volume control. I spent a few minutes on eBay looking at potentiometers as I intended to go analog, but then came across the rotary encoder + display (photographed middle right) for £6 or so.
I have had the piece of wood forever, I think it's the back panel from a chest or drawers from ikea.
I pretty quickly decided I was going to install quite a lot of components inside this enclosure, as I'm quite a hoarder and have silly amounts of electronics say in cupboards, drawers, sheds and carrier bags under the bed.
I knew at this stage I'd need a thermometer installing, and some kind of fuse holders, and the fuses to go in them... and a pretty volume dial. And that's everything from the photo. Total eBay costs around £30. I was planning on running this creation from a 12v wall socket using the plug in the photo originally... but that all changed.
Step 2: The Speakers and the Amplifier(s)
I've had these drive units forever. They were in some damaged bookshelf cabinets made by Monitor Audio, a uk manufacturer of some pretty high-end speakers.
In the original cabinets the tweeters were blown, so I supplemented some Kenwood tweeters which I have installed in several cars over the years.
The Monitor Audios are very nice sounding, they've been sat in a cupboard for years, just waiting for a purpose.
They have impressive excursion and an incredibly low roll-off frequency. Since the cabinet has been built I have performed a frequency test using the Sonic app on iOS... the cabinet registers properly down to 27hz right the way up to 18300hz (it may well be playing higher than that, but at my 37 years I can't hear it anyway!)
The dimensions of the cabinet, which were decided by the size of the sheet of wood to ensure as few cuts as possible with the jigsaw, negated that I had to modify the right-hand drive unit. The overhang for these drivers is quite large, having 8 mounting holes made it possible for me to lose around 1.2cm from the left edge. This left enough room for some led VU meters and their surrounds to be placed below the tweeters. Even though the BB5s are touching, there's still an impressive amount of separation between the channels -giving a pretty decent soundstage.
In the second picture my original amplifier plan was to use some KEMO amplifier modules. They sounded respectable enough, but not great. They claim an output of 40w at 16v, so at my planned 12v it would maybe have been around 20w. Whilst testing and setting up it sounded almost good enough... the trouble with these amplifier modules is that the tie-in signal ground and supply ground, so once I used two of them on the same supply the feedback and ground loop issues were incredible, as the Bluetooth module has its signal ground completely separate from the supply ground... this created a new worry which halted my design... what if the digital volume control also tied the grounds? To be honest I doubted it, as it's a fairly technical piece of equipment, why go to all that trouble and make 'that' mistake? So now I had no amplifier and a possibly unusable volume.
The amplifier problem was solved using two pcbs from the TEAC TE100 centre Speakers. These use the TDA7265 amplifier chips. These ICs are rated at 25w+25w, but these were installed in a car centre speaker, which is obviously single channel. What TEAC did with these chips is use one half of the amplifier for the 2" full range driver and the other half for the 1" tweeter. It appears the frequency is divided prior to amplification on these pcbs so in effect, using these instead of the KEMOs equates to this box being both bi-amped and bi-wired.
These ICs generate a fair bit of heat during operation, so I decided to mount them on the front baffle with the chips 5mm apart, then glued some supports in to hold the temperature probe from the thermometer in the gap, just to keep an eye on things.
The rotary encoder arrived and there was virtually no continuity between the supply ground and signal ground.
The next question that needed answering was:
"What else have I hoarded over the years? And where will it fit??"
Step 3: Lights, Lights... and More Lights
Years ago, at a car boot sale, I spotted a car equaliser with a 7 band spectrum analyser. Once I got this home I took it apart and removed the spectrum analyser, which seemed to be added as an after-thought, as the pcb was mounted above the equaliser board, Lucky for me was there that there were only 3 cables connecting this board to the eq board, 12v, ground, signal. This was also thrown in the shed waiting for a purpose. The bar graph ICs on this board only drive 5 leds, so I tapped off the signal in pins from all 7 of them and connected these to 7 Velleman VU meter boards, to give 10 leds per band. Ideally I wanted them all to be the same colour, but I didn't have 7 bargraph arrays of any one colour. For those good at counting, the very act of installing this spectrum analyser required one hundred and one wires... but it's worth it.
A further 4 of these Velleman boards are used inside here, to run the front VU meters, the tri-colour signal leds, and the two peak indicators.
All led arrays, including the 7x10 spectrum analyser, the volume display, the thermometer surround and the battery meter display were crudely cut using a jigsaw one a hacksaw blade, but tidied up with some silver sprayed wooden edging.
The last two silver edged surrounds are for the status leds for the dsp processor....
Step 4: DSP; the Heart of the Matter
4)Another thing hoarded a while back was the JBL ms2 dsp. This this, for its size, is a technological marvel. Hold the setup button and it plays 2 test tones, measures and analyses it, then corrects the time alignment and equaliser to allow for any sound colouration created by a car's interior.
So... I modified this slightly, by removing the pcb, using nail clippers to destroy all of the SMD LEDs, then removing the microphone. Then I used wires for each side of the leds, switches and microphone to enable me to mount them externally.
By this time I'd already decided I was installing a 7ah 12v alarm battery inside the box to make it portable, so the barrel jack plug and socket were re-purposed for the removable microphone. The switches are now wired to illuminated momentary switches mounted in the top panel, as were the 11 leds originally on the Jbl pcbs for 3 levels of bass, impact and treble and the 2 for image. The setup switch was mounted in the bottom of the unit, so as not to be accidentally pressed without the microphone plugged in. By accident I discovered that this processing takes time, albeit only a couple of milliseconds. I accidentally connected the left input and right output to the amplifiers.... the result was somewhat reminiscent of the old Aiwa dsp setting called 'disco', I have to admit I quite liked it; which in turn meant I needed to drill 2 more holes in the back of the box.
Now there are 2 buttons, in the off position the amps are fed directly from the Bluetooth module, in the on position they're fed from the output of the ms2, as there are 2 buttons left and right are switched independently. There are some pretty good effects achievable from having that ability.
Once I'd played around with it a little bit I then decided I needed to drill another two holes, to install tweeters in the sides of the box. These are from some 6.5" co-axial JBL GTO speakers. These are wired differentially, where they're connected to left and right positive terminals only, only playing sounds NOT present in both channels. This completes the effect of only dsp-ing one channel, as the delay causes EVERYTHING from left and right to sound, twice.
Another added advantage of having the ms2 in the box is that it has an in-line USB socket, which supplies a good clean 5v to the thermometer and volume modules.
In the picture that shows the microphone socket - the green glow which is visible is from 3 colour-morphing RGB leds which are mounted in the bottom of the cabinet.
Step 5: Assembly....
To be completely honest about this whole endeavour, I have put a little bit too much inside this box. There's not an awful lot of room for the air to circulate. It seems to have killed-off a little bit of the low end. I does however play very loud, without any risk of overrunning the speakers. I added a port to the back to help, which did actually make quite a lot of difference. It enters the cabinet just to the left of the battery and reaches to just behind the right speaker. When playing a mono frequency of 30hz the right hand speaker cone has about twice as much excursion as the left.
All edging on the cabinet has the same silver sprayed right angle edging as the front, and I even made a foam-lined remote control holder from off-cuts.
The volume control also has a mute feature, whereby when it's pressed it it goes into mute mode... when I glued the dial on I had the stuck two pieces of wire to the box first to ensure there'd be room for it to press in, once the glue had dried however and I removed the two wires it pulled off quite a lot of the top coating from the box, so I've used 2 paint sample swatches to hide it in red and green.
The problem I had in joining the last two parts was due to the location of the fuses, which meant there was no way of attaching the back to the top. The back is now in two parts, the part near the fuses is 'substantially glued' to the top, and the lower part of the back (where future access is to be made from) is screwed into blocks glued to the sides.
That's about all I have to say on this.
Having never built anything portable before, I have to say I'm actually quite happy with it.
Some of the parts used in here (well, all of the led driver boards) have been used before in a car installation.
If instructables allows links the one above should take you to where they were used.
Thanks for taking the time to read this.