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Building the ULTIMATE Last month we looked at what we wanted in the Ultimate Jukebox. Now let’s start building it . . . A s we explained, the Ultimate Jukebox is actually a powered speaker with a built-in computer running the Ultimate Jukebox software. So all we need to do is come up with a speaker box that will fit an amplifier/power supply and the computer? That’s true – but as the proverb says, there’s many a slip twixt cup and lip. For example, we want to make sure our jukebox makes the most economic use of timber. It also needs to be both stable and sturdy enough to take the punishment of its likely environment (let’s party!) and it needs to be light enough to move around. Those last two requirements are actually rather contradictory. To make it stable and sturdy, it needs to be quite heavy duty. Heavy duty also translates as heavy! The final design had over 32kg of timber in it – before anything was added. We decided on 18mm craftwood (or MDF) for most of the construction. Part of the reason for this is our local timber merchant had a special on 18mm craftwood but we had already decided anything thinner would be too thin while anything thicker would be too heavy. Having said that, we also used a couple of pieces of 32mm craftwood – one for the jukebox base and one for the computer spacer. More on this anon. We used two sheets of 1200 x 2500mm 18mm craftwood (as I said, they were cheap!) but one sheet of 2400 x 1200mm will work quite nicely with the sizes we’ve shown – and leave 78  Silicon Chip some change. It’s also possible to buy 1200 x 1200mm sheets which are easier to work with (and transport). Also, ask your timber supplier if they offer a cutting service. If they do, take advantage of it: their cuts are likely to be smoother and squarer than yours (certainly squarer than mine!) and you’ll end up with pieces that fit together beautifully. Even if they charge for the cuts (and most do, with the average charge about $2.00 per cut plus GST), you’re going to pay not much more than about $15 for cuts – pretty good value in my humble opinion. Changes since last month The Ultimate Jukebox has been a work-in-progress for many months – right up until this issue went to press. One thing we did find was that some notebook computers have more output than others – indeed, some cannot fully drive the SC480 amplifier. To solve this little problem, we added a little (and cheap!) preamplifier into the signal line. Again, we used an existing design, the PreCHAMP from SILICON CHIP July 1994 issue. We made a slight adjustment to allow it to run from the +15V supply we already had on the power supply board and we also throttled the gain back somewhat – as originally published, it was simply too much. Kits for this preamp are still available – in fact, it’s a very popular little kit and one to keep in mind if you ever need a general-purpose preamp. Best of all, it sells for just $6.95. Another change we made was in the port, or vent – and we’ll explain this in just a moment. And finally, we thought that the box lacked something that the “real thing” would have – flashing coloured lights. So we took the easy way out and got some ropelight: presto, instant flashing coloured lights! The speaker “box” While the Ultimate Jukebox is all one piece, it’s possibly a bit easier to look at it as three components. We’ll start with the speaker enclosure. This is a vented (ported) type with an internal measurement of 600 x 440 x 321mm. That gives it a volume of around 84.5 litres; slightly larger than our “Bass Box” calculations dictated but this can be taken care of by adjusting the port size. The reason for this larger size, by the way, was twofold: the extra space is basically width and depth, giving better stability, and the dimensions chosen make for the minimum number of cuts in a standard 1200mm craftwood sheet or sheets. The front, or baffle, is inset 18mm in from the front edge to give some measure of protection to the speaker drivers, even though the woofer is later covered with a metal grille. The baffle slides into a 5mm rebate routed into both sides and the base before the speaker top and notebook spacer are placed. The woofer mounts on the rear of the baffle while the compression horn tweeter mounts from the front, in a siliconchip.com.au JUKEBOX Part 2 by Ross Tester suitably sized rebate (sizes are shown on the cutting diagrams). Screwed to the inside of the enclosure is the crossover, with wiring secured to the timber with electrical staples or cable clamps. Don’t be tempted to use ordinary staples because they have this nasty little habit of cutting straight through wiring insulation! Small holes are drilled through the top and bottom of the enclosure to enable cabling to pass through: power to, and audio from, the laptop and of course the output from amplifier to speakers. When the cables are installed, the holes are made airtight with silicon sealant or similar. The two sides are mirror-image and are 1200 x 375mm. The top of the sides was shaped with a jigsaw into a curve to give a less stark (boxy) appearance. Three 5mm rebates are cut into the sides – these house the bottom (32mm rebate), enclosure bottom (18mm) and finally a 50mm rebate for the enclosure top and notebook spacer. Larger port The 900mm x 450mm back of the speaker also mounts into 18mm rebates in the sides and is the last piece of timber placed. It doesn’t cover the entire back of the Jukebox because we left a 50mm air gap in the bottom to act as the port. This is significantly larger than Bass Box suggested would be optimum for the woofer we used but trial and (ear)or said that we ended up with the best sound. Most jukebox users (ie, party goers!) want thumping bass and this large horizontal back-panel port gave us a great sound – far better than tuning for a flat response. Similarly to the sides, a rebate is cut siliconchip.com.au January 2006  79 into the back to house the enclosure top and the notebook spacer. The amplifier enclosure The amplifier “enclosure” at the bottom of the Jukebox contains the amplifier, power supply and notebook/ laptop power supply, along with the fused IEC mains inlet, on/off switch and USB disk drive. There is no covering over the amplifier section; the back is open to the air for cooling. It is significantly larger than necessary – our amplifier heatsink is only 80mm high and we’ve made the space 200mm high. The reason (and also the reason for being open to the back) is for ventilation/air circulation – while the amplifier heatsink itself is mounted right at the rear, there is still the transformer giving off heat, not to mention the notebook/laptop power supply which also generates heat. Also, we said last month that the jukebox was capable of handling a much larger amplifier, so if you want to go this route there is plenty of space to do so. We mounted our amplifier and power supplies on an aluminium “tray” for ease of assembly (and later service if needed). you may need to make the well a little deeper. Conversely, some modern notebooks are very thin, so you might not need 32mm depth. The other consideration for the computer is heat. Notebooks are not designed to be operated in an enclosed space (hence making the well “U” shaped, allowing air to flow out the back). With the computer we used, the cooling fan is also at the rear, making a “best case” scenario. If you have trouble with heat, some form of forced air cooling may be necessary (you can buy notebook coolers which could be an answer, albeit at the cost of a deeper “well”). The notebook screen is designed to swing up against the back panel with enough angle to ensure that viewers of normal height don’t have to bend down to view it. That pretty well covers the various parts of the Ultimate Jukebox. We added a few “extras” which we’ll get to later (eg, the speaker carpet) but The notebook enclosure Above the speaker enclosure is the space for the notebook/laptop computer. Because we didn’t want to allow any access to the keyboard, this is set into a “well” made from a piece of 32mm craftwood, fixed to the outer surface of the speaker box top. Above this again is fixed a sheet of 2mm aluminium which completely covers the keyboard. The aluminium sheet has a cutout the width of the screen and a depth suitable to allow it to clear. We actually made ours slightly wider than necessary to give somewhat hidden access to the notebook’s power switch. This is something that you might not have to do if your noteboook’s BIOS will allow you to boot after power interruption. Then you can simply run the notebook without a battery and allow it to boot whenever the Jukebox is turned on at the mains. Each laptop/notebook computer will be slightly different and you need to decide if 32mm is enough height to clear the top of the keys – if not, 80  Silicon Chip This cutting diagram, to scale, shows how to get all the jukebox panels (the two 32mm thick pieces excepted!) from a 1200 x 2400 sheet with some left over for other projects. The numbers on the blue saws are the order of cuts (the red dotted lines) – you only need to make seven (plus, of course, the rounded tops which can be done later). If your timber merchant offers a cutting service (about $2.20 per cut at most places), we reckon that’s $15 well spent! siliconchip.com.au now we move on to assembly. Putting it together If you’ve taken our advice and had the pieces sawn by the supplier, you’re going to have an easy assembly. If not, and your cuts aren’t quite true or perhaps not quite even, it’s going to be a bit more difficult. We found the fit was so good as we assembled the pieces that we didn’t even need to cramp the box together as it was glued’n’screwed. Even the rebates (which I will admit I had never done before) came up a treat! Start by cutting the rounded corners on the top of the sides. We simply used a garbage tin lid to get the curve and then cut them with a jigsaw. A bit of rough sanding removed any blade marks – fine sanding isn’t necessary. As long as the curve is true, don’t worry too much about getting it absolutely smooth. We’re going to cover the box with speaker carpet later and this hides a multitude of “oopses!”. (Trust me – I made some). The carpet also hides the majority of the screws used in construction. The next step, rebating, is probably the most important because it will determine just how well the box fits together. We used a router with a 19mm blade (we couldn’t buy an 18mm but the extra millimetre doesn’t really matter) and first cut the rebates which went from front to back on the sides (three each side). Of course, the 32mm and 50mm rebates require more than one cut; the 50mm rebate needs two outside cuts then the “meat” removed from the middle. If it is at all possible, the sides should be clamped side-by-side and the rebates cut across both pieces in one action. That way, you know they are going to line up. With these cut, we were able to get the right places for the vertical rebates on the sides. The front rebate is inset 18mm while the rear is right on the back. Remember that neither of these rebates goes from top to bottom – the front rebate goes from bottom up to the 50mm horizontal rebate; the back rebate goes from the top down to the 18mm rebate. A 5mm x 18mm rebate also needs to be cut across the front of the base to match the rebates on the sides (ie, inset 18mm). Because the back panel doesn’t come down to the base, no rebate is necessary there. siliconchip.com.au And here’s how all those cut-out bits fit together. Compare this drawing with the pics overleaf . . . While you’re in the rebate mood, you might as well cut the two holes for the speaker drivers in the baffle. We used the router mounted on a home-made jig to cut the 280mm circular hole for the woofer and a jig saw to cut the 115 x 160mm hole for the compression driver. We then used the router once more to cut a rebate in the front side of the baffle for the compression driver so its front finished flush with the baffle front. If you think this is a bit of overkill, don’t worry about doing it – there won’t be any difference in performance one way or the other. It makes sense at this point to mark and drill the eight holes for the woofer and six holes for the tweeter. The woofer has 4mm holes which go right through the baffle (it’s held in with bolts and nuts) while the tweeter has 2mm pilot holes for the woodscrews which hold it in. There are two other cuts necessary. One is to make the notebook “well” in the 32mm craftwood – we simply made this as large as we thought would be needed to suit the notebook. In retrospect, we realise this could be just January 2006  81 but whatever you do, don’t glue it in place yet! After checking that everything is still where it should be and that the box is still square, start placing the rest of the screws. You’ll find a power screwdriver or cordless drill is almost a necessity here – we used 30 screws in each side. You’ll probably find some of the glue has been forced out of the joins as the panels are tightened up. That’s fine – simply use your finger to run a bead of the glue back into the join. Once all screws are in and tight, put the box aside for a few hours to dry. Then we come to one of the fun parts – applying the carpet! Speaker carpet Fore and aft views of the assembled box, as yet without the back – for obvious reasons. The amplifier tray slides into the void at the bottom of the unit. as easily done with three appropriate lengths of 32mm craftwood instead of the large U-shaped piece we cut. The other cut is in the back of the box for the air vent/access to the notebook. This is the same width and depth as the notebook well. Again, we cut this with the router but a jigsaw would also handle this quite nicely. That’s all the rebates and cuts completed – now you need to drill holes in the sides for the screws which will hold it all together. Somewhere around 4-5mm holes should be fine. Drill the holes along the centre lines of all rebates – we placed screws 50mm in from each edge and then around 150170mm apart, depending on the length to be covered. Following the rebates means you should end up with holes that are dead centre and will not split when screws are placed. When all the holes are drilled, turn the sides over and countersink each hole so that all screw heads will end up flush with (or even slightly below) the surface. Dummy run Loosely assemble the box (ie, without glue or screws) just to ensure everything goes together as it should. You may need a second pair of hands 82  Silicon Chip here – and if you need to nip a couple of screws to hold it together, that’s fine. Just don’t do them up all the way If everything looks correct, it’s time to start with the glue and screws. We used garden-variety PVA glue and TEK screws specifically intended for chipboard. For box assembly, we used 50mm screws. As we said before, our box fitted together so well it didn’t need cramping – the screws held it securely while the glue dried. If you need to cramp it, so be it. Starting with the sides, run a healthy line of glue in the rebates for the baffle, base and enclosure bottom, stand the sides up, fit the base and enclosure bottom and nip in enough screws (four corners?) to stop it all collapsing. Place the baffle in place in its rebates (make sure the glue hasn’t oozed away) and tighten up the loose screws. Now run a line of glue in the rebate in the speaker top, turn it over and slide it in from the back. Make sure the baffle mates with the rebate and place say four screws to hold the speaker top in position. At this stage, we also fitted the back to make sure the box stayed square. We didn’t bother with all the screws – four hold it sufficiently in place – As well as hiding any sins, speaker carpet is also pretty flexible stuff in its own right. It can be pushed, pulled, prodded and stretched to make it cover just about any shape. We didn’t have any problems at all fitting it to the curved tops to the Ultimate Jukebox (and curves are the hardest part). The whole outside of the box is covered in the carpet, with the exception of the notebook well. The only reason I didn’t cover this was that the thickness of the carpet would have meant that the 32mm craftwood was just too thin and the notebook keys would be starting to compress. The aluminium covering above the notebook was covered in speaker carpet on the top (you could cover both sides if you wish). Contact adhesive secures the speaker carpet to the box. Don’t underestimate the amount of glue you will need: I did! I thought a 1-litre tin would be ample – I went through over two litres (the speaker carpet really soaks it up!). With a bit more care, I could have just scraped through with two. You’re also going to need a notched spreader to apply the glue. These are commonly available where contact adhesive is sold – usually right next to it on the shelf! The easiest way to use contact is to coat the hard surface to be glued, place the carpet on while wet, then separate the two again until they are both just dry (“tacky” is an expression often used). Then carefully place the carpet back onto the surface, stretching it tight as you go. Remember that with contact adhesive, you get just one go! Plan the covering so that you have siliconchip.com.au minimum cuts – it just looks better that way. The simplest surfaces to be covered are the sides and back – so if you haven’t glued speaker carpet before, this is a fairly risk-free area to develop your skills Cut a piece of carpet that will do both sides and the back – allow say 10cm for safety. Do each surface in turn – ie, glue one side, attach the carpet, then the back, then the other side. Finally, do the front edges of the sides. You’ll find as you do the curved surface at the top that the carpet can be stretched tight as you go and it should follow the curve without puckering. You need a very sharp knife to cut the carpet “in situ” – a “Stanley” knife is normally not sharp enough unless you’ve sharpened it on a whetstone. A craft knife is a much better proposition because they have snap-off blades – as the cutting edge dulls you can snap that bit off and get a new, sharp blade. Cutting the carpet is as simple as running the blade down the surface where you want to cut. Remember though that the box is timber and your knife is very sharp – sharp enough to cut into the wood. I generally cut using a thin metal rule following the cut under the knife blade to prevent it knicking or slicing into the wood and cutting the carpet off line. Cut the carpet as you go, so you don’t end up with a whole lot of pieces flapping about. This also means you can perhaps extend another piece to cover any “oopses”. Because the carpet has a grainy finish, slight imperfections are easy to hide. Once you have the sides and back finished, you can do the baffle. Remember that this is inset – you need to turn the carpet up at the edges to meet the piece already fitted. You’ll find that the carpet can be pressed into the corners easily – I used the back of the craft knife to make a nice, neat corner. You can now carefully cut out the speaker holes. A long (~880mm) thin (18mm) strip (precut for convenience) can be glued around the woofer cutout. All that’s left of the box itself is the inside top sides and back – this should be quite easy because by now, you’re getting pretty skilled in gluing speaker carpet! Cutting the back out The back is currently held in place with four screws . . . and the speaker siliconchip.com.au carpet. And, of course, you need to get the back off so that you can wire the speakers and crossover. With the craft knife, cut along the seam between the back and rebated sides, then cut a small slit across each of the four screws. That way you can get a screwdriver in and remove the screws – and the back. If the back is such a tight fit that there is no seam to get the knife into, use a long straight edge to cut along where the seam would be. With 18mm timber and a 5mm rebate, that means 13mm in from the edge. If you get it “pretty” enough, once the back is screwed permanently on you won’t even know there’s a seam there. If your cut is a bit onky, don’t worry too much: it’s at the back! Moving it At 32kg for the timber alone, the Ultimate Jukebox takes a bit of dragging around. To assist this, we fitted a pair of 40mm castors on the base, at the back. Actual height of these from top to bottom is 85mm. At the front, we screwed in a length of 100 x 50mm framing timber, planed down to 85mm high, as a “foot” and covered it with speaker carpet. That way, when let off the wheels, much of the jukebox weight transferred to the timber foot and gives extra stability. The handle We’ll show this in a lot more detail next month but here is the Ultimate Jukebox from the back, without back of course! At top is the notebook computer, centre is the actual speaker box and at the bottom, the electronics. To help move the box, we wanted a pair of handles at the back so that it could be leant back onto the castors and rolled along. But when we priced handles at the hardware shop, we found they were about $4 each and worse, were puny (after all, they were intended for drawers). As we said earlier, the jukebox has significant weight and we were worried about the handles taking the load. So instead of handles, we used bathroom towel rail and rail ends. It cost less than two handles and is a lot stronger. And if you’re all sweaty after moving the Ultimate Jukebox around, you can always hang your wet towel over the rail . . . We positioned the rail/handle immediately under the air vent on the rear of the box. Don’t use the little woodscrews that came with the rail ends; we substituted countersunk head 5mm bolts and nuts which really anchored the thing in place. The box is finito! Now you can fit the speakers, woofer mesh grille, crossover . . . and start the wiring. The grille comes with four bolts and nuts – we discarded these and used the bolts that hold the woofer in place to also hold the grille. A piece of plastic surround comes with the grille – cut appropriate January 2006  83 1 SC480 50W RMS amplifier module [Altronics K5120, Jaycar KC-5345, DSE K3431] 1 power supply to suit [Altronics K5122, Jaycar KC-5347, DSE K3432] 1 28-0-28VAC Toroidal transformer to suit [Altronics KM5120, Jaycar MM1095, DSE M-0144] 1 PreCHAMP Preamplifier (with modifications – see text) [Altronics K2112, Jaycar KC5166, DSE K5608] 1 120kW 1/2W resistor (for PreCHAMP mods) 1 560W 1/2W resistor (for PreCHAMP mods) 1 3.5mm stereo plug 2 5.6kW 1/8W resistors 1 IEC mains input socket with integral fuseholder [Altronics P8324, Jaycar PP4004] 1 IEC mains lead 1 mains-rated SPST rocker switch with neon 1 10kW log potentiometer 1 4-way mains terminal block 1 50 x 50mm piece blank PC board (or used copper-side down) Scraps of aluminium for power supply and hard disk clamps, mains connections safety cover, etc. 1.5m length shielded cable, various lengths mains-rated connection cables, heatshrink tubing, cable clamps, cable ties notches out of its back so that it clears the mounting bolts. Because it’s very flexible, you can simply lift the front out of the way while tightening the mounting bolts. The woofer mounts inside the box while the compression horn for the tweeter mounts in the rebate from outside the box. You can use either wood screws or nuts and bolts to hold the horn in position. Wiring from the crossover to the speakers is self-explanatory – the crossover is clearly marked woofer and tweeter. The figure-8 wiring from the crossover to the amplifier needs to go through one of two holes drilled in the bottom of the speaker box. Only drill a hole as large as you need to get this wire and the audio input wire (from the notebook) through. Later, you’ll need to re-seal this hole with silicone sealant. One point you will note from our photos is the 10W resistor in series with the tweeter. We included this because we thought the system sounded just a little “bright” – ie, too much treble. This is purely a matter of choice – you can include this if you wish (we used an 8W resistor) or not. If you want to experiment with the sound, anything from zero to say 20W would seem appropriate. Obviously, a hole needs to be drilled through the top of the box to allow the audio input cable through. Choose a place where it doesn’t interfere with the computer or its 32mm timber surround (we made the timber surround slightly undersize to achieve this. A second pair of holes need to be drilled in both the enclosure top and bottom to allow the computer power cable and the USB cable between computer and hard disk to pass through. The USB plug will determine how big this hole needs to be. Again, once the project is basically completed, these holes will need to be sealed. You might need a small piece of timber glued over the hole as well as silicone sealant to ensure the hole is plugged! Computer section Oh no! We’re out of room! Parts List – Ultimate Jukebox “Hardware” 1 2400 x 1200 x 18mm sheet craftwood (MDF) (or 2 1200 x 1200 x 18mm) 1 450 x 900 x 32mm sheet craftwood (MDF) (base and notebook spacer) 2 435 x 350 x 2mm aluminium sheets 2m speaker carpet (1.8m wide) 1 380mm length 20mm diameter chromed towel rail 2 20mm towel rail ends 2 40mm swivel castors 1 380mm length 80 x 50mm timber (for front stand, carpet covered) 4 speaker corner protectors 50 50mm TEK woodscrews 8 40-50mm x 4mm (3/16”) csk head bolts with nuts (for speaker and grille) 8 20mm x 8g woodscrews (for horn mounting) 4 30mm x 4mm csk head bolts with nuts (for handle mounting) 8 10mm spacers, tapped 3mm, 62 5mm x 3mm screws and nuts 4 10mm x 3mm screws and nuts 2 20mm x 3mm screws and nuts (for terminal block mounting) 3 solder lugs 2 3mm shakeproof washers (for common earth point) 2 fibre washers (for PreCHAMP PC board mounting insulation) Around 2 litres contact adhesive (for speaker carpet) PVA wood glue (for box assembly) Speaker Section 1 high sensitivity, high power 300mm woofer [Altronics C3212] 1 compression horn driver [Altronics C6110] 1 horn flare to suit driver [Altronics C6130] 1 2-way 150W crossover [Altronics C4007] 1 300mm metal grille [Altronics C3712, Jaycar AX-3524] 1m medium-heavy duty figure-8 cable 1 8W 10W wirewound resistor (if required to attenuate tweeter) Amplifier/Electronics Section 1 Notebook computer with mains power supply (Pentium 100 or better) running “Ultimate Jukebox” and “Winamp” software 1 External USB hard disk drive, if required due to inadequate hard disk space in computer 1 USB extension cable (if needed) 1 Trackball (or optical mouse), preferably USB 84  Silicon Chip We had hoped to complete the Ultimate Jukebox this month but space has once again beaten us. So next month we will cover the electronics assembly, testing and finally, blasting the neighbours. . . SC siliconchip.com.au