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Building the ULTIMATE When we ran out of space last month, we were just about to start installing the electronics. So let’s get that finished and start blasting the neighbours . . . B elow the speaker “box” is the space for the electronics assembly. Inserted from the rear, it consists of (a) the amplifier; (b) the preamplifier; (c) the master volume control; (d) the amplifier power supply (including transformer, fuse and on/off switch); (e) the notebook computer power supply; and (f) the USB hard disk drive (or maybe even two – there is plenty of room). These are all mounted on a 2mm aluminimum plate measuring 435 x 350mm, with the longer edge bent up 90° at the 50mm mark. A 125mm cutout is made in the middle which allows the heatsink to mount on the outer (vertical) surface and the amplifier PC board on its 10mm standoffs on the horizontal plate. Refer to our photographs and diagrams to see the layout. In general, the “noisy” bits – the transformer and computer supply – are kept well away from the amplifier input. The amplifier itself mounts with its heatsink on the outside of the bent-up section and is secured to it with two 3mm screws (we tapped the heatsink for convenience). Two screws from the underside mate with the 9mm tapped standoffs holding the amplifier firmly in place. By the way, we’re assuming you have built the amplifier module and set it up as per the instructions (including setting the quiescent current with resistors), so we are not going to re-invent wheels here! Similarly, the ±40V and ±15V power supply: it’s pretty-much self-explanatory and we don’t envisage anyone having any problems putting this together. Fairly obviously, you need to have this completed to set the amplifier quiescent current! By the way, the -15V supply is not used. We know it’s a waste of a few cents worth of components but if you got them in a kit, you might as well put them in anyway. You never know – one of these days you might need a ±15V supply! With only the mains transformer connected, confirm that you do indeed have +40V, 0V & -40V and +15V, 0V & -15V at the appropriate terminals. The Ultimate Jukebox in block diagram form. The green blocks are pre-existing SILICON CHIP projects, with the obvious exception of the notebook computer and its peripherals and the commercial speaker crossover. Note that the PreCHAMP is slightly modified from the published design – this is fully explained in the text. 88  Silicon Chip siliconchip.com.au JUKEBOX Part 3 by Ross Tester Better to find a power supply error now than have the power amplifier tell you in spectactular fashion! The preamplifier This really is a very simple preamp. Follow the instructions with your PreCHAMP kit but make the following changes: the 100kW resistor in the voltage divider in the base of Q1 should be increased to 120kW and Q1’s 100W emitter resistor should be increased to 560W. If for some reason you find you do need more gain, this resistor could be decreased to, say, 330W. Before use we’d suggest that you measure a couple of voltages to be sure, to be sure. First, with nothing connected except power (+15V and 0V from the power supply board), measure the DC voltage across the output terminals. It might first of all indicate a small voltage but quickly settle down to close to zero (anything up to a few tens of millivolts). Second, check the voltage at the input terminals: again, it should be next to nothing (anything higher than this The output from the computer headphone socket is stereo – two 5.6kW resistors sum this to mono and prevent interraction between channels. We used 1/8W types – but 1/4W should also (just!) fit inside the plug. Make sure neither short to each other nor to earth! siliconchip.com.au February 2006  89 Apart from the speakers, crossover and computer, everything mounts on an aluminium chassis or “tray” with a 50mm vertical lip on one edge. It’s shown here without the safety cover over the mains wiring. Compare this picture with the drawing at right. Yes, there are a couple of minor differences (eg, the earth wire is routed slightly differently)! indicates a fault which could damage your notebook computer). Finally, measure the voltage between Q2’s collector and 0V (eg, across the 2.2kW resistor). It should be pretty close to half the supply voltage (our supply voltage was 15.2V and we measured 7.8V). With these checks all OK, you can be pretty confident your preamp is working fine! plate with “U” brackets made from the piece we cut out of the top aluminium plate – so both were already carpet covered (and hence wouldn’t damage the units underneath). Finally, along the front “lip” is mounted an IEC connector with integral mains fuse and the on/off switch (illuminated type), with their heatshrink-insulated wiring connecting to Putting it all together Refer to both the photographs and the diagram opposite. The power supply mounts on its standoffs immediately behind the amplifier board, with the toroidal transformer alongside. Behind the power supply is mounted the notebook supply (in case we want to use the notebook outside the jukebox in the future, we bought a spare supply for the jukebox on eBay for $25). The supply, along with the USB hard disk, is held onto the aluminium base90  Silicon Chip Here’s the “PreCHAMP” preamplifier from our July ’94 issue – an oldie but a goodie! The green text and components show the altered/added components from the original. They’re basically to throttle the gain somewhat and also allow the circuit to run from a higher voltage (15V vs 12V originally). siliconchip.com.au The complete “electronics” section of the Ultimate Jukebox, which fits into an L-shaped chassis or tray in its own compartment underneath the speaker “box”. Not shown on this diagram (for clarity) are the lengths of heatshrink tubing which protect all the 240V AC connections (they are clearly visible in the photo). To be doubly sure, the entire area (IEC socket, switch and terminal block) is then protected with U-shaped aluminium cover which prevents any possible contact with mains wiring. Remember, this area is open to the back of the jukebox so you cannot be too careful. siliconchip.com.au February 2006  91 the transformer via a mains terminal block, insulated from the aluminium underneath by sitting it on a piece of blank PC board (just in case of a stray strand of wire!). There is a good reason for using a IEC connector instead of a captive mains cord: safety. We didn’t like the idea of a flailing mains cord when the jukebox is being transported so we made it removable. On the opposite side of the lip is mounted a 10kW pot which becomes a master volume control (volume is set on screen but this is effectively an over-ride to ensure noisy parties can be limited by the host as people keep on turning up the on-screen control). Take care with the mains wiring, especially the earth wiring – follow our diagrams to the letter and remember to cover all mains connections (eg, to the IEC socket and mains switch) with heatshrink tubing! When everything is completed, some form of mechanical barrier needs to be fitted covering the mains connector, on/ off switch and terminal block – ie, all the bitey bits. We haven’t shown this in either the diagram or the photographs because we wanted to make sure you could see everything underneath. Don’t you forget it, though! Connecting it all up We’ve already covered the output (speaker) wiring – all you need do is connect the crossover input to the amplifier output. The audio line coming down from the notebook computer headphone socket connects to the preamplifier input. Its output goes to the master volume pot. From the wiper of the pot, the audio line goes to the amplifier input. Back up the top (notebook) end, the audio line connects to the headphone socket via a 3.5mm stereo plug. This has two 5.6kW resistors (one per chan- The notebook computer sits in a “well” made from a U-shaped piece of 32mm craftwood. This depth suited this particular notebook perfectly; other notebooks might need a deeper or shallower well so the craftwood thickness would be adjusted to suit. When the jukebox is complete, a carpet-covered aluminium sheet screws over the top of the craftwood, hiding everything but the notebook screen and giving a place for the trackball to sit. nel) to sum the stereo signal into mono before sending it down to the preamp. These resistors also prevent any interaction between the channels. We used 1/8W resistors and were able to mount them inside the 3.5mm plug, with the solder connection between them and the shielded audio cable insulated with a length of heatshrink tube. Standard 1/4W types should fit – but they’ll be tight. USB cable & notebook supply A USB cable also comes up from below, connecting the USB hard disk to one of the computer USB ports. In our case, the hard disk cable wasn’t quite long enough to make it so we had to use a USB A-A extension cable. While this worked fine, we did find it introduced some computer noise into the system when the wick was wound up (on no signal). Still, for a jukebox, it would hardly be noticed (if at all). The computer power supply also has its output coming up through the same holes as the USB cable. In this case, it was long enough. Finally, the trackball or mouse connects to the appropriate socket: if it’s a serial device, it will need to go into a serial socket (if you have one) or via a USB-to-serial converter to a USB port. If it’s a USB trackball, it plugs (of course) straight into the USB port. Testing it all out First testing should be done without the notebook connected (ie, no music source). Turn the system on for a smoke test and if none escapes, try the “blurt” test – turn the master volume control up a little (not a lot!) and touch your finger to the tip of the 3.5mm audio plug. You should be rewarded with a nice, healthy “blurt”. Turn the master volume back down (otherwise you’re going to get a real crack and thump from the speaker) and plug in the 3.5mm plug. Most PC operating systems include some sample music which you can play to prove that everything is OK. Or you could play a CD. Running “Ultimate Jukebox” By now, we’ll assume you have downloaded at least the trial version of Ultimate Jukebox software (see last month) and have become conversant with it. If so, it’s just a matter of turning on the system, loading the music you want on your hard disk(s) from CD, download, etc, and then telling The tray for the electronics and the notebook cover plate start out the same size but require cutouts – and the tray needs a 90° bend to support the heatsink and house the power input socket, switch and master volume control. The cutout in the notebook cover plate depends on the specific notebook computer you use. Don’t throw any scraps away – they’re handy for brackets to hold the notebook power supply and USB hard disks, along with the mains area safety cover. 92  Silicon Chip siliconchip.com.au The view underneath shows the two castors along with the timber “foot” (camouflaged a bit by the carpet!). Speaker corner protectors are also added – for protection! Ultimate Jukebox to add it to the playlist. When you’ve done this, you can select the tracks you want to hear and include them in your playlists, or choose random, etc. The software is very powerful once you get to know it – and you’ll only learn how to do all this by playing with it, so play away! Just remember that when you disconnect the notebook or turn it off, you should turn down the master volume control first. The beeps and other noises that the PC makes as you do anything can be downright disconcerting at high level! Making it lively! If you saw the Ultimate Jukebox photo in Part 2 (last month) you would have to say that yes, it looks impressive but no, it doesn’t look too “partyish”. As we mentioned right at the start of this series, “real” jukeboxes of the past always had lots of chrome and flashing lights! The chrome is a bit of a tall order but the flashing lights we could handle easily! But which way to go? We thought about including some form of “Discolight” controller and including some coloured lights behind translucent panels. We also gave that idea away as overkill! What we did in the end is simplicity itself: we (very carefully!) attach ed a whole swag of ropelight to the edges of our jukebox using some fine panel pins. The ropelight we used came from Jaycar Electronics (Cat. SL-2820 <at> $34.95). At 10m long, it is arguably siliconchip.com.au Here’s our towel-rail “handle” – it makes moving the jukebox that much easier. It’s both stronger and cheaper than individual handles. too long for this application. But you can’t shorten it, so we were stuck with what we had. We wound it around and around, up and down – and then connected it to the mains terminal block on the amplifier tray. It comes with its own little controller which allows you to set a variety of patterns, so we arranged things to make this accessible (alongside the notebook computer) for the punters to play with! Driving it from iPODs, etc We’ve already been asked several times: can the Ultimate Jukebox be driven from, say, an iPOD or other personal audio devices? The answer is a resounding yes! Just in case you haven’t twigged, if you don’t want to use a notebook computer, the modified 3.5mm plug can also be used with just about any other audio device with a headphone socket. Because we have added a preamp, anything that normally drives Jaycar’s SL2820 Ropelight is 10m long, 240V operated and has a variety of light patterns (set by the black box). headphones should drive the jukebox perfectly. We think you will be pretty surprised by the grunt the Ultimate Jukebox delivers. Despite having “only” a nominal 50W amplifier, when you team that up with the sensitive speaker specified you will have more than enough power to rock your socks off! Given that the sensitivity of typical “hifi” speakers is in the 88-90dB range and the woofer we chose is some 97dB, we’re already starting at least 6dB higher – so the 50W amplifier will perform as well as a 200W amplifier. And also given the fact that the SC480 has a “music power” of 77W into 8W, it’s that much better again. It’s finished . . . I think Well, it’s finished as far as the jukebox itself is concerned. It does exactly what I wanted it to – and does it very well! And it sounds really great! But the first time we used the Ultimate Jukebox was at a surf club Christmas Party and it was when I was dragging the PA amplifier out that I realised the jukebox could have been just that much better had I included a PA function. Nothing particularly elaborate – provision for a microphone with its own preamp/mixer, possibly with a wireless microphone á lá the PortaPAL PA System (SILICON CHIP February 2003). It would also add significantly to its usefulness for weddings, parties, etc. So guess what I’m going to work on next? SC February 2006  93