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Build a state-of-the-art Mini Entertainment Have you wanted to build a really good quality stereo mantel radio with FM/AM reception and the capability for playing music from a flash drive, iPod, iPhone etc? Or perhaps you have lusted over a Bose Wave Music system but have been thwarted by the high price? Well, there is another, much cheaper way and it is based on a goodquality car FM/AM radio/CD player. S CHIP readers love building electronic projects and from time to time we get requests to design a project for a good quality mantel radio. However, over the years it has only taken us a few minutes’ consideration to come to the conclusion that designing an FM/AM stereo radio of reasonable performance would simply not be a viable proposition when compared to the plethora of equipment available from retail stores. The most recent request along these lines had us thinking differently though, especially when considering ILICON 42  Silicon Chip that most such consumer equipment has facilities for playing music from an iPod, iPhone, Android phone, flash drive or whatever. Presumably, any mantel radio project we designed would also need those facilities. Of course, that makes a SILICON CHIP design along these lines even more complicated and less viable. But then we harked back to our first issue, in November 1987 when we used a AM/FM stereo radio-cassette player as the basis of a good quality mantel radio. Then, as now, people hankered after the good sound of an old valve radio instead of the restricted sound from tiny speakers in minuscule cabinets. And then as now, we concluded that using a car radio and car radio speakers was the way to go. Now though, because of the way that consumer electronics has become so cheap, you get far more value; incredible value, in fact. Back in 1987 we could have purchased a no-name AM/FM stereo radio-cassette player for under $80. However, on that occasion we elected to use a top-of-the line Pioneer AM stereo/FM stereo radio cassette player we had on hand. siliconchip.com.au The Mini Entertainment Unit is built into a timber cabinet made from 12mm thick MDF. It uses a Sony CDX1-GT620UI FM/AM radio/CD player and a pair of Pioneer TS-G1044R 4-inch coaxial speakers to deliver good quality sound. Left: the Sony CDX1-GT620UI even comes with a remote control. By LEO SIMPSON Centre It would have cost many hundreds of dollars to buy new. Sony radio This time around we bought a Sony CDX1-GT620UI FM/AM radio/ CD player for under $70. It can play discs in a number of formats and you can plug in a flash drive, MP3 player, iPod, iPhone or the auxiliary plug from an Android smart phone; no adaptor is required. It also comes with its own infrared remote control which seems a silly idea for a car radio but ideal for the application we wanted to use it for. Furthermore, you can control it via your iPhone after downloading an app; something which wasn’t even thought of in 1987. As well, the Sony can drive front and rear speakers, incorporates an equaliser for a variety of sound quality settings and has outputs to drive an external 4-channel amplifier and powered subwoofer. In short, it has all the facilities you would expect in a premium car sound system. Because the radio is designed for use in a car, it has far better RF performance than any domestic radio and has the advantage that you can store all your favourite stations, available at the push of a button. In fact, its overall performance ratings would probably be better than many typical domestic music systems costing many hundreds of dollars. And while it might be controversial to compare its overall sound quality to that of a Bose Wave Music System, it is a great deal cheaper and does not require an external adaptor in order to hook up an iPhone or iPod. (The current model Bose Wave Music system with AM/FM radio/ CD player retails for $699. The top-of-the-line model with DAB+ reception has an RRP of $799). In essence, all you need do to build a complete music system with the Sony car radio (or any other car radio) is provide loudspeakers and a suitable DC supply. Buying the parts Before going further, we should discuss where to purchase the various components. While you will find that there are lots of on-line sellers of car radio equipment, virtually all of it sourced from Asia, we found it was quicker, more convenient and actually cheaper to buy from our local JB Hi-Fi store. At the store, you can physically examine and listen to what you are buying and there are often short-term in-store or website specials available. In the case of the Sony radio we purchased, it had been reduced twice and was way below its recommended retail price of $148.00. The same comments apply to the loudspeakers we purchased. Initially, we purchased Pioneer 6-inch (150mm) 4-ohm coaxial speakers from JB Hi-Fi but when we began to draw up the cabinet plans, we realised that they would make the make the cabinet too bulky. It was a simple matter to go back to JB Hi-Fi and swap them for a pair of slightly more expensive Pioneer TS-G1044R 4-inch (100mm) 4-ohm coaxial speakers, at $49 for the pair. These come with separate 130mm decorative surrounds and mesh grilles which still makes them a little more bulky than we would have preferred. Note that exchanging goods purchased on-line, particularly from overseas sellers, may be inconvenient, costly or simply not possible. The mesh grille on the Pioneer speakers is desirable for most applications because there is a considerable risk that the coaxial tweeter or woofer The Sony CDX1-GT620UI FM/AM radio/CD player (left) features a detachable control panel while the Pioneer TS-G1044R 4-inch speakers are supplied with decorative plastic surrounds and steel mesh grilles. siliconchip.com.au February 2014  43 This view shows the general layout inside the cabinet. The radio is held in place using a curtain bracket and a machine screw, while the switchmode power supply is secured using doublesided foam adhesive. The antenna (brown wire) runs up one side of the cabinet and along the top and is held using gaffer tape. These two photos show the cabinet under construction. The holes in the front panels for the radio and the two speakers must be made before gluing and clamping the assembly together. cone could easily be damaged in normal use. If you want a more compact speaker, you could consider the Response 4-inch 4-ohm coax speakers from Jaycar (Cat. CS-2310). These are quite good performers but in their case, the detachable surround and grille does not fully protect the woofer cone. Power supply The power supply can be as simple as a DC plugpack rated to deliver between 13V and 14.4V at 1A or more. The upper limit of 14.4V is the maximum which is supplied to a car radio in normal use but they are probably designed for a maximum DC voltage of about 15V. 44  Silicon Chip However, standard DC plugpacks may not be satisfactory as there might be too much hum and noise in the resulting sound. By all means try using a DC plugpack if you have one suitable but make sure that it delivers no more than 14.4V DC. Many DC plugpacks are quite poorly regulated, which means that their peak output voltage may be way above their nominal rating. For example, one unit I tried was rated at 12V DC but actually delivered around 19V with light loading. The power supply we actually used was a switchmode unit rated for 12V DC at 2.8A. This proved to be noisefree as far as the radio’s sound quality was concerned while delivering more than enough power (actually very loud in a typical room) for normal listening. This might be a little surprising, given that the Sony radio is specified to deliver up to 52 watts into four channels. Even if this is a music power rating, it would require far more than 2.8A for full power. We did not test its maximum power rating but we would assume that it would pull at least 10A when driven to full power. Fortunately, for normal listening a power supply capable of delivering between 1A and 2A will be more than adequate. If there is too much hum or your plugpack’s DC output is simply too high, you will need to feed it via a regulator module. The one we suggest is our MiniReg adjustable regulator from the December 2011 issue. This was based on an LM317T regulator delivering up to 1.5A but for this application, we suggest changing the LM317T to an LM338T which is rated to deliver up to 5A. The accompanying panel has all the details on the MiniReg. Making the cabinet This is the hardest and most timeconsuming part of this project. Rather than producing a straightforward recsiliconchip.com.au tangular cabinet as we did originally, this time we wanted to produce a unit with more styling and possibly smaller. We had the Bose Wave Music system in mind as our inspiration. This unit comes in a surprisingly compact cabinet (371 x 106 x 218mm – W x H x D) and with a curved front. As already noted, the size of the speakers we selected, combined with the depth of the Sony radio’s case meant that our cabinet would inevitably be considerably larger. We also decided that making a cabinet with a curved front would be far too difficult for the majority of our readers and would add complications when mounting the radio and the speaker themselves. Therefore we decided on a cabinet which has the speakers angled back to make it more compact and also to improve the apparent stereo separation. The resulting cabinet was made MASSIVE ME R SUM LE SA S END H C MARST 31 siliconchip.com.au Packing bonded acetate fibre in behind each speaker significantly improves the bass when combined with a close-fitting back panel (below). The rear panel is made from 12mm-thick MDF and has a stiffener glued along the horizontal centre-line made from 12 x 12mm DAR pine timber. Test Equipment Sale! Big Name Brands at Bargain Prices!!! Agilent, Fluke, FLIR, Extech, Ideal Test & Measurement And many more at savings up to 50% Clearance Sale on New and Ex-demo Stock Accessories on sale too! Visit this link now and grab a bargain: www.triotest.com.au/shop/en/303-clearance-items Example: Digital Oscilloscope 150MHz Or call us on 1300-853-407 for immediate assistance $395.00 +gst only PS: All stock is subject to prior sale, so be quick! February 2014  45 Fitting A Regulator To The Plugpack Supply D2 K CON2 + INPUT 17-20V DC D1 REG1 LM3 38 T K A – ADJ A 1000 µF 25V SC K VR1 C2 2k C3 K K A 100 µF 25V 10µF 25V LM338T LED D1–D3: 1N4004 OUTPUT 14.4V DC – D3 A λ A 2011 R1 110Ω C1 K ADJUST VR! FOR 14.4V OUTPUT CON4 + OUT IN 2.2k LED1 A OUT ADJ OUT IN MINIREG ADJUSTABLE SUPPLY Fig.1: the MiniReg circuit uses an LM338T adjustable regulator. D1 provides reverse polarity protection, while trimpot VR1 adjusts the output voltage. I F THERE IS too much hum or your plugpack’s DC output is simply too high, you will need to feed it to the radio via a regulator module. The one we suggest is our MiniReg Adjustable Supply from the December 2011 issue. This was based on an LM317T regulator delivering up to 1.5A and is accommodated on a small PCB measuring only 35 x 38mm. For this application though, we suggest changing the LM317T to an LM338T which is rated to deliver up to 5A. We are reproducing the main details of the regulator here – see Fig.1. The LM338T adjustable regulator provides a nominal 1.25V between its OUT and ADJ (adjust) terminals. We say it is a “nominal 1.25V” because, depending on the device, it can be anywhere between 1.2V and 1.3V. This doesn’t really matter though, because we can adjust the output voltage to the required level using trimpot VR1. The output voltage from REG1 is set by the 110Ω resistor (R1) between its OUT and ADJ terminals and by the resistance between the ADJ terminal and ground. This works as follows: by using a 110Ω resistor and assuming an exact 1.25V reference, the current flow through the resistor is set at 11.36mA. This current also flows through trimpot VR1. This means that if VR1 is set to a value of 1.15kΩ, then the voltage across this trimpot will be 1.15kΩ x 11.36mA = 13.06V. This voltage is then added to the regulator’s 1.25V reference to derive the output voltage – in this case 14.31V. In practice, the current flow out from a sheet of 12mm-thick medium density fibreboard (MDF) measuring 600 x 900mm. The two panels for the speakers are angled back by 20°. While this might seem like a fairly simple design, it proved to be quite a challenge to get all the angled cuts correct. Ultimately, a certain amount of planing was required to make sure that all panels fitted together reasonably closely. Even then, some wood filler was required to cover minor blemishes before the cabinet was sanded and finished. The finished cabinet dimen- Circuit details 46  Silicon Chip of the ADJ terminal also contributes slightly to the final output voltage. This current is of the order of 100μA, so if VR1 is set to 1.16kΩ, this can add 0.12V to the output, ie, we get 14.43V. In practice, its just a matter of adjusting VR1 to set the output to exactly 14.4V. Diode D1 provides reverse polarity protection. This means that if you connect the supply voltage around the wrong way, you cannot do any damage. Diode D2 protects the regulator if the input becomes shorted to ground while it is powered up. Without D2, current would attempt to flow back from the output capacitor through the regulator to the shorted input and that could kill it. But D2 becomes forward biased and conducts, effectively preventing any reverse current flow through REG1. Diode D3 is also included to protect REG1. It does this by clamping the voltage between the ADJ terminal and the OUT & IN terminals in the event that one of the latter is shorted to ground. Finally, capacitors C1 & C2 reduce ripple and noise by bypassing the IN (input) and ADJ terminals respectively. C3 prevents regulator oscillation by swamping any low-value capacitance that may be connected to this output. Construction All the parts for the MiniReg are mounted on a PCB coded 18112111. Fig.2 shows the parts layout. Begin the assembly by installing the 110Ω resistor (R1) and the three diodes, making sure the latter are all orientated correctly (the banded ends are the cathodes). That done, install the wire link. This link takes the place of CON3 as fitted to the original MiniReg and is installed because an on/off switch is not required in this application. The three capacitors can go in next, again taking care with their sions are 565 x 177 x 218mm deep (W x H x D). These dimensions do not include the speaker escutcheons and grilles and the radio itself. Ideally, anyone attempting to produce a cabinet along these lines needs access to a drop saw or bench saw siliconchip.com.au MiniReg Parts List 1 PCB, code 18112111, 35 x 38mm 2 2-way polarised pin headers, 0.1in spacing 1 120 x 140mm aluminium sheet for heatsink 1 TO-220 insulating washer 1 insulating bush 1 M3 x 100mm machine screw & nut 1 2kΩ horizontal trimpot REG1 LM338T A 1000 µF VR1 D3 4004 4004 110Ω D2 D1 10 µF OUT 1 1 1 1ER CJ LINK K LED1 CON2 17-18V DC – INPUT + IN ADJ 4004 CON4 14.4V DC – OUTPUT + 100 µF 2.2k Fig.2: install the parts on the PCB as shown here. LED1 and its associated 2.2kΩ resistor are optional. orientation since they are all electrolytics. Follow with the three 2-pin headers (CON1, CON2 & CON4), then install the 3-terminal regulator. The latter should be mounted vertically at full lead length (not horizontally as shown in the photo), so that it can later be fastened to a heatsink. The PCB assembly can now be completed by installing LED1 (it takes the place of CON1 in the December 2011 circuit). This LED is optional; simply leave it out if you don’t need it (you can also omit its series 2.2kΩ resistor). Above: the original MiniReg. For this project, mount REG1 vertically and install LED1 and a link in place on CON1 & CON3. SILICONE WASHER INSULATING BUSH M3 x 10mm SCREW Semiconductors 1 LM338T voltage regulator (REG1) 3 1N4004 power diodes (D1-D3) 1 3mm red LED (LED1, optional) Capacitors 1 1000μF 25V electrolytic 1 100μF 25V electrolytic 1 10μF 25V electrolytic Resistors (0.25W, 1%) 1 110Ω 1 2.2kΩ M3 NUT Adjusting the output The input voltage applied to CON2 must be several volts higher than the required output voltage. This is necessary in order to provide regulation. The minimum voltage across REG1 required for regulation is called the “dropout voltage”. For the LM338T, this voltage varies with the current and is typically 1.5V for currents below 200mA, rising to 1.7V at 500mA and 2V at 1A. Note that the voltage drop across diode D1 must be added to the dropout voltage in order to calculate the required input voltage. For example, if the load draws 2A or more and the required out- put voltage is 14.4V, then the input voltage must be 14.4V plus 0.7V (to compensate for voltage across D1) plus 1.5V (for the dropout voltage), ie, the input voltage must be at least 2.2V higher than the output voltage. Therefore, we need to apply at least 16.6V minimum to the input for regulation. This is the absolute minimum to ensure correct regulation. Note also that any ripple on the input supply that drops below the required voltage will cause problems, since the supply will not be regulated during these low-going excursions. Once you’ve connected the supply, it’s just a matter of adjusting trimpot VR1 to set the required output voltage to 14.4V. You will need to make up two matching cables with 2-way polarised header connectors for the input and output connections. If ripple is still present on the output of the regulator, reduce the output – down to as low as 12V if necessary. which can do precision angled cuts. I used a standard circular saw with a facility to angle the blade but making the required precision cuts needs a very steady hand. The photos show how the cabinet was assembled, with cleats, PVA glue and plenty of clamps. By the way, before the cabinet is assembled, you need to make cut-outs in the three MDF front-panel sections, to suit the radio and the two speakers. The Sony radio we used has a control panel which is detachable and it is good idea to have this removed while you do any measurements and installation work. The cut-out for the radio must be very tight; no more than 1mm clearance for the height and width of the case, because the front panel trim will not cover any gaps. It is also most important to have the You must fit a heatsink? The LM338T must be mounted on a heatsink which can be just a sheet of 1mm thick aluminium measuring around 120 x 140mm and mounted vertically in the rear of the cabinet. Note that it will be necessary to electrically isolate the regulator’s tab from the heatsink. The reason for this is that the regulator’s tab sits at the output voltage (ie, 14.4V) To isolate the tab, use a TO-220 insulating washer and bush and secure the assembly to the heatsink using an M3 x 10mm screw and nut. Fig.3 shows the details. siliconchip.com.au LM338T REGULATOR PCB 120 x 140mm ALUMINIUM HEATSINK Fig.3: the LM338T regulator must be isolated from the aluminium heatsink using a silicone insulat­ ing washer and bush. February 2014  47 Our First Car Radio-Based Project These photos show the construction of our first car radio-based project from the November 1987 issue. The Pioneer KE-A433AM car radio in question was quite a good unit, with PLL synthesiser tuning of the AM & FM bands and wide and narrow-band reception on AM. It also featured stereo reception from CQUAM transmissions, 70μs equalisation for metal tape cassettes and 18 presets for the AM & FM bands. We teamed it with a pair of small oval 8-ohm car speakers and housed it in a cabinet made from dressed Radiata pine timber, tinted and finished with matte Estapol. The front panel was covered with beige grille cloth. The cabinet was relatively large but simple to make, with the panels screwed and glued to internal cleats (the rear panel has been removed for these photos). This was before the days of regulated DC plugpacks so we used a conventional power supply employing a 15V 1A transformer feeding a bridge rectifier, a 4700μF 25V capacitor and a regulator circuit based on a 7812 3-pin regulator “jacked up” with two diodes in series with its GND terminal to set the output to 13.4V DC. radio cut-out exactly centred (horizontally) in its MDF panel. Similarly, the circular cut-outs for the two speakers must be made so that they are equidistant from the top and bottom edges of the MDF panels and also equidistant horizontally from the corners of the finished cabinet (the accompanying photos tell the story). We painted the cabinet in a lightgrey semi-gloss oil-based enamel. This was probably a mistake because it is more difficult to apply (and clean up afterwards) than an equivalent waterbased acrylic paint. Either way, the cabinet needs to be carefully sanded and filled where necessary with wood 48  Silicon Chip filler, painted with a water-based acrylic undercoat and then sanded again. Take our word for it and don’t attempt to do the top coats with a brush because you will find it almost impossible to avoid brush marks. Instead, use a small short nap roller intended for matt and semi-gloss acrylic paint – you will get a much better finish. Instead of fitting rubber feet to the base of the cabinet, we used stick-on felt pads which can be purchased cheaply from hardware stores. Installing the components As can be seen from the photo of the rear of the unit, the radio is anchored by a single screw and a curtain bracket at the rear. The various connections for the speakers were brought out to a multi-way terminal block and the speaker connections hooked up. We then simply taped all those connections and the unused wires for the rear speakers to the top of the radio case using gaffer tape (crude but effective). Similarly, we brought the three supply connections (+12V, memory supply and GND) to another terminal block and made connections to the compact switchmode power supply via a jack connection and then again, taped it all to anchor it. The switchmode supply itself was anchored using double-sided adhesive tape. You also need an aerial connection and to do this we used a 60cm length of wire soldered to the tip connection of a 3.5mm jack plug which was then pushed into the aerial socket. We then taped the wire inside the cabinet. In most urban areas this will give good radio reception. Losing memory Now one the drawbacks of the simple supply connection we used is that if you turn off the power at the wall socket, you will lose all the user settings such as the clock, favourite stations, sound set-up and so on. To keep these settings, you need to have a +12V supply permanently connected to the memory supply terminal (as it is in a normal car set-up). The best way to provide a standby 12V supply is to install a small 12V SLA battery and then trickle-charge it from the main supply via a 1N4004 power diode and a resistor, say 2.2kΩ 0.25W, to give it a permanent float charge of just over 5mA. Again, the battery could be simply secured inside the cabinet with double-sided adhesive tape. Improving the bass As a final finishing touch to the cabinet, we fitted an MDF back panel. As shown in one of the photos, this has an access hole for the 2-pin mains plug for the power supply. The rear panel does improve the bass somewhat but it still won’t be as good as it would be if the cabinet (s) were specifically designed to suit the speakers. Incidentally, as a further refinement, you could add extra terminals to the rear of the cabinet to allow rear speakSC ers to be connected. siliconchip.com.au