EASY DIY HEATSINK

Many DIYers might have had difficulties in procuring suitable heatsinks for the LED spotlight. Here is an easy way out, which solves the problem and affords some added DIY pleasure too!


Look around in the junk or visit the friendly neighbourhood aluminium fabricator and you could carry home offcuts of rectangular section aluminium extrusions. I got a good length of 2.5 x 1.5 inch section used for door frames/partitions etc.

The first step is to cut off two pieces of 2.5 inch length. Mark off the mid point of the 1.5 inch side and make saw cuts, so that you now have four U-shaped pieces. File the lengths of two pieces so that they fit within the channel of the other two pieces. The accompanying photos make the procedure clearer.

Do note that heat dissipation depends on the area of the active surfaces and on air cirulation, and also on the colour of the heatsink-- black radiates best. To help with this, make saw cuts on the sides of the U-channel, and using a pair of big pliers, slightly bend the fins to stagger them. Again, the procedure is made clearer if you refer to the photos.

Assemble the four pieces in the order shown and drill the necessary fixing holes to mate the heatsink to the LED holder. Mine needed three holes and another small hole for the wires. Mark and drill one hole carefully, keeping the alignment of all the pieces. Now clamp them together with a nut and bolt and then drill the remaining holes. De-burr the holes, clean all the pieces so that the surfaces mate closely, and then paint the 'free' surfaces matt black. Now dab some heatsink compound on the mating surfaces and screw the heatsink to the LED holder, carefully passing the wires through its hole.

Your home-brew heatsink may not look 'spic and span', but it surely is a "cool one" when it comes to doing its job well!


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EASY LED SPOTLIGHT

# # #  WARNING # # # # # # #  # # #  # # # # # # # #
Eye doctors strongly caution the experimenter/hobbyist against looking directly at a lit LED. The risk of retinal damage is very much there even with low power LEDs on account of their highly focussed and coherent beams emanating from a near-point source. The danger is VERY REAL with higher power LEDs.
The reader is STRONGLY REMINDED of the need to exercise great caution.

The easiest way to ensure eye protection is to fix a small piece of plastic diffuser in front of the LEDs with adhesive tape as the very first step-- I had good results with the speckled plastic that is used to make flexi CD pouches and file folders-- until the assembly is safely fitted into a good diffusing fixture.
# # # # # # # # #  # #  # # # # # # # # # # # # # #

Of late LEDs and LED lights have been, how does one say it, "very much in the spotlight"!

Long service life, reduced power consumption and the plus point of 'going green' were some of the factors that favoured the minuscule semiconductor 'light bulbs'. Increased R&D activity in recent years have raised the bar of Lumens (light output) to higher and higher levels, along with a lessening of costs, so much so that high power LEDs now offered the enterprising hobbyist opportunities for replacing many of the lamps in his/her home with DIY LED lamps.

Seoul Semiconductor (http://www.seoulsemicon.com/en/) is a comparative newcomer in the field, but that has not prevented them from reaching the very cutting edge of the technology in a short time. (The company is an innovator and their latest product 'Acriche' is a case in point. It has no usual --and unreliable-- components like resistors and capacitors and transistors that make up the conventional LED driver, but relies on just a custom IC integrated with the LED chips on a ceramic mount offering DIRECT AC connectivity with NO OTHER driver requirements.) (http://www.seoulsemicon.com/en/product/prd/acriche.asp)

Recently when some higher power yet cheap Seoul Semicon LEDs in the 1W and 2W range came into the market, I thought it was time to wire up a practical spotlight.

Luckily I had an old LED holder and lenses lying about. Many holders (for old 5mm LEDs) and lenses are available in the market and the good thing is that the Seoul Semi LEDs will fit those like a glove.

The 1W LED has a single 'chip', while the 2W one has a couple of chips--easily viewed with a magnifier, NOT when it is lit! The current consumption is of the order of 330 mA and less than 700 mA, respectively. But in the interests of long life, I would opt to operate them at about 320 mA and 630-640 mA, and also mount them on substantial heatsinks for cooling. It is easy to 'spec' the heatsink -- after running for a few hours, one should be able to touch it firmly and keep the finger on the heatsink; anything hotter would be suicidal in the long run.

Unfortunately, suitable round heatsinks with vertical fins (as shown above) are not available in the hobbyist market. But dont despair! A visit to the friendly neighbourhood computer serviceman or the electronic junkyard is sure to yield suitable round or square (just cut off the corners with a hacksaw!) CPU coolers.

This is an 'easy' DIY column, remember! And I found that it was not exactly easy for the average hobbyist to fabricate a mains LED driver. So I opted for an easy solution. The market is flooded with cheap 12V / 1Amp mains 'adapters' of the switching type. Upon opening the plug-pack case, one is presented with a neat, compact SMPS on a 2.5" x 1" pcb.

You need another cheap component-- the LM317 adjustaable voltage regulator from National Semi-- which we will configure as a constant current driver for the LEDs. Be warned that LEDs die an early death if they are operated at currents above their design specs. A simple series resistor might be all right if the driving voltage for the LED is steady as a rock. But any other situation would call for a constant current driver. A couple of small resistors complete the BoM or the Bill of Materials for your spotlight.

Kindly note that here I opted for the 2W LEDs, the holder accommodating three; connected as a series string, they were driven with 620 mA. For a smaller lamp, you could opt for series string of 3 x 1W LEDs (about 320 mA) or if you wanted a 'spread out' light source instead of a spot, for two parallel strings of 3 x 1W LEDs (approx 640 mA).
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A  CAVEAT:
I was lucky to get a '12V' SMPS whose output was way above and as a result, the LM317 constant current driver worked all right even with a series string of three LEDs.
Please note that the series string of three LEDs will need about 10V to drive them and the LM317 needs about 2.5 to 3V more than that at its input to work reliably.
If your SMPS outputs just 12 V, it would be best to put two LEDs in series, which need a drive voltage of about 6.6 V and so the 12 V smps should be more than adequate to ensure correct operation.
Do measure voltages and currents with a reliable and accurate muti-meter.
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It is easy to set the constant drive current by selecting just one resistor (R) as per your requirement. The LM317 while operating produces a constant 1.25 V between its output terminal and the adjustment terminal; that means a constant current flows through the current setting resistor and the load connected. Divide 1.25 by the current in Amperes (320 mA is 0.32 A and 630 mA is 0.63 A) to get the value of the current 'programming' resistor in Ohms. Go for a series or parallel combination of a couple of half-watt resistors so that you get as near the theoretical value as possible. For example, I used two 1 Ohm resistors in series that set the current at 625 mA.

Now onto construction. The three LEDs were wired as a series string with short bits of wire so as to fit the lenses in the holder. Pressing a piece of paper onto the lenses provides you with a template for this.

Cut a 2 mm thick piece of aluminimum sheet to serve as the heatsink backplane for the LEDs.

A disc with holes to clear the backs of the LEDs is cut from say an OHP film or plastic to serve as an insurance against short circuits.

Refer to the photos and make the assembly after spreading blobs of heatsink compound on the backs of the LEDs. The alu disc should now be a bit proud of the edge of the holder.

Now smear heatsink compound onto the disc and mount the heatsink with three screws onto the holder. Please note that the heatsink has to be drilled beforehand with the help of pressed-paper templates.

The LM317 also needs some cooling and has to be mounted onto the heatsink (using the third screw). Now wire up the current setting resistor/s and the connecting wires as per the following wiring diagram.

# Warning #
Please note that the metal heatsink slugs on the backs of the LEDs are fully isolated. But the heatsink tab of the LM317 is connected to its output pin. You don't need an insulator here so long as you ensure that all connections are well insulated and that nothing is connected to the metal holder or the heatsink.



Mount the SMPS pcb within a short piece of pvc pipe screwed to the top of the heatsink. The other end of the pvc pipe carries a mains lamp base salvaged from a fused CFL. Connect up the wires paying attention to insulation and safety.

Switch on and you should be rewarded with a really bright beam.
# # #  Be careful not to look directly at the LEDs  # # #  as that could cause some amount of damage to your eyes. It is better to put the lamp in a diffuser shade unless you want to use it as a spot light.
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Warning:
If you want your lamp to be reliable in the long run, pay particular attention to heatsinking. A heatsink that might look and 'feel' adequate (remember the 'touch test' ?!) on the workbench might prove to overheat when the lamp is assembled into a holder-- if my experience is anything to go by! Use a substantial heatsink I did!) to keep the assembly really cool and drill adequate ventilation holes in the holder assembly. Usually the LED current would rise with rising temperature, but the constant current driver does offer some insurance here.
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Another alternative that a friend tried out was to mount the LEDs onto a 1-foot length of aluminium channel used by fabricators of doors/windows etc. Drill small holes to fit the lens of the LEDs in a suitable strip of transparent plastic. Mount the LEDs smeared with heatsink compound onto the alu channel with a few screws that 'sandwiches' the LEDs between it and the plastic strip. The SMPS pcb, insulated well in a tube of plastic,  maybe slipped into the square tubular alu channel and the LM317 too may be mounted onto the channel. Mount two plastic end-caps (drilled for ventilation) on both ends of the channel and also screw on a piece of diffuser material in front, and you have a good, bright short "tube light" of sorts!

Naturally your imagination and ingenuity are the only limits when it comes to shapes and mounting options. Always be careful about safe wiring practices, the need for insulating connections etc, especially when working with high mains voltages. And don't forget to 'rate' your heatsink adequately with the "touch test" before using the lamp for any length of time.

Happy 'spot lighting' !!

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PHILIPS REDUX - 3

'TOP-OF-THE-LINE' 40 WATTER

Again, here is another popular design with higher power output. Do note the protection circuits that have been incorporated; they worked very well indeed, as many would gladly attest. Quite a few of us had found that with an unregulated power supply and good components and a large, heavy heatsink, this design could take some beating! The circuit works very well without the protection circuit too, and for the experienced and careful constructor, the design has many merits even toay, I guess. If one doesn't want to 'brag' about the 'watts', this power amp could provide you with a solid foundation for your home-built system. Naturally quality of build and "setting up" the power amp are key factors in its sonic quality and reliability. For the younger brigade accustomed to "plug and play" with IC-based designs, setting up a quirky, high power amp would be something like a tight-rope walk, the art of which, once mastered, becomes easy and even enjoyable!

I am sure this foray into the past shall serve as the trigger for many new explorations, especially of a mature kind in search of true fidelity.

Happy DIY-ing !!

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PHILIPS REDUX - 2

15 W & 20 W  POWER  AMPLIFIERS

Back in those days, what separated the 'men' from the 'boys' was the output of their power amps; boys played about in the area below 10 Watts, and there was a 'grey' area between 10 and 20 Watts. The 'real' men occupied the upper echelons of 20 Watts and above. It was an expensive game when for umpteen reasons your power amp could 'teleport' itself into other worlds in a cloud of smoke, and to boot, take your precious speakers too along! And power transistors, especially matched pairs, were not exactly cheap and they surely did not grow on trees!

The 'flip side' of this power game was that in the melee, scant attention was often paid to the sonic merits of the designs. Considered from that angle, here are a couple of truly 'hi-Q' (a Philips trademark) power amps. If you have efficient speakers that do not need a connection to the nearest power house, these are wonderful options even today. I have found that the 15 W version is particularly suited to driving undemanding open-baffle speakers, and, be warned, the combination could sure sound addictive!

Perhaps what works the magic could in part be the circuit topology of these 'vintage' power amps.

Many of us could easily recall the mad race after fully complementary/fully symmetric designs. The designs looked particularly 'sexy' on paper with their picture-perfect symmetry and, of course, when well-designed, they did sound great too. But our obsession with such designs made us forget many of the golden nuggets from the past. Only recently have designers and enthusiasts like Wim de Haan and others done their bit to restore the quasi-complementary output stage as being 'sonically superior' to many other designs.

As a matter of fact the quasi-complementary design evolved out of manufacturing compulsions. It was easier in those days to fabricate high power N-P-N transistors. Fully complementary pairs were confined to the low power levels, and often used as drivers for the output devices. Now it is well documented by many designers in the field that there are subtle differences between the P-N-P / N-P-N transistors and as a result there are audible differences that mark the N-P-N pairs as being superior and "more musical" output devices. Whatever that might be, here is an opportunity for you to test that theory out with good quasi-complementary designs as these. Surely you will not be disappointed with the results!

A PHILIPS REDUX

In these days of sequels and re-makes, it should be no surprise to come upon another visit to the nostalgic past! Here is a collection of data from the yesteryears from the Philips stable. I have posted these in response to steady demand from a lot of fellow DIY-ers and hobbyists, not only in the senior league, but surprisingly from the younger set too. It seems that the youth brigade are none too happy about the "plug-in simplicity" of IC-based designs, especially when it comes to "getting your hands wet" with making a PCB, wiring it up, and finally, after a bit of tense trouble-shooting, arriving at the moment of sweet audition, which, I must say is its own reward.

I would like to stress the fact that the copyright on the material presented rests with M/s Philips and the data is only provided expressly for the benefit of hobbyists and for not-for-profit applications. Philips data sheets and application books are acknowledged fully as being the source of the material.

Philips was a 'household name' with music and hi-fi enthusiasts long before the field of hi-fi was 'hijacked' by the 'high-end' peopled by companies with exotic names. Revolutionary technologies like Motional Feedback Loudspeakers were introduced by Philips and I intend to touch this topic later from the angle of servicing/restoration of these epochal designs. Most of the designs of Philips were of truly high quality and often reflected the state-of-the-art, and were highly "user-friendly". Those who are sufficiently "long in the tooth" will recall many happy hours spent with Philips data sheets planning the next project. It is pleasantly surprising that many of these designs can more than hold a candle to the "cutting-edge" designs of today. Surely this is going to open the floodgates of nostalgia for many and I am sure many constructors, young and old, will once again experience those old thrills!

THE UNIVERSAL PRE-AMP

Here is that perennial 'hot' favourite, the 'universal' pre-amplifier. If somebody had been keeping count, this ought easily have got into the Guinness Book of Records for the sheer number of units constructed by hobbyists and DIYers. As for the many commercial designs that based themselves on this 'pilot design', again, there is no count. Those who begin to think that this is a 'dated design' should do well to remind themselves that circuitry very similar to this was inside the many pro and semi-pro equipment that served duty in the recording chains of yesteryears at least for a while. Carefully built on good quality glass-epoxy PCBs with selected components, they often rewarded the builder with absolutely enviable performance.

Welcome to the first step in this nostalgic trip!