Introduction

In this review of an older kit we examine the aptly-named “Mini Stereo Amplifier” from Dick Smith Electronics (catalogue number K5008), based on the article published in the October 1992 issue of Silicon Chip magazine.

The purpose of the kit is to offer a stereo 1W+1W RMS amplifier for use with portable audio devices that only used headphones, such as the typical portable tape players or newly available portable CD players. I feel old just writing that. At the time it would have been quite a useful kit, paired with some inexpensive speakers the end user would have a neat and portable sound solution. So let’s get started.

Assembly

Larger kits like this one that couldn’t be retailed on hanger cards shipped in corrugated cardboard boxes that were glued shut. They looked good but as soon as a sneaky customer tore one open “to have a look” it was ruined and hard to sell:

The amplifier kit was from the time when DSE still cared about kits, so you received the sixteen page “Guide to Kit Construction” plus the kit instructions, nasty red disclaimer sheet, feedback card, plus all the required components and the obligatory coil of solder that was usually rubbish:

However the completeness of the kit is outstanding, everything is included for completion including an enclosure and handy front panel sticker:

… all the sockets, plenty of jumper wire and even the rubber feet:

The PCB is from the old-school of design – without any silk-screening or solder mask:

However the instructions are quite clear so you can figure out the component placement easily. Which brings us to that point – all the components went in with ease:

… then it was a matter of wiring in the sockets, volume potentiometer and power switch:

Instead of using a 3.5mm phono socket for power input, I used a 9V battery snap instead. The amplifier can run on voltages down to 1.8V so it will do for the limited use I have in mind for the amplifier. However in the excitement of assembly I forgot the power switch:

However it wasn’t any effort to rectify that. You will also notice three links on the PCB, which I fitted instead of making coils (more on this later). So at that point the soldering work is finished:

Now to drill out the holes on the faceplate. Instead of tapering out the slots on the side of the housing, I just drilled all the holes on the front panel:

Turns out the adhesive on the front panel sticker had lost its mojo, so I might head off and get some white-on-black tape for the label maker. However in the meanwhile we have one finished mini stereo amplifier, which reminds me of an old grade seven electronics project:

How it works

The amplifier is based on the STMicro TDA2822M (data sheet .pdf) dual low-voltage amplifier IC. In fact the circuit is a slight modification of the stereo example in the data sheet. As mentioned earlier, the benefit of this IC is that it can operate on voltates down to 1.8V, however to reach the maximum power output of 1W per channel into 8Ω loads you need a 9V supply. The output will drop to around 300 mW at 6V.

Finally the Silicon Chip design calls for a triplet of coils, one each on the stereo input wires – used to prevent the RF signal being “shunted away” from the amplifier inputs. The idea behind that was some portable radios used the headphones as an antenna, however we’ll use it with the audio out from a mobile phone so it was easier to skip hand-winding the coils and just put links in the PCB.

Using the Amplifier

The purpose of this kit was to have some sound while working in the garage, so I’ve fitted a pair of cheap 1W 8Ω speakers each to a length of wire and a 3.5mm plug as shown in the image above. And for that purpose, it works very well. In hindsight it turns out the speakers were rated at 1W peak not RMS, however they still sound great.

Conclusion

Another kit review over. This is a genuinely useful kit and a real shame you can’t buy one today. And again – to those who have been asking me privately, no I don’t have a secret line to some underground warehouse of old kits – just keep an eye out on ebay as they pop up now and again. Full-sized images and much more information about the kit are available on flickr.

And while you’re here – are you interested in Arduino? Check out my new book “Arduino Workshop” from No Starch Press.

In the meanwhile have fun and keep checking into tronixstuff.com. Why not follow things on twitter, Google+, subscribe  for email updates or RSS using the links on the right-hand column? And join our friendly Google Group – dedicated to the projects and related items on this website. Sign up – it’s free, helpful to each other –  and we can all learn something.

The post Old Kit Review – Silicon Chip Mini Stereo Amplifier appeared first on tronixstuff.

Introduction

In this review of an older kit (circa 1993~1997) we examine the Diesel Sound Simulator for Model Railroads kit from (the now defunct) Dick Smith Electronics, based on the article published in the December 1992 issue of Silicon Chip magazine.

The purpose of this kit is to give you a small circuit which can fit in a HO scale (or larger) locomotive, or hidden underneath the layout – that can emulate the rumbling of a diesel-electric locomotive to increase the realism of a train. However the kit is designed for use with a PWM train controller (also devised by Silicon Chip!) so not for the simple direct-DC drive layouts.

Assembly

The diesel sound kit was from the time when DSE still cared about kits, so you received the sixteen page “Guide to Kit Construction” plus the kit instructions, nasty red disclaimer sheet, feedback card, plus all the required components and the obligatory coil of solder that was usually rubbish:

Everything required to get going is included, except IC sockets. My theory is it’s cheaper to use your own sockets than source older CMOS/TTL later on if you want to reuse the ICs, so sockets are now mandatory here:

The PCB is from the old school of “figure-it-out-yourself”, no fancy silk-screening here:

Notice the five horizontal pads between the two ICs – these were for wire bridges in case you needed to break the PCB in two to fit inside your locomotive.

Actual assembly was straight-forward, all the components went in without any issues. Having two links under IC2 was a little annoying, however a short while later the PCB was finished and the speaker attached:

How it works

As mentioned earlier this diesel sound kit was designed for use with the Silicon Chip train PWM controller, so the design is a little different than expected. It can handle a voltage of around 20 V, and the sound is determined by the speed of the locomotive.

The speed is determined by the back EMF measured from the motor – and (from the manual) this is the voltage produced by the motor which opposes the current flow through it and this voltage is directly proportional to speed.

Not having a 20V DC PWM supply laying about I knocked up an Arduino to PWM a 20V DC supply via an N-MOSFET module and experimented with the duty cycle to see what sort of noises could be possible. The output was affected somewhat by the supply voltage, however seemed a little higher in pitch than expected.

You can listen to the results in the following video:

I reckon the sound from around the twenty second mark isn’t a bad idle noise, however in general not that great. The results will ultimately be a function of a lower duty-cycle than I could create at the time and the values of R1 and R2 used in the kit.

 Conclusion

Another kit review over. With some time spent experimenting you could generate the required diesel sounds, a Paxman-Valenta it isn’t… but it was a fun kit and I’m sure it was well-received at the time. To those who have been asking me privately, no I don’t have a secret line to some underground warehouse of old kits – just keep an eye out on ebay and they pop up now and again. Full-sized images and much more information about the kit are available on flickr.

And while you’re here – are you interested in Arduino? Check out my new book “Arduino Workshop” from No Starch Press.

In the meanwhile have fun and keep checking into tronixstuff.com. Why not follow things on twitter, Google+, subscribe  for email updates or RSS using the links on the right-hand column? And join our friendly Google Group – dedicated to the projects and related items on this website. Sign up – it’s free, helpful to each other –  and we can all learn something.

The post Old Kit Review – Diesel Sound Simulator for Model Railroads appeared first on tronixstuff.