NICAM Tuner:

Back in 1991, any commercial NICAM product was completely out of my price range. Inspired by the Arcam tuners available at the time, I decided that a DIY stand-alone tuner was the best approach.. In the long summer between leaving school and starting university, I produced this:

At the time, an uncle was working for Ferguson. Under development was a sound panel for an upmarket chassis, and I was given a spare pre-production board. Later, these boards became available in the small-ads of Television. Here's a picture of one, minus the heat sink and a few other components...

My problem was that I had no diagrams or documentation for the board. So it sat around until Television magazine ran a series of articles on NICAM. These included lots of details on how NICAM itself worked, and the series ended with a brief look at the this chipset. That was all the data I had, but it was better than nothing!

I spent a while studying the articles and the board and eventually managed to get some sound out of it! The board takes in the baseband signal, and drives loudspeakers via the on-board power-amps - it also deals with external sources, and even has a graphic equaliser. Most of these functions are controlled by the I2C bus (and hence useless to me), but I was able to identify the DAC, and sniff the output from that...

The next problem was the baseband signal. I was experimenting with an old tuner/IF panel from a VCR but the SAW filter was, quite reasonably, rolling off the 6.552Mhz NICAM carrier. While I was able to get a signal that proved the NICAM decoder was working, that was not good enough...

The Maplin NICAM kit was available by now, but even that was rather expensive. However, I noticed that the UHF tuner was available as a separate kit and was reasonably priced as well (around £40). That resulted in perfect NICAM operation from the lashed up decoder, but as most of the Ferguson panel wasn't required, I decided to 'modify' it slightly. A cut 'n' shut operation resulted in this:

It looks a bit crude, but it works well enough. It runs off a single 12 volt supply, accepts a baseband signal and outputs stereo sound via the 7-way connector (top-left)...

Quite a lot of electronics is required to interface this with the real world. A control system is required to enable the unit to be operated, and an interface board is required to provide NICAM/FM switching. Other functions include I/II channel switching (for bi-lingual broadcasts in theory, but never really used in practice), AV input selection, remote control, tuning, etc, etc...

Active view of the NICAM Tuner:

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Conclusion:

The unit was in use until I got $ky Digital. Even when I was able to buy a NICAM tv and VHS machine, I still preferred to use the tuner because I preferred the sound and picture quality (obviously, I'm extremely biased!). The Maplin tuner is a rather high quality device, and compares well to modern devices. It uses separate demodulators for sound and vision, which results in excellent performance. Indeed, it is possible to get good NICAM sound when the picture is almost unrecognisable...

I spent quite a lot of time working on the 'user-interface', and getting the details right, so that things like muting worked properly - quite unlike the Maplin kit, as I discovered when I met someone who'd built the whole kit. It makes the most horrible noises when you change channel!

I'll be installing it somewhere else soon, possibly in the workshop. Before that, I need to fix a couple of minor problems - when I moved from Surrey, I noticed that it suffered from a minor hum-bar. The mains voltage was obviously slightly lower here. I was trying to keep the regulator dissipation to a minimum as this unit sat underneath my Musical Fidelity A1, so I added series-resistors to take some of the heat from the regulators (a good technique when current demands are fairly constant). Shorting out the 1.2 ohm resistor makes the problem go away. I'm also planning to replace the 7812 with a low-drop-out version and replace the reservoir capacitors, which have had more-or-less continuous use since 1991.

Another minor problem is caused by the audio stages being powered from a single 12 volt supply. My S-VHS machine is able to generate enormously high signal levels with certain pre-recorded tapes which can cause clipping. The answer would be to generate a negative supply to power the op-amps and analogue switches from it. There's enough space on the board to allow that relatively easily. However, as that VHS machine is no longer connected to it, I suspect I'll never get around to it...

Finally:

Several people have emailed me asking for schematics, parts lists, assembly instructions, etc. Just to be clear, this is not intended to be a project!

The first-generation NICAM chipset, the Maplin UHF tuner kit, the remote control and SAA5012 decoder chipset, and M491 tuning microcontroller are all obsolete. Indeed, NICAM itself is nearly obsolete in this country thanks to the fast take-up of digital TV. Also, the CMOS logic used in the control board is not worth trying to copy - these days you could replace all 13 IC's with a single PIC!

It's possible that scans of the schematics might find their way onto the site at some point - currently they're somewhere in storage. But they would be for academic interest only - there are much better ways to do things these days...