Support for valve preamp

Congratulations on the valve preamp project in the November 2003 issue! You have succinctly summed up the appeal of this project - for "people wanting to satisfy their curiosity about valve circuits".

The fact that valve amplifiers do not have the performance and cost advantages of solid-state does not mean that such projects have no value. If electronics is to flourish, the importance of projects that stimulate curiosity and provide educational value cannot be underestimated. The value of such projects is not measured in terms of technical performance.

One aspect of SILICON CHIP's success is the technical excellence of the projects. However, SILICON CHIP would not be harmed in the slightest if it continued to include the occasional project that is designed from a different perspective. This can only broaden the appeal of an already excellent magazine.

Sometimes, the most fun to be had in electronics is simply satisfying one's curiosity - the project doesn't have to be a world-beater! To draw an analogy, people (including young people) still take joyrides on steam trains and Tiger Moths - just to see what they're like. Judging by the smiles on the faces of these people, none seem disappointed with the fact that it's not the latest in transportation technology. Why should electronics be any different?

It would be great to see more of these types of projects. It would enrich rather than diminish SILICON CHIP and help to keep the interest in electronics alive!

Older DVD players won't play some new DVDs

I'm writing this in reply to a letter in the November issue regarding an issue of older DVD players being unable to read new DVDs.

I am an apprentice electronics technician working in Bendigo, Victoria. Just a few days after reading the letter about older DVD players being unable to read some new DVDs, I was confronted with such a unit on my bench. The fault description went something like this: "Plays older DVDs fine but not new ones".

I had it on my bench for a few hours testing different DVDs and it played without a hitch and just before I gave it back to the customer, I tried a few other DVDs which we don't normally test with.

With just one turn of the DVD the player decided it could not play the disc. It came up with a message "This type of disc cannot be played, please insert another disc". It wasn't that it had trouble reading it, it was just not supported by the player.

I tried another new disc I had on hand and the same thing occurred!

These two discs were the classic "The Great Escape" and "The Scarlet Pimpernel". Both discs were quite new and played fine on other newer DVD players. Region codes matched. It should have worked but it didn't. Anyway after this I thought of that letter in the recent issue of your magazine and it dawned on me that this was what I was encountering.

A quick phone call to the manufacturer concerned confirmed my suspicion. He told me that some older machines can't play some new discs due to the copyright method used on the disc and that there was nothing that could be done to the unit to make it play them.

By the way, this particular DVD player was part of a home theatre amplifier setup, so it would cost a fair bit to replace with a new one! When you buy a DVD player, you would expect to be able to play any suitable region coded disc but apparently not.

Logging your driving nightmare

A comment on the "Logging Your Every Driving Moment" article on the November 1003 issue: why stop at logging just a subset of parameters for a short duration? Why not add a differential GPS receiver and the ability to receive database updates from roadside transmittters?

With what would be, in effect, a map of the local area (and speed limits) onboard the vehicle, the GPS position and velocity would make it possible to record speeding violations, perhaps based on time-of-day or day-of-week, on every single street, road and expressway in the country, 24 hours a day. A stylish LCD could even display the car's accumulated fines, payable at the next renewal of rego!

No poor radar/laser operators standing in the hot sun for hours at a time. No speed camera photos to develop and print. Cities would not have to maintain thousands of parking meters and ticket machines - the car would always know when and where it was parked, and for how long, and record this information to determine periodic payments as well.

I have no doubt that I could throw together a rough prototype of such a nightmare system for well under one thousand dollars. What could a team of professional designers accomplish? With the economies of scale - imagine such a device fitted to every single automobile and truck in the nation - and the potential revenue to be collected, governments would do well to pay for the development and manufacturing costs and give the devices to the auto makers for installation.

With a bit more sophistication and complexity it might be possible, at the driver's discretion, to have a mode where the vehicle simply would not exceed the speed limit on any given road at any time. The driver could then concentrate on looking out the windows and not at the speedo. Couple this with a decent navigation system and the "big brother" implications become (slightly) more palatable.

I'll bet I will live to see such a system or something very much like it.

Beating Macrovision nuisance on an old TV

With DVD taking over in the video shops, we got a player. Our old TV has only an antenna input so the AV output from the DVD player has to pass through our VCR to be converted to RF. This is fine except that the Macrovision protection on the DVD makes it impossible to watch, as the picture fades, tears and pulsates.

So I built the SILICON CHIP "Dr Video" (April 2001) kit from Jaycar to stabilise the picture. It took an hour and 20 minutes to assemble, all the components were present and fitted perfectly and all the holes in the panels were in the right place. The stabiliser works perfectly. Thanks for a great circuit and a very professional and inexpensive kit. It is credit to SILICON CHIP and Jaycar.

Argument about feedback

I bought the November 2003 issue with the valve preamp and would like to comment. For starters, your feedback from the plate of the second triode back to the cathode of the first is in fact positive feedback, though once its on the cathode the effect on the plate of the first triode is then negative. I know this is a small thing but an application of non-inverted signal is always positive feedback and an application of inverted signal is negative feedback - or am I wrong?

I have been a musician for many more years than I have been into electronics and one thing I've learnt is that, in the creation of music, as opposed to its reproduction, the controlled use of harmonic distortion is very, very useful and a significant part of sound shaping. For this reason it might be that your first version of the valve preamp, with the addition of a logarithmic pot instead of the grid resistor on the second stage, is actually of more use than the second version for the simple reason that the harmonic distortion is greater even if the amplification factor isn't so great.

I have a mixer using 5534 and TLO op amps and if I want valves, I would put them between the instrument and the mixer where amplification needs to be controlled. This is important and their use is mainly for an injection of harmonic distortion and a kind of DC bias shaping. Even if I were going straight to an amplifier I would still need these qualities more than pure gain. So I think you guys should be a little more mindful of the end uses of musical equipment and not be so concerned about what your own conditions of excellence are.

Also while the inverter power supply is nifty, it's basically a non-starter for musicians who usually have 9V effects and anyway it's a lot easier just to use two small transformers, with the second backwards, to build the power supplies for preamp duties.

Please get the help of real musicians if more attempts are made at "musical" effects as up to now they have been mostly non-musical. In future, you will give your good selves much more credibility to "serious" musicians if you realise the vital importance of harmonic distortion.

These two waveforms show severe overload occuring in a push-pull valve guitar amplifier on a tone burst signal. This is far worse that would occur in a typical solid-state amplifier.