Skype can have a costly drawback

I’d like to make a comment regarding Skype, as mentioned in your VoIP article in the September 2005 issue.

As a long-time professional and audiophile, I have been bemused by the apparent acceptance of P2P (peer-to-peer) technology. I have also been amused (constantly) by the number of friends and acquaintances who get into never-ending trouble by their unthinking use of such technologies. Spam, spyware, malware, call it what you like, if there’s one sure way of opening up your computer to anyone at all, it’s by installing P2P applications.

Having said that, I was keen to become involved with VoIP some months ago. I installed Skype and have been using it for many months.

Now for the bad bit. As I’m connected via Optusnet cable broadband, I’ve always had a good quality firewall solution installed. A few weeks ago, I started noticing a fairly significant increase in my usage but thought nothing of it until my Optusnet "unlimited" account usage went into speed limitation (22kB per second throughput). After checking my data with network analysers, verifying firewall settings and so on, I found that Skype had been going berserk in terms of IP port usage and data throughput. Since the start of October, I’ve logged over 2GB throughput in three days.

After some head-scratching and in-depth discussion with my networking mate, we "discovered" that my system, as part of the Skype P2P network, is currently hosting more than 300 individual concurrent Skype conversations. The peak so far is 621 conversations, the average per 24-hour period is 180 conversations.

The Skype official response to my enquiry is "well, that’s what a peer-to-peer network does!". I forgot that this is the same mob that wrote Kazaa.

Since I have no option of redress and since Skype (and I have now learned, all other VoIP P2P applications) have no plans for allowing a sucker – sorry, user – like myself to limit the number of Skype hosting sessions on my machine, I have no option but to remove Skype and lose all the benefits of such an application. I know, I know, it’s P2P and I should expect some pain with the gain. But not a 700MB per day penalty. After all, I’m paying more for other people’s conversations than I ever use!

I thought you might like to be aware of the pitfalls of VoIP and that your less network-savvy readers might benefit from understanding the limitations of this "free" technology.

There are VoIP tools available that work just fine if you know the other party’s IP address and with most ISPs providing good DHCP leases for always-on systems like mine, this might be a viable and useful alternative. Perhaps you guys could investigate this side of VoIP in a future article.

Peter Naus,
Mitcham, Vic.

Valve amplifiers not as good as solid-state

While reading your August issue I could not contain myself any more. Are valve amplifiers better than solid-state amplifiers? In my opinion, no. Was the development work of solid-state power amplifiers, by such eminent design engineers as H. C. Lin, Dr A. R. Bailey, P. J. Baxandall, M. J. Otala, W. G. Jung and J. L. Linsley Hood all in vain? The term "High Fidelity" (not hifi) meant what it said: "reproduction as true to the original sound as possible".

My first power amplifiers were valve and had output powers of 8-10W RMS. The benchmark then was the 15W valve design by D. T. N. Williamson, 1947. In all valve designs, the quality of the output transformer was the main component in achieving this benchmark. Speaker systems were usually 15W in large boxes and as efficient as possible. This current valve design doesn’t meet the Williamson benchmark, although no-doubt a fine amplifier.

I made a number of early semiconductor amplifiers with transformer-coupled germanium power transistors, none of which performed as well as my DIY valve amplifier. Then in April 1969, J. Linsley Hood (JLH) published his 10W class-A amplifier in Wireless World. After building and testing this amplifier, I found it to be superior to my valve and semiconductor units. This amplifier had only four transistors per channel!

To this day, there is still an internet site just devoted to the JLH Class-A amplifier, with improvements, testimonials and updates. www.tcaas.btinternet.co.uk/index.htm

Exponents of valve amplifiers use such emotive (non-technical) terms as warmth, sweet, soft on the ear, etc and are really referring to the lack of uneven harmonics (mainly 3rd) and introduced inductive/capacitive effects and thermionic noise from the valves.

Having lived and worked in London, I used to go to concerts in the Royal Festival and the Queen Elizabeth II Halls. The acoustics in these halls and the Sydney Opera House are superb. This was a great way to hear a musical standard that is difficult reproduce.

A home reproduction system would have to reproduce these concerts with their dynamic and transient range as near as possible. A modern well-designed semiconductor amplifier will add very little colour (if any) in reproducing sound from recordings. I can not say that of valve amplifiers. Also, the mutual conductance of the valves drops in time due to cathode depletion or they become gaseous and some produce microphonic noise or clicks and pops, etc.

Is a 1955 Silver Cloud Rolls Royce as good as a 2005 Holden or Ford? Take them up a country road for a test run. While the modern cars do better, one still has to admire the Rolls as a thing of beauty.

Chris Baker,
Dungog, NSW.

Games port solution for PowerUp

I have read the feedback on your USB PowerUP project (SILICON CHIP, November 2004), regarding modern motherboards which have the USB ports permanently powered. However, every modern motherboard I have checked does not leave the 5V on the 15-pin joystick connector when it is powered down. I have used this source of power on three PCs at home, to switch the screens, printers, speakers, etc off.

I solder male and female DB15 sockets back to back, then a short length of figure-8 wire to the +5V and ground pins, the other end of which I solder to a female PS2 line socket (available from Jaycar). The figure-8 wire is wrapped around the DB15 pins a couple of times so they cannot be broken off, then electrician’s tape wrapped around it a few times, with the wire coming out at one side.

The arrangement works well and leaves the joystick port available for use if required. The arrangement could be applied to the PowerUp project.

John Bagster,
Hamilton, Qld.

Valve amplifiers like old Harleys

First of all, congratulations on a first-class publication. You have proved your versatility once again by "biting the bullet" and publishing the valve amplifier project in August and September. This amplifier certainly is innovative with its output configuration and the large monetary saving on output transformers which will make it desirable in many hobbyists’ eyes.

While valve amplifiers may or may not be everybody’s cup of tea and some may even consider it a waste of time, many still like valve sound, similar to many people liking old Fords, Holdens or Harleys. They may be technically inferior to the high speed, economical modern equivalent but the unmistakable sound of an old V8 sedan or V-twin motor-cycle is very pleasing to the ear for some.

The same can be said for valve amplifiers.

Greg Johnson,
Cooma, NSW.

Power supply capacitors still a problem

Back in May 2003, you featured an article regarding Taiwan-made motherboard capacitors. This situation has still not gotten any better. We still see computer motherboards on a daily basis afflicted with this problem; always under two years, if the system is always on. While a few manufacturers have switched to Japanese-sourced
capacitors, most are just trying different brands of Taiwanese-made units to see whether the problem will go away.

Well, I haven’t yet seen a Taiwanese low-ESR capacitor that won’t fail in under two years in an "always on" system. What is worrying is that these capacitors are now finding their way into other items.

A friend of mine recently had two very expensive switchmode power supplies blow up right at the 2-year mark. The problem: bulging, leaking Taiwanese-made capacitors. My gigabit network switch just blew up too, again caused by the same capacitor issue. When the capacitors failed, the 12V switchmode supply also failed, taking out the network ports on a couple of motherboards

Apart from being out of warranty, the companies won’t even talk to you if you mention that dirty capacitor word. How long before these things get into our expensive fridges, washing machines, vacuum cleaners, cars and airplanes?

Ross Peacock,
via email.

Adaptive cruise control can be uneconomic

I read with interest the article on Adaptive Cruise Control Systems in the September 2005 issue. In a "Moffat’s Madhouse" article in the now-defunct "Electronics Australia", Tom Moffat saw adaptive cruise control as an example of technology wasting energy.

He quoted his experience of driving an ageing Volvo between two points in USA and attaining a fuel consumption nearly twice that of 100% driver control, by allowing the Volvo’s speed control to maintain a constant speed for the journey.

He compared this with the "latest technology" adaptive cruise control which accelerates and decelerates the car to follow the driving pattern of the car ahead. Naturally, if the car ahead is being driven in an uneconomic way, the adaptive cruise control will duplicate this driving practice.

Greg Mayman,
Dover Gardens, SA.

Comment: there is little doubt that if a car with ACC is driven behind a car which keeps fluctuating in speed, then it will not be as fuel-efficient as it otherwise would be. The only way around this would be for the driver with ACC to pass.

Fairly obviously, some cruise controls are much better than others when it comes to saving fuel and most recent designs would be far superior to that in an old Volvo.

For example, a recent long trip in a current model Honda Accord V6 with cruise control returned figures of around 7.2l/100km (at constant 110km/h and with aircon) – that’s close to 40mpg. It is difficult to see how driver control could improve on this result.

The correct way to wire a 240VAC socket

I read with interest the letter in the September 2005 Mailbag from Ray Smith about 240VAC plug and socket wiring. To my knowledge, this is the only way to wire them as I was taught this in my Electronics Engineering apprenticeship in the early 1980s at the South Brisbane College of TAFE.

From memory, it was illegal to wire the plug and socket wrongly as it caused undue strain on the connections and could possibly cause the wiring to come loose. I also believe the teaching was that if the outer sheath was removed by wire cutters or a knife and if the inner wire sheaths were nicked and this wasn’t noticed, it was possible for the leads to come together and short out.

Mr Smith has made a valid point and I see some electrical contractors committing the error all the time.

Colin Leonelli,
via email.

Lead acid battery zapper caution

I read with interest Jim Rowe’s article on the Lead Acid Battery Zapper. It is certainly an interesting project and the article has an excellent description as to how the lead sulphide crystals reduce the life of the battery.

One comment I have is that at the end of the article, Jim very sensibly advised that a choke should be used to protect a battery charger if used in conjunction with the Zapper.

I suggest an even bigger warning should have been added advising that under no circumstances should the Zapper be used on a battery installed in a vehicle, especially one with a computer system. That nice big spike could play havoc with the automotive electronics and probably void the vehicle warranty!

John Parncutt,
Glen Iris, Vic.

Studio 350 Power Amplifier Is A Beauty I thought you might be interested in some pictures of a project a young bloke I know is working on. It is a computer with two Studio 350 power amplifier modules shoe-horned in! This forms the heart of a jukebox which he is building himself. He has done the donkey work of fitting the components into the case. I helped build and test the amplifiers and did the mains wiring and power supply wiring. These pictures are of the "working prototype", as there is still a lot of tidying up of the wiring yet to do and the fitting of various bits and pieces. The biggest concern with the whole concept was whether the amplifier and the computer would have a "happy marriage" together in the one box. Many of his peers, myself as well, said that there quite possibly might be too much noise induced into the amplifier from the motherboard. He was dogmatic that it had to be this way to fit into the jukebox. Well we had the big test and we were all amazed! After the amplifier was tested and adjusted outside the case, we fitted it, powered up and turned on the computer. We were expecting all sorts of noises but apart from a couple of small clicks from the sound card, the amplifier remained silent! So much so that we wondered if it was still working until the jukebox software kicked in. We almost blew the cones out of the speakers! The Studio 350 is an awesome amplifier and we commend SILICON CHIP and those involved with producing such a brilliant design. We were all very impressed! Dave Vieritz, via email.