Mixed equalisation preamps have delicious sound

I read with interest the comments in the June 2005 issue of SILICON CHIP, about the phono preamp described back in July 2002, utilising passive equalisation. Having built that preamp circuit shortly after its publication, I can confirm the sort of sound, typical of full passive equalisation designs. Subjectively anyway, its overall distortion seemed quite acceptable and not excessive.

The equalisation may not have been absolutely accurate, however this is not necessarily a major condemnation, as many "high end" phono preamps are "biased", apparently deliberately, to give a specific sound, something regarded highly in some audio quarters!

I was somewhat bemused by SILICON CHIP advocating a conventional feedback circuit design approach. As a self-confessed audiophile and vinyl-phile, and having looked at phono preamp design in considerable detail and also having built quite a few different designs, my firm opinion is that conventional feedback designs, tend to sound dull and lifeless with poor transient response, although that approach admittedly, can produce potentially very low distortion and accurate equalisation.

My preferred approach is a combination of "active" low frequency and "passive" high frequency equalisation. Increasingly, on the internet and elsewhere, this sort of approach appears to be gaining popularity for its sonic and other merits. In recent times, I have built several phono preamps of different circuit design but using this general circuit approach of split active/passive equalisation and as a general rule, I find them not only
superb "specs-wise" but sonically, they are delicious sounding.

The best of both worlds? Yes, I think so.

Felix Scerri, VK4FUQ,
Ingham, Qld.

Comment: your comments about transient response are curious, given that, regardless of whether passive or active equalisation is used, an RIAA preamplifier is effectively a big low-pass filter or integrator (with a more or less constant -6dB/octave slope). In other words, the transient response is largely set by the RC time-constants and not by the circuit configuration.

If a phono preamp sounds dull and lifeless (or alternatively, bright and lively), that suggests that it has incorrect equalisation or maybe the input loading is not optimum for the particular magnetic cartridge.

We do not feel qualified to comment on preamps with "delicious sound".

Colour TV nostalgia enjoyable

I would just like to say how much I enjoyed reading the two-part article on the "Start of Colour TV in Australia" in the March and April 2005 issues of SILICON CHIP. This brought back lots of memories, especially the sections on the Philips and Kriesler sets.

At the time of startup of colour in Australia, I was working in the North Queensland distribution warehouse for Kriesler TV and Audio products which included the first colour chassis, the 59-1.

We would receive regular semi-trailer loads from the factory in Sydney and then they would be pre-sale tested before being despatched to retailers around North Queensland. We kept a large range of spares for these sets and regularly had to supply service shops around the district with parts that had failed under warranty, especially the BU126 transistor in the power supply and the BU108 line output, along with the triplers.

I recall that many parts for the first Kriesler and Philips sets were common and interchangeable. Thanks again for a great read.

Warren Ray,
Townsville, Qld.

DVD region codes I saw your reference to DVD region coding in the article on laptop PCs in the June issue. You can get rid of this annoyance by using a small program called DVD Region Free which is available from www.dvdidle.com Its costs are not that much in the overall scheme of things and if you want to play other zone disks, it is one way to do so permanently. This software allows you to play DVDs on your PC with no change to the drive’s region setting, bypassing the setting as it is set in the drive properties. It also allows you to burn disks "region free". As far as stand-alone DVD players are concerned, regional encoding is a thing of the past on many models. I will not buy a player unless it will play my disks which I legitimately purchased in or from the USA. Many of the music videos I have are simply not available here and hence a Zone 4 disk does not exist. The player must be also capable of playing a "slab of burnt toast" if I put one in. By this I mean as far as DVD, DVD-R, DVD+R, CD, Audio DVD, MP3, Kodak CD, etc, it must play all formats. Also, my price limit for a player is no more than $100. If it lasts two or three years and then dies, so be it. I’ll go and get another one. Having had problems with players before, I now take a disk that I’ve burnt, which I KNOW should play, to the store when I get a new player. I test it in the player to make sure it’ll play my burnt disks and then buy THAT player – even if it’s the display model! Hey – if it says on the box that it’ll play DVD-R, then it should do so without any sticking, stalling, etc. And a note on burning: burning DVDs at maximum speed is one way to get drink coasters on many stand-alone players. It’s similar to burning audio CDs over about 12 or 16 times. Over this speed, they play on your PC but on your portable they can skip and stick like there’s no tomorrow. Slow the burn speed down and they play OK on just about everything. The same goes for DVDs. 2x is the maximum at which I’ll burn a DVD. Check out the region-free software – it works like a treat! Brad Sheargold, Collaroy, NSW.

DVD region-free

In his review of laptops in the June 2005 edition, Ross Tester complains (rightly) about regional coding on DVDs and DVD drives. There are software packages available that get rid of this nonsense.

I use one called "DVD Region+CSS Free". Once it is running, my PC will play a DVD from any region. Very useful as I import – through Amazon (USA and UK) – DVDs that are just not available in Australia.

You can get details of this software from www.dvdidle.com. There is a 30-day trial version available and the paid version costs $39.95 US.

Nick Booth,
Epping, NSW.

Coolmaster cannot maintain a constant temperature

I think that there is a major problem with the Wine Cooler application of your Coolmaster project, featured in the June 2005 issue. As I understand it, the actual temperature that wine is stored at is not crucial but it is important that this temperature is constant. So how will the Coolmaster maintain, say, a temperature of 15°C when the outside ambient temperature is 10°C? It will not, as in its present form the Coolmaster is only suitable for maintaining a constant temperature when the ambient temperature is above the fridge temperature.

The answer would be to add a fan and a heater inside the fridge. This heater could be left on continuously or be switched on when the compressor is not running.

We have a product that would fit this application as it can control cooling and heating. See ZC0606 at:
http://www.oatleyelectronics.com/bcorner.html.

We also have a mechanical controller that would be suitable for the refrigerator application as its minimum setting is 4°C.

Branko Justic,
Oatley Electronics Pty Ltd,
Oatley, NSW.

Comment: it is true that the Coolmaster will not maintain a fridge’s internal temperature at 15°C or indeed, at any temperature above the room temperature. We assume that the same comment would apply to most commercial wine fridges. However, we do not think that is generally a problem with storing wine in most houses and a drop in room temperature to 10°C or lower is not likely to cause a degradation in the wine.

Photocopiers going to waste

I’d like to add to the comments from Todd Noyce in the June Mailbag concerning photocopiers. Earlier this year, I was at a computing and AV auction here in Brisbane. Among the lots on offer were a number of photocopiers, including one model that I had used through work when they were new about six years ago. When they came up, there were no bids and a number of them were passed in, not even attracting interest at $5 (it was quipped that there was probably this value of paper still in them). These machines had been "state of the art" and truly capable, and cost as much as a small Japanese motorcar when new.

Apart from the bulk of these machines, I seem to recall that one of the models offered had a gross weight, including collator and recirculating automatic document feeder, of about 70kg. But as our previous correspondent mentioned, they are a treasure trove of electronic and mechanical bits and pieces. Any one with an interest in tinkering would be in heaven with one of these to recycle. Of course, the machines were offered in running order so any purchaser would’ve soon got their money’s worth from them from their original function. It was a pity that I had neither the room at home for one, nor the room in my car to bring one home.

One prize that I came away with, and I hope that maybe a reader may be able to tell me more about it, is a Philips LBB 1149/00 8-channel audio mixer. It appears to be a professional level mixer but I have been unable to identify it specifically. I have tried some web searches and spoken directly with both Philips and Thompson, with no answers to date. I believe that the unit is less than 15 years old and is in, apparently, good condition.

Perhaps one of your readers may know something of the history and true performance of this mixer?

Campbell Sharp,
Yeronga, Qld.

Possible cure for STB electrical interference

Following Robert Parnell’s letter the July 2005 issue about impulse noise affecting set-top boxes, you might be interested in how I solved my electrical interference problems for my Digital STB.

The glitching on my reception was quite intolerable (every few seconds), so rather than go back to analog I sought a solution. I put a 1.8m earth stake in the ground and connected it to the antenna system signal ground, just before the distribution amplifier. It made a huge improvement and I have no quad-shield coax!

One possible explanation is that cleaning out the LF garbage in the coax braid has removed spikes that were sufficient in amplitude to drive the tuner front-end into non-linear overload.

Firstly, if there is any part of the VHF spectrum that you can filter, then do this. I fitted a -50dB VHF filter (Kingray DPO-UV diplexer) and this made a difference but I am lucky because all my stations are UHF only. The best general alternative is a triplexer that can be used to filter out all non-TV frequencies and any unused TV bands.

Electrical trade wholesalers such as Lawrence and Hanson, Middendorps, Active, etc sell 1.8m copper-plated earth stakes for about $20. I located mine in the wettest part of the garden, taking note of underground gas pipes, etc. The location was a shade-clothed fernery with a built-in mist-spray watering system and it also happened to be close to where the TV distribution amplifier is located. I also purchase 6m of some very heavy mains (green-yellow) insulated copper wire.

I soldered the wire and clamp that comes with the stake and soldered the other end to the shield/braid at a splitter just before the distribution amplifier. (Leave out the soldering bit if that is too hard but it does help reduce the earth path impedance).

This arrangement almost completely eliminated audio/video drop-outs, pixellation and "no signal" on my digital tuner.

I would not recommend to anyone to try using the mains earth for the antenna as this is "very dirty" and could make matters worse.

Those people with STBs that run extremely hot might also benefit from my clean earth idea as the problem is eliminated if you don’t have isolated TV outlets. Before I earthed my antenna it "measured" 2000V! This is fairly common but not usually dangerous and is caused by leaky TV sets. But it does cause tuner modules to run very hot.

Neil Hecker,
Morwell, Vic.

Comment: the earth stake sounds like it is worth a try. As a bonus, it would also give some lightning protection to the set-top box and TV.

Big energy shortages looming I wish to raise a few points about the infrastructure debate that currently has the politicians bubbling. There are a few simple points that there is data to support: (1) Our population has increased by millions since we last built an AC mains generating station in Australia. (2) In some states, 50Hz is regularly not maintained to "support capacity problems". (3) The number of mains-powered devices that are available has proliferated in the last 20 years. Witness the number of powerboards (6, 8 even 10-outlet that are sold. Try and rewire an old Victorian double brick house. Each room has only one power point and except for large rooms, only one light. Home-theatre systems, computers and home air-conditioning did not exist in the 1920s. Every year in Victoria, we have power shortages at peak times; eg, mid-winter and mid-summer. There is much finger-pointing but NO doing (that is visible). This goes for the water supply and other infrastructure. I have done some of the research and the data is unsettling at best. We do not have the generating capacity of a modern developed country and nor do we have fresh water or conservation of water programs adequate to support industrial growth nor the projected population growth of the Federal Government. Jason Walters, Melbourne, Vic.

RFID sensor makes a great cat door

Thank you for designing the RFID module featured in the June 2004 issue. I adapted its design to make a pet door which has now been in service for about nine months now. No longer do I have to put up with the smell of cat spray around the house and as a bonus, bandicoots can no longer get in the house and spread the cats’ food around the laundry.

I did modify it slightly with a bigger ID20 module to increase its range to 15cm and I adapted a commercially made electric cat door which relied on reed switches and a rather large magnet, attached to the cat. I mounted the sensor module in the plastic housing of the door and have the electronics in a wall box nearby. It fires the solenoid in the cat door to open it.

Lloyd Jury,
via email.

Photocopying cost to SILICON CHIP

With regard to the editorial in the June 2005 issue on the topic of photocopying, I would say that you are spot on with regard to the amount of photocopying of articles of various journals that goes on and I do sympathise.

There appears to be little understanding of the rules in this area and that includes myself. I hear different accounts from my colleagues regarding acceptable use such as "it’s OK to photocopy just one article" or "one chapter of a book is legally allowed". I have heard "10% of a book is legally allowed".

Maybe in your next editorial you could briefly describe your understanding of the limits to which training organisations can legally copy materials and when such use would be a copyright infringement. I’m sure in many cases the reason is simply ignorance or old information.

I have really enjoyed the Picaxe articles you have published recently. I find this a remarkable device and I’m planning to get a few experimenter kits as soon as Microzed gets itself back on its feet.

Richard Bailey,

Regency Institute of TAFE,
Regency Park, SA.

VU meter makes good ammeter

Because VU meters are very sensitive, it is easy to use them to measure current up to, say 5 amps. All you need is a suitable shunt.

Take a length of twisted pair from some Cat-5 cable, solder them together at one end and to the meter terminals at the other. To "fine tune" the shunt, use a suitable power supply, a variable load and a digital multimeter to do the calibration, then use a utility knife blade to "short" across the twisted pair by cutting through the insulation at various points until you get the required FSD and current reading on the multimeter. Finally, trim and resolder the two ends back together.

I was able to make a 5A meter using a 17cm length. How cheap is that?

Robert Paterson,
via email.

Open-wound jug elements not usable on DC

With reference to your shunt-regulating battery charger article in the June 2005 issue, mention was made of using the jug elements, as described, for heating water. Doing this is likely to result in short element life due to electrolysis and possibly even accelerated corrosion of the water tank.

Heating elements of open construction as used in electric jugs are only suitable for AC operation. This is why in areas where DC mains have been common (eg, the UK until the 1960s), sealed elements have been used. In fact, I recall a story where an electric jug of the open element type was used in Sydney’s CBD during the 1940s, when DC mains were used by some consumers. The result was that the boiled water had an unpleasant taste due to the "electroplating" taking place.

Note also that 12V coffee makers/immersion heaters use a sealed element for this reason. If a water heater dummy load is going to be used for this project, it would be better to use a parallel combination of the cheap 12V immersion heaters as sold by auto accessory and $2 shops. For a 24V system, series parallel combinations would be used.

John Hunter,
St Leonards, NSW.