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Letters and emails should contain complete name, address and daytime phone number. Letters to the Editor are submitted on the condition that Silicon Chip Publications Pty Ltd may edit and has the right to reproduce in electronic form and communicate these letters. This also applies to submissions to "Ask SILICON CHIP" and "Circuit Notebook".

Sceptical of merits of extreme low distortion

I have just read the Publishers Letter on the quest for ultra-low distortion in the July 2011 edition of SILICON CHIP.

While I can understand the thrill of the technical chase in getting the distortion down, I wonder at the practicality of .0006% distortion. Would I actually hear the difference or would I need an anechoic chamber and the latest distortion measuring doo-hicky to know what the distortion is?

While you may think that iPods offer mediocre performance, I and millions of others think that they are great.

Peter Williamson,
Wollongong, NSW.

Comment: .0006% total harmonic distortion is extremely low but we have little doubt that if we set up “double-blind” listening tests, most people would be able to detect the subtle differences between our Ultra-LD Mk.3 amplifier and other amplifiers with lesser performance (provided their ears had not been damaged by listening at high levels to MP3 players).

It is very significant that our Class-A amplifier has such a well-deserved reputation for very clean sound. Our latest Ultra-LD Mk.3 design is very close to the Class-A’s performance but has the big advantage of delivering a lot more power.

As to your comment about iPods “being great” we can only say “compared to what?” The fact is that “millions of others” simply don’t know any better.

CD-ROM drives can make powerful motors

With respect to the question raised by B. L. on CD-ROM drive motors (Ask SILICON CHIP, July 2011, page 98) the following may be of interest.

The conversion of CD motors by rewinding them and most importantly by fitting “super” NdFeB (neodymium iron boron) magnets was pioneered by German enthusiasts and has long since become world-wide. They are capable of powering worthwhile models.

The brushless motors used in model aircraft are amazing. Their power-to-weight ratios are better than their IC equivalents in many cases and they can be monsters; the biggest I know of is 15kW and weighs less than 2kg.

CD motors are a good source of small motor stators; larger ones can utilise armature laminations from a dead motor such as an electric drill.

The controllers are readily available from model aircraft shops but kits and DIY data is scarce. The only one I know of was in the February 2006 issue of Elektor magazine.

To obtain information on magnets for motors, just Google “supermagnetman” and select “motor magnets”.

Arthur Davies,
Ainslie, ACT.

First-hand experience with converting CD-ROM motors

I have just read the response in Ask SILICON CHIP in the July 2011 about converting an old CD-ROM motor for model aeroplane use as well as circuits for brushless controllers. The answer is not correct and the whole area is an accepted modeller’s DIY discipline and covered reasonably well on the web (though you have to know where to look for such articles).

The fact is one can make a very powerful brushless motor on a par with or even more powerful than what can be sourced commercially. The answer to the question also talks about brushless motor controllers and is quite negative, however there are several excellent and relatively simple designs using readily available “analog” electronic components (as well as PICAXE-type stuff) on the web for those interested.

As an avid aero-modeller and experimenter, I have made dozens of these motors from dead CD-ROM drives sourced through my computer repair company. These motors are absolutely brilliant and very usable. In fact, some of the commercial motors purchased from Chinese manufacturers have the exact same chassis as a CD-ROM motor-based unit, proving their suitability for the job.

For the avid DIY modeller, there is no need to invest in expensive motors and brushless controllers when they are easily built using everyday parts. The only hard-to-source part needed, and even then these are not that difficult to find with many people on the web selling them (including me if I am asked), are the required neodymium rare-earth magnets (reasonably cheap at about $7.00 per dozen and 12 are required per motor).

All one has to do is source the right-sized motor (about 40% of CD and DVD drives use them), carefully disassemble it and remove the existing graphite magnet ring, add the rare-earth magnets (straight or curved), strip and rewind the stator with heavier-gauge wire and connect it to a controller, self-made or commercial. Add a LiPO battery and away it goes, ready to mount in a model.

Dave Thompson,
PC Anytime Ltd,
Christchurch, NZ.

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