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Running a 120V cassette recorder I have recently obtained a Sony 25W CD/radio cassette-corder from the US. My only problem is that it needs a 120VAC 7A power supply. I do though have a 115VAC 0.53A transformer that I can plug the Sony straight into but as you have already guessed, it is no substitute as the tape deck will run at a slower speed. I would like to know if there is a transformer that I can use in place of my existing one or can I pump up the current rating on it by building a circuit for it (if there is such a thing)? (C. R., Winston Hills, NSW). • It should be possible to power your Sony CD/cassette player from your 115VAC transformer without problems, in spite of the fact that our AC mains system is 50Hz instead of 60Hz. These days we would expect that most cassette decks would be run from an internal DC supply and thus are not locked to the frequency of the AC mains supply. Give it a try; you are unlikely to do any damage. On the other hand, if the cassette transport mechanism is lock­ ed to the mains frequency, then you could drive it with an inverter which delivers 60Hz. Unfortunately, we have not designed a project to deliver 110VAC at 60Hz although we did publish a 12V DC to 240VAC 40W inverter in February 1992. This was able to be modified to deliver 60Hz. K ALEX The UV People ETCH TANKS ● Bubble Etch ● Circulating LIGHT BOXES ● Portuvee 4 ● Portuvee 6 ● Dual Level TRIMMER ● Ideal PCB DRILL ● Toyo HiSpeed MATERIALS ● PC Board: Riston, Dynachem ● 3M Label/Panel Stock ● Dynamark: Metal, Plastic ✸ AUSTRALIA’S NO.1 STOCKIST ✸ to the ignition side of the circuit and, depending on the engine speed, vary the amount of advance. In your opinion would a kit of this nature be relatively easy to design and build? (S. B., Casino, NSW). • Such a project would really only be feasible if it contained a microprocessor which would have to be programmed with the characteristics you require. While it is feasible, we do not think we could justify the development cost in view of the rela­tively small number of readers who would want to make this radi­cal modification to their cars. Power amplifier failure For the past five years I have been using the Studio 200 preamplifier and power amplifier combination without any problems whatsoever. Recently, however, I combined the two with an active crossover network and proceeded to destroy the power transistors in both channels of the amplifier. Failure of these components was not instantaneous. There was a gradual degradation in the performance of the system over about a week before the amplifier failed completely, blowing the speaker protection fuses. During this period, I reversed the outputs from the crossover into the power amp on several occa­ sions while attempting to diagnose the problem. This may be the reason for both channels failing. I would appreciate any help you may be able to provide regarding possible reasons for my problem. (P. K., Picnic Point, NSW). • While we cannot be sure, it seems likely that the electronic crossover is the cause of the problem since the combination of the power amplifier and preamplifier had been reliable. In our experience, this preamp/power amplifier combination is very reliable and so we suggest that you have the electronic crossover checked for high frequency instability. If the electronic crossover is oscillating at a supersonic frequency it could cause the power amplifier stages to become very hot and ultimately, to fail. The clue in this is that you said the performance was degraded. Often, one of the symptoms of supersonic oscillation is that the sound does not seem quite right. We suggest you make sure that the electronic crossover is completely fault-free before using it with any system again. Notes & Errata Coolant Level Alarm, June 1994: the circuit on page 21 has an error in that the indicator lamp is connected to the decoupled +12V supply line; ie, after D2. It should go to the +12V line from the ignition switch, as shown correctly on the wiring dia­gram on page 22. K ALEX 40 Wallis Ave, East Ivanhoe 3079. Phone (03) 9497 3422, Fax (03) 9499 2381 TRANSFORMERS • TOROIDAL • CONVENTIONAL • POWER • OUTPUT • CURRENT • INVERTER • PLUGPACKS • CHOKES STOCK RANGE TOROIDALS BEST PRICES APPROVED TO AS 3108-1990 SPECIALS DESIGNED & MADE 15VA to 7.5kVA Tortech Pty Ltd 24/31 Wentworth St, Greenacre 2190 Phone (02) 642 6003 Fax (02) 642 6127 February 1995  93