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A second coil charges the discharge capacitor to a high voltage before triggering. It may be possible to fire the unit using the reluctor input from the magneto. However, we have not tried this. A suit­able capacitor for C3 should be 0.15µF. UHF remote control for car alarm In your August 1990 issue, you featured a transmitter which I bought from Dick Smith Electronics as a kit. I selected a code to work with my “commercial” car alarm. It works fine except that the range is a bit low (despite tweaking it on a spectrum analys­er). I haven’t seen the circuit for your 2-channel UHF transmit­ter (also avail from Dick Smith Electronics) but can you tell me: (1) Does it transmit on the same frequency? (2) Does it use the same encoder chip? (3) Does it have a greater range? (4) Will it therefore work (1-channel of course) with your old UHF remote control receiver kit? (O. W., via email). • The 2-channel transmitter transmits at 304MHz but does not use the same encoder. We expect that it has a similar range to the earlier design but cannot state whether it could be made to work with your car alarm. Enhancing the class-A amplifier I have a few questions regarding the 15 watt class-A ampli­fier project. I wish to provide extra inputs for CD, tuner, stereo VCR and tape in/ out sockets. The plan is to use gold RCA input sockets on the back panel. These would be selected via two Notes & Errata Low Distortion Audio Signal Generator, February & March 1999: on the circuit diagram on page 28 of the February issue, trimpot VR4 is incorrectly labelled as 100kΩ rather than 10kΩ. Also on the circuit there should be shown a 10kΩ resistor in between the 20kΩ resistor connecting to the 330µF capacitors at the output of IC1b and the pin 2 inverting input of IC4b. The PC board includes this resistor and this is shown on the overlay diagram, on page 63 of the March issue, as the third 10kΩ resis­tor below diode D2. The overlay diagram also has transposed the anode and cathodes (A & K) labelling for LED1 & LED2. The package outline orientation is correct. The polarity shown on the circuit is also correct. Electric Fence Controller, April 1999: the supply leads to the battery, as shown on the wiring diagram on page 28 (Fig.7) are reversed. In addition, the transformer bobbins for T1 & T2 may differ from those used in our prototype. The difference will be that the five rows of pins on each bobbin may be spaced wider than allowed for on rotary switches mounted toward the back of the case and con­trolled by an extension shaft to keep the wiring for the inputs as short as possible. If I take this approach are the performance figures likely to be degraded? All other construction details would be as per the article. One final question: was the rack the PC board. You can either bend the pins on the bobbin inward so that they will fit into the original holes or new holes can be drilled at the wider spacing. The larger bobbins mean that the transformers will be easier to wind and there will be more room to insert the ferrite cores. A revised PC board has been produced to provide for both bobbin types. Multi-Spark CDI, September 1997: transistor Q1 in the impulse tachometer circuit on page 30 should be labelled a BC327 and not BC337 as shown. LED Ammeter, January 1999: the circuit diagram on page 55 has an error. The 10µF capacitor associated with IC1a should have its negative electrode connected to pin 4. Capacitance Meter, February 1999: the wiring diagram on page 70 has a number of errors. The 100µF capacitor associated with D1 & D2 is unmarked and is shown with reverse polarity. Also VR3 & VR4 are swapped, although their values are the same. Bass Cube Subwoofer, April 1999: the rear panel should be screwed into place but not glued, although some sort of sealant should be used to avoid leaks. case used in the prototype a commercially available unit or was it built from scratch to incorporate the two heatsinks? (J. W., Five Dock, NSW). • Provided your input switching is well-shielded, it should not degrade the amplifier’s performance. Our case was an obsolete rack case to which we SC attached the heatsinks. WARNING! SILICON CHIP magazine regularly describes projects which employ a mains power supply or produce high voltage. All such projects should be considered dangerous or even lethal if not used safely. Readers are warned that high voltage wiring should be carried out according to the instructions in the articles. When working on these projects use extreme care to ensure that you do not accidentally come into contact with mains AC voltages or high voltage DC. If you are not confident about working with projects employing mains voltages or other high voltages, you are advised not to attempt work on them. Silicon Chip Publications Pty Ltd disclaims any liability for damages should anyone be killed or injured while working on a project or circuit described in any issue of SILICON CHIP magazine. Devices or circuits described in SILICON CHIP may be covered by patents. SILICON CHIP disclaims any liability for the infringement of such patents by the manufacturing or selling of any such equipment. SILICON CHIP also disclaims any liability for projects which are used in such a way as to infringe relevant government regulations and by-laws. Advertisers are warned that they are responsible for the content of all advertisements and that they must conform to the Trade Practices Act 1974 or as subsequently amended and to any governmental regulations which are applicable. MAY 1999  93