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• Diode D3 was initially intended to be optional depending on application. The photograph was taken before the decision to keep it in-circuit in all cases. The unit was tested with D3 in circuit as well as out of circuit. Using the 4-channel remote I am helping out a team from Sailability (volunteers who help disabled people to sail) who have a buoy fitted with a beeper which is used to guide vision-impaired sailors around a marker. At this time they are using a 12V reversing beeper which they have to go to and switch on. As a result, it is operating for some time and the constant noise is upsetting some of the locals. We are assembling the Long-Range UHF 4-Channel Remote Con­ trol to solve the problem. But my question is, if another buoy was fitted with a receiver, could the transmitter be used to trigger the two buoys on independent coding or could channels A and B be used? (F. N., via email). • If you have the receivers in latched mode, you could have up to four for your application, with each receiver operating off one channel. Another solution for ignition breakdown I have just read response to the question entitled “Cross­fire Problem in Multi-Spark Ignition” on page 92 of the December 2002 edition. Rather than being crossfire, the problem is more likely to be that the Hall effect sensor is firing prior to the rotor button being lined up with the distributor cap. The vacuum advance will be causing the behaviour. If he removes the distributor cap, there will LM3876 amplifier module re-rated I was looking to build some of the LM3876 amplifier modules featured in the March 1994 issue for an active crossover system. I just want to confirm the performance measurements quoted in the original article. Does the amplifier really supply 55W into 4Ω? Looking at the data sheet for the LM3876 chip, I cannot see how this would be possible. If you look at page 9 on the data sheet it has a plot of output power vs. load resistance. This shows that for an RL of 5Ω, the output power would only be 15W. (B. H., via email). • We certainly measured 55W into 4-ohm loads when we presented the device in 1994 but we don’t be obvious spark marks on the leading or trailing edge of the rotor button. The solution is to remount the sensor back or forwards by about 10 degrees or play with the vacuum advance. (P. Y., via email). Reluctor problem with multi-spark CDI Having completed the Multi-Spark Capacitor Discharge Ignition (SILI­CON CHIP, September 1997), it appears the triggering from my reluctor distributor is not happening. What could be wrong? The distributor is fine and swapping the reluctor wires over to it does not help. When power is first applied there is a discharge into the coil, as I can hear it and see it with my timing light. On test­ing the inverter circuit to your recommendations, I can measure 300V between the case and the tab of have access to the original data handy. Looking at the current data on-line, it looks as though the chip has been re-specced to severely limit power for loads below 8Ω. In that case it will be better to use the higher-spec device LM3886. This is optimised to deliver more power into 4-ohm loads – up to 68W (typical). This was featured in a dual power amplifier module in February 1995. It uses the same basic circuit as that in March 1994 but the supply rails must be reduced to ±28V for operation with 4-ohm loads. In view of the supply/load limitations, you may want to consider using the SC480 module featured in the January & Febru­ary 2003 issues. These deliver quite a lot more power with typi­cal program signals. Mosfet Q6. (W. M., via email). The reluctor signal sensitivity can be altered by changing the 47kΩ resistor which connects from the cathode of ZD5 to the other 47kΩ resistor which connects to the base of transistor Q8. Use a 200kΩ trimpot first and adjust it until the ignition fires. Then replace the trimpot with a fixed value resistor SC of the same value. • Notes & Errata 50W Amplifier Module, March 1994: the LM3876 used in this design has been changed to severely limit its power output into 4-ohm loads. If you want to use a 4-ohm load, the solution is to use the LM3886 which can deliver over 60W. However the supply rails should be reduced to ±28V, as recommended in the article for the LM3876 when using 4-ohm loads. 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. www.siliconchip.com.au August 2003  97