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Woofer Stopper has stopped I have assembled the Woofer Stopper kit and it worked fine for one day but it was accidentally left on overnight and hasn’t worked since. I have replaced every component except the ICs and I was hoping you could shed some light on what is wrong with it. I am getting 12V out of the tweeter terminal but it still doesn’t work. (D. F., Bradbury, NSW). • If you don’t have test equipment to verify that each stage is working then you will need to test the unit audibly. To do that, you must connect pin 1 of IC2 to pin 7 of IC1 (instead of pin 9) as described on page 29 of the article in the May 1993 issue. This makes the circuit capacitors to the Active and Neutral as filters plus tried different relays. Is my answer an opto-coupler plus Triac combination? I usually have no problems in assembly or trou­bleshooting kits but have no idea about inductive loads or RF noise on mains or DC. (D. D., Morley, WA). • The problem about switching any sort of incandescent lamp is that there are very large surge currents involved. These currents can be as much as 15 times the normal rated currents of the lamps and must be completely isolated from the relay board and the circuitry of the Southern Cross computer. It is also likely that the surge currents are causing momentary dips in the supply voltage to your computer and causing it to crash. The cure is to use a much better regulated power supply which will not be af­ fected by momentary drops in the mains voltage. We would not recommend connecting capacitors of the size you mention to the Active and Neutral lines. The Champ goes mobile I have built the “CHAMP” amplifier (SILICON CHIP, February 1994) and find it works exceptionally well with my mobile phone, driving a small 8Ω extension speaker. This set up has only been used as a bench test and I 92  Silicon Chip work at a frequency of 2kHz. You should not have 12V DC across the tweeter terminals. There should be 0V DC and about 10VAC (at 2kHz) present across the tweeter. You should also be able to measure about 6V DC between both sides of the tweeter and the 0V line. If the circuit fails these tests, check that +5V is present at the output of the 78L05 regulator and at pins 14 or 16 of the ICs. The output of each respective IC in the frequency divider should sit at somewhere between 0 and 5V DC. For example, pin 2 of IC5a should be at about +2.5V. Naturally, you should also carefully check the back of the PC board for bad or broken solder connections. would like your comments regarding the suitability of this idea for an in-car installation and hence a way of providing a clean regulated 12V supply. I also have a question for the Serviceman. I have been trying to locate a number of ICs for a Commander 48cm colour TV, model CHT-9102, for quite some time without success. I hope you can help. Without a circuit diagram I cannot be sure what these ICs do, however they are both located on the circuit board for chan­nel programming and frequency lock control. Any help would be appreciated. (B. G., Deception Bay, Qld). • There is no need to run your CHAMP from a regulated 12V supply as it will quite happily run up to +16V with an 8Ω load – see Fig.3 on page 47 of the February 1994 article. However, it would be a good idea to protect it from spikes and transients by connecting a 16V 1W zener diode across the supply rail, fed by a 10Ω 0.5W resistor from the 12V battery. We are unable to help you with circuit information for your TV set. You will need to approach the distributor direct. Using the voice recorder in loop mode I wish to use the ISD2590P voice recorder in continuous loop mode. Your data article in the February 1994 issue adequate­ly describes how this may be done. Is it possible to connect a higher quality microphone to the device? What additional circui­ try would be required if the device were to be connected to the line out level connection of, say, a CD or tape deck? I assume that the ISD2545 with its higher sampling rate would produce better output sound quality. Who supplies this range of devices in Australia? Your assistance in these matters would be much appreciated. Congratulations on a magazine of consistently high quality. (A. C., Woodford, NSW). • Since this device produces voice quality only, it is not really worth using a better microphone and this comment would still apply to the ISD2545. If you did want to use a dynamic microphone, you would omit the 2.2kΩ and 10kΩ resistors and the 10µF capacitor associated with the electret bias network. The microphone signal would then be fed in via the existing 0.22µF input capacitor to pin 17. If you want to connect a CD player or other line out source, you will need an attenuator to bring the signal down to a few millivolts. We suggest a 50:1 attenuator consisting of 47kΩ and 1kΩ resistors. The ISD range is distributed by R&D Electron­ics. Their phone number is (02) 638 0077. Notes & Errata 12-240VAC 200W Inverter; February 1994: Transistor Q16 on the circuit diagram (Fig.4) is incorrectly labelled as a BC338; it should be a BC328. In addition, the transistor marked Q12 near Q13 (Fig.4) should be designated Q14. On the overlay diagram (Fig.5), transistors Q13 and Q14 are transposed, while the .047µF capacitor near T2 should be a .0047µF capacitor to agree with the circuit. The parts list should also show a .0047µF MKT capacitor instead of a .047µF capacitor. Fast Charger for Nicad Batteries; May 1994: The circuit (Fig.2) shows a 680Ω current limiting resistor for LED 1. This should be changed to 470Ω to agree with the parts layout diagram (Fig.3). The parts list should also be SC altered.