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Advertising Index Altronics.................................41-44 Blackmagic Design....................... 7 Dave Thompson........................ 103 DigiKey Electronics..................OBC Emona Instruments.................. IBC Hare & Forbes............................... 9 Jaycar............................. IFC, 24-27 Keith Rippon Kit Assembly....... 103 LD Electronics........................... 103 LEDsales................................... 103 Microchip Technology.................. 5 Mouser Electronics....................... 3 PCBWay....................................... 11 PE Back Issues............................. 8 PMD Way................................... 103 SC Micromite Explore-40......... 103 Silicon Chip PDFs on USB......... 82 Silicon Chip Kits...................... 101 Silicon Chip Shop.................98-99 Silicon Chip Subscriptions........ 83 The Loudspeaker Kit.com.......... 89 Wagner Electronics..................... 10 cable and replacing it with a shorting plug (or not!) results in both speakers being dead quiet! Playing music loud to consign the hum well into the background and the stereo pair sounds just fantastic, better than my late-model Yamaha power amplifier. Has anyone else had the same problem? Have I missed an erratum? Any help would be appreciated as this is a superb amplifier, but I can’t stand the hum late at night when the volume is down. (J. D. S., Endeavour Hills, Vic) ● It sounds like there is an Earth hum loop. We suggest you try disconnecting one of the 10W resistors at the input of one of the circuit boards. The 10W resistor is intended to reduce any hum loop current, but it appears not to be sufficient in your case. You could use a 100W resistor instead, or just remove one. You should also check the power supply Earthing arrangement. Ensure you use a common point for all the power Earths and it should not be at the capacitor bank. Note: J.D.S. responded that disconnecting one of the 10W resistors from input to Earth completely eliminated the hum. Controlling many relays using two wires I am a long-term subscriber and have bought every issue. I think you do an amazing job. I am wondering if you can suggest or point me to a project or circuit for me. I’d like to control 32 LEDs or relays from 32 switches, on a oneto-one basis, but with only two wires between the loads and the switches. Visualise one box with 32 relays, another box with 32 switches about Errata and on-sale date for the next issue Simple USB Power Monitor, June 2026: the alternative regulator was specified as the MIC1973-330OT but it should have been MCP1793T-3302H/ OT. Many of the MIC5233-3.3YM5 regulators available from both DigiKey and Mouser around the time of publication appear to be faulty, producing no output. If you purchased a kit and the regulator doesn’t work, contact us and we’ll send you a replacement MCP1793T-3302H/OT regulator (no such problems have been reported with those). USB-C Power Monitor, September 2025 (part two): the caption at the bottom of p79 states “A row of header pins can be fitted to CON5…”. It should refer to CON3 instead. Next Issue: the October 2026 issue is due on sale in newsagents by Monday, September 28th. Expect postal delivery of subscription copies in Australia between September 25th and October 14th. 104 Silicon Chip Australia's electronics magazine say 10m away, but only two wires between them. I’m imagining some kind of scanning of the switches, serialising the data in the ‘switch box’ and decoding and driving at the other end. Can you point me to anything suitable that may already exist, or do you have any ideas? Thank you. (C. B., Seacombe Heights, SA) ● The simplest way to do that would be to take our 10-Channel Remote Control Receiver from the June 2013 issue (siliconchip.au/Article/3811) and remove the infrared receiver. A twinwire cable can connect to its pads 1 and 2 instead. A device like an Arduino can send RC5-encoded signals over those two wires to switch any of the ten attached loads on and off. Multiple Remote Control Receivers can be connected to the same pair of wires and set to use different RC5 encodings. While this would involve developing some Arduino software to sense switch inputs and send the required on/off codes, that should be pretty simple. Sensing switch closures is done easily by adding pull-up resistors (or enabling pull-up currents) and then checking the digital input state. There are many infrared encoding libraries available; while they are intended to drive IR LEDs, the signals are the same, so they should do the job. A board like the Arduino Mega2560 would likely be required to get enough inputs for 32 switches. Replacement transformer for EA amp A while ago I built the Electronics Australia High Quality Audio Amp Module (88ma12, January 1989). The transformer has failed and I can’t find suitable E-core transformers anymore. Can I use a toroidal transformer? I have seen a 160VA 25-0-25V 3.2A toroidal transformer. Will this be too much for the 50/80W amplifier? (W. O., Miller, NSW) ● The 160VA 25-0-25 transformer would be a good match for the amplifier. The amplifier will only draw the power it requires, so provided that the supply voltages are correct for the amplifier module (which they will be in this case), there’s nothing wrong with using a transformer with a higher power or current rating. It won’t cause the amplifier to draw SC any more power. siliconchip.com.au