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microcontroller in the VU/Peak Meter with LCD Bargraphs (May 2007 issue; siliconchip.au/Article/2232). Lapel Mic Adaptor SNR & PCB query I am curious about the signal-tonoise ratio for the Lapel Mic Adaptor described in the January 2004 issue (siliconchip.au/Article/3330). Sadly, you do not have the PCB in your inventory, but I understand you can’t have everything in stock. (P. S., Mount Pleasant, SA) ● The signal-to-noise ratio (SNR) was not measured for the published specification as it depends on the noise from the electret lapel microphone itself. That information can be found in the electret microphone manufacturer data. We expect the circuitry to provide an SNR of at least 100dB with respect to 1V RMS output. When tested at the time it was published, the noise was not audible and was better or at least comparable to a Advertising Index Altronics.................................29-32 Dave Thompson........................ 111 Digi-Key Electronics...................... 3 Emona Instruments.................. IBC Jaycar........................ IFC, 9, 11, 13, ............................. 23, 43, 71, 91, 95 Keith Rippon Kit Assembly....... 111 Lazer Security........................... 111 LD Electronics........................... 111 LEDsales................................... 111 Microchip Technology.............OBC Mouser Electronics....................... 4 good-quality commercial radio microphone system. The SNR could be improved to as much as 114dB with respect to 1V output by using an NE5532 op amp instead of the TL072. We could add this PCB to our Online Shop if you want to order some. There are two versions of the PCB. If you are interested, please tell us which one you want and how many and we can estimate the cost. In most cases, as long as we have the artwork on file and the rights to it, we can get PCBs made for pre-2010 projects. We already stock PCBs for pretty much all post-2010 projects (it is now available SC6627). Variac won’t filter generator output I have a 2.5kW petrol generator that I use to power an older refrigerator, lights etc if there is a blackout. I don’t use it for computers, TVs and other electronic appliances as I suspect these might be damaged by voltage spikes and harmonics from the generator. Is there a straightforward way to filter the generator’s output to enable it to be used with electronic items? I thought of using a 2kW variac since it is basically a large inductor with resistance, but I need some advice on whether this will work and be safe. On another subject, I recall reading Jim Rowe’s articles in Electronics Australia many years ago describing how he built a home computer. This was long before IBM developed the PC architecture, so components such as memory, communication systems, software, processors etc couldn’t be bought off the shelf. If I remember correctly, he was the first person in the world to complete a working home computer, or was narrowly beaten by an American. It might interest readers to hear Jim’s recollections of his achievement and the challenges he faced. (I. P., Fullarton, SA) ● The autotransformer probably will provide little filtering, especially at its full voltage setting. A commercially-­ available line filter will remove some of the RF hash, and a surge-­protected power board can reduce voltage spikes. Concerning the computer, it was just about the first published home constructor article for a computer but was beaten by a month. The computer was called the EDUC-8, and a scan of its 80-page manual is still available to purchase at siliconchip.au/ Shop/3/1816 Help with a power supply kit from AEM I assembled a power supply from a kit many years ago. As I was an Electronics Australia subscriber at the time, I assume it was one of theirs. The only information I have on it is that it is labelled “VERSATILE LAB SUPPLY” and “AEM2521” on the front panel. It is a 30V supply with an ammeter and an inbuilt crowbar circuit inbuilt. I have no idea where I purchased the kit. Do you have any information on this supply? (O. A., Boort, Vic) ● The AEM2521 is from Australian Electronics Monthly magazine. Unfortunately, we do not own the rights to that magazine, so we cannot provide copies of articles. The National Library or your state library would have a copy; the main challenge is figuring out the month of publication; we suspect that the project was published in the July & August 1988 issues. As far as we know, Dick Smith Electronics sold the kit for the AEM2521 supply. SC Oatley Electronics..................... 111 Silicon Chip 500W Amplifier..... 12 Silicon Chip PDFs on USB......... 94 Silicon Chip Shop.................60-61 Silicon Chip Subscriptions........ 42 Silicon Chip VGA PicoMite...... 109 The Loudspeaker Kit.com.......... 93 Tronixlabs.................................. 111 Wagner Electronics....................... 7 112 Silicon Chip Errata and Next Issue SC GPS Analog Clock............... 107 Bass Block subwoofer, January 2021: the specified Altronics C3055 driver is no longer available. The SB Acoustics SB16PFCR25-8 is a suitable substitute available from Wagner Electronics for $46.50 at the time of writing. See the February 2023 Ask Silicon Chip column for advice on tweaking the design to suit this new woofer. High-Performance Active Subwoofer, December 2022: in the parts list, two 3.7-4mm crimp eye terminals are required, not one, and the 377 × 140 × 1.5mm aluminium sheet listed is slightly too small. It needs to be at least 377 × 150mm. Next Issue: the March 2022 issue is due on sale in newsagents by Monday, February 27th. Expect postal delivery of subscription copies in Australia between February 24th and March 15th. Australia's electronics magazine siliconchip.com.au