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• Dual Tracking ±50V Power Supply (April 1990; siliconchip.com.au/ Article/7258) • Dual Tracking ±18.5V Power Supply (January 1988; siliconchip.com.au/ Article/7828) the Jaycar Cat SY4080 (3A rated) and SY4084 (40A rated). These would need to be wired up and housed in an Earthed metal enclosure and wired according to the Australian wiring standards for mains equipment. Reducing switch wear from arcing Direct Injection Box query I have a computer (Apple Mac), a printer (Brother) and several other small items plugged into a powerboard fitted with a switch. After I have finished using the computer, I shut it down, wait until all the screen displays have switched off, then turn all the power off via the switch on the powerboard. Occasionally, there is a ‘blat’ sound that comes from the switch. I assume that this is a spark. I have had to replace the switch several times over the years, as the contact points in the switch have become stuck or welded together. Is there any way to reduce or eliminate this sparking? (G. H., via email) • One method to reduce switch contact wear due to arcing is to place an X2-rated 10nF 250V AC capacitor across the switch contacts (eg, Jaycar Cat RG5230). This will reduce the transient voltage across the switch contacts as they open. Adding the capacitor leaves a residual current flow that bypasses the open switch (around 8mA). Higher value capacitors can be used, and might suppress the sparking more effectively, but with a higher residual current. Another method is to switch the mains supply using an electronic switch such as a Triac. There are electronic relays that do this, such as Some years back, you presented an active direct injection box for guitars to plug into a PA system. The design included a low-cost transformer from Altronics or Jaycar and a JFET front end powered via the audio mixer phantom power supply. We built several of these for our local church and need to make more. While you can buy a commercial unit for around $100, I recall that these DI boxes were very cost-effective; certainly a lot less than $100. I can’t remember whether it was EA or Silicon Chip magazine. The DI boxes we constructed have proven to be very robust and deliver excellent sound quality. Can you advise when that project was published? (N. A., Canberra, ACT) • The DI Box design you are after is probably the one from Electronics Australia, February 1998 (97di12: “Direct Injection [active] Preamp using a JFET” ). You can order a scan of that article via www.siliconchip.com. au/Shop/15 Alternatively, Silicon Chip has published passive and active DI Boxes. Our passive version (October 2014; siliconchip.com.au/Article/8034) uses a high-quality transformer from Altronics, while the Active DI Box (August 2001; siliconchip.com.au/ Article/4158) does not use a transformer. SC Advertising Index Altronics...............................83-86 Ampec Technologies................. 49 Analog Devices........................... 7 Control Devices Australia............ 9 Dave Thompson...................... 111 Digi-Key Electronics.................... 3 Emona Instruments................. IBC Hare & Forbes............................. 5 Jaycar............................ IFC,53-60 Keith Rippon Kit Assembly...... 111 LD Electronics......................... 111 LEDsales................................. 111 Microchip Technology...... 13, OBC Ocean Controls........................... 6 SC Colour Maximite 2............... 75 Silicon Chip Binders............... 111 Silicon Chip Shop.............. 87, 98 Silicon Chip SiDRADIO............ 19 Switchmode Power Supplies..... 12 The Loudspeaker Kit.com......... 10 Tronixlabs................................ 111 Vintage Radio Repairs............ 111 Wagner Electronics................... 47 Weller Soldering Iron................. 11 Notes & Errata High-Current Battery Balancer, March 2021: in the parts list on p27, several Mosfets (Q11,Q12…) are listed as “S6M4” types. The correct type code is QS6M4. Arduino-based Adjustable Power Supply, February 2021: while the specified SY4030 relay from Jaycar is rated to carry 1A, it only has a 500mA switch rating. The similar S4100 relay from Altronics specifies a 1A switching current. Power supplies built using the Jaycar part should set the current limit no higher than 500mA to avoid damage to the relay. Other similar relays are available with a 1A contact rating; it appears that this refers to the carry current only, and not the switching current, so check the data sheet if substituting a different part. LED Party Strobe Mk2, August 2015: the link at lower-left should be positioned as shown in the photo on p87, not the overlay diagram (Fig.2) on p86, which incorrectly has it shown in the “MAX” position. The May 2021 issue is due on sale in newsagents by Thursday, April 29th. Expect postal delivery of subscription copies in Australia between April 27th and May 12th. 112 Silicon Chip Australia’s electronics magazine siliconchip.com.au