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Advertising Index Ask SILICON CHIP . . . continued from p109 and connected in series. However, the Hearing Loop Receiver is generally used upright and so there is no need for an alternative orientation inductor for pick-up from the horizontal loop. Using the SoftStarter in the USA Can the SoftStarter be used in the USA with 125VAC mains? (H. E., via email). • We are not sure sure whether you are referring to the SoftStarter for devices like computers, in the April 2012 issue or the SoftStarter for power tools, in the July 2012 issue. In both cases the circuits should work with 125VAC mains but it will be necessary to double the size of the 330nF supply capacitor, to ensure that the relay operates properly. Headphone socket for a Fender guitar amplifier I recently purchased a 15W Fender guitar amplifier and now want to fit a headphone jack to it. Can I disconnect the speaker wires completely and fit a resistor in series with the headphone wiring and drive the headphones that way or do I have to use some type of resistor-capacitor network? Any suggestions would be much appreciated. (C. D., via email). • The first question which must be asked is “Is it a valve amplifier?” If so, then you must always have a resistor to substitute for the loudspeaker resistance. For example, if the loudspeaker is 15Ω or 16Ω, you can probably get away 112  Silicon Chip DOWNLOAD OUR CATALOG at www.iinet.net.au/~worcom WORLDWIDE ELECTRONIC COMPONENTS PO Box 631, Hillarys, WA 6923 Ph: (08) 9307 7305 Fax: (08) 9307 7309 Email: worcom<at>iinet.net.au with a 22Ω 5W wirewound resistor. Then you need a series resistor to the headphones to reduce the volume level. A 1kΩ 1W resistor should be suitable for 32Ω headphones. The left and right headphones can be wired in parallel. If the amplifier is solid state, then you can dispense with the need for the SC 22Ω 5W dummy load resistor. Notes & Errata Induction-Motor Speed Controller, May 2012: a number of changes must be made to the original PCB to ensure reliable operation. These changes are described on page 80 of this issue. In addition, one of the holes is incorrectly positioned on the heatsink drilling diagram. A corrected drilling diagram is shown on page 83. Barking Dog Blaster (September 2012): the 10Ω resistor shown on the overlay and PCB screen print to the right of the S2 start switch terminals should be a 100Ω resistor to match the parts list and circuit. High-Power Class-D Audio Amplifier (November 2012): the two 3/8-inch x 20mm-long machine screws listed in the parts list (to secure the heatsink to the PCB) should be 3/16-inch x 20mm. ADM Instrument Engineering......... 5 Altronics.................................. 76-79 Apex Tool Group........................... 17 Circuit Labs Ltd.............................. 9 Cleverscope................................. 89 element14.......................... insert,63 Emona Instruments...................... 65 Gooligum Electronics................... 88 Grantronics................................. 111 Harbuch Electronics................... 107 Hare & Forbes.......................... OBC HK Wentworth.............................. 21 IMP Printed Circuits..................... 42 Instant PCBs.............................. 111 Jaycar .............................. IFC,53-60 Jimojo........................................... 88 Keith Rippon............................... 111 Kitstop.......................................... 88 LED Sales.................................. 111 Linkwell.......................................... 9 Mastercut..................................... 22 Matrix Multimedia........................... 8 Microchip Technology................... 35 Mikroelektronika......................... IBC Mektronics.................................... 23 Mouser Electronics......................... 3 Oatley Electronics........................ 89 Ocean Controls.......................... 103 Ozcommfile.................................. 89 Prime Electronics......................... 20 Quest Electronics....................... 111 Radio, TV & Hobbies DVD.......... 109 RF Modules................................ 112 Sesame Electronics................... 111 Silicon Chip Binders............ 102,111 Silicon Chip Bookshop............... 110 Silicon Chip Order Form............. 105 Silicon Chip Partshop................. 104 Silicon Chip Subscriptions........... 87 Siomar Battery Engineering....... 111 Splat Controls............................. 111 Tekmark Australia......................... 88 Telelink......................................... 89 Tenrod Pty Ltd.............................. 43 Trio Smartcal.................................. 4 Truscotts Electronic World.......... 111 Upton Australia............................. 19 Wiltronics..................................... 6,7 Worldwide Elect. Components... 112 siliconchip.com.au