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Notes & Errata Pocket TENS Unit for Pain Relief, January 2006: the IR2155 IC used in this project is now obsolete and difficult to obtain. According to International Rectifier, the IRS2153DPBF is the recommended replacement (see https://ec.irf.com/v6/en/ US/adirect/ir?cmd=catProduct Detail&productID=IR2155). Ask SILICON CHIP . . . continued from page 103 and 30 turns for the primary I figure the output should be close to 10kV. Now given that the minimum number of turns for the secondary with 10kV output is 160 turns, it may be possible to get away with fewer than 500 turns. I was thinking of say 320 for the secondary and 18 for the primary; this should lower the impedance and take less time to wind. Besides, I have plenty of 0.8mm diameter wire and this is the most I can get on to the former unless I go to 0.6mm. My questions are as follows: (1) If I lower the number of turns, will it shorten the pulse length or affect the output voltage? (2) Could it possibly overload the transformer? (3) Is it better to stick to 500 turns or possibly more? (D. D., via email). • The turns ratio of the output pulse transformer was wound to comply with the Australian Standards AS3129. It states that the energy produced by an electric fence is limited to a maximum of five Joules into a 500-ohm load. Open-circuit load voltage is restricted to 10kV (ie, >1MΩ load in parallel with 100pF). The turns ratio does not necessarily set the voltage that will be delivered to a 500Ω load. The output depends on the pulse width, the impedance of the transformer and the inductance of the windings. If you use fewer turns on the transformer primary, the transformer may deliver less energy (fewer Joules) to the output. With an unknown core, you will have to experiment with the number of turns and the turns ratio. The output must ultimately comply with AS3129 for safety’s sake. Champion for a guitar practice amplifier I was wondering if the Champion (January 2013) and the Champ (February 1994) amplifiers would be compatible with an electric guitar in their kit form, as sold at Jaycar and Altronics. I am interested in building a simple guitar practice amplifier and both are stocked by stores near me. (O. M., via email.) • The Champion from January 2013 would be quite suitable. This has sufficient output power for good volume through efficient loudspeakers and the input sensitivity should be sufficient for a guitar without needing the preChampion that is incorporated on the Champion PCB. We don’t recommend the Champ from February 1994 for a guitar practice amplifier as the input impedance is too low and output power is insufSC ficient. Next Issue The August 2016 issue is due on sale in newsagents by Thursday 28th July. Expect postal delivery of subscription copies in Australia between July 28th and August 10th. Advertising Index Allan Warren Electronics............ 103 Altronics.................................. 72-75 Australian Exhibitions & Events.... 31 Digi-Key Electronics....................... 3 DSCAPE.................................... 103 Emona Instruments.................... IBC Front Panel Express..................... 15 Hare & Forbes.......................... OBC Jaycar .............................. IFC,49-56 Keith Rippon Kit Assembly ........ 103 LD Electronics............................ 103 LEDsales.................................... 103 Master Instruments.................... 103 Microchip Technology................... 11 Minitech Engineering..................... 9 Mouser Electronics......................... 5 Ocean Controls............................ 13 PCB Cart........................................ 7 Pinfold Health Services................ 43 Sesame Electronics................... 103 SC Radio & Hobbies DVD.......... 101 SC Online Shop...................... 25,91 Silicon Chip Binders................ 66,79 Silicon Chip Subscriptions........... 67 Silicon Chip Wallchart.................. 83 Silvertone Electronics.................. 15 Tronixlabs.............................. 45,103 WARNING! SILICON CHIP magazine regularly describes projects which employ a mains power supply or produce high voltage. All such projects should be considered dangerous or even lethal if not used safely. Readers are warned that high voltage wiring should be carried out according to the instructions in the articles. When working on these projects use extreme care to ensure that you do not accidentally come into contact with mains AC voltages or high voltage DC. If you are not confident about working with projects employing mains voltages or other high voltages, you are advised not to attempt work on them. Silicon Chip Publications Pty Ltd disclaims any liability for damages should anyone be killed or injured while working on a project or circuit described in any issue of SILICON CHIP magazine. Devices or circuits described in SILICON CHIP may be covered by patents. SILICON CHIP disclaims any liability for the infringement of such patents by the manufacturing or selling of any such equipment. SILICON CHIP also disclaims any liability for projects which are used in such a way as to infringe relevant government regulations and by-laws. Advertisers are warned that they are responsible for the content of all advertisements and that they must conform to the Competition & Consumer Act 2010 or as subsequently amended and to any governmental regulations which are applicable. 104  Silicon Chip siliconchip.com.au