Fullscreen HTML5Med Res (??MB)HTML4

Advertising Index Altronics.................................43-46 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 PMD Way................................... 103 SC Micromite Explore-40......... 103 SC Ideal Bridge Rectifiers........... 42 Silicon Chip Binders................ 103 Silicon Chip PDFs on USB......... 23 Silicon Chip Kits........................ 37 Silicon Chip Shop.................88-89 Silicon Chip Subscriptions........ 73 Silicon Chip Test Tweezers......... 8 Another test I repeated was to use a fresh, ‘out of the packet’ 100μH choke (actually 110μH) and a 1000pF (1070pF in my case) polystyrene capacitor. Assuming an accurate measurement of the reference capacitor, the software calculated the actual inductor value to about 0.2%. Other factors make the overall measurement accuracy worse. We suggest anyone who has built the kit and can’t reprogram the chip emails Silicon Chip to organise for it to be swapped or reprogrammed. SC200 amplifier questions I have powered up the SC200 Amplifier module I built (January-March 2017; siliconchip.au/Series/308) and measured a 1.2mV output voltage with no input signal. Is that OK? The emitter resistor voltage drops are 0.4mV and 0.47mV. Could you please advise if it is OK to have such a difference between the voltages across the emitter resistors? Nevertheless, I decided to test the amplifier and I did not see sinewave distortion at the output. Then I checked the sound quality, and it was OK as well, with a low supply voltage (about ±20V) and at low volume. I started building the second channel; it will be interesting to see the difference in measurements there. I will test the amplifiers at full power later. I found a possible problem in a footprint on the PCB. Transistor Q19 in the clipping detector seems to be reversed to me. If follow the footprint on the top of the PCB, the emitter is connected to the 100kW resistor and the collector to -56V. (Y. A., Kellyville, NSW) ● 1.2mV is more than an acceptable output offset voltage. Anything less than 20mV is acceptable, but the lower it is, the better. Many amplifiers have an output offset voltage exceeding 10mV unless they are designed for PA use, since output transformers have a low primary impedance and thus demand a low offset. It is normal to have slightly different voltages across the emitter resistors. That’s part of the reason they are there, to help balance out differences in the transistors. No two transistors will be exactly the same, even from the same batch. Your readings under 1mV are quite low and suggest that VR1 (the bias adjustment trimpot) is fully anti-­ clockwise or close to it. You will get slightly better sound quality if you turn the bias up until you see a few millivolts across the emitter resistors. Just make sure they don’t go too high as the transistors warm up. The suggested target is 4.4mV. We don’t see a Q19 in the circuit; we think you mean Q16. Pin 2 is the emitter, and it connects to the -56V rail. Pin 3 (the one by itself) is the collector, and it connects to the resistor. Its pinout is the same as the BC846C shown on the main circuit diagram. So we believe it is wired up correctly on the PCB (the clipping indicator on our prototype passed all testing). Query on RIAA and valve preamps Next Issue: the November 2026 issue is due on sale in newsagents by Monday, October 26th. Expect postal delivery of subscription copies in Australia between October 23rd and November 11th. I am thinking of adding some ‘colour’ to the sound of my transistor-­ based amplifier. I will need a lot of preamplifier gain and RIAA compensation to handle the output from my Shure V15 MkII. Have you published such a project? What about a standalone valve preamp? (J. K., Freshwater, NSW) ● Our latest standalone RIAA preamplifier project was in the August 2006 issue (“Build A Magnetic Cartridge Preamplifier”; siliconchip.au/ Article/2740). It is suitable for use with a valve preamp. The gain is adjustable between 1× and 11×. We have also published a couple of valve preamplifiers: • January & February 2016: Valve Stereo Preamplifier For HiFi Systems (siliconchip.au/Series/295) • November 2003 & February 2004: A 12AX7 Valve Audio Preamplifier SC (siliconchip.au/Series/293) Australia's electronics magazine siliconchip.com.au The Loudspeaker Kit.com.......... 10 Wagner Electronics..................... 87 Errata and on-sale date for the next issue Simple USB Power Monitor, June 2026: the original firmware had a bug that caused it to incorrectly display values with a zero to the left of the decimal point. Updated firmware is now available for download that fixes this error, and all kits and pre-programmed chips we sell have been updated as of 12/08/2026. Simple LC Meter, May 2026: the original firmware had a bug that caused it to assume the onboard inductor L1 had a value of exactly 100μH. That could result in inaccuracy if the inductor’s actual value differs significantly from nominal. Updated firmware is now available for download that fixes this error, and all kits and pre-programmed chips we sell have been updated as of 10/08/2026. 104 Silicon Chip