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Ultra-LD amplifier has low sensitivity I have at last completed building a stereo Ultra-LD ampli­ fier with loudspeaker protection, as featured in SILICON CHIP, in March, May and August 2000. It is cool-running, silent and has crystal-clear sound. I’m very pleased with the result, thank you. I measured 114W on each channel into a 7Ω resistor. However, I have the distinct impression from listening that none of my audio sources can drive each amplifier to 100W at 0dB. For example, music played from ABC’s Classic FM station is set at -5dB for general background listening. A CD of Richard Strauss’s “Thus Spake Zarathustra” is a good test of dynamic range. Yes, the sound was loud but not overly so. Commercially recorded tapes produced a similar sound in­tensity. The sound level achieved is adequate for all my purposes and I lose its 5V supply output and the PIC resets itself. Try a power source which can deliver more current than the one you are using. Alternatively, try changing the 7805 used for REG1 to an LM2940T-5 regulator. This has a lower dropout voltage and may solve the problem without changing the power source. The regulator is available from Dick Smith Electronics (Cat. Z-6600). Music effects box wanted I was wondering if you have ever published a kit for pro­ducing effects like echo, reverb, flanger, phaser, chorus effects etc, that can be used with line levels (CD output, mixer output). like the idea of having the volume control near 0dB. But I would also like the amplifier to be able to reach its full output should the need arise. I could install an op amp with a gain of 2 after the volume control with in/out switching but before I do that, would you kindly clarify your design decision on an input sensitivity of 1.8V for 0dB full output? (G. C., Palmwoods, Qld). • We originally set the sensitivity of the Ultra-LD amplifier at 1.8V to limit the possibility of overload on CDs. In typical situations, with pop, jazz and rock music, the sensitivity is generally more than adequate but it can be a little low on soft passages in classical and opera. The solution is to build the preamp featured in the later version of the Ultra-LD 100, in the Nov­­em­ber & December 2001 issues. This was revised in June & July 2002, to go with a remote motorised volume control. We can supply these issues for $8.80 each, including postage. I need this to plug in the mixer output and then control the line level output to the amplifier. Also, I was after a kit that does the reverse of a karaoke kit; ie, removes the music and leaves the vocals only. Have you ever produced a kit like this? (R. L., via email). • For a music effects box, have a look at the Digital Effects Processor published in the February 1995 issue of SILICON CHIP. As far as cancelling the music and leaving the vocal, that is not possible. You can have a look at the Vocal Canceller published in the April 1982 issue of “Electronics Australia”. That circuit effectively cancels the inphase components of the left and right channels to remove the centre vocal sound and leave a rather anaemic L-R signal. But you can’t do the opposite and end up with no vocal and the instruments unchanged. We can supply a photostat copy of the EA article and the SILICON CHIP magazine, for $8.80 each, including postage. Identifying a dead component I’m fixing a high power amplifier which may have been one of the Playmaster series. The output stage contains three 2SK133 and 2SJ48 Mosfets, if that’s any help. Anyway, there is a shorted component which I cannot identi­fy. It looks like a zener or signal diode (it has the clear & orange glass body) and is marked C19. Judging by its physical size, I would say it’s about a 1/2-watt device. I’ve tried looking in the Farnell and WES catalogs but nothing with C19 in the device part number seems to be listed. I can’t think of anybody better to ask than yourselves as to what this device may be. If it’s blatantly obvious please accept my apologies; I have never been any good at decoding semiconductor markings! (R. M., via email). • The failed component is almost certainly a zener diode, rated at around 12V. There would normally be two on the board and each connected in series with a 1N914. These would be used to limit gate drive to the Mosfets. We can’t place the amplifier but might be able to help further if you can identify the PC board code. Notes & Errata Printer Port Simulator, May 2003: the PC board code should be 07105031, SC not 04105031. 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 Trade Practices Act 1974 or as subsequently amended and to any governmental regulations which are applicable. 92  Silicon Chip www.siliconchip.com.au