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Drastic MeasureIt was suggested to me that the low-level ticking sound that plagues my Synsonic originates in the DC-to-DC converter where, according to the manual, Zener diode VR1 shuts down the converter when the -9V line exceeds 10 volts — that is, periodically!Since more filtering on -9V or the other supply voltages hadn’t helped much, I decided to do something drastic, and I honestly CAN’T recommend this to everyone -- especially knowing what I know now. I supplied +5V to the microprocessor and RAM from a 7805 connected to Vcc1, removing that load from the DC-to-DC converter. This resulted in the greatest reduction — but unfortunately not total elimination — of the ticking.
 I was criticized and my judgment questioned for doing this because it quote eliminates the isolation unquote. To which I respond: WHAT isolation? Ground is ground is ground and common on both sides of the transformer. Furthermore, the non-converted, raw DC Vcc1 that powers the DC-to-DC converter also powers the LM386 output amplifiers, so WHERE’S the isolation? Be that as it may, this bit of surgery, as I said, reduced the ticking but did not eliminate it. Adding power supply decoupling capacitors, which were noticeably absent, at each IC doesn't hurt, but doesn't help, either. The ticking is not caused by the DC-to-DC converter: It's caused by the microprocessor. If the uP Reset pin 7 is held low (ground) the ticking completely stops. Unfortunately, so do all uP controlled functions: the buttons, Record/Playback, the so-called Bass, and the LED indicators. The first three of those functions are of no concern to me because as I've said, I think the programming is atrocious and the Bass is miserable. Devising LED indicators is no big deal, but I'd still rather not disable the uP unless I absolutely have to. I am open to any reasonable suggestions. email rocking at softhome.net If nothing else, my drastic measure has freed the DC-to-DC converter from providing the milliAmps used by the uP and RAM. That can't be more than the maximum current rating of D26, the 1N914 diode I removed in the 5 volt line -- 75mA -- but that should be enough to power the D.I.Y. circuits I want to hang off +/-9V.
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