XO controlled 480Hz Oscillator
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From: RFI-EMI-GUY on 23 Feb 2010 14:45 On 2/23/2010 1:30 PM, Chris wrote: > On Feb 17, 8:08 pm, RFI-EMI-GUY<Rhyol...(a)NETTALLY.COM> wrote: >> On 2/16/2010 11:46 AM, Chris wrote: >> >> >> >>> I finished the this part of the project. The design with the 3.9Mhz >>> crystal with a CD4060 works perfectly. My tape deck is running >>> again. However, there is a small 480Hz hum in the record/play audio >>> now. This is very slight hum, not noticeable when there is dialog. I >>> did not notice this when the unit was running from a tuning fork time >>> reference. However, the tuning fork itself was audible outside the >>> chassis, and maybe masking my ability to hear the hum through the >>> headphones. >> >>> There is a voltage divider resistor (1k) in series with the circuit. >>> This was in place because the tuning fork ran off of 12V and the >>> supply was 24V. My circuit is using a voltage regulator to drop the >>> voltage down to 12V. There is now about a 8V drop across the >>> resistor. If I remove the resistor, the hum gets much louder. If I >>> shunt the power with a 1000uF cap after the resistor the hum gets >>> louder. If I shunt before the resistor the hum drops into the Nyquist >>> noise when I monitoring through the preamp. It is still there, but >>> buried. Is there a better way to get rid of this hum/ripple? The cap >>> is rather big and not as effective as I would like. >> >>> Thanks, >>> Chris Maness >> >> Problem could be that when using a tuning fork oscillator, the signal >> was a sine wave. Now dealing with digital divider you have a square wave >> and what you are hearing are harmonics. Look up 'super filters' these >> are capacitor/pass transistor arrangement to effectively increase >> capacitance through gain of the transistor. >> >> -- >> Joe Leikhim K4SAT >> "The RFI-EMI-GUY"� >> >> "Use only Genuine Interocitor Parts" Tom Servo ;-P > > The output of this tuning fork was digital (square). > > Chris Are you grounding the new circuit to same (presumably digital) ground point as the original? -- Joe Leikhim K4SAT "The RFI-EMI-GUY"� "Use only Genuine Interocitor Parts" Tom Servo ;-P |