XO controlled 480Hz Oscillator

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.

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.

You could use a parallel T (sometimes called twin T) filter with a high Q
to get the sine wave back.

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

On Feb 17, 8:08 pm, RFI-EMI-GUY<Rhyol...@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