finally found the
clock that seems to be quite decent for my Philips CD350
btw, could anyone pls advice which transformator is better to choose as clock's PS? should it be toroidal obligatory and what should be the min VA (10 or 20 or even higher?)
Hi dtses,
That's a nice ocillator with 1ppm temperature compensated but
let's say we take it as face value the claim of 1ppm accuracy,you need a very
low noise power supply and the one on the pcb is well a standard one perhaps
better than a plain 3 pin regulator.Anyway you get what you pay for.
It's easy to calculate the VA (volt ampere or power in watts) needed for a transformer by using Ohm's law.You can check for a typical TXCO how much current it uses from the datasheet and the 74hc163 it would actually not be much.
So for illustration we use a figure of 100mA which is way in excess of the
true value.The input voltage needed by clock pcb as shown is from 7-20 volts
DC.For lowest noise pick a lower voltage,eg. 9V is commonly available.
(Assuming TXCO and 74hc163 are 5V rated.3V headroom for 3pin regulator.)
VA=current X voltage =100mA X 9V= 0.9VA ~ 1VA
Add some 10% or more for transformer losses and the common VA values
you will see in catalogues is from 2 ,3,4,5,6 etc. So closest will be 2VA.Even
a 3VA is no harm.Do not use one that is too big as the space available in the
cd player is limited.
PS as you can see it has a "frequency divider in 74hc163" ,if you are only using
16.934Mhz you tap from the stated take off solder pads and it is preferable to
cut the power trace to 74hc163 and reconnect from the output of TXCO removing one noise source in the 74hc163.(ie. not use the 74hc163).
If you don't feel confident about diy then use as is.
Singa.