[Project] Sync Generator modification

Forum DIY
21

I haven’t done more tests with the mods, but as stated in my previous post, main issue is the logic being powered by +5V on Cadet Sync Gen and the 27MHz VCXO being +3.3V only. So maybe using a logic level converter to go from +5V at the output of the PLL to +3.3V to feed the lag/lead filter just before the VC input of the VCXO could work, there will surely be a bit of propagation delay, though might be negligible enough.

Else, most logic chips have a Vcc/2 input threshold (here 2.5V) , so in most cases, a +5V powered logic chip can accept a +3.3V signal at its input fine. The only critical part here is the VCXO VC, that needs to be +3.3V, since it expects a linearly changing signal, so it requires to be in the right range for the genlock feature to work as it should.

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22

All - I just found this. A little dated, but it has a schematic for a PLL and VCXO that might be useful. And it runs at +5V !!! Are you guys aware?

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23

As was mentioned previously, it would be cool if the HC4046 oscillator could be used directly, without the need for a crystal at all. But as someone noted, the stability might be an issue. Anyone tried it yet?

24

Is anyone still thinking about taking this further? I have only 1 cadet sync generator but 2 RGB encoders. The plan always had been to have a second sync generator but they sold out before I got around to it

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