Castle sync in Gen3 system

Say I want to build a Gen3 system (TBC2, DWO3, DSG3, ESG3) and add Castle Clock VCO and Flip Flops / Shift Reg.

What is the best way to sync the Clock VCO to the Gen3 part of the system?

1 Like

Pulse outputs from DWO3 should suffice to prevent Castle VCO from scrolling. Experimenting with what you send into a front panel sync input usually produces interesting results.


Wouldn’t the DWO3 essentially be able to replace the Castle Clock VCOs? Seems to do everything the Castle VCOs do and more. Plus the Castle VCO is the only Castle module that takes sync.


You can probably plug a dummy cable into either H/V inputs on DSG-3 to get only a H or V ramp on the Sum output.

Plug that ramp into a voltage processor (Passage, TVP, Fox Access, etc.) to bias it up or down and then plug that into Clock VCO’s sync input. If you don’t add the bias, the oscillator can be synced in either range but would only cover half of the frame.


Been using the sawtooth out of VU009 to sync my Castle VCOs with the front panel sync input, so I can use them in my HD system, need to play with the offset of the sawtooth in the high frequencies, but it works decently, even though it would work better with a pulse/square waveform I guess.

Then it feels a bit wasteful to use VU009 as a kind of RCA sync extractor, so a dedicated module as in this thread would be super neat Sync extraction circuit in order to free the “master” VCO for something else.

Castle VCO would probably benefit from changing the timing caps to reach higher frequencies, as I often use it to clock Castle Shift Register and obviously, it doesn’t do as small/fast “sampling” in HD as in SD. Haven’t tried replacing the caps yet, but since VU009 is derived from Castle VCO, pretty sure it can go faster.


Maybe swapping the castle SPDT switch to single pole triple throw (do these exist?!) would allow a third ‘HD’ range cap

1 Like

SP3T toggle switches in this format are not super common (not sure either if it does exist).

Then, another solution could be to use a ON/OFF/ON toggle switch (as the one used for sync selection). This way, the switch could be replaced and a capacitor added between two pads of the board.

Since capacitors values add up when in parallel, connecting a low value (let’s say 22pF) between pin 6 and pin 7 of the CD4046 would allow for higher frequencies when the switch is set to OFF. Then replacing C12 by 27pF, so once this capacitor is selected, the total capacity is 22+27=49pF (close to C12 original value, 47pF). Since C14 is 100nF, adding the 22pF won’t make much of a difference as its value is really negligible in comparison to 100nF.

A lower capacitor value can probably be used, as long as C12 is changed accordingly, if the goal is to keep the original frequency range of course. Not sure how fast the VCO can go/how low of a capacitor value it can handle, will give it a try once my workshop is up and running again.