As a hobby I have been dabbling in cinematography (movies with real film). As a result of the digital revolution there are very few ways to project film with a synchronous sound track without investing in a small fortune in gear/services. However, there is a work around. In the first half of the seventies when prosumer level movie makers wanted to make a film with a sound track that could be edited along with the film, they used two system sound (a separate recorder). This could either be a regular 1/4-1/2" reel-to-reel deck, cassette deck, perforated tape deck (fullcoat deck). Since the cameras of that era did not have a crystal oscillator to regulate the speed of the drive motor, the deck would be attached to the camera with an umbilical cable a pulse sync or pilot tone reference. This was either resolved by the deck or recorded on a separate track to be resolved later. Nagra type recorders performed this function.
The deck that I have purchased has the ability to resolve pulse sync sound built in to the deck. This would allow me to slave the deck to a projector running at an arbitrary speed, and the sound will stay in sync. I purchased this deck on ebay, and after some fiddling and investment of parts, I was able to get it running and recording.
Here is the problem; I have no documentation for the deck, and I cannot be certain as to what type of reference that deck syncs to from the camera. There are some industry standards for pulse sync. However, there are several, with no particular standard being universal.
To resolve this problem I have traced out the DIVIDER board and entered the schematic into LTSpice (a very cool and free circuit simulation program). I would assume that this board is fed by the built 480Hz tuning fork frequency standard. This signal is in turn divided by eight by the DIVIDER board. This signal is fed to an inverter. The AC from the inverter, in turn, powers a constant RPM stepper/sync motor. This allows the perf tape to run through the machine at exactly the same rate film would run through a camera at 24 frames per second.
The deck has a setting to sync off of the camera as well. When I switch the deck to camera sync mode, the tape transport does not run. I assume that it is waiting for a signal from the camera to generate
60Hz for the inverter to turn the motor.What I have tried:
At this point because of the position of the board I am not able to probe all of the inputs/outputs of the card with a scope. However, I know that the line from the camera goes to pin six (B6 on the schematic) on the bottom of the divider board. I also see that there is a very ugly square wave at pin 3 (12V P2P per my scope). There is also a tiny 60Hz sawtooth at the camera sync in pin. I have not been able to find out by probing where or/if the tuning fork reference goes to the DIVIDER board. The tuning fork is marked 480Hz. However, its output is 2X (960Hz) square wave (2V P2P) per the scope. I have tried to model this input, and tried injecting it on all of the different ports in my model in LTSpice, however, I have not been able to get it to divide. I am not sure what port this goes into. I have also tried with another circuit that is on the same simulation to feed the camera input 1000Hz 20ms pulses at 24 pulses per second as this is one of the more popular standard. However, the DIVIDER in my simulation does not seem to be doing what it is doing in the deck. I have provided a link to my ASC file for you guys to poke around at. I have a lot of theory background, but I have not spent much time working with these type of problems. My training is in physics/ham radio. Maybe one or two of you can see a little more clearly how this thing is supposed to work. Thanks for the help.
Here is a pdf schematic:
Regards, Chris Maness KQ6UP SoCal