The club standard provides for a one volt video signal. That said, I don't think a robust input circuit for an experimental televisor should bank on that level of standardization.
Question (a) What range of amplitudes might the televisor have to accommodate?
For example, from what I've read, consumer audio gear "line outs" are set up for -10 dBV. I compute 0.316 VRMS. Assuming a sine wave (admittedly not the case with video) I compute a pk to pk value of 0.894 volts.
It follws, then, that the televisor front-end must provide a gain factor of 1.12.
Professional audio gear has +4 dBu outputs. I compute 3.47 volts pk to pk, which means the televisor front end would have to attenuate the input signal by a factor of 0.288.
If the televisor is being fed from a CD player or other media device via its headphone jack, the input signal could be almost anything.
It's easy enough to add a level pot to the input of a televisor, but it would helpful to be able to scale the circuit appropriately. Making the gain/attenuator circuit broader than necessary only serves to make the proper adjustments more "touchy."
b) Should the televisor's input circuit be designed for a certain input impedance? I think consumer "line input" impedance is on the order of 1000 ohms, pro-gear impedance is figured at 600.
It has been my past experience that the headphone outputs of some equipment won't deliver signals properly unless the jack is driving an appropriate load. This implies to me that a well-designed televisor input circuit would feature a load switch that would cut in a low-value resistor, perhaps 47 ohms, to emulate headphones and act as a suitable load for the media device providing our video signal.
Your thoughts?
Pete
AC7ZL