[sdiy] video thru a spring reverb?

[Grant Richter]

The device I built uses a phase locked video synch generator, LM318  
op-amps and solid state switches to format any signal to video  
standards.

The RGB standard is basically from +100mv. to +1.0 volt only during  
non-blanking and non-synch intervals. The op-amps negative clip the  
signals and the synch generator only turns the solid state switches  
ON during non-blanking times. RGB signals are the same as three black  
and white signals (with no color sub-carrier on 3.58 mHz). When the  
color sub-carrier is added it is called "composite" video. A black  
and white video signal doesn't have the 3.58 mHz color sub-carrier.

Synch (-300mv) and blanking (0 volts) are "forced" onto whatever  
signal is input to the RGB inputs before being sent to the RGB to  
NTSC encoder.

There is a method called a "back porch clamp" which is used to DC  
restore AC coupled video. It is a 0.1 uf cap followed by a solid  
state switch to ground, and an op-amp unity gain follower. The switch  
is normally driven by a clamping signal/burst gate from an LM1881 or  
similar synch chip.

I made the drive signal to the solid switch "NOT-blanking" and added  
a diode to the unity gain buffers so they only go positive. That  
allows the external RGB signals through only during non-blanking  
times and keeps them out of the negative synch region.

On Aug 8, 2006, at 3:23 AM, denshi wrote:

> on grant's paia page he shows some video effects done
> with his paia modular.  maybe grant or someone on this
> list could go into greater detail about how this is
> accomplished?  im particularly interested in spring
> reverbing a color seperated from a video signal
>
> thanks!
> seth
>
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