CYGN-B

[laserist]

i took a look at preset #9.. I don't if by "gain" you mean intensity or something else, but LFO1 and LFO2 are sending some data to the intensity channel and that may make it less responsive than what you're expecting. If you unroute those signals, it might be smoother for you.

Color mod before PCAOM's changed everything was done with a scanner. When you turned up the gain (or amplitude if you prefer) the color mod signal drove the galvo to whip a RYGB ribbon of discrete beams across the 4 adjacent scanner pickoff mirrors. With the gain at zero, the RYGB images were just RYG & B images. As you turned up the gain slightly you woul get just a bit of yellow in part of the red image, a bit of red and green in the yellow image, and so on. As you turned the gain up higher eventually you get A RYGB stripe in Y & G, higher the RYGB stripe in the R &B too. Still higher and the RYGB stripes get smaller with the appropriately greater amount of black. A flick of your fingers could go from zero to full on or anywhere in between. Eventually I'll see if I can recreate Abaddon's Bolero from Laserium I & shoot some video. that should help.

[Greg]

The schematic for the CYGN-B includes a section that appears not to be connected to anything else on the board except four pins on the card edge: W, 19, V, and 18, labeled +-13V SQUARE WAVE, RAMP OUT, DOWN INPUT, and UP INPUT. These pins are not referenced in the wiring list. Obviously this looks like an oscillator or function former with a couple of outputs and control inputs. Any recollection what this was used for?

[laserist]

The schematic for the CYGN-B includes a section that appears not to be connected to anything else on the board except four pins on the card edge: W, 19, V, and 18, labeled +-13V SQUARE WAVE, RAMP OUT, DOWN INPUT, and UP INPUT. These pins are not referenced in the wiring list. Obviously this looks like an oscillator or function former with a couple of outputs and control inputs. Any recollection what this was used for?

That's the evidence that the CYGN-B was originally intended to replace the CYGN-A. The same circuit is on the CYGN-A board. It's the core of the color mod II circuit.

[Greg]

That's the evidence that the CYGN-B was originally intended to replace the CYGN-A. The same circuit is on the CYGN-A board. It's the core of the color mod II circuit.

Fascinating. We wait with baited breath to find out what the inputs may have wanted to see. Especially hoping for a comment regarding the expected polarity / amplitude limits of the input signals.

[laserist]

Fascinating. We wait with baited breath to find out what the inputs may have wanted to see. Especially hoping for a comment regarding the expected polarity / amplitude limits of the input signals.

It's a clever little circuit. There's a 100k pot across the diodes, and the wiper from that pot is connected to the wiper of a 10k pot one side of that pot is connected to the "square wave" output and the other side is connected to ground. (Looking at the schematic I don't see how the "square wave" output could actually be a square wave.) The remaining pin is the color mod II signal. The 10k pot is the freq. and the 100k pot is the symmetry for the ramp. Run the color mod signal across a 10k pot to ground and the wiper controls the color mod II gain.

[Greg]

That's useful information indeed. Attached photo shows the color mod II signal, which, as described, has beautiful ramp symmetry control. Frequency only goes up to around 10Hz. Capacitor value was reduced to increase frequency for the photo.

[Greg]

I wonder if any of the spiral generating or audio modulation sub-systems of the mark VI used a sweep circuit similar or identical to the colormod2 core.

[laserist]

I wonder if any of the spiral generating or audio modulation sub-systems of the mark VI used a sweep circuit similar or identical to the colormod2 core.

No, the spiral ramp circuit used AD811 & AD821 matched dual transistors which are pure unobtainium today. The thing about the spiral circuit was it had a signal where both the up ramp and down ramp rates were programmable and an inverse of that signal, but also a reset. The audio mod use a (again) no longer produced log gain control chip for the input stage. If you look at some of the odds and ends I sent last you'll find four of those chips. Schematics to follow...

[Greg]

I certainly noticed those (photo). They're in a bank vault for now.

I figure might as well make the colormod2 signal available to the axis summing input of the CYGN-B. Attached schematic shows the plan for this.

[laserist]

I certainly noticed those (photo). They're in a bank vault for now.

I figure might as well make the colormod2 signal available to the axis summing input of the CYGN-B. Attached schematic shows the plan for this.

The spiral, multiplier, multiplier summing, multiplexer multiplier, and fixed cycloid boards all used a two quadrant multiplier module that Laser Images designed. I assume they went to the trouble because the AD533's they used on the audio mod board needed three trim pots, were a pain to adjust, and took up a fair amount of board space. All in all Ad532's at $25 each in 1980 dollars always seemed a better choice. Today the AD633 is even more economical.