CYGN-A

[laserist]

Yesterday I ran across a pdf of the IEEE Journal of Solid State Circuits from April of 1971 that contained this diagram:

IEEE Journal od Solid State Circuits April 1971.png

It looks pretty simple, and it is, but I started looking for that circuit for a long time ago. Those triangles are inverting op-amps. The grounds on the plus inputs aren't shown. That's basically Laser Images' CYGN-A. There's a couple of Zener diodes added in line with R6 that was copied from this example from the IC Op-Amp Cookbook:

op-amp cookbook quadrature osc.png

R1 and R2 were broken into a two fixed resistors and a dual reverse log potentiometer that controlled coarse freq. R3 was broken into a fixed resistor and a 50K linear pot that controlled fine freq. and introduced a bit of a gain difference between the sine and cosine signals, but nobody cared enough to spend the extra money to use a dual potentiometer in line with the reverse log pots.

I've wanted to post this for a long time, but wanted to do it this way...

[Greg]

Terrific information. I've been avoiding mentioning the CYGN-A so as not to appear too greedy in my appetite for Laser Images' secrets. I do love those "Ahh... THAT'S how it was done!" moments. Sorry for the delay in posting results from the complete CYGN-B, my hands are a bit full until mid next week. And I expect to be home and back to my parts inventory in late January. Also, thank you Steve, for the obscure information you sent that will increase the probability of successfully rebuilding the SPGN (Spiral Generator Card).

The attached image provides an annotation to what Brian just posted that makes it a bit clearer what we are discussing here.

[Greg]

Any words of wisdom regarding operational parameters of the 2QMM I could test to discern if it is working, if I endeavor to build some?

[laserist]

Any words of wisdom regarding operational parameters of the 2QMM I could test to discern if it is working, if I endeavor to build some?

I'd just use AD633 - 4 quadrant multipliers in place of the two quadrant modules that were scattered throughout the Mark 6. The output is the same if you're driving them with 0-10 volts... They're what I was using in my build when I broke my hand and Jon offered me a Mark 6 back in 2013.

[Greg]

Wondering if I'm on the right track regarding substitution of the 2QMM for AD633. (see attached)

[laserist]

Wondering if I'm on the right track regarding substitution of the 2QMM for AD633. (see attached)

That's close, the 2QMM was a current multiplier. "I" in & out.
2QMM plug and play replacement.png
The resistors are 22k 1%
note: the inverting input to correct for the inverted signal due to the op-amp.
And you don't necessarily need to do the whole current thing if you're not trying for plug and play into an existing Laser Images design.

[laserist]

That's close, the 2QMM was a current multiplier. "I" in & out.
2QMM plug and play replacement.png
The resistors are 22k 1%
note: the inverting input to correct for the inverted signal due to the op-amp.
And you don't necessarily need to do the whole current thing if you're not trying for plug and play into an existing Laser Images design.

Sorry, my drawing is wrong. The resistor on the input to the AD633 shouldn't be there. Basically the input to the 2QMM was a summing junction and the output was always coupled to an inverting op-amp with a 22k feedback resistor.

[Greg]

I was going to ask how to deal with the unavailability of the IH5012CPE Virtual Ground Analog Switch (excerpt from datasheet attached), which is used in the SPGN, but once again, they are not unavailable. Ordered a batch.

Regarding the CYGN-A, am I correct that the component placement chart and the PCB in the attached photo are not the same circuit?

[laserist]

I was going to ask how to deal with the unavailability of the IH5012CPE Virtual Ground Analog Switch (excerpt from datasheet attached), which is used in the SPGN, but once again, they are not unavailable. Ordered a batch.

Regarding the CYGN-A, am I correct that the component placement chart and the PCB in the attached photo are not the same circuit?

The board pictured is the cycloid rotator.

[Greg]

The board pictured is the cycloid rotator.

That's great news! The CYGN-B needs the Z axis to fully be what it was. Ok, I'll be patient and keep putting together the parts order for the cards you and Ron have given me info on, and post when I get home in a couple of more weeks.