Cadet IX OSC Hi/Low bandwidth opamp question

Forum DIY
1

I’m re-reading the IX schematics, and i’m getting slightly confused concerning the choice of TL072’s vs LM6172’s in the signal chain.

U1B and U9B being low bandwidth makes perfect sense, and the SQW buffer being high BW also does.
My confusion arises especially around U1A and U9A.
With U9A, I can see how it being a modulation input (and low voltage range giving headroom on slew) lets you get away with the bandwidth, but then spending two high-speed amps (U10) for the attenuverters seems wasteful.

With the VCO core buffer (U1A), slew and bandwidth seem more relevant, and with pal, the ~3Mhz of the 072 seems like it would kick in at harmonics around 100/horizontal lines, and the maximum slew seems like it would plateau around the same area (Which matches my experience of the max rate for my oscillators).

I guess odd-numbered packages makes buffering the slow signal with a fast amp for TRI out makes some sense, but apart from rounding out the bom this is as far as i can see just another buffer (and offset) of the same signal with a higher bandwidth amp.

The SQW at least makes perfect sense.

Any thoughts/insights i’m missing?

2

In this case it’s more about the context of publishing an example circuit for an attenuverter for these modules. I wanted to standardize that. You could try AD8034 for the expo converter and core buffer. I think input offset on the LM6172 can cause some issues.