Understanding Filters in Choruses

[t1redhands]

Hello!

I'm curious about the use of transistors in chorus schematics, specifically those used in active filters before and after the BBD.
For example, here's an excerpt of Caesar Chorus (Walrus Julia) schematic (link to full schematic):



To my ignorant eyes, these are Sallen-Key filters, usually aiming for a 5kHz cutoff. That much I can ascertain.
But: why are they using BJTs? Even in "new" BBD chorus designs? Does it have something to do with the input/output impedance that makes BJTs preferred in this application over an op-amp?
Some designs have two filters in series for a second-order cutoff effect. Why duplicate the BJT design when an second-order Sallen-Key filter using an op-amp would be more efficient?

Super grateful for any insight into this!

 

[t1redhands]

I know this is a niche case, but this design is even more confusing: the infamous Korg CX-3 Rotary Emulator



The top modulated line uses only BJTs in Sallen-Key filters (4 of them, including one with a resonance peak, I think?). The lower modulated line uses one BJT filter before the BBD, but then uses an op-amp before the summing stage. What's up with that?

 

[darwin999]

But: why are they using BJTs? Even in "new" BBD chorus designs? Does it have something to do with the input/output impedance that makes BJTs preferred in this application over an op-amp?

Perhaps just simplicity and lower cost, and maybe reduced PCB footprint.

 

[jwin615]

Where's a @bean when ya need him?