Back to Leslie simulators, briefly.

[Mark Hammer]

Mike Irwin (aka Vsat) drew my attention to this one recently.  The old Korg CX-3 organ included an analog Leslie simulator, implemented with a pair of 512-stage MN3004 BBDs.  Mike built it with some MN3207's (this required board redesign) and offered a favourable opinion of it.

The CX-3 schem can be found here: http://oldschoolsound2.free.fr/manuels/cx3tech.zip

It's a 1.5M zipfile with scans of the schematics for the CX-3.  The schematic for the Leslie sim is the file name s3.gif.  The board layout is s6.gif.

[Paul Perry (Frostwave)]

Mark, what is the basic principle on this one?
The CX-3 dates from a very good Korg era.. is there anything weird?
(i'll try to decode the circuit later, but any hints..)

[MR COFFEE]

Thanks, Mark

A schematic well worth studying a while.

Not quite in the class with the Dynacord CLS222, but a very worthy circuit.

Thanks for finding .. and sharing ..  it.

Bart

[Paul Perry (Frostwave)]

I knew it! it has the crazy Korg voltage controlled amplifier, see Q5 & Q6!

[Mark Hammer]

1) Thank Mike/Vsat, not me.  I'm just the guy who passes it on.

2) The VCA.  On one of the recent threads about Leslie simulation, I suggested that a more realistic "throb" would be achieved if there was some light modulation of both amplitude and upper bandwidth to mimic what happens when the rotor is momentarily pointed away from you.  Apparently this design covers off part of that and has a pleasing throb.

It would appear from the presence of a highpass filter in the path to the BBD in the upper half of the schematic that the design attempts to mimic a dual-rotor Leslie.

[Vsat]

Mark, Paul and List,
Yes - this one does simulate an upper and lower rotor, with a Sallen-Key high-pass filter for  the crossover. Each "rotor" has it's own BBD and LFO - spinning at different rates - and they ramp up/ramp down in speed when you change the High/Low switch. That simple Korg VCA is reputed to be hissy, but so are the BBD's... compander  good idea for use as a standalone fx unit. Not perfect, but a lot of functionality in this little circuit.
Regards, Mike