Rotary effect schematic(Korg CX3, schematic inside)

Started by ferdinandstrat, August 13, 2021, 10:21:13 AM

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ferdinandstrat

So I decided to try and recreate the schematic for the Korg CX3 rotary emulation but with several updates like using 3207 chips. What do you guys think?


I have no idea if this schematic will actually work and honestly I never heard the CX3's rotary emulation either which is the real bummer here for me

Kevin Mitchell

At first glance that doesn't look far off from the Hammond XB-2 rotary circuit - or how I remember it.
I'm curious about the changes you've made. I can't find a clear schematic of it to compare.
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ferdinandstrat

Quote from: Kevin Mitchell on August 13, 2021, 03:02:39 PM
At first glance that doesn't look far off from the Hammond XB-2 rotary circuit - or how I remember it.
I'm curious about the changes you've made. I can't find a clear schematic of it to compare.

This is what I had to work with, sadly



Kevin Mitchell

That's much better than what I was digging up :icon_lol:

Other than small things like needing to flip the BBD's VGG resistors around to accommodate the polarity change it looks good so far. Great work!

Winter will be here soon - the season of breadboarding for me. I just might play with this one!
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ferdinandstrat

Quote from: Kevin Mitchell on August 13, 2021, 03:22:11 PM
That's much better than what I was digging up :icon_lol:

Other than small things like needing to flip the BBD's VGG resistors around to accommodate the polarity change it looks good so far. Great work!

Winter will be here soon - the season of breadboarding for me. I just might play with this one!

Really? Any other issues you might see?

Also, you mean switch the ground and voltage source around? Along with turning around the cap?

Kevin Mitchell

#5
Quote from: ferdinandstrat on August 13, 2021, 03:50:21 PM
Really? Any other issues you might see?

Also, you mean switch the ground and voltage source around? Along with turning around the cap?
Well my first thought was if the CD4046 would still produce clean enough clock pulses after doubling it's frequency but after looking at the datasheet I don't think it would be a problem but I'm not certain. If it is a problem you'd have to add a buffer for each clock line which is common practice for retrofitting a 1024 stage BBD in place of a 512 stage one.

The VGG cap is fine. And yes I do mean swapping the voltage source for the resistors. VGG should be 14/15th of the supply voltage so it's reverse of what the MN3004 had.
I also see you've changed the BBD's output resistors to pull down rather than pull up which is correct.

It's not really a simple, small schematic lol. I'll keep looking and chime in if I catch anything else.
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ferdinandstrat

Quote from: Kevin Mitchell on August 13, 2021, 04:11:01 PM
Quote from: ferdinandstrat on August 13, 2021, 03:50:21 PM
Really? Any other issues you might see?

Also, you mean switch the ground and voltage source around? Along with turning around the cap?
Well my first thought was if the CD4046 would still produce clean enough clock pulses after doubling it's frequency but after looking at the datasheet I don't think it would be a problem but I'm not certain. If it is a problem you'd have to add a buffer for each clock line which is common practice for retrofitting a 1024 stage BBD in place of a 512 stage one.

The VGG cap is fine. And yes I do mean swapping the power for the resistors. VGG should be 14/15th of the supply voltage.
I also see you've changed the BBD's output resistors to pull down rather than pull up which is correct.

It's not really a simple, small schematic lol. I'll keep looking and chime in if I catch anything else.

Well over at the other forum there was a version of the circuit retrofitted with mn3007s so I figured the 3207s will work with minor alterations

If you can look for a bit that would be great help, thank you for your help anyway

As for the resistors you mean like this?



Kevin Mitchell

Quote from: ferdinandstrat on August 13, 2021, 04:20:43 PM
Well over at the other forum there was a version of the circuit retrofitted with mn3007s so I figured the 3207s will work with minor alterations

As for the resistors you mean like this?


Yes like that. The MN3007 runs negative just like the MN3004 so polarity would not be a concern in that design.
If there's a verified version of the MN3007 retrofit then that dismisses my thoughts on the clock source's accuracy.

And it's my pleasure! Analyzing and prototyping circuits is how I grow stronger  :icon_cool:
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ferdinandstrat

Quote from: Kevin Mitchell on August 13, 2021, 04:30:22 PM
Quote from: ferdinandstrat on August 13, 2021, 04:20:43 PM
Well over at the other forum there was a version of the circuit retrofitted with mn3007s so I figured the 3207s will work with minor alterations

As for the resistors you mean like this?


Yes like that. The MN3007 runs negative just like the MN3004 so polarity would not be a concern in that design.
If there's a verified version of the MN3007 retrofit then that dismisses my thoughts on the clock source's accuracy.

And it's my pleasure! Analyzing and prototyping circuits is how I grow stronger  :icon_cool:

Thank you very much for this


Steben

Cool. Thx.
Basically a split double vibrato + dry dignal.  :icon_mrgreen:
But no tremolo addition.
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ferdinandstrat

Quote from: Steben on August 14, 2021, 04:53:41 AM
Cool. Thx.
Basically a split double vibrato + dry dignal.  :icon_mrgreen:
But no tremolo addition.

Actually...see that part where it says "AMGain"? Its amplitude modulation

Steben

Quote from: ferdinandstrat on August 14, 2021, 07:13:30 AM
Quote from: Steben on August 14, 2021, 04:53:41 AM
Cool. Thx.
Basically a split double vibrato + dry dignal.  :icon_mrgreen:
But no tremolo addition.

Actually...see that part where it says "AMGain"? Its amplitude modulation

Aha, oopsydaisy...
But only effects the treble modulated sound I see. I would suspect more amplitude effect on the lower frequencies....
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anotherjim

The bass rotor of a Leslie mostly does AM, or so I've read somewhere. Depends on the wavelength I'd think. Waves long enough should wrap past the rotor like it's not there? Probably not an issue with guitar use.
But the treble rotor is a horn and more directional, so when it's pointing away from your ears it should get quieter hence AM.



ElectricDruid

Quote from: anotherjim on August 14, 2021, 11:09:46 AM
The bass rotor of a Leslie mostly does AM, or so I've read somewhere. Depends on the wavelength I'd think. Waves long enough should wrap past the rotor like it's not there? Probably not an issue with guitar use.
But the treble rotor is a horn and more directional, so when it's pointing away from your ears it should get quieter hence AM.

The bass rotor goes more slowly too, which reduces the pitch shifting effect. The treble horn moves quicker, so you get more doppler effect as it comes round.

ferdinandstrat

Quote from: anotherjim on August 14, 2021, 11:09:46 AM
The bass rotor of a Leslie mostly does AM, or so I've read somewhere. Depends on the wavelength I'd think. Waves long enough should wrap past the rotor like it's not there? Probably not an issue with guitar use.
But the treble rotor is a horn and more directional, so when it's pointing away from your ears it should get quieter hence AM.

The problem is I have no idea how this thing sounds even on the keyboard it was designed for, not to mention a guitar

Steben

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ferdinandstrat

Quote from: Steben on August 15, 2021, 03:04:31 AM


I have to admit it sounds decent on an organ, but I am not sure how much can be attributed to the organ sound itself

anotherjim

I used to have a Multivox FO.999 clonewheel from the same era. The rotary effect sounded good on that. I can't be certain but it wouldn't surprise me if it wasn't that different from a CE-2 chorus with the addition of slowdown/speedup timing. The stereo was fake with dry on one side. It was remarkably effective at adding to the Hammond illusion. Without the rotary, it sounded more like a Vox Continental, which was no bad thing at the time.


Steben

Cool experiment though to think about using less tremolo for bass than for treble.
Bass frequencies are less dimensional. Subwoofers you know...
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ferdinandstrat

Quote from: Kevin Mitchell on August 13, 2021, 04:30:22 PM
Quote from: ferdinandstrat on August 13, 2021, 04:20:43 PM
Well over at the other forum there was a version of the circuit retrofitted with mn3007s so I figured the 3207s will work with minor alterations

As for the resistors you mean like this?


Yes like that. The MN3007 runs negative just like the MN3004 so polarity would not be a concern in that design.
If there's a verified version of the MN3007 retrofit then that dismisses my thoughts on the clock source's accuracy.

And it's my pleasure! Analyzing and prototyping circuits is how I grow stronger  :icon_cool:

Hey man I have my doubts about the position of C7 & c23, shouldnt it be from the middle of the voltage divider to ground?