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Casio CZ-1 Expansion Shifter Mod
Old 6th July 2016
  #1
Casio CZ-1 Expansion Shifter Mod

So here's another bizarre exercise in mucking with internal operation of an electronic instrument.

The Casio CZ-1 has a circuit called the Expander circuit.
It takes the compressed waveforms post DAC and applies offsets to shift the amplitude of the signal to kinda inflate the flattened out compressed waveforms.
The circuit is fairly simple. The signal is fed into a tapped resistor ladder and a digital switch is addressed to select from 5 possible taps in the ladder. This gives an amplitude shifting in the range of E/0 to up to E/16 depending on the selected tap.

So I thought what happens if you shift the DC operating point of the entire ladder?

Essentially all of the taps will get shifted up retaining their respective intervals until the Expander simply has no effect anymore and the signal can pass without any expansion being applied thus letting through the compressed waveshapes.

Naturally this results in hearing the distortion of the contractions in those waves.

In essence this mod gives you a built-in distortion on the CZ-1. As boring as that sounds I'd like to point out that this is a unique form of distortion. It isn't the process of adding harmonics by overdriving a gain stage or clipping the peaks with diodes. The harmonics come from the waveshapes themselves because they are what is distorted. It is a digital distortion and it has a unique character.

Here are details regarding the Expander circuit from the CZ-1 service manual.
Casio CZ-1 Expansion Shifter Mod-expander-2.jpg
Casio CZ-1 Expansion Shifter Mod-expander-1.jpg

For this mod we must disconnect all of the ground nodes from the resistor ladder and then place a potentiometer between those nodes and the actual ground.
This requires a bit of surgery. Not for the faint of heart mind you.

1st we cut the ground bus trace for the resistor ladder.
Casio CZ-1 Expansion Shifter Mod-kimg0019.jpg

We then restore the ground bus to the circuits below with a jumper wire.
Casio CZ-1 Expansion Shifter Mod-kimg0020.jpg

Then with another jumper on the top of the PCB we restore the ground bus to the opamp circuits buffering the signals. To do this we simply cut the existing jumpers 125 and 150 and use them to attache the wire. This also isolates the ground of the resistor ladder further. It is now totally isolated from the ground bus.
Casio CZ-1 Expansion Shifter Mod-kimg0021.jpg

Then solder two long wires to either end of jumper 125 and run those to a 10K potentiometer.
Casio CZ-1 Expansion Shifter Mod-kimg0022.jpg

Wire the potentiometer so that the actual ground bus is on the left outside pin.
Casio CZ-1 Expansion Shifter Mod-kimg0023.jpg

Add a knob to control the amount of distortion and you are done.
Casio CZ-1 Expansion Shifter Mod-kimg0024.jpg

Ain't it pretty? Why bother? Because you just can't leave things alone like me. And you like distortion. And subverting the use of things is fun.

This mod is safe for the synth. It does not interfere with normal operation or cause failures in any way.

It is VERY tricky though. The thin traces on the PCB can be very problematic.

Sound samples will be posted soon.
Attached Thumbnails
Casio CZ-1 Expansion Shifter Mod-expander-2.jpg   Casio CZ-1 Expansion Shifter Mod-expander-1.jpg   Casio CZ-1 Expansion Shifter Mod-kimg0019.jpg   Casio CZ-1 Expansion Shifter Mod-kimg0020.jpg   Casio CZ-1 Expansion Shifter Mod-kimg0021.jpg  

Casio CZ-1 Expansion Shifter Mod-kimg0023.jpg   Casio CZ-1 Expansion Shifter Mod-kimg0022.jpg   Casio CZ-1 Expansion Shifter Mod-kimg0024.jpg  
Old 9th July 2016
  #2
If i hadn't sold mine, id have tried this!
Old 31st July 2016
  #3
Lives for gear
 
CatManDeux's Avatar
 

Any word on those sound samples?
Old 5th August 2016
  #4
Quote:
Originally Posted by CatManDeux View Post
Any word on those sound samples?
ummmm, oops?

I forgot. I'll whip some up this weekend
Old 28th June 2018
  #5
Lives for gear
 
wjmwpg's Avatar
Quote:
Originally Posted by Hollowman9 View Post
ummmm, oops?

I forgot. I'll whip some up this weekend
Ooooohhh ... I am super curious about these sound samples! Were they ever posted elsewhere?
Old 29th June 2018
  #6
Quote:
Originally Posted by wjmwpg View Post
Ooooohhh ... I am super curious about these sound samples! Were they ever posted elsewhere?
No I never got around to it. The bassline in the chorus parts of this track uses sounds from this mod.


I'll try to find some time to make better examples over the weekend.
Old 29th June 2018
  #7
Lives for gear
 
wjmwpg's Avatar
Quote:
Originally Posted by Hollowman9 View Post
No I never got around to it. The bassline in the chorus parts of this track uses sounds from this mod.


I'll try to find some time to make better examples over the weekend.
Ohhhhh . . . That’s all I had to hear! Love it!!! Thanks!

(Also love how that chorus just seems to erupt outta nowhere.)
Old 28th July 2020
  #8
Here for the gear
 

I may have missed the boat on this, but was wondering if there was any chance to get some audio clips of this mod. Also, is there any similar mod available for the CZ-101? Just got one for cheap and plan on bending it. Thanks!

edit: Found the expander circuit in the schems... maybe ill give it a go

Last edited by gdspackm; 29th July 2020 at 04:46 AM.. Reason: checked schems
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