Casio HT-3000 User Manual download pdf

Filter Mod for Casio HT-3000 (MT-600/HT-700/HT-6000)

The Casio HT-3000 uses the unique chip NJM2090, a 4-pole voltage-

controlled filter. It runs with (only) +5V supply, so that an

optimized functionality for battery powered keyboards is

guaranteed. There is one chip for the upper-tone voices and one

for the lower tones.

The useable cutoff swing of the filter is from 0V to 2.5V and the

resonance runs between 0V and 3.5V. To control them by your own

manually with pots, you need to eliminate the fixed voltages of

the CPU, which values are dependent on the selected voices.

The input for the cutoff voltage is on PIN 2 and for the resonance

voltage on PIN 9. So you have to cut the traces which lead to

these PINs. To get selfoszillation you have to replace the

upstandig blue 5,1 kOhm resistor opposite to Pin 9 against a 8-10

kOhm resistor.

Now you can grab the +5V voltage and the GND from the IC supply

(or directly from the power supply) and reduce it with a voltage

divider to +2.5V (cutoff) and +3.5V (resonance). Connect the GND

and +V to the outer pins of the pots and connect the middle pin to

the cutoff/resonance inputs.

Thats it...

A good working combination was a 47 kOhm lin poti with 75 kOhm

resistor for cutoff and a 22 kOhm lin poti with two 22 kOhm

resistors for the resonance. Just look at the pictures on the next

pdf.

Summary of Contents

Page 1

Filter Mod for Casio HT-3000 (MT-600/HT-700/HT-6000)The Casio HT-3000 uses the unique chip NJM2090, a 4-pole voltage-controlled filter. It runs with (

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Casio HT-3000 User Manual

Browse online or download User Manual for Musical Instruments Casio HT-3000. Filter Mod for Casio HT-3000 (MT-600/HT-700/HT-6000)

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