Casio HT-3000- User Manual
Casio HT-3000– User Manual, read for free online in PDF format. We hope this helps you resolve any issues you may have. If you have further questions, please contact us through the contact form.
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.
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