User manual

(Cut Off, Env Mod, Filter Tracking, Accent and Filter FM) plus the AC-coupled audio

modulation from the tip of the old headphone socket.

The filter is not a precise system and this input has a nominal 1 volt per octave response.

This response is not tested or guaranteed. It may change with temperature, and with the

many other things which are driving the filter frequency.

A good way of driving the Filter CV In would be a 0 to 5 volt Mod Wheel output from a

MIDI to CV converter. That will give approximately a 5 octave frequency range, which

is pretty drastic. If your MIDI to CV converter only has a 0 to 10 Volt or 0 to 12 volt

output, or if you find the input too sensitive with 0 to 5 volt, then drive this input via an

external 100k resistor, or something higher. You can use a 500k pot in series to provide a

good range of sensitivities. If you don’t know how to solder a lead with a resistor in

series, then ask a technician to make one for you.

Due to the nature of the TB-303 / Devil Fish circuitry, large step-like changes to the filter

frequency (those from the external CV input or the Filter Tracking pot) do not cause a

perfect change to the filter frequency. Perhaps 99.8% of the change occurs

instantaneously (less then 1 millisecond), but there is a residual drift towards the final

frequency over the next 500 msec or so. This is caused by a number of capacitors in the

machine, which are resistively coupled to a summing point for filter frequency which

changes its voltage slightly. This is only noticeable with the filter self-resonating, and

with relatively large changes in filter frequency.

The final frequency of the filter depends on a number of internal and external factors.

• The Cutoff Pot.

• The Main Envelope Generator via the Env Mod Pot.

• On accented notes, the Main Envelope Generator via the Accent Sweep Circuit

(three modes controlled by the Sweep Speed switch), if the Sweep-Resonance

switch is in positions 1 or 2.

• The AC coupled output of the VCA (which incorporates the Muffler) via the

Filter FM Pot.

• The CV (from the internal sequencer or from the external CV input) via the Filter

Tracking Pot. (Linear.)

• AC coupled signal from the Audio Filter FM input (tip of old headphone socket).

(Linear as well.)

• DC coupled signal from the Filter CV Input. (Exponential: ~ 1 volt / octave.)

The Tuning pot does not affect the filter frequency. It only affects the Voltage Controlled

Oscillator.