TLN-428 Voltage Controlled State Variable Filter

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Last updated: March 6, 2007

Description

The TLN-428 is a state variable filter built around a Curtis Electromusic Specialties CEM 3320 chip. Four simultaneous outputs (all with two pole response) are provided: low pass, high pass, band pass, and notch. A built in mixer allows for two audio inputs. The filter frequency can be set using a panel mounted pot, a "one volt per octave" external control voltage, or via two external FM inputs with attenuators (one reversing). Filter resonance can be set using a panel mounted pot or an external control voltage with a reversing attenuator.

Total current draw for TLN-428 is 20 mA @+15V and 23 mA @-15V.

Availability

As of March 6, 2007 this module is completely sold out. Thanks to everyone who bought a kit.

MOTM-style front panels for this module can be ordered from Stooge Panels.

Downloads

The User Guide does not contain detailed explanations on how to install parts or which kinds of solder to use. The intended audience is the experienced kit builder who is quite comfortable building a circuit from a description, a parts list, and a schematic. Calibration routines are included.

View the TLN-428 User Guide rev 1.1 (pdf)

Graze over the TLN-428 Schematics rev 1.0 (pdf)

Pictures


Prototype	Stooge Panel	Tempco Detail

PCB Top View	PCB Bottom View	PCB With Parts

Sound Samples

These demos feature the TLN-428 in some simple patches that were recorded without any added effects.

Freq and Res Mod - An example of modulating the frequency and resonance settings. The filter frequency is swept from minimum to maximum to minimum twice while the resonance increases from minimum until the filter self-oscillates. Four MOTM-300 oscillators (pulse output) provide the audio signal. An MOTM-800 EG provides rapid frequency sweeps. All four outputs were recorded simultaneously: Lowpass, Bandpass, Highpass, and Notch.
Self Oscillation - The filter becomes an oscillator when resonance is increased to the maximum. An MOTM-300 oscillator (pulse output) modulates the filter frequency.
Throat Singing - Another example using the filter as an oscillator when resonance is increased to the maximum. An MOTM-300 oscillator is applied to the audio input and overdriven to create nasty distortion. An Ernie Ball guitar pedal plugged into an MOTM-850 pedal interface controls a second MOTM-300 that feeds the filter's frequency input.
Cry Baby - An example of using the bandpass output to create a wah-wah effect. A Fender Stratocaster is plugged into a Marshall amplifier. The TLN-428 is patched into the effects send-return loop on the Marshall. An Ernie Ball guitar pedal plugged into an MOTM-850 pedal interface sweeps the filter frequency. Sorry about the lame guitar playing, I ain't a guitar hero.