TLN-442 Voltage Controlled Lowpass Filter


Back to Synth DIY Projects

Last updated: February 1, 2007


The TLN-442 is a four pole low pass filter built around a Curtis Electromusic Specialties CEM 3320 chip. A built in mixer allows for three 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.

A four pole low pass filter built with a CEM 3320 was used in the Sequential Circuits Prophet Five (rev. 3) and Pro One synthesizers.

Total current draw for TLN-442 is 12 mA @+15V and 15 mA @-15V.


As of May 31, 2003 this module is completely sold out. There were only 20 printed circuit boards made. I have no plans to make any more of these since I no longer have any CEM 3320 chips. Thanks to everyone who bought a kit.

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


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-442 User Guide rev 1.1 (pdf)

Graze over the TLN-442 Schematics rev 1.1 (pdf)


TLN-442_p1s.jpg TLN-442_p1s.jpg TLN-442_pcb_ts.jpg
Prototype Stooge Panel Tempco Detail
TLN-442_pcb_fs.jpg TLN-442_pcb_bs.jpg TLN-442_pcb_ps.jpg
PCB Top View PCB Bottom View PCB With Parts

Sound Samples

These demos feature the TLN-442 in some simple patches that were recorded without any added effects.

  • Freq and Res Mod - An example of modulating the frequency and resonance settings. Two MOTM-300 oscillators (sawtooth output) provide the audio signal. An Ernie Ball guitar pedal plugged into an MOTM-850 pedal interface controls the filter frequency along with an MOTM-320 LFO (sawtooth output). Resonance starts out at minimum and gradually increases until the filter self-oscillates.
  • Classic S & H - Classic sample and hold applied to filter frequency. Two MOTM-300 oscillators (sawtooth output) provide the audio signal. An MOTM-101 provides the sample and hold signal.
  • Self Oscillation - Two examples of the filter in self oscillation. No oscillators are used, the filter becomes an oscillator when resonance is set to the maximum.