TLN-865 Trigger Extractor & Window Comparator


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Last updated: March 17, 2013


The TLN-865 Trigger Extractor & Window Comparator is an adaptation of a window comparator from Jung's Op-Amp Cookbook. This circuit can also function as a trigger extractor. A window comparator produces an output that is high if the input signal is greater than the lower threshold and less than the upper threshold. Otherwise the output is low. In other words:

If ( In > Lower_Threshold ) and ( In < Upper_Threshold )
  Out = High
  Out = Low

The TLN-865 uses a center point and both high and low offsets from the center point to define the Lower_Threshold and Upper_Threshold. These CENTER, HIGH, and LOW voltages can all be set manually using front panel controls, or via external control voltages. Reversing attenuators are used for the input signal as well as the center, low offset, and high offset signals.

When the MODE switch is set to COMP, the circuit operates as a window comparator with the output signal going from 0V to +13.5V whenever the input signal is within the upper and lower threshold. When the MODE switch is set to TRIG, the circuit operates as a trigger extractor that senses abrupt changes in the input signal. The threshold level can be set individually for both upwards and downwards changes using the HIGH and LOW controls. When the circuit senses an abrupt change in the input signal that exceeds these thresholds, it will output a brief pulse from 0V to +13.5V.

An inverted version of the output signal is also provided (from +13.5V to 0V).

The panel controls are as follows:
  • IN: reversing attenuator for input signal (normalled to +5V reference).
  • CENTER: reversing attenuator for CENTER input (normalled to +5V reference), sets the center point for the window comparator.
  • HIGH: reversing attenuator for HIGH input (normalled to +5V reference), sets the upper threshold offset from center for the window comparator, sets the trigger extractor sensitivity for rising voltages.
  • LOW: reversing attenuator for LOW input (normalled to +5V reference), sets the lower threshold offset from center for the window comparator, sets the trigger extractor sensitivity for falling voltages.
  • MODE: selects either trigger extractor or window comparator mode.
  • LED: indicates if the output is high or low.

The TLN-865 makes a great companion to the TLN-864 Switching Comparator.

Note that the panel layout for this module (and the rest of my MUUB utility modules) uses the smaller type of knob found on Encore Electronic's UEG and Frequency Shifter. Most people will probably hate this, but I wanted to get the most functionality in the least amount of space while still maintaining some semblance to the MOTM standard. To this end, all of my MUUB utility modules use a new layout grid that allows up to 6 pots with 4 jacks, or 4 pots with 8 jacks, on a 1U wide module.

The TLN-865 Trigger Extractor & Window Comparator can be built using MUUB daughterboards.

Contact me if you wish to purchase PCBs.

Total current draw for the TLN-865 is 43 mA @+15V and 25 mA @-15V.

After building this module I found some circuits that are similar in design and functionality: Ken Stone's Slope Detector and Mark Media's Trigger Differentiator.


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-865 User Guide rev 1.0 (pdf)

Graze over the TLN-865 Schematics rev 1.0 (pdf)

Detailed panel cutout diagram (pdf) with notes for those who want to build their own panel.

I copied an FPD file from Dave Brown and modified it for the TLN-865. I then printed out a screenshot of the FPD file using an inkjet printer and pasted it onto my plastic panel. It doesn't look too bad, especially in a dark room.

Click here to download the FPD file.


TLN-865_panels.jpg TLN-867_fpd_s.png TLN-865_panels.jpg
Prototype with Plexiglass Panel FPD Panel With Paper on Plexiglass Panel

Sound Samples

These samples demonstrate some uses of the TLN-865. All samples are recorded without any added effects.

  • Basic Window Comparator - An LFO (sawtooth output) modulates the frequency of an oscillator. The LFO is also fed to the window comparator. When the sawtooth wave passes through the window, an EG fires and opens up a filter. The window center starts at zero volts and is gradually increased to +5V in the left channel. The window center starts at zero volts and is gradually lowered to -5V in the right channel.
  • Sputtering Window - The exact same patch as above but another LFO is patched to the HIGH input of the TLN-865 to modulate the window's upper threshold. This produces a sputtering effect as the sawtooth LFO passes through the window.
  • Note Detector - Remember that Road Runner cartoon where Wile E. Coyote hooks up some dynamite and a detonator to a specific key on a piano? Well, with the TLN-865 you can do that too.
  • Basic Trigger Extractor - A simple 8 note sequence demonstrates how the trigger extractor can be used to fire an EG under certain conditions. By manipulating the IN, LOW, and HIGH controls to adjust the sensitivity, the following results are possible: