TLN-864 Switching Comparator


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Last updated: March 17, 2013


The TLN-864 Switching Comparator combines a comparator and an analogue switch. A typical comparator has two inputs (A & B) and produces an output that is high (H) if A > B, and low (L) if A < B. Rather than using fixed voltages for the H and L states, the TLN-864 allows the voltages to be manually set using two front panel pots. For example, H can be -1V and L can be +3V. In addition, two front panel jacks allow any external signal to be used for the H and L states. For example, H could be the SINE wave output from an oscillator and L could be the inverted output from a sample and hold module. Anything goes in, anything goes out. Reversing attenuators are used on the A, B, H, and L inputs so that all input signals can be scaled and inverted. When nothing is plugged into the A, B, H, and L inputs, the front panel pot is used to select a fixed voltage reference from -5V to +5V.

The switching portion of the comparator has two modes of operation. The first mode (HL:X) is a 2-to-1 switch in which the signals at A and B determine which of H and L appear at output X. In other words:

If ( A > B )
  X = H
  X = L

The Y output is not used in this mode.

The second mode (H:XY) is a 1-to-2 switch in which the signals at A and B determine whether H appears at the X or Y output. In other words:

If ( A > B )
  X = H
  Y = H

The L input is not used in this mode.

The panel controls are as follows:
  • LEVEL A: reversing attenuator for A input (normalled to +5V reference).
  • LEVEL B: reversing attenuator for B input (normalled to +5V reference).
  • LEVEL H: reversing attenuator for H input (normalled to +5V reference).
  • LEVEL L: reversing attenuator for L input (normalled to +5V reference).
  • MODE: selects the switch mode, 2-to-1 or 1-to-2.
  • LED: indicates if A is greater than B.

The TLN-864 makes a great companion to the TLN-865 Trigger Extractor & Window 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-864 Switching Comparator can be built using MUUB daughterboards.

Contact me if you wish to purchase PCBs.

Total current draw for TLN-864 is 30 mA @+15V and 25 mA @-15V.


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-864 User Guide rev 1.1 (pdf)

Graze over the TLN-864 Schematics rev 1.0 (pdf)

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

MOTM-style front panels for this module can be ordered from The Bridechamber.


TLN-864_prototypes.jpg TLN-864_final_panels.jpg
Prototype with Plexiglass Panel Final Version with Bridechamber Panel

Construction Photos

Sound Samples

These samples demonstrate some uses of the TLN-864. All samples are recorded without any added effects.

  • Rhythmic Sequence - No sequencer is used, just several MOTM-300 oscillators and an MOTM-320 LFO feeding various inputs on a TLN-864 in H:XY mode. Left channel is OUT X, right channel is OUT Y.
  • Drone Wave - The exact same patch as the rhythmic sequence but using different waveforms from the oscillators and LFO, and slightly different knob settings on the TLN-864.
  • Triangle Wave Modulation - Several MOTM-300 oscillators (triangle wave) are feeding various inputs on a TLN-864 to create a composite waveform at the X output. The harmonic content of the waveform changes as an MOTM-320 LFO slowly sweeps another input on the TLN-864. At the beginning and end of this sample the waveform is a triangle.