TLN-904 Veeblefetzer


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Last updated: September 19, 2009


The TLN-904 Veeblefetzer is a signal level meter for modular synthesizers. This module produces no sound; it is used to indicate signal level (voltage level) for both audio and control signals. I built this module because I got tired of hauling the scope over to my synth every time I wanted to check the level of a signal, or to figure out if a signal was bipolar or unipolar. It also provides lots of blinkenlights to mesmerize anyone who comes within visual range of your synth.

The Veeblefetzer features:
  • A 10 segment LED display driver for positive voltages (typically set for half volt increments from 0.5V to 5.0V).
  • A 10 segment LED display driver for negative voltages (typically set for half volt increments from -0.5V to -5.0V).
  • A zero LED driver for voltages that are too small to register on either the positive or negative displays.
  • An adjustable positive peak detector LED driver.
  • An adjustable negative peak detector LED driver.
  • Two jacks on the front panel make it easy to hook the Veeblefetzer into a patch without having to use a multiple.
Description of panel controls:
  • The MODE switch selects either BAR or DOT mode on the two 10 segment LED display drivers.
  • The RANGE switch selects either a FIXED range for the two 10 segment LED display drivers (typically -5V to +5V) or an adjustable range that follows the PEAK knob setting. The adjustable range mode would be used to zoom the display out for viewing 20Vpp signals or to zoom the display in for viewing 1Vpp signals.
  • The PEAK pot sets the level of the positive and negative peak detectors: 0V to +10V for the positive peak detector, 0V to -10V for the negative peak detector. This control also sets the range of the two 10 segment LED display drivers when the RANGE switch is set to PEAK mode.

Total current draw for TLN-904 depends on the number of LEDs, the type of LEDs, and how the LEDs are powered. For the example shown at the bottom of this page (using 25 high brightness LEDs powered from an onboard +5V regulator) the maximum current draw is 50 mA @+15V and 14 mA @-15V.

Availability: Sold Out

MOTM-style front panels for this module can be ordered from The Bridechamber and 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-904 User Guide rev 1.3 (pdf)

Graze over the TLN-904 Schematics rev 1.2 (pdf)

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

Display Samples

Get creative with your LED display.



Complete with Stooge Panel

Construction photos (with temporary plastic panel).