Jürgen Haible
Variable Slope Filter / Phaser

Note:  The original Jürgen Haible website is no longer active but PCBs are being released at http://www.jhaible.com.

I built the Jürgen Haible Variable Slope Filter/Phaser module as discussed in the Electro-Music forum.  I left off the output buffer components since I am replacing it with my modifications.  Be sure to check out Scott Juskiw's varislope page and documentation.

 Parts List Notes:

  1. There are nineteen 15K resistors, not twenty.

  2. There are three 51K resistors, not two.

  3. There are no 430K resistors, the BOM lists has value with no quantity listed.

 Assembly Notes:

  1. Resistors R176 and R187 mount radial on the PCB.

  2. There is limited clearance between R1 and the 8 pin connector.  Slightly bend the resistor away from the connector.

  3. There is limited clearance between R185 and the 3 pin Depth connector.  Slightly bend the resistor away from the connector.

  4. The silk screen clearly shows the correct orientation of U9, U10, and U11 which are rotated 180 degrees from the other semiconductors.

  5. R62 is the 1V/Oct calibration and is not listed in the adjustment procedure.

  6. The configuration for SW1 thru SW6 is open for low pass filter and closed for all pass filter.

  7. The configuration for the Clean/Dirty switch is open for clean and closed for dirty.

  8. Power consumption: 85 mA +15, 85 mA -15

Variable slope filter/phaser Mouser part numbers


I was working on a panel when I saw the design posted by Scott Juskiw on the Yahoo ModularSynthPanels group.  He included several enhancements that I liked and adopted for my module.  After construction, I noticed the LFO output was 20V pk-pk.  I lowered the gain of the LFO circuit to 10V pk-pk by changing R175 and R178.  Since the module was already built, I added 100K resistors on U20 from pin 4 to 8 and from pin 8 to 14 to adjust R175 and R178 to the approximate values.


 Scott Juskiw enhancements: (from ModularSynthPanels posting)

  1. Added a summing amp for 3 inputs with 100K attenuators.

  2. Added an inverter to the MOD2 input so that FM2 is a reversing attenuator.

  3. Deleted the MOD3 input, Output attenuator, Output Level, and Bypass switch.

  4. Added a LFO Out bi-color LED.

  5. Added an op amp output buffer.

 Varislope Modifications:

  1. Changed R1 and R2 to 100K for unity gain input.

  2. Changed R127 to 82K for unity gain Aux input.

  3. Changed R37 to 50K trimmer to adjust output for unity gain through filter.

  4. Deleted R46, R47, R48, Q1, and C16 (Out buffer).

  5. Replaced R45 with jumper to add second ground to 8 pin connector (replaces Mix).

  6. Wired R47 (at C16 node) to R175 (at R176 node) to add LFO Out to 8 pin connector (replaces Out).

  7. Deleted R178 and LFO Out connector.  Added a op amp voltage follower to LFO Out to improve drive capability.

  8. Change R175 to 43K and R178 to 50K for 10V pk-pk LFO output. (modified differently as described above)

Variable slope filter/phase enhancements schematics  (updated)


I calibrated my varislope but went back and recalibrated it again using Juskiw's very nice documentation.

I made a quick demo ... it's challenging to think, talk, twiddle, play on the keyboard, and not bump the microphone.  It's not great, but it does demonstrate some of the characteristics of the filter and phaser.  The patch is a saw wave input with ADSR on FM2.

   Varislope demo



This image shows the MUUB-4 enhancements with the added op amp to buffer LFO Out.



I made aluminum brackets to mount both the Varislope and MUUB-4 PCBs.  I used  P260P potentiometers from BI Technologies, and potentiometer chiclets from John Loffink.



Wiring complete!




This panel is a modification of Scott Juskiw's design.  I moved the switches and added nomenclature to the Wave control.  To allow room for the Wave label, I rotated the control 180 degrees and made the waveform legends tangential to the tic marks.

Variable slope filter/phaser FrontPanelExpress design file  (updated)