JH Variable Slope Filter/Phaser: Building a Prototype

Front panel of the JH Variable Slope Filter/Phaser first posted here and here.

notes from JH:
"Well, the first prototype was part of my JH-3 Modular, of course.
But for testing the PCB layout and fine-tuning the circuit for which I
intent to offer PCBs, I wanted to build a standalone effect. For this, I'm
using the same tabletop enclosure that I've used for my Wasp Filter Clone
some years ago. (Pultgehäuse from Conrad Electronic, Best. Nr. 520772 -
Manufacturer is APW)
The focus is on the on-board LFO modulation, so you won't find any
potentiometers for external CVs on this front panel. (The circuit allows a
lot of external CVs, of course.)

Here's a screenshot of the panel in Frontplattendesigner (Schaeffer):

http://www.jhaible.de/varislope_filter_phaser/varislope_proto_fpd.jpg [pictured]

Input Level - Audio signal input level control
Feedback - Resonance Loop. Can burst into self-oscillation. Inverted or
non-inverted feedback for unusual effects.
Mix - Wet / Dry mix of filtered and unfiltered signal. Inverted or
non-inverted mix. Mandatory for phasing; interesting for LPF mode because of
phase cancellation effects.
Ouput Level - Output attenuator for audio signal
APF / LPF - Switches to change the function of the 6 filter stages from All
Pass Filter (Pole/Zero pairs) to Low Pass Filter (Poles only). 3 Switches
for 3 pairs. (6 individual switches would be possible as well.)
Mix / Filter - In "Filter" position the "Mix" potentiometer is disconnected
for 100% filter signal without any crosstalk from the dry signal (important
for powefull 36dB/Oct LPF effect).
Clean / Dirty - Dirty applies some dynamic load to the single-ended buffer
of the last filter stage.
Active / Bypass - True hard bypass
Slope - Spreads the pole frequencies of the individual stages. This means
less filter steepness in LPF mode (ccw end is 36dB/Oct), and wider notch
spacing in Phaser (APF) mode.
LFO Amount - Modulation amount of on-board LFO
LFO Wave - Crossfade between LFO waveshapes: Tringle -> Sine -> Square ->
Sample&Hold -> Audio-Rate Self-Modulation (see video).

Also possible, but not on Front panel:
Slope Control Voltage Input
LFO Amount Control Voltage Input
LFO Waveshape Control Voltage Input
LFO Rate Control Voltage Input
External Filter or Phase Control Voltage Input (for ADSR etc.)
External 1V/Oct Control Voltage Input (no tempco, though.)

Project page with audio samples:
http://www.jhaible.de/varislope_filter_phaser/varislope_filter_phaser.html"