Bill and Will's Synth
Jürgen Haible Wasp VCF
Construction

December 2010 - We began this page way before we'll get around to building this thing... but we wanted to begin documenting our thoughts about the module.

Gino Wong is, again, to blame. He wrote to us saying he was going to make some PCBs - among them a PCB for the Wasp Filter and he would send one to us. Now - we had never heard of this Filter... so he pointed us to Jurgen's site and to Matthias Herrmann's Fonitronik site too.

Matthias has two implementations. One is the straight JH filter and one adds some cool features of his own.  It's Matthias' straight interpretation PCB layout that Gino used to burn the PCB.  You can download Matthias' design, schematics, and documentation here.  On his site, Matthias notes that in his documentation, the hook up for the RESONANCE pot is reversed - we're mentioning it here to make sure we don't forget it.

Table of Contents

Here's a table of contents that we hope will make this page easier to traverse:

Background - presents an explanation and Jurgen's initial description of the effect

Recapitulation of Construction/Feature Options - presents a simple list of the different possible implementations

Parts - presents a Bill of Materials and notes about it

Panel - presents our FPE panel design - ultimately perhaps Scott Deyo at Bridechamber will fabricate one

Construction Phase 1 - Resistors, Capacitors, IC Sockets, Power Plugs, MTA headers

Construction Phase 2 - Trimmers - OK, this is where we've left off for now

Set up / Testing

Background

Jurgen writes about the module on his site:

"It sounds considerably different than the ordinary SEM-type state variable filter. The maximum Q is lower on the Wasp version. And there is an additional distortion coming from the CMOS inverter nonlinearities. This distortion is gradually increasing with input level, and you can slightly hear it way before the circuit actually clips. The CMOS inverters seem to be the dominant source of distortion; the CA3080 input dividers are rather on the save side. (100k / 1k ; but remember the absolute maximum voltage swing is limited to 5V anyway.) I have replaced the 100k resistors with 51k without noticeable increase of distortion.

"Ok, the Wasp Filter sounds different than other state variables. But what is it good? IMO, every filter's overdrive characteristic has its own special applications. The SSM2040 in LP configuration, for example, is unbeatable when you want to process a full chord of buzzy "Jump"-type saw voices. The Wasp Filter works best on Farfisa-type *organ* sounds. I tried various sounds from my OB-8, and really, the best results came with bright organ sounds. My favorite patch is the filter in LP mode with medium cutoff, and then an envelope with slow attack opening the filter (resonance quite low). This certain "edge" that is added by the filter's distortion is hard to describe, but very pleasant.

"I had this circuit at the breadboard first, and I was so pleased with its sound that I build it again on a tiny veroboard. The whole filter consists of 3/6 CD4069 and two 3080's, counting the active components. I built a notch filter from another 1/6 CD4069 (add HP and LP), a heavy distortion section (1/6 4069 with 1meg feedback resistor, and 100nF input capacitor without series resistor), and a fixed 2pole, 5kHz LPF from the remaining 1/6 4069 as a speaker simulator for the distortion section. Now use the SVF to preshape the frequency response of some input signal, and then go into the overdrive / speaker simulator. LPF, BPF and even HPF settings sound pleasant thru the overdrive, with or without resonance. For some reason the notch filter doesn't work well in this configuration. (But it makes a great "one notch phaser" without the overdrive, and controlled by an LFO.)

"I was really astonished what you can get out of one single CMOS chip (the OTAs just act as variable resistors, so they don't get much credit here.)"

PCB

Many thanks go to Matthias for the PCB design, and to Gino for burning us one. Here are Matthias' overlay diagram for the PCB - and the PCB pattern.

Power

Matthias has told us that he has run this module on 15 Volts. So we're going to try leaving out the power regulator and putting a jumper across its location:

We'll also drill holes for a four pin MTA .156 header for the power connection.

Recapitulation of Construction/Feature Options

Option Details

Parts

Will and I have developed a parts-list / bill-of-materials in the form of an XL spreadsheet. Jürgen has been very patient and helpful answering our pesky questions. As of today, 9 December, 2010, it's almost complete.

Corrections to BOM:

None yet -

Notes:

None yet -

Click here to download the spreadsheet (apx. 350K). 

Panel

With input from Matthias, Will and I developed the Panel design at the top of the page, reflected in this FPE panel.  To download the .fpd file, click here.

Construction Phase 1

All the stuff in Phase 1 gets soldered using "Organic" Solder.  At every break in the action, we wash the board off to get rid of the flux.

Construction Phase 2

All the stuff in Phase 2 gets soldered using "No-Clean" Solder and the PCB doesn't get washed off from here on.

Set up / Testing

Use Notes