Monday, May 6, 2019

CGS blast from the past--Steiner Filter

Hello Again! This time, I repair Ken Stone's take on The Steiner Parker Synthacon filter.

Repaired Filter is working!

The filter design is a classic in the analog synth world, maybe not as famous as the Moog Ladder or Korg's MS20 incarnations, but it's definitely in thetop 40 anyway. Sound demo is here.

There have been a lot of commercially sold version of this filter: TipTop has one for Euro; Elby has a few incarnations for sale. (Elby took over CGS's site and sales....)  The awesome and insanely productive Osamu Hoshuyama has one w/ variations on his site. It's an unusual design, having LP/BP/HP inputs (not outputs--inputs!) and an odd buzzy harsh sound.

Back in about 2005 I tied my own CGS build--one of my first attempts at audio DIwhY.  But the filter soon broke--no audio--so I junked it and forgot about it. When I recently found it at the bottom of the junk box I asked around, no one in my Meetup synth nerd group wanted to take a crack at fixing it, so I decided to repair the damn thing myself.

My repair skills have improved somewhat I guess because it was really easy to find the issues. I scoped the BP audio all the way to the output, but there, right by the wire to the output jack, an important trace had lifted, probably during the initial build, and failed. There was enough of the trace left to solder a new wire in place. Now HP and BP work! I found another broken trace near the Low pass input. Easy repaired with a "kludge" or "bodge" wire:

You fix PC's by rebooting.  You fix audio with kludge wires.

Happy to say it's working again. To my ears Ken's CGS design has the same nasal sound the Synthacon at the local Synthesizer Museum has. OK last thing to do is record it!  Update! Demo done, soundcloud file is here. Have fun!


  1. So ... which filters are the top 40?


  2. Granted, this is MY top 40--I will list my top 20 anyway.

    Clones of these, if well done, definitely count!

    1. Moog ladder (lowpass) such as Minimoog
    2. Roland SH-5 (multimode, w great BP!)
    3. MS20 or 10 filter (no OTA: "Korg 35")
    4. MS20 filter (OTA versions)
    5. Oberhiem SEM. Love that notch setting baby!
    6. WASP
    7. Arp 2600 (blue meanie)
    8. Arp 2600 (halloween)
    9. MaxiKorg
    10. Buchla Lowpass gate, eg, 292
    11. Roland SH-101
    12. Steiner Synthacon
    13. prophet T8
    14. EMS Putney diode filter
    15. Roland TB303
    16. Oberhiem OBX and the like
    17. Moog 914
    18. Serge VCFQ
    19. Mutron III
    20. Vactrol VCF (shameless self promotion)

  3. Thanks! It may be subjective but it's still interesting to see the major ones listed.


Bluetooth Bench Mixer

Readers: If you want to build the project featured in today's post, please go to PCBWAY's Community pages--gerber files (front panel...