Updated : nov. 1st, 2013 Improved Steiner VCF
En français 
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Description

This is my latest take at the Steiner-Parker VCF, in which I tried to improve the design in order to correct some flaws of the original design : scratchy resonance potentiometer, untamed auto-oscillation.

As a matter of fact I introduced most of these modifications when I designed the Arturia's MiniBruteTM synthesizer. I wanted to provide a Seiner Parker filter with all its nice features and harsh sound while suppressing its chaotic behaviour.


NOTE :
The PCB can be used either with a Synthesizers.com PSU socket or a MOTM PSU socket. This module can be either powered with dual -15V/+15V or -12V/+12V power supply make it suitable either for 5U modulars or Eurorack modulars. 

You can still acces my old design of the Steiner filter here :


Schematics





Printed circuit board and component layout

PCB

Component layout
5U                                     Eurorack
      
                                  




Get the schematics as a PDF file
Get the PCB as a PDF file
The PCB is designed to use either two matched BC547C (Q1-Q2) or a single 2SC1583 dual transistor. Also, one may use either a Synthesizers.com PSU socket or a MOTM PSU socket or even Eurorack socket.


Building details
reference
 value
 quantity
IC1
 TL074
 1
Q1,Q2
 BC547C (matched pair) or one 2SC1583
 2
D1,D2,D3,D4,D5,D6
D7,D8,D9,D10
 1N4148
 10
R1,R2
 10
 2
R30
 82
 1
R28
 220
 1
R10
 390
 1
R11,R12,R15,R21
 1K
 4
R9,R13
 1.8K
 1
R29
 3.9K
 1
R18* 8.2K
 1
R3*,R4*,R5*,R19*
 10K (* adjust to obtain the desired input and output levels) 4
R16
 22K
 1
R6,R17,R26* 47K (* adjust for desired cut-off range)
 3
R27
 150K
 1
R7,R8
 180K
 2
R20,R22,R24*,R25*,R31*
 220K (* selected for V/OCT scaling)
 5
R23
 1M
 1
R14
 2.2M
 1
C9,C10,C11
 1.5nF (preferably matched within 1%)
 3
C12
 680nF or 1µF LCC cap (polyester)
 1
C5,C6
 2.2µF 30V
 2
C1,C2,C3,C4,C14*
 10µF 30V, in some it may be necessary to reduce to 1µF (in case of pronounced slew in the resonance tweaking)
 5
C7,C8,C13
 47µF 30V
 3
T2
 1K 1 turn trimmer
 1
T1
 2K 1 turn trimmer 1
P1
 47K or 50K audio curve
 1
P2,P3,P4
 47K or 50K linear curve
 3
P5
 47K or 50K reverse audio curve (C or see note below)
 1
SW1
 3P4T rotary switch : 3 circuits 4 positions (make before break)
 1

NOTE CONCERNING P5 :
The required model is REVERSE AUDIO (C curve) but since it is a potentiometric divider, it can be replaced by a 100K LINEAR potentiometer with a 100K  tapping resistor connected between the CW lug and the WIPER lug.
Wiring



Front panel
Download the silkscreen mask as a PDF file

Download the silkscreen mask as a JPEG file



Trimming
Set both trimmers to mid-range position.
Adjusting CV rejection (trimmer T2)
  1. Set the audio input potentiometer to 0.
  2. Set the cut-off potentiometer to mid-range
  3. Connect a square-wave signal (LFO or VCO) with a frequency of 50 Hz and a positive amplitude of 5V to CONTROL#1 input and set the CONTROL LEVEL#1 pot to maximum.
  4. Connect the output to an amplifier or an oscilloscope, then you must hear some low frequency sound or view some modulation on the scope.
  5. Adjust T2 in order to minimize the low frequency sound. If you cared to match the transistors and use matched resistors for R9 and R13, the minimum must be found close the mid-range position of T2.
Adjusting filter tracking (trimmer T1)
  1. Plug a CV/GATE keyboard or a scaled source of voltage in the V/OCT jack.
  2. Set the filter resonance in order to auto-oscillate.
  3. Adjust the 2k trimmer in order to obtain a V/octave tracking (octave increment for 1V increment). Don't expect a good tracking over more than two and half octave.


References
Here are interesting links where to find schematics and infos about the Steiner VCF :
Original Nyle Steiner's paper I photocopied back in 1978 with my handwritten anotations
 original article
Re-edited Nyle Steiner's paper by yusynth edited article
Motohiko Takeda's site http://www.aleph.co.jp/~takeda/radio/steinerVcfE.html
Marc Bareille's site http://m.bareille.free.fr/modular1/vcf_synthacon/vcf_synthacon.htm
RadioJunkBox site http://homepage2.nifty.com/rjb/labo.htm

By the way, pay a visit to Nyle Steiner's homepage !

The DIY builders' gallery
Here are the photographs of the yusynth Steiner VCF modules (all versions)  built by other synth geeks around the world.
Thank you  guys for sending me these nice photos.

Name : Meic
Modular project : Scaff beat
Location : Hamburg, Germany
Website : http://www.myspace.com/scaffbeat 		Name : Olivier Abplanalp
Modular project : Cave Studio
Location : Schaffhausen, Switzerland
Website : http://www.cavestudio.ch
Name  : Patrick
Pseudo : Baronrouge
Modular project: JHC live lab
Location :Toulon, France
Web site : http://myspace.com/patjhc


Name  : Julien
Pseudo :
Modular project:
Location: France
Web site : 		Name  :
Pseudo : Sebo
Modular project:
Location: France
Web site :http://www.cosaquitosenglobo.com.ar 		Name  : Frédéric Monti
Pseudo : Zarko
Modular project:
Location: Gradanne, France
Web site :
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