This is my take on the Steiner Parker filter. It is based an article in Electronic Design 25, December 6. 1974. You can find various implementations on the net. Very interesting are those from YuSynth and Ken Stone. You can still find them on the web as well as the original article. With my input stage it is possible to use the three filter inputs LP, HP, BP in parallel. The LP input is normalized to the others, so only one patch cable is needed. All inputs have attenuator.
Specs and features
- Low pass, high pass, band pass input with attenuator
- Positive and negative ENV control with sign changer
- CV inputs for linear TM, log TM, envelope, V/Oct tracking and emphasis
- Runs on +/-12V and +/-15V (with minor resistor value changes for best performance)
- Power consumption below 20mA each rail
Please refer to the original article and other implementations on the web.
First make a gross function test. All in and outs should work as expected and all potentiometer have some effect.
- CV rejection
- Set all audio input potentiometer to zero.
- Set cut off potentiometer to 12 o'clock.
- Set Q potentiometer to zero.
- Connect a square wave with 50Hz +5V to TM log input.
- Set TM log potentiometer to maximum.
- Connect the output to an oscilloscope.
- Adjust TR_1 (main board) to minimize the amplitude.
- This adjustment is not critical. With the given values this Filter is not very well suited for controlled self oscillation.
- Apply a scaled voltage reference or Keyboard to the V/Oct input.
- Measure the voltage at the basis of Q1.
- Adjust TR_2 so, that when you change the input voltage for 1V the voltage at the basis of Q1 changes around 17mV.
- Apply a 100Hz square signal to the Low Pass input.
- Turn the LP potentiometer to maximum.
- Turn the feedback potentiometer to maximum.
- Turn the cut off potentiometer to maximum.
- Adjust TR_1 (control PCB) to your liking.
- Experiment with the settings. I recommend to start with quite high settings for Q.
- Match transistor Q1 with Q2
- Match R8 with R9.
DownloadSteiner Parker VCF control board documentation download
Steiner Parker VCF control board Gerber files download
Steiner Parker VCF main board documentation download
Steiner Parker VCF main board Gerber files download
Steiner Parker VCF *.fpd file download