Hello everybody, I built the Steiner Parker filter from Eddy Bergman’s site. It works perfectly fine but I have a problem with the unfiltered sound coming through when the cutoff pot is turned left. It looks like the original signal is mixed with the filtered signal. On Eddy’s site i read that that is normal for this filter. But I like to get rid of it. Is there anybody who can help me with this?
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Where exactly does it say that? I don’t see it, and in the YuSynth schematic I don’t see any mixing going on. The input goes only to a switch, and the outputs of the switch go only to points within the filter core.
Links:
https://www.eddybergman.com/2020/04/synthesizer-build-part-26-steiner-vcf.html
http://www.yusynth.net/Modular/EN/STEINERVCF/index-v2.html
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This is what Eddy wrote:
In the first instance I didn’t notice a big difference between the different modes of the filter. That was until I discovered I had forgotten to earth pin 3 of the TL074. Now that I’ve done that the filter sounds even better than it already did. I noticed that with this filter you can hear the original sound coming through the filtered sound if you turn Cut-Off and Resonance way back. I’ve done some research and this does seem to be exactly how this filter should sound so my build is spot on. Here’s the filter in action in the Arturia MatrixBrute:
The Arturia MiniBrute was designed by Yves Usson aka Yusynth with help from Nyle Steiner, the original developer of this filter from whom it gets its name…
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I really like to understand what is going on with this filter. I also didn’t see any mixing going on if I look at the schematics. What makes the unfiltered sound appear at the output? (at a low level)
Chances are it is actually always going through, you probably just cant hear it anymore when you start opening the filter.
That is what is probably going on I think but it is way to audible for me unfortunately. So, I am looking for help to get rid of it 
Maybe @EddyBergman can explain somthing to you
I built one of these filters directly from the YuSynth schematics and on a custom PCB rather than on stripboard. In LP mode this also has some audible bleed-through with the cutoff at minimum. The circuit is very susceptible to noise pickup generally - simply putting a hand near to the wires to the mode switch will induce a noticeable hum. So I suspect there’s some inadvertent crosstalk, possibly within the TL074 which handles both the input and output signals in the YuSynth design. So it might be worth using a separate TL071 (or half a TL072) for the output stage, physically distanced from the input signals. Screened cables for the panel wiring may help too.
I also built the CGS35EURO Steiner-Parker filter and the bleed through from this is at a much lower level (though you can hear it if the volume is turned up very high). Perhaps interestingly, this circuit uses physically separated op-amps for the input and output signals. In some ways it’s also more flexible as you can mix the LP, BP & HP responses, though you lose AP. Mine is built on a single custom PCB - the bleed-through may be even lower in the original multi-PCB layout.
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Yes this seems to be a characteristic of this filter. I’m afraid I can’t tell you how to get rid of it but this filter sounds awesome so I don’t have a problem with that aspect of it. It’s my most used filter in fact.
The crosstalk option could be a good one to investigate. Like Clarionut says the filter is rather susceptible to noise.
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Thanks clarionut, this is interesting info ! I will certainly try a seperate opamp. That CGS35EURO filter is interesting as well
I seem to have solved the problem. I made some changes in the whole system in the grounding of parts and that did it. It sounds really awesome now with no bleed at all
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