[sdiy] Steiner filter mods

[Peter Grenader]

While investigating the Steiner filter architecture on the Frequensteiner,
Mike Brown came across no less than four different feedback paths that Nyle
had used. In fact, on the two Synthasystems I have personally torn into, one
that I own and one a repair, both routed the feedback differently.

- P 

HOSHUYAMA wrote:

> Hi Michael,
> 
>> It's interesting
>> that you use 2 feedback paths here as this is what I found in the actual
>> Synthacon I serviced a few years back.
> 
> I got to remember your schematic.  It inspired me to use the 2-path
> feedback.  AC coupling of the pot leads to longer life span.
> Thank you very much for the schematic.
> 
> Sam HOSHUYAMA
> 
> 
> Michael Ruberto wrote:
>>> 
>>> http://houshu.at.webry.info/200511/img_1.gif
>>> 
>>> Constant current source Q2 reduces common-mode gain of the
>>> differential amplifier to almost zero, resulting in far less
>>> CV feedthrough.
>>> 
>> 
>> hmmm this is very interesting as it sheds some light on another circuit
>> that's currently giving me a headache.
>> 
>>> Another modification is the output point to the buffer U1.
>>> Response of the resonance pot is more like Korg MS20.
>>> 
>>> I also used a diode limiter as Yves Usson.
>>> 
>> 
>> I have to say this is slick. I have my version of the filter on the
>> breadboard still and I'm gonna give this a try. On my VCF I have an FET
>> boosting the output signal from the circuit but the side effect is it's
>> also amplifying the gain changes from from resonance. It's interesting
>> that you use 2 feedback paths here as this is what I found in the actual
>> Synthacon I serviced a few years back.
>> 
>> M. A. Ruberto
>> 
>> 
>> 
>> 
>