[sdiy] How does the Filter of the Roland SH5 work?

[Florian Anwander]

Hi Scott

> Highpass is the same as bandpass, only the highpass filter is also mixed into the output signal.  This is clever as the high harmonics that the LPF removes are added in again, thus approximating (sort of) a resonant highpass filter.  I don't know what sort of phase cancellation, etc. results from this, though.
The highpass is mixed inverted into the lowpass-signal! I assume, that 
this way the phase cancellation does the most of the "highpass"ing job. 
The allover low frequency reduction is assumingly much steeper than the 
6dB/Oct from the highpass around IC501/502. But I cannot say this 
definitely because I do not own a SH5 (unfortunately).

> I was very interested to see this as I've been looking for it for a long time.  I've found SH-5 schematics online but they don't include this page.  I wanted to find the schematics after hearing it used in some very wild (sample and hold, ring modulator, etc.) synth solos...
This schematic without the filter is the one on my page (which I 
originally received from Ken) ;-)

I now bought the full service manual from Mark Glinsky, so I could 
provide the cutout of the filter.

I don't will publish the full service manual, because I think it is 
unfair against Mark, who does a great job providing all kind of manuals.


> The Jupiter 6 also has an interesting arrangement (standard Roland VCF chips arranged as a cascaded state variable filter) to achieve its LP/BP/HP responses.
I know. I asked this question, because I am doing an overview of all 
voltage controlled filters used in roland synths starting from a 
discussion on the forum sequencer.de.

Florian