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<DIV dir=ltr align=left><SPAN class=085092304-10062017><FONT color=#0000ff
size=2 face=Arial>Yes, it does, but not in the same way, exactly. We take
all four output and the feedback, and with those five signals, we can get a
whole slew of other modes. Resonance works perfectly on all of
them.</FONT></SPAN></DIV><BR>
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<FONT size=2 face=Tahoma><B>From:</B> Synth-diy
[mailto:synth-diy-bounces@synth-diy.org] <B>On Behalf Of </B>Jason
Proctor<BR><B>Sent:</B> Friday, June 09, 2017 8:18 PM<BR><B>To:</B> Andrew
Simper<BR><B>Cc:</B> synth-diy@synth-diy.org List<BR><B>Subject:</B> Re:
[sdiy] Untangling the Oberheim OB-8 filter<BR></FONT><BR></DIV>
<DIV></DIV>
<DIV dir=ltr>the Intellijel Polaris also does something similar, if i'm not
mistaken...
<DIV><BR></DIV>
<DIV><A
href="https://intellijel.com/eurorack-modules/polaris/">https://intellijel.com/eurorack-modules/polaris/</A></DIV>
<DIV><BR></DIV></DIV>
<DIV class=gmail_extra><BR>
<DIV class=gmail_quote>On Fri, Jun 9, 2017 at 8:03 PM, Andrew Simper <SPAN
dir=ltr><<A href="mailto:andy@cytomic.com"
target=_blank>andy@cytomic.com</A>></SPAN> wrote:<BR>
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class=gmail_quote>Tom: another alternative to switching the input signal to
the base of<BR>the cap to get the high pass response instead of low pass is
to do<BR>this operation "manually", that is to take away input from the
output<BR>of the low pass stage, and feed this differenced signal, which is
the<BR>high pass, to the next stage. If the input to the low pass is
already<BR>inverting then you need to sum the input with the output to
generate<BR>the high pass response.<BR><BR>Cheers,<BR><BR>Andy<BR>
<DIV class=HOEnZb>
<DIV class=h5><BR>On 10 June 2017 at 10:53, Andrew Simper <<A
href="mailto:andy@cytomic.com">andy@cytomic.com</A>> wrote:<BR>> A
word of warning: Craig Anderton's multiple identity filter will not<BR>>
give "correct" shapes for all responses, the resonance path doesn't<BR>>
always work. You need to change the resonance feedback path to be<BR>>
either at the input, or at the base of the first cap, and if I
recall<BR>> correctly you also need to sometimes invert it depending on
the<BR>> responses.<BR>><BR>> Cheers,<BR>><BR>>
Andy<BR>><BR>> On 10 June 2017 at 09:20, Doug Terrebonne <<A
href="mailto:dougt55@yahoo.com">dougt55@yahoo.com</A>>
wrote:<BR>>><BR>>> Yes, Craig Anderton did this with the 3320
-<BR>>><BR>>> <A
href="http://www.synthdiy.com/files/2002/MIF.pdf" rel=noreferrer
target=_blank>http://www.synthdiy.com/files/<WBR>2002/MIF.pdf</A><BR>>>
Doug<BR>>> <A href="http://synthparts.com" rel=noreferrer
target=_blank>synthparts.com</A><BR>>>
______________________________<WBR>__<BR>>> From: Tom Wiltshire <<A
href="mailto:tom@electricdruid.net">tom@electricdruid.net</A>><BR>>>
To: Sean Ellis <<A
href="mailto:TensionType@hotmail.com">TensionType@hotmail.com</A>><BR>>>
Cc: "<A href="mailto:synth-diy@synth-diy.org">synth-diy@synth-diy.org</A>
List" <<A
href="mailto:synth-diy@synth-diy.org">synth-diy@synth-diy.org</A>><BR>>>
Sent: Friday, June 9, 2017 6:09 PM<BR>>> Subject: Re: [sdiy]
Untangling the Oberheim OB-8 filter<BR>>><BR>>> Thanks Sean, but
they're not very similar. 4PM is a 2164 VCA-based pole-mixing filter,
similar to the Oberheim Xpander and not very much like the OB-Xa/OB-8
CEM3320 filters. OB-Xa/OB-8 use a standard 4-pole cascade as per the CEM3320
datasheet for the 4-pole filter and a 2-pole state variable filter
(completely *unlike * the datasheet) for the 2-pole filter. The 4-pole
version was then developed into the pole-mixing filter that appeared in the
Xpander/Matrix-12, but by that point, it was using the CEM3372 rather than
the 3320 (although I don't see why you couldn't do the same trick with the
CEM3320 - now, there's a thought…)<BR>>><BR>>>
Tom<BR>>><BR>>> ==================<BR>>>
Electric Druid<BR>>> Synth & Stompbox
DIY<BR>>> ==================<BR>>><BR>>><BR>>> On 10
Jun 2017, at 01:13, Sean Ellis <<A
href="mailto:TensionType@hotmail.com">TensionType@hotmail.com</A>>
wrote:<BR>>><BR>>> The 4-pole Mission filter for the Shruthi is
at least a bit clearer to read:<BR>>> <A
href="https://mutable-instruments.net/archive/shruthi/build/4pm/"
rel=noreferrer
target=_blank>https://mutable-instruments.<WBR>net/archive/shruthi/build/4pm/</A><BR>>><BR>>>
I believe it's a similar topology.<BR>>><BR>>>
______________________________<WBR>__<BR>>> From: Synth-diy <<A
href="mailto:synth-diy-bounces@synth-diy.org">synth-diy-bounces@synth-diy.<WBR>org</A>>
on behalf of Tom Wiltshire <<A
href="mailto:tom@electricdruid.net">tom@electricdruid.net</A>><BR>>>
Sent: Saturday, 10 June 2017 12:55 AM<BR>>> To: <A
href="mailto:synth-diy@synth-diy.org">synth-diy@synth-diy.org</A>
List<BR>>> Subject: [sdiy] Untangling the Oberheim OB-8
filter<BR>>><BR>>> Hi All,<BR>>><BR>>> I've been
doing some research on filter designs that use analog switches to
reconfigure the filter (as part of a series of blog posts on multimode
filters that I'm working on):<BR>>><BR>>> <A
href="http://electricdruid.net/multimode-filters-part-1-reconfigurable-filters/"
rel=noreferrer
target=_blank>http://electricdruid.net/<WBR>multimode-filters-part-1-<WBR>reconfigurable-filters/</A><BR>>><BR>>>
Among these is the Oberheim OB-8, which uses a 4016 and a 4053 to mimic the
effect of the two independent filter circuits in the OB-Xa (one four-pole
lowpass, one 2-pole state-variable, used as lowpass only). The circuit looks
like this:<BR>>><BR>>> <A
href="http://electricdruid.net/wp-content/uploads/2017/06/ob8-sm-24.jpg"
rel=noreferrer
target=_blank>http://electricdruid.net/wp-<WBR>content/uploads/2017/06/ob8-<WBR>sm-24.jpg</A><BR>>><BR>>><BR>>>
I'm struggling to untangle this. It's safe to assume that the two separated
circuits are close to the OB-Xa designs (they are - that much is clear).
I've already documented those here:<BR>>><BR>>> <A
href="http://electricdruid.net/cem3320-filter-designs/" rel=noreferrer
target=_blank>http://electricdruid.net/<WBR>cem3320-filter-designs/</A><BR>>>
CEM3320 Filter designs | Electric Druid<BR>>> <A
href="http://electricdruid.net" rel=noreferrer
target=_blank>electricdruid.net</A><BR>>> Like my SSM2044 page, this
page is a look at how various synths implemented the CEM3320 filter, with
the datasheet design as a reference standard. Whereas the SSM2044
...<BR>>><BR>>><BR>>> Despite having a good idea what I'm
looking for, I haven't yet been able to get the two different OB-8 designs
untangled. I've got the schematic open in a image editor with multiple
layers, so I can delete irrelevant parts of the schematic from the "4 pole"
and "2-pole" layers and so on. This is getting me closer all the time, but
I'm not there yet. I think it's also the case that in 2-pole mode there are
a number of components hanging off things that are connected but basically
irrelevant, since they're there for the other circuit, and similarly for
4-pole mode. That makes life more of a mess.<BR>>><BR>>> Any
advice on how to untangle this? I'm feeling a bit like I might have to
redraw the schematic into a clearer layout first, and then deal with
separating the two versions, but that seems like adding another
step.<BR>>><BR>>> Thanks,<BR>>>
Tom<BR>>><BR>>> ==================<BR>>>
Electric Druid<BR>>> Synth & Stompbox
DIY<BR>>>
==================<BR>>><BR>>><BR>>><BR>>><BR>>><BR>>>
______________________________<WBR>_________________<BR>>> Synth-diy
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