[sdiy] Roland System 100 - Circuit details.

[Rob B]

Well, fwiw, there are really only 3 basic things that make up the sound of
an osc:

1) linearity of response of the freq/cv
2) waveshaper
3) stability

Some ppl will say otherwise, and thats fine.. But the tangible sound of an
osc is comprised mainly of these 3 things.

So, you need to figure out what makes this osc particularly different.. In
the case of say a 303, its the timing pulse being fed into a integrator, and
then into a wierd discrete saw to sqr waveshaper which has a very sloppy
response and basically turns into a sine wave as freq increases. With some
others, its the odd way the square wave is synthesized, as in an Arp, where
they use threshold driven logic gates as waveshapers.

i have done some experiments with using a microprocessor as a core sending
timing triggers to an osc core and have gotten good results and this is how
i isolated the essence of many of the osc circuits down to the waveshaper
stages.

If you have a schematic, it would be fairly easy to pick out..

Rob



aim : cybrgzr0 <--last thing is a number
----- Original Message -----
From: TooManySynths <p8051 at yahoo.com>
To: <synth-diy at dropmix.xs4all.nl>
Sent: Thursday, September 06, 2001 8:23 PM
Subject: [sdiy] Roland System 100 - Circuit details.


> Hi All,
>
> As mentioned, I've been considering getting rid of one
> of my Roland 102s.   I have the schematics of the 101
> and I assume that the basic components are the same as
> the 102.
>
> Looking at the schematic it's much clearer why I think
> what I think. The VCA is a simple 3080 design, nothing
> exciting there.  The adsr is also cheap and
> uninspiring.
>
> The two pieces that are significant, imnsho, in the
> system 100 is the VCO and VCF.
>
> First, the VCF.  Looking at the schematic it's obvious
> why I like it.  It is a roland ladder (diode) filter
> design.  It uses some opamps, TA7504 and 1458, and the
> lader is made from 2SC945Q transistors.
>
> Now, it seems to me that there is no reason why this
> couldn't be easily duplicated as a diy project with a
> high probablility of nailing the system 100 filter
> sound pretty damn closely. The schematic says the
> ladder transistors are "selected".  Could someone
> explain the process of "selecting" transistors?
>
> Now the VCO is a different story. It's centerpiece is
> the UA726.  It seems silly to even try to duplicate
> this design.  I do, however, really like the sound of
> the 102 VCO, especially the triangle wave.  Is it
> likely that the UA726 contributes that much to the
> sound?  Or, perhaps it is just the waveshaping, If I
> duplicated the saw to triangle wave converter and
> attached it to a CEM, would I get close?  Should I be
> looking at modern discrete VCO designs?
>
> Thanks
> Daryl
>
>
>
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