[sdiy] Roland System 100 - Circuit details.

[TooManySynths]

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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