Oberheim,Memory Moog and naked men in africa!

[Bjorn Julin]

Bye!

It seams to be very silent on diy now
maybe this can make some fuzz!

You are all f.....h i.........s! :-)
Now, all at once,, fuzz, fuzzz!

Seriously, looking at the OB Xpander i was
suppriced to find that they used a switched
mode power supply? Now haven't you all said
from time to time that a switched ps is no no!

Another quite strange thing in the Xpander
in regard to the use of the supply is that
it uses a special mode of DAC.

Oberheim has put a lot of efforts into get
smooth DAC step transitions by using RC lag
nets on the 14 bit DAC. But not only that,
they also extend the DAC range by first writing
out a DAC value to a separate S/H who then
later are mixed in with the actually DAC value,
to get the final mux voltage, a sort of
14bit + 14bit/scaling resistor!

So Oberheim has tried to reach ultra high
resolution but probably render some of it by
using a switched mode power supply. On the
other hand i can understand why they used
such a power supply, the 3 displays of course

But maybe,,,maybe a switched PS is not such a
totally bad idea after all, if one match the
switching frequency to the frequency response
of the following voltage regulators and take
attention on the current surge of the load
one could probably get a quite decent power
supply, DIY has so far ,what im aware of only
been talking about the usage of PC's supply
boxes in use for synths, and that is a
different matter!

Now i have been looking into other designs,
like the P5, Jupiter8/MKS80, Rodhes Chroma.
In the Chroma they use similar scheme as
the Xpander, a RC lag network to smooth DAC
step stuff, but the chroma uses a 12bit main
DAC and a 8bit as a programmable reference
voltage for the main DAC, quite a interesting
move to get higher reso.

The MKS80 and probably the Jupiter8/6 uses
a 14 bit DAC straight out, no lag stuff
or extra scaling.

On the other side are the slightly older designs
of OB8, Memory Moog, P5 etc. As far as i have
heard the latest models of P5 uses a 14 bit DAC.

The MMoog supricingly uses a 12bit, now both
P5 ad Mmoog uses 3310 envelope generators so a
higher resolution then 12 bit would be overkill
even a 12bit software LFO could stand out
pretty well.

But using a 12bit DAC for controlling the pitch
and filter tune in a polyphonic synth with
18 VCO's, no wonder that the machine sounded
out of tune as many customers say it does.

I wonder if the Moog engineers was relying by
selecting 3340's for tune uniformity in the
machine?!

And i wonder if Rudi Linnhart has replaced
that DAC with a higher resolution in his mod
for the Mem Moog? He says that he replaced the
entire MCU board.

Finally, i wonder how they all would perform
compared against each other, particularly
how much better (supposed to) would the
Xpander/Matrix12 and Chroma perform against
the MKS80??? Most interesting!!
MKS80 is a Jupiter8 in a rack box)

BJ
(who just mining his nose for naked men.... ho hum....
...sorry...tigers in africa, eh,,,a tiger in africa?).
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