Oberheim,Memory Moog and naked men in africa!

[Harry Bissell]

Hi Bjorn

The P5 used two outputs from the DAC... one for rough NOTE...
and a second word for offset (very fine tune...)  so that is like the
extended range trick of oberheim.  The tune routine dynamically
uses the fine trim from a lookup table that it computes, and then
interpolates.  It was seldom "out of tune"

so what is f......h  i......s ??? (reply offlist if you like ;^)

H^) harry

Bjorn Julin wrote:

> 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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