SV: [sdiy] DSI Mopho analysis: Oscillator Slop, sub osc, etc

[karl dalen]

The pinout are quite similar to 3996 just aditional
signal out, pan in L/R out, and one pre filter ext in
to mix int osc with.

i tought you allready had sold off the Mopho since last time? :)

At the prophet forum there are photos of the PCB.

KD


--- Den mån 2010-01-18 skrev Dave Manley <dlmanley at sonic.net>:

> Från: Dave Manley <dlmanley at sonic.net>
> Ämne: [sdiy] DSI Mopho analysis: Oscillator Slop, sub osc, etc
> Till: "Synth DIY" <synth-diy at dropmix.xs4all.nl>
> Datum: måndag 18 januari 2010 12.28
> I bought a Mopho, and started scoping
> out a few simple internal signals tonight.  I decided
> to look at the oscillator slop parameter.  The UI
> allows a value of from 0 to 5.  Before looking at it
> with the scope, I expected the slop setting to slowly vary
> the reset time of the ramp integrators on the PA397.  I
> was a little surprised to see that the reset time is changed
> about every ~3 seconds.  For freq=261Hz, the reset time
> changes in quantized steps of ~900nS.  I set freq=523,
> and the steps are quantized ~500nS.
> 
> The reset time changes randomly.  Watching it for a
> while with slop=5, iit had this characteristic:
> 
> 0,-1,-2,-1,-2,-3,-4,-5,-4,-3,-2,-3,-1,0,+1,+3,+2,-1,+1,0,+1,+2,+3,+2,+3,+4
> 
> Where the numbers = number of quantized steps.  I'll
> do a more thorough check on step size vs frequency later.
> 
> The sub osc is a simple divide by two of the integrator
> reset pulse.  The pulse is used as the clock into a
> 74HC74 DFF.
> 
> I'll post more results as I have time.  If anyone has
> specific questions let me know.
> 
> I plan on walking around the dsPIC, and the PA397 on a pin
> by pin basis to see what they are doing.
> 
> Eventually, an annotated pic of the pcb, a detailed block
> diagram, scope captures, and/or perhaps some schematics of
> sub-circuits.  The layout looks well organized and
> straight forward to trace.  Of course, one of the items
> of interest is the previously discussed weird behavior when
> switching from a high frequency to a lower one.
> 
> I'll also post a list of the ICs in use, there's not any
> big surprises.
> 
> -Dave
> 
> 
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