[sdiy] Semi-Discrete (3046) Minimoog Oscillator Theory Of Operation?

[Tom Wiltshire]

Excellent work. I had a good read around the minimoogwiki site - very enjoyable.

One question; Presumably you are keeping the original three-control contour generators? I never understood why so many minimoog clones don't take the opportunity to add a separate "release" control to give a full ADSR envelope. It increases the range of the envelope a fair bit, and isn't going to alter the sound any. Or is that last part after the comma too controversial?

Thanks,
Tom

On 8 Aug 2010, at 09:28, JR wrote:

> Robert & Tim,
> 
> Thanks for your help.  I got that second oscillator working finally.
> It ended up being that the collector of Q8 had a cold solder (well,
> technically Q19 I guess, since it was for oscillator 2 -- Q8, Q19, and
> Q32 are all the same thing across each of the 3 oscillators) .  I
> guess I was in a bit too much of a hurry when I was putting the board
> together originally.  I think that's the only cold solder I've had on
> this whole project... I thought I was past that kind of silly mistake.
> 
> So, now I've got all 3 oscillators making that warm Moogy sound, the
> filter seems to work, and the dual contour generator sweeps the filter
> and vca (well, more or less... something seems a bit out of adjustment
> since the DCG seems a bit slow).  I've also got several of the panel
> potentiometers wired backward (oops), but all in all it's sounding
> really good compared to where I started.
> 
> Now I'm going to rig up something to interface to the keyboard circuit
> (a MIDI2CV interface built on a MIDIBOX core).  I'm going to set it up
> so if I ever find a cheap mini keybed I'll be able to use either the
> midi interface or the keyboard).
> 
> Thanks again for your help.
> 
> --Joe
> 
> https://sites.google.com/site/minimoogwiki/home
> 
> 
> 
> On Mon, Aug 2, 2010 at 2:31 PM, Robert Hume <robert.hume at gmail.com> wrote:
>> The oscillators in the dashed lines are getting inputs from the left. From
>> top to bottom the inputs are GND, +10V, a current that determines pitch,
>> -10V, -4V, -10V.
>> The current that determines pitch is sunk by the 3046 collector on the left
>> and goes through capacitor C6, which creates a ramp. The ramp gets reset by
>> transistor Q21 (capacitor shorted) periodically to make a sawtooth.
>> Q18 is a JFET differential input stage with Q22 setting the current. The
>> output of the first stage goes to another differential amplifier stage made
>> up of Q19 and Q20. The output of that stage goes to emitter follower Q15.
>> The Q18/Q19/Q20/Q15 amplifier is really a discrete op amp with negative
>> feedback. It has a closed-loop gain of 2 (1+R75/(R56//R76)) and also
>> corrects the DC offset.  Q16 and Q17 are two grounded emitter stages
>> that act as a comparator. The comparator monitors the saw output and sends
>> the reset pulse back to Q21.
>> 
>> 
>> On Sun, Aug 1, 2010 at 12:09 PM, JR <calphool at gmail.com> wrote:
>>> 
>>> Hi everyone,
>>> 
>>> Does anybody know where I can find some documentation that describes
>>> precisely (down to the individual component ideally) how the middle
>>> style semi-discrete Minimoog oscillators work (This design:
>>> 
>>> http://www.fantasyjackpalance.com/fjp/sound/synth/synthdata/16-minimoog/002/903-osc-print-schem-below.gif)?
>>> 
>>> I've been building a clone and I've got 2 out of the 3 oscillators
>>> working, but I don't understand the schematics well enough to use them
>>> to debug the middle oscillator (#2).  I have kind of a general idea
>>> how an op amp works for example, but how this collection of
>>> transistors and op amps works together sort of eludes me (especially
>>> the main oscillator source -- the saw -- it seems to come from the
>>> combination of what's going on outside of the dashed lines and what's
>>> inside them -- you don't seem to get anything if you just connect the
>>> circuits labelled "Oscillator 1, 2 or 3" [in the dashed lines] to
>>> power -- instead they seem to be cooperating with the left half of the
>>> diagram to create the main saw that drives the whole circuit).
>>> 
>>> Thanks,
>>> 
>>> Joe
>>> _______________________________________________
>>> Synth-diy mailing list
>>> Synth-diy at dropmix.xs4all.nl
>>> http://dropmix.xs4all.nl/mailman/listinfo/synth-diy
>> 
>> 
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