[sdiy] Moog Rogue question...

Wed May 7 06:23:50 CEST 2014

Many thanks to all, especially Roman.  Put a 2.2M in series with a
510K and a 500K trimmer and it works very well.  More work to make it
permanent of course.  Final tweaked resistance (which will be tested
again, of course) was 2.9 M.

On Tue, May 6, 2014 at 9:06 AM, Roman Sowa <modular at go2.pl> wrote:
> The line that goes to summing node via 100k resistor is marked in the
> schematics "1V/oct" so to reach 5 semitones shift we need to source 4.16uA
> from the summing point. Sunk by -12V that gives resistance value of about
> 2,88M. So 2M7 with 300k trimmer should catch needed value more or less in
> the middle.
>
> OTOH in the same schematics there are 2 lines marked as 1V/oct, and there is
> 0.909 gain between them, so an error in the schemo, or another unsolved
> mystery (until you measure it).
>
> Roman
>
> W dniu 2014-05-06 15:36, Pete Hartman pisze:
>
>> So to be sure I get it:  90.9/2700 x -12V = -.4V == not quite 5
>> semitones down, and 90.9/3000 x -12V = -.36V == a little more than 4
>> semitones down.  When you figure in tolerances, this puts us in the
>> right range to pull the F down to C.  90.9K is the feedback resistor
>> on the summing node.
>>
>> I don't actually have any 2.7M or a 300K trimmer so I will add some
>> resistors together and work out what does roughly the same thing with
>> the values I have.
>>
>> Thank you :)
>>
>>
>> Pete
>>
>> On Tue, May 6, 2014 at 8:12 AM, Roman Sowa <modular at go2.pl> wrote:
>>>
>>> Such trimmer would have tuning range of about 4 octaves, impossible to
>>> tune
>>> precisely. And since you need to turn it only to negative side (-12)
>>> anyway,
>>> so better have it from GND to -12, hence 2 octaves range.
>>> It's only about reducing full rotation tuning range so it's easier to
>>> tune
>>> precisely down to lower C.
>>>
>>> Roman
>>>
>>> W dniu 2014-05-06 14:28, Pete Hartman pisze:
>>>
>>>> What advantage does that configuration have over a 10k trimmer wired
>>>> as +12 / -12 divider, with the wiper in series to 620K to the summing
>>>> node?
>>>>
>>>>
>>>>
>>>> On Tue, May 6, 2014 at 1:42 AM, Roman Sowa <modular at go2.pl> wrote:
>>>>>
>>>>>
>>>>> 2.7M resistor in series with 300k trimmer from -12 to summing node (2
>>>>> of
>>>>> U2A).
>>>>>
>>>>> Roman
>>>>>
>>>>> W dniu 2014-05-06 06:01, Pete Hartman pisze:
>>>>>
>>>>>> Yah, it's an inverting op amp.
>>>>>>
>>>>>> I'll try simulating this setup so I get a better feel for it, but that
>>>>>> makes sense.
>>>>>>
>>>>>> Thanks!
>>>>>>
>>>>>> Pete
>>>>>>
>>>>>> On Mon, May 5, 2014 at 10:34 PM,  <eidorian at aladan.net> wrote:
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>> Oops, forgot to answer your second question: no, I don't think you
>>>>>>> need
>>>>>>> it.
>>>>>>> Presumably the summing op-amp is an inverter so you will need a
>>>>>>> positive
>>>>>>> voltage to offset the F down to the C below it (that's what I'd do,
>>>>>>> anyway).
>>>>>>>
>>>>>>>
>>>>>>> Cheers,
>>>>>>> A.
>>>>>>>
>>>>>>>
>>>>>>> On 2014-05-05 20:11, Pete Hartman wrote:
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>> I'm working on a Moog Rogue...  One thing that bothers the owner is
>>>>>>>> that the Rogue's voltage range is 'rooted' at F -- the lowest key on
>>>>>>>> the keybed is F and that's 0V -- but most CV sources are 'rooted' at
>>>>>>>> C
>>>>>>>> (for example both of the MIDI-CV modules I have generate
>>>>>>>> 0/1/2/3/4/5V
>>>>>>>> at C0, C1, C2, C3, etc on the keyboard).  This can be worked around
>>>>>>>> with the pitch wheel and tune knob in concert, but then you can't
>>>>>>>> really use the pitch wheel for anything else if you want things to
>>>>>>>> stay in tune.
>>>>>>>>
>>>>>>>> My thought is that it ought to be feasible to add another voltage
>>>>>>>> source that is switched between 0V and whatever is necessary to
>>>>>>>> offset
>>>>>>>> things so that the incoming voltage maps to an actual "C" for the
>>>>>>>> Rogue on the even 1V boundaries.  I expect that something with a
>>>>>>>> trimmer that matches the pitch wheel's input to the CV summing op
>>>>>>>> amp
>>>>>>>> ought to be good.  Switch the "input" from 0V for no effect to the
>>>>>>>> trimmer for the correct offset.  (obviously I'll be testing this
>>>>>>>> theory with clips before taking an iron to it).
>>>>>>>>
>>>>>>>> However, there's a detail in that section whose purpose I'm unsure
>>>>>>>> about.
>>>>>>>>
>>>>>>>> http://elmegil.dynathome.net/~elmegil/rogue-pitch.png
>>>>>>>>
>>>>>>>> The pitch wheel is a simple +12V / -12V divider that goes through
>>>>>>>> parallel diodes pointing in opposite directions, then through a
>>>>>>>> resistor into the summing node.  I don't understand what the diodes
>>>>>>>> are intended to accomplish, and I'm unsure whether the specific type
>>>>>>>> is important or not.  It's hard to read in the screenshot, but they
>>>>>>>> are FDH333--available inexpensively, but with some delay and
>>>>>>>> shipping
>>>>>>>> expense.
>>>>>>>>
>>>>>>>> So the questions are:
>>>>>>>>
>>>>>>>> 1) what does this diode configuration accomplish?
>>>>>>>>
>>>>>>>> 2) Given whatever that purpose is, is the type of diode important?
>>>>>>>> This isn't a common signal diode, the datasheet describes it as
>>>>>>>> "high
>>>>>>>> contraction, low leakage".  So low leakage is obvious enough, but
>>>>>>>> I'm
>>>>>>>> not clear on what "high contraction" is.
>>>>>>>>
>>>>>>>> Thanks for any insight :)
>>>>>>>>
>>>>>>>> Pete
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>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
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