[sdiy] Moog Rogue question...

[Roman Sowa]

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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>>
>