[sdiy] [AH] Re: Minimoog non-linear keyboard response

[Eric Frampton]

It ended up being a dodgy - but still functioning - 3046. Thanks for the pointers, y’all!

e

> On May 2, 2016, at 1:04 PM, Michael E Caloroso <mec.forumreader at gmail.com> wrote:
> 
> Also check the delay compensation (if installed, it's the dotted
> subsection after IC3/5/10).
> 
> MC
> 
> On 5/1/16, Pete Hartman <pete.hartman at gmail.com> wrote:
>> Each of the oscillators has its own expo converter.  You might compare the
>> output of oscillator summers to see that each of them is responding the
>> same.  If not, then the problem is between the common point of the CVs and
>> the summer for Osc 1.  If they are the same, then your problem is likely in
>> the expo converter or possibly the core for Osc 1....
>> 
>> One also wonders if a fault in the high end compensation could possibly
>> lead to this kind of response.
>> 
>> When you say " slightly out of tune" between and above the high F ...  are
>> we talking sharp between and flat above, or vice versa?  Or is it flat or
>> sharp in both places?  Does the octave range of Osc 1 have any impact on
>> how good/bad the tuning is?  Does an external CV work any better than the
>> keyboard CV?
>> 
>> Thanks
>> 
>> Pete
>> 
>> 
>> On Sun, May 1, 2016 at 5:00 PM, Eric Frampton <eric at ericframpton.com>
>> wrote:
>> 
>>> A follow-up to this:
>>> 
>>> For starters, I’m on the old oscillator board.
>>> 
>>> The floating component mod for the key/envelope board has not been done
>>> on
>>> this unit.
>>> 
>>> It’s only oscillator 1. #2 and #3 seem to be tracking fine.
>>> 
>>> Furthermore, if I try tuning Osc 1 so the low and high F’s are in tune,
>>> not only are the notes in between them slightly out (especially in the
>>> 3rd
>>> octave), but the half an octave above the top F is out of tune as well.
>>> 
>>> I’ve put in a matched resistor set on the incoming CV lines, so that’s
>>> probably not it.
>>> 
>>> I’m seeing similar 20mV changes in octaves when measuring pin 6 of the
>>> summing 741’s on all three oscillators. Not identical, of course, but not
>>> wildly different on any one oscillator.
>>> 
>>> e
>>> 
>>>> On Jul 23, 2015, at 12:15 AM, Eric Frampton <eric at ericframpton.com>
>>> wrote:
>>>> 
>>>> …or “unevenly exponential” might be a better way to put it.
>>>> 
>>>> If I can get the A’s on each end of the keyboard to scale up perfectly
>>> for each oscillator, and I can get the octaves on all three oscillators
>>> to
>>> switch evenly, what would cause the internal intervals between those A’s
>>> to
>>> not be linear? In other words, if A1 and A4 are correct, A2 might be a
>>> little sharp and A3 might be a little flat, but it’s enough of a
>>> deviation
>>> that when switching octaves, the oscillators don’t stay in tune with each
>>> other.
>>>> 
>>>> The same situation happens whatever octave it’s in - the keyboard
>>>> itself
>>> seems to be triggering non-linearly (non-exponentially) internally, no
>>> matter where the tuning on a given oscillator is set. If the ends are
>>> right, the middle is wrong.
>>>> 
>>>> I’ve got a buffer board installed, so I don’t think it’s that.
>>>> 
>>>> Thoughts? Time for new resistors on the actual pratt-read assembly? Or
>>> was this what the field service mod on the keyboard PCB was supposed to
>>> solve?
>>>> 
>>>> e
>>>> 
>>> 
>>> 
>>