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

Michael E Caloroso mec.forumreader at gmail.com
Mon May 2 19:04:57 CEST 2016


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
>> >
>>
>>
>



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