[sdiy] scanned pots "jumping"

[cheater cheater]

Dave,
no, it is very simple and an absolute must.

D.

On Wed, Feb 3, 2010 at 15:35, Dave Kendall <davekendall at ntlworld.com> wrote:
> Thanks.
>
> I could have written that a bit clearer I guess. I leave the pots at certain
> settings to prevent them jumping. The actual knobs are fine - they don't
> move, only the parameters jump.
> Interesting that it's a known technique to apply a LPF to the scanning - the
> sounds and general build quality are good, I was surprised that to see the
> jumping behaviour. Come to think of it, I've twice had to disassemble it
> because a key stopped working. In each case a bit of crud had got under the
> plastic membrane housing the 2 key contacts for each key - this was enough
> to kill that key. Removing it fixed the problem. I guess that's a mechanical
> issue - the membrane is not entirely flush with the pcb - it has some small
> holes where I guess the dust got in.
>
> Shame that the software issue is there - is that sort of thing hard to
> implement?
>
> cheers,
> Dave
>
> On Feb 3, 2010, at 14:18, cheater cheater wrote:
>
>> Dave,
>> parallax mode is a way of processing the position of the knob. It
>> requires the potentiometer to be scanned too.
>>
>> If the knobs jump around without you touching the synth at all, then
>> the knobs are most probably jumping because they have no lag
>> processor/low pass filter applied to them. If the knobs jump around
>> when you hit the keyboard hard, then it's a mechanical issue that
>> cannot be addressed in software.
>>
>> Either way this is not something that should be happening except in
>> the cheapest equipment.
>>
>> D.
>>
>> On Wed, Feb 3, 2010 at 15:04, Dave Kendall <davekendall at ntlworld.com>
>> wrote:
>>>
>>> Hi all.
>>>
>>>
>>> Following on from the pots/vs. encoders thing, when playing a Nord
>>> Electro
>>> (with scanned pots, not in parallax mode) occasionally a parameter
>>> setting
>>> will jump, presuambly from the vibration of the instrument being played
>>> hard. I've got used to leaving the knobs in a "safe' position before a
>>> gig
>>> in case something drastic happens, which on occasion it has..
>>>
>>> Is this a common fault with such systems? FWIW, the machine did this more
>>> often when it was brand new...
>>>
>>> cheers,
>>> Dave
>>>
>>> On Feb 3, 2010, at 00:35, Dave Manley wrote:
>>>
>>>> When an encoder becomes unreliable is it because
>>>>
>>>> 1. the switches are worn out
>>>> 2. the switches are contaminated and need cleaning
>>>> 3. the mechanical cam that operates the switches is worn out
>>>> 4. debris from wear on the cam/switches is blocking the switch operation
>>>> 5. ???
>>>> 6. any and/or all of the above?
>>>>
>>>> Anybody take one of these apart and do an analysis?  Does spraying
>>>> cleaner
>>>> into an encoder really do anything?
>>>>
>>>> -Dave
>>>>
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>>
>
>