[sdiy] scanned pots "jumping"

Dave Kendall davekendall at ntlworld.com
Wed Feb 3 15:35:37 CET 2010


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 


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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