[sdiy] Trimmers

[ASSI]

On Samstag, 28. Februar 2009, George Hearn wrote:
> The Oberheim XPander appears to have a mere 6 trimmers total for
> its 6 Voices!  It 'Autotunes' its oscillator pitch and scale, VCF
> pitch and scale, it even auto-calibrates its own resonance controls
> for the VCFs so all the voices break into resonance at the same
> point on the dial.  It's quite an achievement I think.  This is a
> design that doesn't use pots or DACs or digital pots but
> circumvents the need for trimming entirely..  bravo to them.  G

The XPander uses multiplying DACs for temperature compensation and the 
autotune basically calculates a CV distortion function to first 
measure and then accommodate the imperfections of the circuitry.

The Waldorf Q+ (and the AFB16 which uses the same filters) has a 
different scheme that sorts out all the first order errors with 
digitally controlled resistors directly in the circuit and then 
corrects the higher order errors on frequency and resonance via CV 
pre-distortion like the XPander (i.e. it is applied to the data that 
goes to the CV DAC).

I would not think of any of these approaches as "circumventing the 
need for trimming entirely".  Trimming removes imperfections and 
variations from a circuit and so do these autocalibration routines.  
They are designed to cope with a rather wide variation actually so 
that cheaper components can be used.


Achim.
-- 
+<[Q+ Matrix-12 WAVE#46+305 Neuron microQkb Andromeda XTk]>+

Waldorf MIDI Implementation & additional documentation:
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