[sdiy] Roland TB-303 filter responses graphed

Kylee Kennedy kmkennedy at gmail.com
Wed Oct 21 02:16:22 CEST 2015


Love the 303! Thanks for posting the info.
Kylee

On Tuesday, October 20, 2015, Richie Burnett <rburnett at richieburnett.co.uk>
wrote:

> For anyone interested, this graph shows the response of a real TB-303
> filter set at full resonance for a range of cutoff frequencies:
>
> http://www.richieburnett.co.uk/temp/303vcf.gif
>
> There are lots of theoretical responses, mathematical transfer functions,
> and simulation results on the net, but i've never seen any real measured
> responses before.
>
> These responses were generated at the same drive level that the sawtooth
> VCO drives the filter in the TB-303.  (The shape changes if the drive level
> is changed.)
>
> Notice how the resonance is much stronger at higher frequencies, and runs
> out of steam at low cutoff frequencies.  The little peaks and dips to the
> right of the normal resonant peaks, are due to harmonic distortion in the
> filter and the VCA that follows it in the TB-303.  Also notice how the
> actual resonant peak of the TB-303 has a steeper slope on the right side,
> than the left side when the Q is high.  This "lop-sided" resonance is
> another artefact of the filter's non-linearity and occurs naturally in
> mechanical resonators as "hardening".
>
> http://www.zainea.com/lowresonances.htm
>
> Hopefully this is interesting to some TB-303 scrutinisers.
>
> -Richie,
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