Hi John,
thanks a lot for the info. Checking my steiner VCF, with res at
oscillation, it cover all audible spectrum between 2.5 and 6, I`ll do
the mods you posted but I like that extra sub-audio at 0-2.5 for
modulation.
Best Regards,
Josue.
----- Mensaje Original -----
De: Richard Brewster <pugix@...>
Fecha: Sábado, Enero 3, 2004 3:31 am
Asunto: Re: [cgs_synth] Steiner VCF Tweaks DIY
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thanks a lot for the info. Checking my steiner VCF, with res at
oscillation, it cover all audible spectrum between 2.5 and 6, I`ll do
the mods you posted but I like that extra sub-audio at 0-2.5 for
modulation.
Best Regards,
Josue.
----- Mensaje Original -----
De: Richard Brewster <pugix@...>
Fecha: Sábado, Enero 3, 2004 3:31 am
Asunto: Re: [cgs_synth] Steiner VCF Tweaks DIY
> <html><body>SRC="http://servedby.advertising.com/site=552006/size=300250/bnum=107309
>
>
> <tt>
> Nice work, John! I printed out your email for my notebook. This
> is
>
> really helpful, as I am about to build two Steiner VCF boards.
>
>
>
> Thanks,
>
>
>
> -Richard Brewster
>
>
>
> John Loffink wrote:
>
>
>
> >To recap, I built my Steiner VCF and noticed that the entire
> frequency range
>
> >was covered by knob positions 0 through 5. I also wanted the
> direct control
>
> >voltage input to track to approximately 1 V/octave. Here are
> the tweaks I
>
> >did to bring this circuit up to snuff. Your circuit may vary,
> so proceed
>
> >with caution if changing anything from the nominal values
> recommended by
>
> >Ken.
>
> >
>
> >Output "level" jumper/resistor: I put 180K in the
> level position, in
>
> >addition to the 47K already in the op amp feedback path, or
> just put 220K
>
> >total in the 47K position. This gave the maximum resonant
> oscillation
> >amplitude without clipping and brought the normal non-
> oscillating output to
>
> >a better level.
>
> >
>
> >FREQ knob adjustment. As stated, my original range of 0 to 5
> (out of 10)
>
> >covered 20 Hz to 20 KHz. There are two resistors to adjust
> for this.
>
> >First, decreasing the size of the input divider resistor on
> the CV input
>
> >section, 1K in Ken's circuit, increases the range of the
> frequency control.
>
> >I put 2.2K in parallel with the 1K resistors, or you can swap
> the 1K with a
>
> >680 ohm resistor. Note that this also affects the Control
> voltage inputs,
>
> >so they will need to be adjusted. I also added 220K of series
> resistance to
>
> >the FREQ knob. This tends to center the frequencies on the
> FREQ knob so 200
>
> >Hz is near the center. With these values the knob range 0 to
> 10 sweeps
>
> >approximately 5 Hz to 25 KHz. This was measured by putting 20
> Hz and 20KHz
>
> >sine waves into the LPF input and measuring the amplitudes at
> min and max
>
> >FREQ positions. I also tested audibly using white noise as an
> input.
> >
>
> >I wanted my direct CV input (no knob) to sweep approximately 1
> V per octave.
>
> >Just realize that the tracking on this filter is not that
> accurate. I
>
> >measured this by putting the filter into self oscillation and
> reading the
>
> >frequency with a frequency counter. Note that the filter
> oscillates from
>
> >about 200 Hz to 6.5 KHz, so that's the only range that was
> measured. For
>
> >this adjustment I added 148K in series to the existing 220K
> input resistor,
>
> >or just exchange the 220K input resistor with a 360K. Note
> this setting is
>
> >dependent upon the above mentioned input resistor divider
> modification.
> >
>
> >For the attenuated CV input, I wanted a 5 volt MOTM envelope
> to sweep the
>
> >entire frequency range. In the original circuit the range was
> fine, but
>
> >when I changed the CV input resistor divider the range became
> too small.
>
> >This requires decreasing the size of the input series resistor
> from the pot
>
> >wiper. In Ken's circuit it is 220K, I put 300K in parallel,
> or just swap
>
> >the 220K resistor with a 120K resistor.
>
> >
>
> >Ken, if there is this much variation per circuit you may want
> to consider
>
> >adding some trim pots to any future revision of the PCB. I
> double checked
>
> >all transistors, resistors and diodes in the circuit and
> everything was
>
> >originally built to your BOM.
>
> >
>
> >This is a great filter, by the way, with lots of character.
> It sounds very
>
> >Moog ladderish with the low pass input, and mixing VCOs into
> the LP, HP and
>
> >BP inputs gives some great effects.
>
> >
>
> >John Loffink
>
> >The Microtonal Synthesis Web Site
>
> >http://www.microtonal-synthesis.com
>
> >The Wavemakers Synthesizer Web Site
>
> >http://www.wavemakers-synth.com
>
> >
>
> >
>
> >
>
> >
>
> >
>
>
>
> </tt>
>
>
>
>
> <tt>
> See the following URLS for the CGS Modular Synth home page:
>
> Main: http://www.cgs.synth.net/
>
> Secondary: http://otherunicorn.0catch.com/synth/</tt>
>
>
>
>
>
>
>
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