In principle both A-171 and A-129-3/4 are VC slew limiters. But the working
principles and the features are very different.

The A-171 uses an operational transconductance amplifier (OTA CA3080) to
create the slewed voltage. It has a continuous output (no quantization).

For the vocoder modules we searched for a solution to control up to 15 slew
limiters simulateously at low cost. And the solution should include the
freeze and follow feature with (digital) control inputs for these functions.
We found that a time-division method with a constant frequency meets this
requirements. In principle a PWM signal (like the rectangle output of a VCO)
controls a voltage controlled switch that is used to interrupt the line
between the CV input and a capacitor that is used to slew the voltage. So
the time share used to charge/discharge the slew capacitor is voltage
controlled. Consequently the CV output of the A-129-3/4 is not really
continuous (in contrast to the A-171 output) but a sequence of capacitor
charge/discharge curves with constant time intervals (~ 10ms as the
oscillator frequency is ~ 100Hz). For the vocoder control this type of slew
limiter is OK but if you want a real VC slew limiter I'd recommend the
A-171. Besides the A-171 has a much wider control range than the A-129-3/4
and the CV control is much more sensible.

Best wishes
Dieter Doepfer

> -----Ursprüngliche Nachricht-----
> Von: Doepfer_a100@yahoogroups.com
> [mailto: Doepfer_a100@yahoogroups.com ]Im Auftrag von Bakis Sirros
> Gesendet: Dienstag, 28. Juni 2005 10:41
> An: Doepfer_a100@yahoogroups.com
> Betreff: Re: 1 a171 vs a129/3 and a129/4
>
>
> hello bryan,
> the a129/3 + a129/4 process(with vc-slew limiting)the
> DC cv signals that come from the a129/1 analysis
> section module. these are standard DC cv signals that
> are used to control the 15 vca's(of the a129/2
> synthesis section module) that come after the 15
> filters of the a129/2.
> so, this means that the a129/3+a129/4 combi can work
> exactly like the a171. they both provide vc-slew
> limiting for cv signals.
> dieter correct me if i'm wrong.
> best regards,
> bakis.
>
>
>
>
>
> --- Bryan E Cornell < bcor@... > wrote:
>
> > Sorry, I got the wrong number in my last post. I
> > meant to say,
> >
> > "Will the a129/3,4 do everything that an a171 will
> > do " I'm talking about the vocoder submodules.
> >
> > Bryan
> >
> >
> >
>
>
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