[sdiy] Moog Ladder in HP mode!

[harrybissell]

what YOU wnat to do is study Osamu (Sam) Hoshuyama's website
really carefully. He's got an idea for loading the signal at the top of the
ladder that is really interesting. (not sure its tested, but it looks like it
will work with very high probability of success)

Simulation results show that feeding the ladder at the top is really a
highpass...
but as you noticed, not a perfect one. I'd prefer this method to the original
Moog hipass design anyday for ease of making it work well.  The Ladder
filter is much easier to keep control voltage from breaking through.

H^) harry

Karl Dalen wrote:

> Hi!
>
> Maybee someone has a clue to this!
>
> I have been experimenting with the 24db ladder filter and wonder,
> has any one any good ideas for getting a HP response out of that
> filter in simple way? Has anyone taken a look under the Moog Voyager
> hood to se how Moog did it?
>
> I have tested a trick which i found at the web somewhere (cant remember
> where) it involves to send the input signal to the top left emitter of the
> first transistor pair (top) through one capacitor, this works to some
> degree but as it seams it alter the output impedance the extra capacitance
> so it then shift the last pole of the filter and this affects the ability
> to resonance , (one can do a differential input and send it to both
> emitters aswell) it still oscillates but has quite difficulty to do so
> and as it seams the resonance disappear at low frequency, which i guess
> is the natural behavior after one have alter the phase shifts of the last
> pole !? The responce is somwhat like of a HP but i think it sounds
> somewhat strange! I might be completely wrong in my assuming but anywhay!
> I wonder would it be a insane thing to use two OTA's feeding the emitters
> through series resistors to the emitters so they see just a current
> instead of a capacitive load? Has anyone tried to use the base of the
> top trannys as HP inputs? Would that work?
>
> Thanks!
>
> Regards
> KD
>
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