[sdiy] Mood Ladder Filter: Many Questions!

[HOSHUYAMA]

Hello List,

harrybissell wrote:
 > iirc Osamu Hoshuyama has a scheme to do highpass with the ladder

This schematic?

   http://www5b.biglobe.ne.jp/~houshu/synth/Vcfv0212.GIF

Transistor/diode ladder can be used as a Sallen-Key filter as in Alisa.

   http://www.ruskeys.net/eng/pasp/alisa1377/pasp.php#sc
   http://www.ruskeys.net/eng/pasp/alisa1387/pasp.php#sc
   http://www.geocities.com/rusynth/alisa.htm

High pass input and band pass input can be added to obtain a multimode 
filter like the Steiner VCF, which is the easiest way IMO.

http://www-timc.imag.fr/Yves.Usson/personnel/SDIY/Modular/EN/STEINERVCF/

Best,

Sam Hoshuyama
Saitama, JAPAN.

harrybissell wrote:
> MOOD ladder...  ?
> 
> I've heard of mood ring  :^P
> 
> iirc Osamu Hoshuyama has a scheme to do highpass with the ladder
> structure.  The idea is not his, but he added a really clever implementation
> where he uses capacitors to form the voltage divider at the top of the ladder.
> 
> This gives about an 18dB hipass.  I think you can get bandpass as well by
> injecting
> the input to the top and bottom of the ladder at the same time.
> 
> The Oberheim multi-mode filter is 'possible' with the moog ladder, but I would
> NOT recommend that.  You need to buffer each stage of the ladder, have inverted
> outputs, AND be able to kill one stage.  If you were willing to forego some of
> the
> outputs, you need not kill the one stage (hardest to do imho).  All told the
> amount
> of circuity would be incredible.  Use some four pole chip like the SSM2040,
> 2044,
> CEM 3320 and start from there for this method.
> 
> You can add extra poles... until you run out of power supply voltage. Someone
> made
> a five pole version.  As you add poles, the cutoff becomes more abrupt (or
> should... if they track well).  Might not be as musical as you might like.
> 
> H^) harry
> 
> D A F wrote:
> 
> 
>>Hey gang,
>>
>>I'm thinking of building a Moog (or ARP) style transistor ladder VCF.  I had
>>some thoughts about possible variations on the basic design.
>>
>>Can this style filter be made into a multi-mode filter, where you can have
>>high-pass or low-pass options?  I think that's usually done with a
>>state-variable filter, no?  But I am guessing you could somehow include the
>>ladder inside a feedback loop to get a high-pass response instead.  Or what
>>if you used AC - coupled inductors in place of the caps in the ladder?
>>
>>Could you "tap" the filter at various points to obtain different numbers of
>>poles?  I mean to say that whereas the stock circuit has the differential
>>buffers at the top of the ladder and thus yields a 4-pole filter, could you
>>move down the "rungs" of the ladder to get 3 pole or 2 pole or 1 pole
>>responses?
>>
>>Is there any reason why you couldn't add more "rungs" to the ladder to get
>>even more poles?
>>
>>Also I'm wondering if there is some consensus on how to get the 'best' sound
>>from this style filter, by 'best' I mean the "moogiest" sound.  I have
>>schematics for the Moog circuit and also the ARP 4034 which use CA3086's
>>"selected" (for matching, I presume).  I have both 3046 and 3086 chips so
>>was going to use one of those.  I think I remember hearing someone say
>>something about using different capacitor values for the different rungs of
>>the ladder - was this ever done stock or was this a mod someone came up
>>with?
>>
>>I've never made one of these before, so I'm just doing some thought
>>experiments before I decide on the final circuit.  Sorry for all the
>>questions... any insights cheerfully welcomed!
>>
>>Dave
> 
> 
> 
>