[sdiy] Re: [motm] Re: Taking pre-orders for JH. 36dB/oct LPF now

[JH.]

>> I've ordered the boards from the factory already, but I always
>> get more than I've ordered (and have to pay them: small print of
>> contract that I have to take over-production),
>
>Interesting commercial practice.

I think it's pretty standard in that business. They have to make more PCBs 
than I ordered, in order to make sure they'll have enough that test good (my 
PCBs are tested with a needle adapter). And when they have more good ones 
than I ordered (which is to be expected), I have a chance to sell them, but 
*they* could only throw them away.

>> The waveform crossfading ("scanner") is arranged ina way that
>> S&H is adjoining "square" on the left side, and
>> "self-modulation" on the right side. That means, in S&H position
>> you have true random staircases. Turn the waveform pot slightly
>> to the left, and you get a tad of regular rectangle mixed in:
>> the steps become less random in a way that large steps are more
>> likely. Turn the waveform pot slightly to the right, and the
>> random S&H gets mixed with the dirt of an audio-rate
>> self-modulated filter. That's especially impressive at high
>> resonance settings. I got the idea for this from the Prophet 5's
>> Poly-Modulation and the CS-50's and Minimoog's external
>> modulation input, and - for a phaser application - from the EMS
>> Synthi HiFli.
>
>Thanks for the explanations. Where does the self modulation comes
>from ? lfo_mod seems to be in the wrong direction. Perhaps AUX
>MOD IN should be normalled to something else than ground ?

Sure. In my prototype, I've hard-wired it to the "DRY" output (pre-amplified 
input signal).

>This is what I had in mind :
>
>CV Pole 1 Pole 2 Pole 3 Pole 4 Pole 5 Pole 6
>       ~ 0.42 V LP LP LP LP LP LP
>0.42 V ~ 1.25 V LP LP LP LP LP AP
>1.25 V ~ 2.08 V LP LP LP LP AP AP
>2.08 V ~ 2.92 V LP LP LP AP AP AP
>2.92 V ~ 3.75 V LP LP AP AP AP AP
>3.75 V ~ 4.58 V LP AP AP AP AP AP
>4.58 V ~       AP AP AP AP AP AP
>
>The idea is that the higher the CV, the more high frequency
>content there is.
>
>Looks like it could be done with an LM3914-type circuit.

> But the 6 stages are interchangeable only with the "Slope" (or
> pole spread) potentiometer at ccw position. When the poles are
> spread apart, it makes a difference which one gets the
> complementary zero (= switchet to all pass), and which one
> doesn't.

I see. Yes, you should be able to add this (off-board) with a couple of 
comparators.
But then again, the "SLOPE" parameter already lets more high freq contents 
in, gradually.

JH.