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

JH. jhaible at debitel.net
Thu May 28 08:45:39 CEST 2009

>Thank you. I hope the pre-order phase is not closed

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), and I also order a few more than I have pre-orders 
for. :)

>I guess a third way to build the varislope would be to omit the
>modulation source but keep the DG419 so it can still be a phaser
>or filter.

Yes. And there are probably a hundred other options, too. I leave this to 
the diy-builder himself.

>Personally, I'm not sure about this modulation source. I suspect
>that, on my unit, the waveform pot would be permanently stuck in
>pure sine position, making the scanner redundant.

I am *very* sure about this modulation source, because I came to love it in 
my JH-4 synthesizer module over many years.
Don't under-estimate the Sample&Hold modulation on a phaser with high 
resonance! And this is a very special S&H, with a kind of overshot or spike 
(for lack of better description) at the beginning of each new random sample, 
which makes the S&H more "agressive" than a "perfect" S&H would be.
But there is more:
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 

>The other
>sources I see myself using (velocity, EG and sawtooth LFO) all
>have to come from other modules anyway.

Yes, it makes a lot of sense to use external modualtion sources. My on-board 
modulation source is kind of special (I hope!), but it doesn't have saw 
waveforms, for instance. And for VCF applications, you need an ADSR of 

>In theory, each pole could individually be switched between
>all-pass (phaser) and low-pass (filter) under voltage control. If
>all poles are sonically interchangeable, a single CV could be
>used with the number of LP poles being 6/5 of the CV. No idea how
>to do that, nor how useful it would be.

I'm not entirely sure if I understand what you mean. 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.


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