[sdiy] Substitute for IMF-3958 ARP 4015 S/H SubModule

[James Dunn]

If I understand you correctly and you just want to replace the 4015 S/H 
module with Yves Usson's circuit, I think I would try the following:

1) Connect wiper of S/H level pot R319 (100k lin) to R10 of Yves Usson's 
S/H.
2) Connect R391 (47k) of S/H clock input to pin 12 of Yves Usson's S/H.
3) Connect R393 (1k) of S/H output to pin 7 (U2b) of Yves Usson's S/H OR 
pin 8 (U2c) if using the slew rate function.

> 2. The Circuit gets a nice Square wave. That ARP pulse stuff just 
> won't work. I have no Idea why they changed the clock from Square to 
> _|_ this ??

The transistor in the ARP S/H circuit needs to be turned on for a split 
second to sample the input voltage, so C119 reduces a gate signal to a 
trigger signal.
>
> Anyhow if I'd remove R321 and C86 from the Noise Source / S/H Input it 
> will probably work. But then what effect would the 100K S/H Input 
> Slider have ? HMM...
As mentioned above, I would just leave them be and you can use R319 as a 
level control for the attenuation of the input signal (ie noise)
>
> Also if I forget about R391,R392,C119,R390 and just jumper the whole 
> thing straight from the INT Clock Output then it would work too.

These do a similar function to C4, D2 and R11 in Yves' circuit. I would 
just use the original ARP parts and save the bother of replacing this 
section.
>
> What is the deal with that "ELECTRONIC SWITCH" I never understood what 
> it 's supposed to do. With the A, B, C Outputs? Can somebody explain 
> that part of my synth?
It's a bidirectional switch for audio or control voltages and switches 
one input to 2 alternate outputs, or two outputs to 2 alternate inputs 
according to the S/H master clock rate.

James