Fast analog sw. as VC resistor (0/1)

[Mark Smart]

> Hello again, everyone.
> 
> I've been working to *complete* the VC ADSR generator idea I littered
> this list with last week. I still don't have a complete breadboard, as
> I've changed the MUX to the MUCH better DG409, and have to wait for
> samples to arrive from Maxim before I can wire it all up.
> 
> However, I wanted to share the design (this far) with the members of
> this list, and get some feedback on the complexity. I've never seen a
> complete ADSR gen based on the SSM chips, so I have nothing to compare
> with my design. 
> 
> Is this circuit substantially more complex than a COMPLETE circuit
> based on the SSM chip? Admittedly, this design COULD be made simpler
> by removal of the output filter and input protection circuitry - but I
> personally HATE this idea being, as I am, of the "bulletproof" academy
> - in fact, this is one reason I specifically chose the Maxim DG
> series: they have some SERIOUS input protection, obviating the need
> for more external protection. 
> 
> I've included a shrunken schematic. It's ugly, but it's small. Soon as
> I get the whole thing complete I'll add a revamped "tech" section to
> my own web space and include full details. I've also been working on a
> VC 4 channel mixer/dual VCA/dual four quadrant multiplier (four
> inputs, two outputs; make whatever you want of it) which uses just
> three chips: a quad opamp, a 339, and yet another Maxim DG series
> switch. It's a bit more complex than a basic LM13600 based dual VCA,
> but it's MUCH more flexible. Again, I'll put complete details on this
> at my webspace - probably early next month.
> 
> And, for those who asked: here's the parts list for the circuit as it
> exists in this rev (0.9). The passives are all incredibly cheap;
> C_adsr should be of good quality and LOW ESR, and C_cv_filt is
> essentially a S/H cap and so should be a halfway decent film - but the
> rest of the circuitry can be just about anything, (Note, 'tho, that in
> ANY HF switching circuitry like this you should use LOW ESR power
> supply bypass caps; I use Sanyo OSCONS, 'tho Panasonic HFQs might be a
> bit cheaper.)
> 
> Qty  References                                             Value  
> -----------------------------------------------------------------
>  3  R_opt,R_adsr,R_pullup4                                    1K  
>  1  R_hyst                                                    1M  
>  4  Rp1,Rp2,Rp3,Rp4                                          100  
>  8  Rg,R_div,R_lp1,R_lp2,Rg_div1,Rg_div2,R_pullup1,          10K  
>     R_pullup3
>  1  R_bias3                                                  47K  
>  4  Rpd,R_bias1,R_bias2,R_pullup2                           100K  
>  6  Cp1,Cp2,Cp3,C_lp1,C_lp2,C_opt                          100pf  
>  2  C1,C2                                                  4.7uf  
>  1  U1                                                     DG409  
>  1  U2                                                     LM339  
>  1  C_cv_filt                                             0.01uF  
>  1  C_adsr                                                0.33uF  
>  1  U3                                                   LMC6082  
> 
> Many thanks go to Mark Smart and Christopher List - and to Daniel,
> whose "challenge" spurned me to start this whole mess. Looks like I
> might be able to make my own multiphonic VC synth after all - WITHOUT
> those rare and 'spensive chips!
> 
> Oh: does anyone HAVE a fatman? I'm wondering how the LM13600 based VCF
> performs. It's a pretty simple circuit; should be inexpensive enough
> to duplicate over four or eight modules.
> 
> 
> > http://radioactive.home.ml.org <-------------------------------
> 
> 

Cool! Now I just have to figure out how to view the schematic!

************************************************
*     Mark Smart                               *
*     Network Technician                       *
*     University Communications Inc. (UCI)     *
*     smart at medusa.nn.com                      *
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