synthy filters for guitar..

[nick d]

http://www.diystompboxes.com/smfforum/Themes/diytheme/images/bbc/quote.gif

           I know , max current for13700 is 2mA , so it anybody is not familiar with Ohm's law , learn it NOW !

[deadastronaut]

Cool vid nick...sounds great. 

[nick d]

          Thanks , Rob !  When I clear up the bench a bit , I'll mess with a 9V version . Not tried the Escebedo version , the resonance section on that looks odd compared to the others - most have an op-amp with diodes  (like a TS ) in that area . Perhaps that's why you had trouble with it . I think I'll try mine as it is re-arranged for single-ended 9V , and tweak it up .

         Assuming it works , I will share my results .

[deadastronaut]

Nice one,  i removed the resonance pot entirely..

i had a thought about having 2 lots of filter caps on each opamp...

so it can be 4 in total using both opamps....2 each side....

ill give it a go on one opamp to see if it works...

[nick d]

        I have good news ! My 9V version of the MS20 clone works ! Not put any modulation on yet , just varied the control current to pins 1 + 16 with a pot  . 
        The schematic I used is basically the Rene Schmidt version ( RS 20 ) , with  +15 = 9V
                                                                                                                     Gnd = Vref
                                                                                                                     -15V = GND

        Vref is from a pair of 100k's as a potential divider into an op-amp buffer . The buffer is important , without it , Vref is all over the place
       
        Lots more work and tweaking to do , but the basic circuit is a runner !

[garcho]

The buffer is important , without it , Vref is all over the place

I ran into that problem right away.

[deadastronaut]

cool nice one nick..

i just ordered a couple of 13700's from tayda, ...hopefully these ones will work.

then i can try it...AGAIN.

[nick d]

         I usually get mine from Bitsbox , £1.24 at last look . I got 10 last time , heard rumours that they were getting scarce .

[deadastronaut]

ahhh bitsbox..of course, oh well ,  i'll wait..

just messing around with a crude envelope detector...( different sound to light circuit , no 386)

[garcho]

i just ordered a couple of 13700's from tayda, ...hopefully these ones will work.
then i can try it...AGAIN.

Yay! You'll be happy you did. A true VCF with a real current source sounds so super synthy!

[nick d]

          Got this running with an LFO now , after a lot messing with the control node . The sweep is not as extreme
            as the  +/- 12V version , but that is as expected . At low LFO rates , the effect is very mild on a clean signal
            unless you crank the resonance - sounds OK with some dirt , though !
         
         Hopefully , I'll post a schematic soon , after a little more twiddling .

[Strategy]

I'm still dreaming about a "frostwave resonator" workalike - ms20 lp and hp filters in same box!!!...

Strategy

i just ordered a couple of 13700's from tayda, ...hopefully these ones will work.
then i can try it...AGAIN.

Yay! You'll be happy you did. A true VCF with a real current source sounds so super synthy!

[nick d]

                     



                                  [/URL][/img]                                                         




                                  Did that work ?   ( Using PhotoBucket for the first time )

[nick d]

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[nocentelli]

nope

[nick d]

                                                                                                                                                                 



                 Aaaahhhhh .... GOTCHA !
                             
                 Scanners , don't talk to me about scanners.......... ! It's been one of those days , y'know ?
                 
                   Anyway , here's a schematic of what I've got in the breadboard right now . One or two points to note -

                   Separate  V/2 connections for filter and LFO , marked as " Vref " and " Vr " . The op-amp buffer for Vref is essential ,
                      Vr for the LFO probably should be .

                      I didn't use a level control , the LFO is at max output . If needed , it works just like a volume control ( See box at
                        bottom of schem ) .  

                      Extra CV inputs can be added at point " X " , via separate resistors - I used 33k , any less and the LFO
                       output seems to " bottom out "  and " thump "

                      I used 100nF for the LFO rate capacitor which gives a long , slow sweep , several seconds a cycle up to around
                       5 Hz - adjust to taste !    Slight thump noticed at high rate .
                       
                       The pot values and tapers are just what was handy , could well be improved on .
         
                       There is a slight volume loss at low resonance , so a simple boost at the input would be useful .

                        Overall , the sound is similar to the +/- 12 V version , but the modulation level needs to be pretty well
                         maxxed out , though . Sounds good with the resonance well up and fed with some dirt , mind you !
     
                        I have to say that the control node section looks a right mess , as a result of my semi-random
                          fiddling - that 47k to ground looks WRONG - but if you pull it out , it don't work !
                       
                       Anyway , breadboard it and  see what you can come up with - envelopes could be worth trying .  

[nick d]

               Oh , in my infinite stupidity , I omitted to label the pots - DERRRR !

                  47k Log = Resonance
                  100k Lin ( at bottom )   Frequency
                  100k Lin ( in LFO )     err , LFO rate
       

                   Also , the 270R 's in the filter were 220R in the original , but I ran out . Probly makes no odds .

[nocentelli]

Anyway , here's a schematic of what I've got in the breadboard right now

Thanks for this! Going to try it out soon. Quick question - All other MS20 schematic I've looked at (not that many tbh) have the control voltage going to pin1 and 16 simultaneously, here the LFO seems to connect via a tiny cap to pin 5 where the resonance feedback also connects - What difference, if any, does this make?

[nick d]

             Well spotted , Sir ! My boo-boo - pins 1 and 16 SHOULD be connected to the control voltage node , collector of the 3906 .
              The 470pF should connect to the output of the op-amp in the resonance circuit .

              Been looking at filter schems so much my brain has gone cross-eyed !
              Thanks for pointing that out !

[nocentelli]

No problem, I haven't tried a filter with an opamp for the resonance before, and it's good to kno that it works with that LFO: Thanks again for posting it up.