Ok, i have a good pure sawtooth at the output of CA3140 but after it
goes though the next TL072 the sound gets mangled and acts like a
lowpass filter. I changed the 68pF cap to 18p and i get a better range
over the octaves, but i have opted just to remove it. I also had to
lower the value of the 330k Resistor because the gain was too high.
Thanks for all your help. It seems to be working fine now.
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--- In cgs_synth@yahoogroups.com, Richard Brewster <pugix@e...> wrote:
>
> Double check all the capacitor values again. A 68pf cap is in the
> feedback loop of the sawtooth buffer op amp. If this is a large value
> by mistake it would act as a low pass filter, cutting off higher
> frequencies. I used 18pf there. It is only to prevent parasitic
> oscillations.
>
> Richard Brewster
>
> josh wrote:
>
> >Thanks for the reply,
> >I'm double checking everything but nothing seems abnormal. When i
> >apply CV it changes octave correctly and can be tuned but the lower
> >notes have so much gain that the upper haves of the signal are clipped
> >and the output is about 6V pk-pk. when i play the higher notes the
> >gain starts to decrease. two or three octaves up the amplitude is less
> >than 1V pk-pk. Should i get a clean saw with this? Is decreasing gain
> >normal for the higher octaves? I'm going to go on the assumption that
> >i have an improperly placed resistor. Does amyone have any suggestions
> >or things to check to narrow down the fault?
> >
> >--- In cgs_synth@yahoogroups.com, sasami@h... wrote:
> >
> >
> >>I suggest you look elsewhere for the fault - more likely a wrongly
> >>
> >>
> >placed
> >
> >
> >>component. Using 2% resistors will at most cause a slight
difference in
> >>stability. It certainly won't be the difference between it working
> >>
> >>
> >or not.
> >
> >
> >>Ken
> >>
> >>
> >>
> >>>Hey. I just built the ken stone vco and i am trying to test it. I
seem
> >>>to be having a problem. The oscillator with no CV applied looks
> >>>clipped. When i add higher CV voltages the amplitude decreases and it
> >>>is no longer clipped. It also does not give a clean saw output. It
> >>>looks more like a half rectified sinewave. I believe my problem might
> >>>lie in that i used alot of 2% metal film resistors since i had
alot of
> >>>them already. Does anyone have any sugestions.
> >>>Thanks
> >>>Josh
> >>>
> >>>
> >>>
> >>>
> >>>
> >>>
> >>>
> >>>The CGS Modular Synth home page: http://www.cgs.synth.net/
> >>>
> >>>Yahoo! Groups Links
> >>>
> >>>
> >>>
> >>>
> >>>
> >>>
> >>>
> >>>
> >>>
>
>>_______________________________________________________________________
> >>Ken Stone sasami@h... or sasami@c...
> >>Modular Synth PCBs for sale <http://www.blaze.net.au/~sasami/synth/>
> >>Australian Miniature Horses & Ponies
<http://www.blaze.net.au/~sasami/>
> >>
> >>
> >>
> >
> >
> >
> >
> >
> >
> >
>