[sdiy] sync circuit woes

[Simon Brouwer]

Ian Fritz schreef:
> At 01:17 AM 11/21/2008, Simon Brouwer wrote:
>
>> >Still, is the value of this cap all that
>> > critical?  Also, would it be necessary at all if an opamp had been
>> used as
>> > a
>> > comparator here instead of the LM311?
>>
>>Yes and yes.
>>
>>If this capacitor is too small the sawtooth will not be completely reset,
>>so that its amplitude is decreased and its frequency will be too high.
>>If the capacitor is too big the duration of the reset will be too long so
>>that the sawtooth shape is affected and the high notes will be flat.
>
> Exactly. And as a corollary would you agree that it is impossible that a
> 10
> pF cap would work, but a 22 pF cap would not.  :-)

If the channel resistance of the FET is low enough that a 10 pF would work
well, a 22 pf would also work, but it would result in longer reset time
than necessary. You want a capacitor which is just big enough (with some
margin to account for tolerances).



-- 
Vriendelijke groet,

Simon Brouwer
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