[sdiy] Keyboard controller question

[Gustav Andersson]

Fixed it! :)

I replaced c13 with 6,8uF and c14 with 10uF which is what I could find 
lying around. Seems to work now at least
If i understand everything correctly C14 should be controlling the delay 
of the trig pulse and 10uF should give me about 5 mS which I like better 
than 11 ms with 22uF (I also tried 680uF and got like half a second of 
delay before the pitch changed, felt really weird).

But I still don't know exactly what caused the problem :(  Something 
about the pulse shaping probably.

But the S&H seems to be stable anyway, I had it on for about on minute 
with no discernible drop in frequency. And I'm only using a TL082 for 
IC4 instead of the pricier LT1112 Ray recommends.

/gustav

Needham, Alan wrote:
> Gustav, hi,
>
> I wondered if this was a S-H fault, kind-of agreeing with Anthony, but ...
> IF the S-H circuit is leaky, there will be a 'glissando'? to one end of the range when you release a key, probably quite slow.
>
> If the S-H gate stays open just a fraction too long after you release the key, the key bus ramps from the current key voltage down to about -12v at a rate determined by R10 and C1 (1M and 5nF). If the gate is still open then this ramp will be seen by the S-H, causing a fairly constant drop in VCO pitch (some semitones) regardless of what key is pressed.
> If the above is true then as long as you hold a note the above problem will be hidden - only on key release will it be seen.
> I guess the actual fault will be in the pulse-shaping section (circuit diagram page 2).
>
> Does the trigger out behave properly ?
> is the trig out signal a quick pulse on key press?
> is the Gate out active all the time a key is pressed?
>
> 	Alan
>
> -----Original Message-----
> From: synth-diy-bounces at dropmix.xs4all.nl
> [mailto:synth-diy-bounces at dropmix.xs4all.nl]On Behalf Of Gustav
> Andersson
> Sent: 23 May 2007 8:38 AM
> To: Synth-diy at dropmix.xs4all.nl
> Subject: Re: [sdiy] Keyboard controller question
>
>
> Thanks for the tip, however I think the S&H is actually working as it 
> should since the output voltage remains the same as long as I hold at 
> least one key down. At least for a minute or so.
>
> /gustav
>
>
> Anthony Rolando wrote:
>   
>> There was a good discussion about S&H circuits last week... check the 
>> archives because it sounds like you have some sort of leakage (wrong 
>> cap type) or DC input offset problem (wrong op-amp type). Just a thought.
>>
>> T
>>
>>
>>