[sdiy] Keyboard controller question

[Gustav Andersson]

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
>
>
>> From: Gustav Andersson <gusand at etek.chalmers.se>
>> To: synth-diy at dropmix.xs4all.nl
>> Subject: [sdiy] Keyboard controller question Date: Tue, 22 May 2007 
>> 18:57:04 +0200
>>
>> Hi
>> Some 2 years ago I built one of Ray Wilsons keyboard kontrollers ( 
>> http://www.musicfromouterspace.com/analogsynth/keybrdcontroller.html 
>> ), I never really got it to work properly then but after replacing a 
>> few broken ICs it now seems to be working fine except for one thing. 
>> Whenever I release the keys the s/h voltage drops half a volt or so 
>> resulting in the pitch dropping 5 or 6 semitones.
>>
>> I dont have scope at home but it seems I am getting a small pulse at 
>> the trigger input at IC3 (pin 13) that seems to discharge the 
>> capacitor slightly.
>> I'm powering the whole thing of +/- 15 volts instead of 12 volts 
>> which might screw things up.
>>
>> I'm thinking maybe the delay for the trig pulse is to short so I have 
>> tried larger caps for c14 and c13 but that didn't help. Though I must 
>> confess I dont understand exactly how that part of the circuit is 
>> supposed to work.
>>
>> Any suggestions are more than welcome.
>>
>> /gustav
>>
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