Problems with ADSR circuit....

[Tony Allgood]

Chris wrote:
> 
> Hi Folks, 
> I've gott a wierd problem...I've built the ADSR circuit from 
> Electronic Synthesiser Projects by Berry IIRC. It's a basic 4011B 
> logic gates controlling a 4066B design charging and discharging a
10uF 
> tantalum cap....the problem is the Release control seems to be acting

> as a voltage offset. If the Release is set to minimum then the A, D, 
> and S portions of the envelope are fine, but if I turn it up the 
> output increases up to a max of nearly 11 Volts....anyone seen this 
> problem with this circuit before?...there is a discharge path 
> available through an LED, so it's not some kind of open output
effect, 
> and the logic switching seems to be fine....I'm lost...

This as you have correctly said should not happen. But it would if the
4016 has died. However, the circuit does suffer from other pitfalls.
IC2c should not be used like this. CMOS circuits really should not have
analogue inputs, they can handle it for short periods of time, ie. 10mS
monostable..etc, but the timing cap of an ADSR!! This is a sure way to
kill a chip. Also, the circuit has no faciltiy to reset an attack
portion if the gate is released. Thus the A portion is always carried
out. Yukkkk!  There should be an additional mono to reset the flip-flop
when the gate goes low. Much better circuits are available.

Tony Allgood.

Penrith, Cumbria, UK     

e-mail: oakley at enterprise.net

'I may live in the middle of nowhere, but the views are nice'