Problems with ADSR circuit....

[Chris Crosskey]

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...

chrisc