simple attack-release envelope circuit is acting bizzare

Thread Starter

Green Bean

Joined Mar 31, 2017
126
I designed this circuit as an AR envelope generator:

http://tinyurl.com/y6vj5o2s

The top pot controls the attack time, the bottom controls the decay time. The envelope is triggered when the switch is clicked. In practice, the LED would be part of a vactrol, but there isn't a way to simulate that in this sim. The voltage buffer is there so that only the voltage is transferred from the charging capacitor part of the circuit (otherwise the pots would affect the brightness of the LED). I'm just a noob, so this is only how I think it should work. I guess I must be missing something because...

At first the circuit seems to work fine. The attack time was working completely. However, I noticed that even when the decay pot was turned all the way down (which should have produced an instantaneous release) the release was still very long. Actually, changing the position of the pot didn't seem to have much of an effect at all, the release time was always about the same length, very long. When I removed the pot, I got the exact same result. I even removed the diode, and I was still getting the same long release. Here's that in the sim:

http://tinyurl.com/y7kvcpc8

Anybody got any ideas as to why this is happening?
 

ericgibbs

Joined Jan 29, 2010
8,868
hi GB,
One cause of the delay is the forward resistance of the diode, could be in the order of 500R to 800R, path to the cap.
E
 

crutschow

Joined Mar 14, 2008
23,506
The bottom pot can do nothing because it is either open (no connection) or connected to +5V through a reverse biased diode.
If you reverse the switch so the two diodes are connected to the common terminal, with the other terminals going to +5V and ground, then the circuit should work.
 

Thread Starter

Green Bean

Joined Mar 31, 2017
126
The bottom pot can do nothing because it is either open (no connection) or connected to +5V through a reverse biased diode.
If you reverse the switch so the two diodes are connected to the common terminal, with the other terminals going to +5V and ground, then the circuit should work.
Ahhhhh, ok. So it was like floating sort of. I see. Changed it and now it's working properly, thanks. :)
 
Top