Eurorack ADSR Envelope - I'm not hearing the decay

[waldenpotato]

I've a eurorack envelope gate input being controlled by a Mutable Instruments Yarns module. This module has a gate output of +5V.

I then have the envelope controlling a classic vca.

I've got the shortest attack and release settings and the sustain at about 50%. When I adjust the decay I hear no difference when listening to the volume. It appears as though the sustain is just controlling the overall volume level.

I would expect the decay to adjust the time it takes to get from the envelope's peak to the sustain level, but I'm not hearing any difference. Am I doing something wrong?

[Synthbuilder]

I would expect the decay to adjust the time it takes to get from the envelope's peak to the sustain level, but I'm not hearing any difference.

This would be the expected behaviour. Turn the sustain down to zero and see if the Decay control still does nothing. If it doesn't then something is most certainly wrong.

With no gate connected put the module into loop mode. Set the attack time and sustain to zero. Does the output LED flash and can you control the speed of the flashing with the decay control? If not we can say for sure now that the decay pot is not doing what it should.

Possible faults:

The decay pot is broken or pin 1 of the pot is not soldered. The way to test this is measure the voltage on pin 4 of CN2 (accessible from the back of the module). This should vary between 0V and 10V. If it's stuck at 10V that is your problem.

U3 is partially dead which may have been caused by a short from pin 15 to pin 16.

Tony

[waldenpotato]

I just got the chance to look into this. I have 8 envelope generators and 3 of them are having the same issue. It's as if the sustain level is controlling the peak of the envelope. When the sustain is at 0 the envelope doesn't open at all - I took a look on my oscilloscope.

In loop mode - with the attack and sustain at 0 - the decay *does* control the speed of the output led as expected.

I also checked the voltage at pin 4 of CN2 for all of the affected modules. This pin's range for all of them does indeed range from 0V to 10V.

Any other ideas? I looked over the circuit boards and didn't see any obvious shorts on the ics or missed solder joints.


Thanks.

[Synthbuilder]

Any other ideas?

To be honest I'm not sure. That it's on three modules and not the other five suggests a wrong component somewhere on those three.

Look at pin 2 of CN5. This is the sustain pot's output pin. It should go from 0V (min) to +5V (max) when the sustain pot is turned.

In loop mode what is the maximum voltage you see at the peak? It should be +5V.

Check that D1, D2, D3, and D4 on the pot board are the right way around. Check D3 is the right way around on the main board.

[waldenpotato]

Check that D1, D2, D3, and D4 on the pot board are the right way around.

I just checked and D3 on the pot board is in the wrong orientation on all of them. All other diodes are okay, though. This must be the problem! I should have known better and checked all the components where orientation matters.

Shoot - no matter how careful you think you're being this is a lesson to be more careful.

[waldenpotato]

Update:

I was able to desolder and resolder in the correct orientation. The envelopes are behaving as expected now.

[Synthbuilder]

The envelopes are behaving as expected now.