VCA bleed?

Hi all,

Well just received my 301 and I’m getting very noticeable vca bleed with level to 0 and gain set to 1. Any idea how to correct this or am I doing something wrong? Just have a sin osc and a linear vca that’s it!

What source do you have assigned to the VCA’s level sub-chain? In other words, if you set the gain to 0 does the bleed go away?

Just a simple AD envelope from mutable peaks, yes the bleed goes away when I set the gain to 0.

Peaks leaking some voltage when it should be outputting zero?

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That means the voltage from mutable peaks is not exactly zero. In the analog domain, it never really is. The reason why you are not expecting this behavior is probably because you are not used to using a Linear (bipolar) VCA for audio. Which reminds me that I should get that Exponential VCA out the door.

Anyway, in the meantime, put a Rectifier in the level sub-chain. Assuming Mutable Peaks outputting a slightly negative voltage when closed then that will remove the bleed. If not, then you might need to put a Offset before the Rectifier and set its offset to a small negative value.

Let me know if the reason why this works doesn’t make sense to you.

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Thanks Brian, yes the offset + rectifier in the vca’s level sub chain does the trick! awesome :smiley: the reason why this works escapes me though as I’m not sure what the rectify module does yet. Thanks for your help.

The rectifer in this case cuts out all negative voltage. Put a sine wave before the rectifer and check the scope. You will see what it does to the wave…

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I happen to have this diagram that describes the effect of the Rectify unit.

(from http://wiki.orthogonaldevices.com/index.php/ER-301/Rectify)

The purpose of the Offset unit is to add a value to the incoming signal. It could just as well have been called the Add unit. For example if you have an envelope that is still outputting a positive voltage when closed then you can add a small negative offset to it to bring it down to zero.

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Aaaahhh I see totally makes sense now thanks for the explanation guys and link to wiki.

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