Classic VCA stereo panning artifact

[eljay]

I am using the panning capability of the Classic VCA to generate rhythmic effects by supplying a series of discrete positive voltage steps from my MFOS step sequencer into CV2, there is no input to CV1. The CV1 gain pot is set to about 9 o'clock to provide a 'negative' bias so that the positive input voltage (approx 0V - 7V) gives left and right outputs from OUTA and OUTB.

What I have noticed is that each voltage change generates a small click that is noticeable at all speeds but is readily apparent when running the sequencer at a 'rhythmic' speed , this click can be removed by using the slew output from the sequencer so there is a slight ramp up or down to the next voltage level.

My question is, is the audible click just an artefact of the VCA design or is there a component change I should make or a calibration parameter I need to tweak. I have built two of these modules and they both demonstrate the same 'feature'. It's not a major issue as using a slewed input seems to avoid the problem and if this is the answer it appears to be an acceptable solution.

[Synthbuilder]

What I have noticed is that each voltage change generates a small click that is noticeable at all speeds but is readily apparent when running the sequencer at a 'rhythmic' speed , this click can be removed by using the slew output from the sequencer so there is a slight ramp up or down to the next voltage level.

Does it click without any audio input? If so, this is CV breakthrough and a small amount is inherent in the design. You may be able to tweak OFFSET trimmer to reduce it further. The DVCA-X is probably a better choice if you need a really quiet VCA. A single DVCA can do panning better anyway as it has a dedicated VCA for each side of the stereo field.

If it clicks with an audio input then you are probably hearing the additional harmonics created when you rapidly change the gain of the signal. Slewing the CV is usually the best way to avoid this. Or making sure there is no audio at the point of the gain change, eg. the decay time is smaller than the length of the sequencer step.

[eljay]

Does it click without any audio input?

Yes.

A single DVCA can do panning better anyway as it has a dedicated VCA for each side of the stereo field.

I have a DVCA-X, I will experiment and see what I can achieve. Thank-you for the feedback.