LM13600 envelope follower

[StephenGiles]

I've started a new thread on this to preserve a separate line of discussion.



The envelope follower I have posted above provides a similar start frequency/stop freqency type of sweep to that of the EH Microsynth, so that you get a normal or reverse sweep with a VCF dependant upon the settings of the pots. Remember that on the Microsynth, this is achieved by making the start frequency slider lower than the stop frequency slider (I think, or is it the other way round?), BUT......the sweep is the same however hard a note is played.

Now, the LM 13600 envelope follower is different in that it's peak is proportional to the strength of note played, but it's decay time is set by the sweep time pot, so there is little or no ripple. I have tried this with the Bi Filter Follower twin filters and it works very well.

The grounding looks a little odd, but I gather that the 324 can handle it, and I suspect this is why Joe Truchess at EH UK chose that amp - he also tried a 339 in the design stage of the Space Filter, but it was too heavy on power in the battery unit. If someone could come up with a decent opto contolled filter using the other half of the LM 13600 and unused amp in the 324, we would have a superb triggered filter with just 2 chips, and great for the little boxes you all like!!

One other point is that it could be worth using a separate pot and fixed resistor instead of the series resistor from the EG to the opto - I used a VTL5C4/2 which worked fine in the Bi Filter. 2 NSL32s worked equally well
Stephen

[StephenGiles]

Thought I'd remind you about this which got a huge response

[frequencycentral]

Looks interesting - I'll try this with 13700 when I get the chance.

[Mark Hammer]

What I'd like to find, but which I haven't found quite yet, is an envelope follower that can provide longer attack/rise times.

Perfect case in point. The Boss VB-2, and its recent Behringer clone, provide a delayed rise time intended to mimic the way in which vocal vibrato increases the longer you hold a note.  The rise/attack time is no where nearly long enough in my estimation, and not the right sort of rise either.  I imagine max delay/rise-time should be about 20% longer, and also have a logarithmic response.  It appears to be linear.

[StephenGiles]

Some lag needed?

[Mark Hammer]

Hell, yeah!

[Boogdish]

What is the 100k pot on the far right of the schematic controlling?

[StephenGiles]

Sweep rate - good sign that the circuit is being looked at!