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

[Bill Bergman]

Are CA3094's hard to find?

[StephenGiles]

Well, they don't make them anymore, and the moaners here complain about the cost of 3094s when they find them! But I found a circuit I did a few years ago lurking on a floppy disk and stuck it on breadboard - and it worked, so feel free to take it further. I was thinking it might be good to turn it into a free running LFO.
Stephen

[R.G.]

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!!

How about a Twin T using the other section of the LM13x00 for the resistor in the T? Faking a resistor is something that OTAs are good at.

You could also do a multiple-feedback filter bt varying the input resistor to ground.

Clever envelope extractor!

[Bill Bergman]

I'm not sure if they are still there, but I knew of parts store here that had a trey full of about 100 or so metal can type CA3094 for a buck or two a piece.

[zeta55]

I once built the Penfold autowah. It had a LM13700 and a CA3130 for triggering.
Maybe that schematic could be of help?

[StephenGiles]

Where is the Penfold circuit - I'm sure that his trigger circuit is nothing like this one - no where near as clever??? But the VCF could be interesting.

RG - do you have anything circuitwise in the Twin T line as you suggested?
Stephen

[zeta55]

Here we go.

[gez]

LM13700 data sheet shows how to use one half of the chip as a variable resistance to ground Stephen.  Formula is there for calculations, just sub it for the variable resistance of a T-filter/MFB filter.

[StephenGiles]

Umm Gez, I don't do formulas except in Excel - =SUMIF(#NAME!(INDEX(F$1:F$32000;$H$1500);INDEX(F$1:F$32000;ROW()-1));"period variance";#NAME!(INDEX(G$1:G$32000;$H$1500);INDEX(G$1:G$32000;ROW()-1))) and the like.

Anyway thanks, I'll look at the data sheet
Stephen

[col]

Penfold uses lots of LM13700 chips in his book "Practical Electronic Musical Effects" (I think). I have built a few and they have all worked. The autowah in this book uses one but not the CA3080. The metal effects unit (NOT a distortion, makes your guitar sound like a gong!) that uses one half of one in this book is incredible, I don't think there is a commercially available unit that does the same thing. It is also a very threatening sounding vibrato/tremelo at slow speed! The sustainer, tremelo etc. in this book are all based around this chip.

Col

[Paul Perry (Frostwave)]

Col, that so-called Metal Effect unit from Penfold, is a ring modulator.
The LM13700 is being used as an analog multiplier (not a frequency multiplier). The extensive application notes on the LM13700 (and equivalent NE5517) show this app and more.