MFOS ENVELOPE FOLLOWER IS HIGHLY RECOMENDED

[edd29]

http://www.postimage.org/image.php?v=Pq1UE5kA

no modification just stock this is really cool pedal THANKS to Mark  Hammer for posting the web site.

http://www.youtube.com/watch?v=CoaWfgv9byk


http://www.musicfromouterspace.com/analogsynth/ENVELOPE_FOLLOWER/ENVELOPE_FOLLOWER.php

here's schematic
http://www.musicfromouterspace.com/analogsynth/ENVELOPE_FOLLOWER/pdf/schematic_pg1_schem.pdf

[Akridosity]

The pics not showing up, I assume its the schematic? Sounds good.

[edd29]

my MFOS is now been update to three controls and one switch for  high and low signal input.
RANGE, ATTACK, SENS.



I need help putting wet/dry mix control anyone can suggest . thanks!

EDD

[liquids]

Highly recommended indeed.  I've been messing with a couple of different LM13700/13600 style envelope filters lately, and I think this one is fantastic.  I'm not super picky about up-sweep filters, as I hardly EF this way, and most sound good to me when all is clean, if they are fairly quick and low gurgle...add some dirt before them and they can sound quite odd.   So finding one that is usable in that regard is difficult.   

This one sounds quite good, even as is!   Despite only having one pot, it doesn't go for the 'simple is better' methodology, so all the components of a good EF are there at the expense of many op amps, so it''s fairly comprehensive at its core--however, that might not be clear since it only has one stock pot!   No fear, many of the resistors can be made variable to nearly mind numbing proportions to where you twiddle more than play.   I think the envelope generator is really a great snippet in its own right for other similar filters.  And in the end I think I like it as much as any others I've tried - mxr envelope filter-type and even my previous far, the q-tron/mutron.  It's easier and cheaper to get an OTA than two vactrols, though, so I've been trying to find something to my liking from an OTA style EF.   

So of course, I can tweaked and modded endlessly, too.  I wouldn't bother trying it without a buffer before it, for one.  Also, all I've done, I've got it on a bipolar +/- 9v supply right now, haven't tried it at 9v yet...may go up to whatever the chips can take using an +/-18v supply from an LT1054 and regulators after I double check all the datasheets - but note that this is more for the EF section than the filter, which will probably be little benefited from the higher voltage...

As another side note, the the dial diodes is an excellent full wave rectifier/octave effect.  A bit like a tame and clean Jawari even more than an octavia, as it has a bit of a quick decay.

Mods and tweaks: for one, tapping output off of the filter pin 8 (the buffer out) gives you a BP response that can be VERY wah like---not to hype it, but I am convinced it can be tweaked (read more below) by ear to sounds not unlike the samples I've heard of the Mad Professor snow white auto wah if you know what you are doing, & some breadboard trial/error sessions (which is my M.O.)     Granted, if you want a true wah sound, use your foot...but it's still really cool sound!   I'm usually a low-pass down sweep filter for synthy sounds, but this thing in LP up sweep is really addictive, and even more so if you use it in BP....

For down sweep, instead of simply making U1-D inverting (using a 100k resistor in the loop to match the 100k going in, which didn't work for me, but may have been my error and impatience),  adding an inverting buffer following the non-inverting buffer (similarly with two 100k or 47k, even) does give you a down sweep, which is what I was after.

The attack is set with R1 and C4 as mentioned.  I'm a fan of quicker attack for down sweep-the decay is 'set' to very slow since there is no decay resistor, and that's a problem with the down sweep I want.  It's almost unusable if you merely add an inverting buffer to the EF.   It sweeps into oblivion as it seems it needs more gain going into the EF, and then it doesn't return for a while, stock, making it difficult to dial in.   But like most EF, a resistor from U1-D to Vref (or ground, if you are using bipolar rails, as I am) makes this an easy control  to add.   Direct connect (no resistance)offers no or next to no sweep (nearly instant decay).   Adds a little resistance to get a fast, synthy decay, or more resistance to get the 'stock' type decay.  What value pot depends on how much you like slow decay and what you consider slow.   Likewise, I have mostly made C4 small like 1.5n, but R1 could probably be pot controlled for attack time control, and is another reason why it's better to add a separate inverting buffer for down sweep than trying to make U1-D inverting.

R5 could be a pot...you can control the standard 'sensitivity' or gain of the EF this way--- can be very useful.  A 1M pot is not bad...still tinkering there, depending on what other mods you do, you may want more or less control..but there likewise may be better options.

Tinker with C10 and C11.  No need to match them even, as it is stock, but results will vary...stock is fine, but I've generally liked making C11 smaller (like 100pf), as R23 is so big.  Making R23 smaller works to a degree but seems to more so add ripple and distortion.   My only understanding of this is seeing R22 and 23 as working both as voltage dividers in conjunction with R26 and R24 respectively...in order to keep the OTA inputs from clipping, but likewise R22 and R23 working in conjunction with the OTAs which are acting as current variable resistors to form R-C filters, with C10 and C11.  If so, the two R-Cs are not matched for frequency anyhow since R22 and R23 are so different in value, so no need to make C10 and C11 match, either.  Ive also liked making  C10 bigger, from 470pf to 1.5n...mess around and see what you hear.

A little more resonance can be had by making R31 up to 47k.  R30 and R19 can be tweaked too, but they are all pretty close to the edge using 33k resistors ( I don't have 30ks), following what Ray suggesting that he likes his Reducing resonance via the feedback resistors made it very subtle for me rather quickly, so they are all pretty 'particular' resistors, and probably not worth making any a pot, in my opinion.  R31 is my choice if there is one to choose since it actually offers a tad of useful range...seems increasing it rather than decreasing it (like the other two) gets toward oscillation, should double check.  but much past 50k and you lose everything.  I started with all of them at 33k since I don't have 30ks.  At best, I might want to set R32 at the stock 33k and add a 10k pot in series for a little control, if I just must have a resonance control...or go all out and try to do a diode clipping arrangement in one of the feedback loops as in MS20 clones ( I may get to that)...YMMV.  But if you don't like resonant filters...this is probably not a good build for you anyway.     Likewise, I'm pondering pairing this envelope generator with an MS20 type filter later...hmm.

Alas, the unique beauty of this circuit is in the unassuming R10 and R11.  I've not noticed this kind of arrangement before.  They are like a current/voltage mixer.   The wah range pot is beautiful....but as stock, it seems like an unassuming control much like a general 'start frequency' pot would be...but there seems to be more...

The wah range pot controls...well, your wah range , in conjunction with R5 if you make that a large value pot.  The wah range controls your start sweep frequency, something like that -  in short, it sets a bias voltage that sets where the filter 'starts,' which is more like a current for the OTA when it passes through 300k.   Then, the EF generates its own voltage that adds (or reduces) the voltage from that start point, to set the sweep.... again, I suppose R10 and R11 function to make the voltage more like a current.  All that said, within reason, they work like a mixer as well,  in the sense that the wah range pot and R10 set 'idle' current affecting the OTAs, and R11 sets/limits how much 'drive' the envelope voltage modifies that idle current.  If you make R11 smaller (down to say 22kish may be safe) and/or R10 larger to a point, you allow the envelope voltage to more easily 'overcome' the idle bias voltage.  There are limits, since the OTA can only handle so much current...smaller resistors here mean more current...but so far so good!   

So then, in a way, you have the EF filter control which can kind of set the 'maximum' or 'sensitivity' of the filter, and then, for example, controlling R11 via a pot would give you a kind of 'decompression' control.  When set at 100k or more, the 'range' of the filter sweep is limited in the amount of current that can be put across it.  When turned down, the envelope dynamics can be very dramatic on the other and easily overwhelm the bias voltage.  The benefit of this is that changing R5 to a variable pot and making it 'big' for more sensitivity, it reaches a point where that stage itself clips, meaning that the true decay and dynamics of the envelope are clipped, and hence affects attack/decay characteristics.... like sending a distorted signal into the envelope  would do.  I think if I had to choose one, especially if working off a single sided 9v supply, I'd make R11 a set resistor (10k, 22k?) and pot combination (100k, 250k?) and make R5 a stock value resistor of your choosing.  Likewise, I think I like R10 a little bigger than stock - say 470k or so. If you were creative, you could have two set resistors and have a voltage divider that simultaneously increases one and decreases the other along a range, too.

Again, I haven't tested all this under 9v either as the schematic assumes.  And I only understand so much about these things, but hopefully this helps another interested tweaker.    So far I have a up sweep BP filter going that is approaching wah like, and sound great before a gain pedal, and also a synthy down sweep that I like as much if not more than what I can get out of my microsynth's 'triggered' filter, as the EF allows for some dynamics, even off a fuzzed out signal...though it's almost always best when integrated with fuzz/octave so that a clean signal goes to the envelope portion and the fuzz/octave/etc goes only to the filter.  Have fun!