enveloped rate-control for trem or vibe

[duck_arse]

if you've got a tremolo. vibe or something modulated with a phase shift oscillator, here is a method for envelope control of (in particular, but not limited to) the oscillator rate.

shown is the circuit for the "vveet" tremolo, with envelope-controlled lfo. a complete vero layout is shown, as well a version for the envelope section alone, for those who might like to add-it-on to something already built. (some here may need de-coloured layouts, just ask; they gets a bit hectic.)
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click for a bigger:


the envelope started with the circuit shown in "Following envelopes with transistors" by jatalahd, with bits of the "Mini-Mu" by RRing, both since modified. IC1A provides impedance-buffering and isolation for the clamping-amping-rectifier, Q1. Q2 buffers and drives the smoothing caps, C2 and C3, via the attack-setting R6. R7 and R8 set the decay time and provide a divider to reduce the smoothed "up" envelope-peak to a bit more than V+/2.

R9 feeds the full envelope to upside-down phase-splitter Q3. the "down" envelope appears at the collector, and swings from just above V+/2 to near 0V. both up and down envelopes are available at the same time.

centre-off switch SW1 selects envelope up, down or no, and feeds the selected to IC1B, which drives the LED1 in its feedback loop, with R13 selected for appropriate led brightness. connecting R12 to 0V will correctly park the IC1B input when SW1 is in the centre "envelope off" position. the blow-out SW2 is used with R14 to shift the LED1 brights and the osc-range swept, and to trick the LDR1 such that it may or may-not kill the (slow) oscillator.

the only gain-control provided is RT1. more rectifier gain can be had by increasing R3, or shorting R4, which will affect how RT1 works. more signal in can be had by taking the pin3 input to the drain of Q5.

the oscillator is a standard phase shift design, straight from an EA tremolo or a million other similar, and the basis of the univibe osc. its "fixed R" leg provides a constant, sweepable option not readily available in opamp osc designs. the oscillator may tend to stopping on envelope peaks, producing spiffing of the tremolo.

the tremolo is a simple shunt-to-ground transistor, as used in the Vico Vibe and millions of others. an "Orman" type high-impedance mosfet front-end, Q5, is added to prevent any tone-sucking, in the same manner seen in Midwayfair's "Blue Warbler" design. output from the source is fed to the envelope buffer, with DC bias adequate for that stage; output to the Q6 tremolo transistor is taken from the drain, with some signal gain due to the ratio of R23 to R26.

--------short notes-----------------------
IC1  needs to be (part of) LM358, LMC6482, TLC272, TLC2262, M5223, LM324, etc. your favourite mosfet at Q5. use a high gain transistor at Q4, the other transistors are as ordinary as you have, any should work. matching these transistors will degrade performance.

up and down are probably both misnamed, the "up" setting produces a slowing trem rate as the envelope decays, while the "down" produces a faster trem rate with envelope decay.

the 220k R13 suits a waterclear superbright red LED1 and was determined using the "stroke your leds" method, threaded elsewhere, to suit my unknown, 4mm dia, coarse-channel type LDR1, min light resistance ~4k. GL5516 should be perfectly adequate, vactrol users might provide a suitable substitute part #.

use poly caps for C6, C7, C8. the rate pot can be a 100kC, 100kA backwards, a 100kB (and just put up with it), or a 250kB with a 150k or 180k tapering resistor for a semi-reverse log taper.

the value of ZD2 is not critical (any from 4V7 to 6V8), its voltage is scaled via the Suarez pot value and R32. the values shown at R34, R35, R36 and C9, C16 provide helicopter style chopp. modified values will produce some subtlety.

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a (much) more complete build document is available in pdf form. the modern PC integrated sound card has me totally flummoxed, so no sound samples are currently available.

does anyone know of an account-free/anonymous hosting site for media like pdf and ogg files?

[duck_arse]

- the vero -

the vero layout is presented in two forms: the complete vveet tremolo, and a stand-alone version comprising just the envelope section, from IC1 across to LED1. this can be grafted to any cod-ordinary pso based effect you may wish to make totally unusable to modify.

these are my first fully-flat layouts, and there is a million cuts, loads of hidden links, and tracks going up-under-and-back (it looks a lot like a perf layout). doesn't mean I'm happy seeing all that wasted copper, mt holes ..... any linked tracks are coloured so they can be clearly followed from end to end.

separate tracks are provided to keep audio-ground from IC-ground. there needs to be 3 flying links installed between each pair of coloured spots right-hand side. each section has its own power supply RC filter. polarity protection is left to the builders discretion.

the board is fairly clearly divided into 3 sections: the oscillator entirely above the line of RT1, the envelope between +9V and the V idle line, and the audio/tremolo below the bottom IC ground track. any of the sections can be substituted for.

click for bigger:


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click for bigger:

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the stand-alone envelope board - some bias needs to be supplied to IC1A, whatever your buffer-stage output sits at will be fine, or add some DC blocking cap and divider resistors. the bottom blue trace can be deleted if a mid-board wire connection fits your build rules. the R12 "V idle" connection needs terminating. if not bandspreading, it can be mounted east-west to connect pin4, or flying-linked to a ground trace.

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as of V0.3, the circuit has been tested on the breadboard, but neither layout has been built. the pdf file contains further layout info that may be needed to complete the veros.

eroors, feedback, abuse, etc please.

[Mark Hammer]

In many instances, it can be done more simply, assuming the LFO design itself permits.  I tacked a simple Dr. Q-type envelope follower onto a Phase 90.  The output of the rectifier feeds an LED, and the LDR is simply placed in parallel with the normal Rate control.  Play harder, and it speeds up fro wherever you set it.  Of course, the degree of speed-up will depend on the combined parallel resistance of the Rate pot and the LDR, so if you already have it set relatively fast, you won't notice much change.  But it works as well as I need it to.

Kudos on working this all out from scratch, though, and producing a layout.  I'm not that industrious.

[midwayfair]

In many instances, it can be done more simply, assuming the LFO design itself permits.

Well, yeah ... http://www.geofex.com/FX_images/vibmatic.pdf and http://www.diystompboxes.com/smfforum/index.php?topic=106813.0

But duck_arse's envelope control is insanely stable and has a lot of interesting bells and whistles, and it works with probably any LFO. Take a look at a gutshot of the Pigtronix Envelope Tremolo, which has a similar feature set, and duck_arse's actually looks simpler by comparison! (That's a really great pedal, by the way.)

This has a super simple MOSFET booster audio stage, but I'm betting that something could be designed which goes way beyond that for different types of effects.

[duck_arse]

thanks mark, jon. the whole idea came from the fact that the fixed leg R in a pso sits about doing nothing, and could be increased from the usual few k value, and the the swept range would remain somewhat constant, as opposed to sweeping part of the rate pot.

I've got plenty of connection permutations/mutations going on in my head already, some stereo, but I don't know what any of them will do or sound like. anyone wanna suggest?

[samhay]

the whole idea came from the fact that the fixed leg R in a pso sits about doing nothing, and could be increased from the usual few k value, and the the swept range would remain somewhat constant, as opposed to sweeping part of the rate pot.

It's a nice idea.

[duck_arse]

and here is the full-scale pdf. (there may or may not be some colour-shiftings, there was when I looked at it.)

http://www.aronnelson.com/DIYFiles/up/vveet.post.pdf

[Mark Hammer]

Nicely done!  Gotta love documentation that explains what does what.  A great resource for the newbies here, and yet to come.  Kudos.