Adding Slew/Lag/Slope to Stompbox? Lag Theory of operation?

[loss1234]

I am working with circuits for stompboxes. I am taking an envelope follower and then feeding its CV into things like filters,etc. What i am looking for are interesting ways of then messing with the CV like slew limiters. AND i am trying to understand how a slew circuit works. (is it an integrator? a feedback loop,etc)

I have found Henry Bissells Morph Lag but am looking for more schematics or ideas to further my understanding and experiments.

I know one of the many experts on here could write volumes again on this so i figured i would take a chance.

thanks a lot.!

[Mick Bailey]

I'm currently looking at a similar thing - I've got a successful envelope generator triggering reliably from a guitar signal. The EG is 555 based and gives attack, sustain, release (thought he sustain can never be longer than the guitar's natural sustain, but it can be shorter, which gives interesting effects).

My intention is to use this to control a VCA to give a variable envelope pedal.

I still have a couple of things to sort out;

1. A simple, low-distortion VCA with minimum component count.

2. Retriggering the 555 - I'm integrating the positive input pulse to give a negative trigger pulse to the 555 which works very well, but each envelope has to time out  before the next can be retriggered. If the 555 is reconfigured as retriggerable there is a delay before the retriggering occurs (may change capacitor values to get this sorted)

A nice pedal to use this on is the Uglyface to further expand its synth sounds.

Do you have a schematic for what you have? 

[Mark Hammer]

http://www.wiseguysynth.com/larry/schematics/Morph-Lag/Morph-Lag.gif

There are a few ways to think of altering the timing of envelopes used to control things.  One is a circuit such as Harry's that makes the transitions between contrasting control voltages more sluggish.  Another way is to have envelopes offset in time via a gate-delay or trigger delay.  These circuits (of which there are many posted around; one I think is to be found in the archived scans of now-defunct "Synapse" magazine: http://www.cyndustries.com/synapse/intro.cfm ) delay the arrival of a gate or trigger to the envelope generator by a fixed interval.  Once the gate or trigger arrives, the EG works as per normal, however mixing delayed and non-delayed envelope CVs allows for more complex kinds of sounds.

One example of  how to put delayed envelopes to work is something like what one sees in the Boss VB-2 pedal.  There, the modulation of vibrato can be delayed by a period of time and ramped-up to fade in over time, in a way akin to how finger vibrato or vocal vibrato normal occurs after a note is held for a while.  (Personally, I don't find the delay times to be realistic or sufficiently manipulable in the pedal, but that's another matter).  So, imagine that you have an LFO control voltage whose output is controlled by a VCA.  The VCA, in turn, is controlled by a simple attack/decay envelope, set for very slow attack/rise time.  That envelope generator should turn on only after the note/chord itself has been held for a little while.  In which case, you want the trigger/gate to initiate the envelope for the overall signal immediately, but delay the trigger/gate pulse used to initiate the ramping-up of the modulation by a bit.

In theory, I guess, Harry's circuit could achieve something like that, but realistically it would only extend the time required for ramping up, rather than delaying the point at which the ramping-up begins.  Both types of circuits are quite useful, though.

[loss1234]

thanks for the ideas. I WILL check out the vibrato pedal you refer to! are there any other pedals that take a control voltage from the signal and then really mess with it?


mick-do you have a schematic for what you are playing with? i have thought about finding an envelope circuit.

at first i thought you could just trigger a vca with the envelope follower, but it seems most circuits take the follower into a comparator and out of that they get what i assume is a gate. then that gate triggers something like your 555 envelope and then that triggers the vca. right?



what about ramping down? i have seen both negative and positive slew circuits before but as they used transistors, they didnt make a lot of sense to me right away.

here is another negative slew

http://www.cgs.synth.net/synth/serge/pic/serge_negative_slew_schem.gif


if this makes any sense to you, please let me know. i have perf-boarded the negative slew but its pretty bulky. id love to find a one quad opamp solution for making positive and negative slew. or even if i could just understand what is going on this circuit, it might help me to further experiment with it.

anyway, i am not just interested in subtle changes in the CV.  i am not going for realism of any kind, and am going for FAR OUT sounds, that dont have to end up being related to the original guitar AT ALL.
what i am trying to do is create the illusion or the actual act of RANDOM sounds, which will initially be triggered by the guitar, but may go off on their own tangents. a cloud of sound....maybe lots of things triggered and then being filtered to make it all sound like one big sound.

sorry for all the rambling and questions. it just seems as i learn more, more and more schematics get printed out and more and more ideas pop out, but along with it, more and more questions.

thanks a ton!

[frequencycentral]

Here is the Integrator from the Korg MS50 synth:



Its very similar to the slew part of a Roland 100m Modular Sample and Hold.

It allows slides between voltage changes.

I designed an AR generator based on this, just added an extra inverting opamp, another pot and three diodes. I can dig this out and add it to this post if anyone's interested.

The 2M pot can be replaced with a 1M. Replacing the 1uf cap with a higher valve gives longer slides. Experiment - socket the cap and play with 1uf, 2.2uf, 3.3uf. Generally tantalum caps are used here for their accuracy.

[frequencycentral]

Originally built to be powered +/-15v. I have built a few and used them down to +/-6v. Would probably work off a 9v battery, using a vref for earth. I usually use a LM324.

[loss1234]

thanks a lot for these great schematics!

i am definitely going to breadboard them up. so from what you are saying and what i have been reading, slew generators, envelope generators, and low pass filters all have something in common. interesting.

hey btw, where do you guys all buy your cap and transistor sockets? i had never heard of socketing caps till i started hanging out with stomp box builders!

[loss1234]

rick

the more i compare your schematic to the original, the more i dont quite understand how you got from one to the other. they dont seem to have many values in common and yours has that extra opamp up top. what does it do?

could you explain a bit more your thought process and how you turned a slope into an AR?

thanks

[Mick Bailey]

Here is the design I've been working on;

http://www.avwz35.dsl.pipex.com/env gen.bmp

The 386 acts as a sensitive preamp to generate the trigger signal. The transistor inverts the signal and is fed into a signal conditioning/bias arrangement for the 555. This works very well as a breadboarded experiment and I've driven a primitive VCA with good results, apart from the VCA distorting too much. I've also used it to operate a DIY vacrol. I haven't shown the VCA as it was so bad and I scrapped it as soon as the rest of the circuit was found to be OK.

If you wanted just to generate a pulse to fire another circuit you could take the output straight off the 555 and use the sustain control to vary the pulse length.

To make it re-triggerable, connect the 555 pin 4 to pin 2 instead of pin 8.

In operation, the sustain control merely controls the output pulse duration of the 555 and the attack/decay controls affect the charge/discharge rate of the 4.7uf cap. I've also used a 10uf with good results.

You can get slow gear, violin, blip, machine gun and other effects. You need to ensure that the controls are set so that the sustain always represents the total length of the envelope, otherwise it will cut off before the envelope has completed. If you have 2 Meg pots these may be an improvement for the timing.

I would welcome any suggestions for improvement, and especially a good, simple circuit for the VCA. 

The guitar signal to the VCA needs to be taken off the input to the circuit.

[frequencycentral]

rick

the more i compare your schematic to the original, the more i dont quite understand how you got from one to the other. they dont seem to have many values in common and yours has that extra opamp up top. what does it do?

could you explain a bit more your thought process and how you turned a slope into an AR?

thanks

I did a lot of research into AR gens at the time (6 years ago!). I looked at the Octave Cat synth (using CMOS) and the ARP Odyssey (using transistors). Then I saw the similarity between both circuits and Korg/Roland synth slew limiters/integrators. Then I played around.

I don't really understand this stuff myself on an individual component level, tending to work with 'blocks' of components that I know do a certain job well. I think the configuration of the attack opamp (top left) I stole from a sequencer schemo (Superseque). The release opamp (bottom left) is just an inverter. The third opamp is a buffer. The key is that the bottom (release) section is a mirror of the top (attack). Take away the top (attack) section and it's just a slew limiter.

So basically I wanted to make quad opamp AR. I gleaned info and put it together. It closely resembles the CAT and ARP versions. I used the fourth opamp as an inverter (same config as the release opamp) to give negative slopes - a mirror image of output.

I can dig out the Arp and CAT shemos if you want. What I can't do is give a blow by blow account of what those pesky electrons actually do in my schemo - I'm not clever enough!!

I hope this helps! And if anyone can explain why and how my little circuit does what it does - that would be great too!!

[frequencycentral]

.........and it would give me a BIG kick if you build my circuit!

NO-one except me ever did before!

[Mick Bailey]

Just improved the action of the circuit and updated the schematic. Diodes are 1N914. A switch is recommended to connect the 555 pin 4 either to pin 8, (one shot) or pin 2 (re-trigger) to give a wider range of effects.

[loss1234]

can anyone recommend a good circuit for turning my guitar into a gate to trigger your circuits?  (would a comparator work?)
thanks

[Mick Bailey]

My circuit has the trigger built in - just plug your guitar in and go. An LED and 1k series resistor from the output to ground will demonstrate the function of the circuit. If you want this to drive someone else's circuit, ignore everything after the 555 timer output and use the output as the trigger source.

[frequencycentral]

hey btw, where do you guys all buy your cap and transistor sockets? i had never heard of socketing caps till i started hanging out with stomp box builders!

I use these for caps, resistors and transistors if I want to socket them, IC's sometimes to if I run out of IC sockets, just cut off what length you need.

http://cgi.ebay.co.uk/Turned-pin-SIL-socket-strip-14-Way-Lot-of-10_W0QQitemZ180240698936QQihZ008QQcategoryZ36332QQssPageNameZWDVWQQrdZ1QQcmdZViewItem

[loss1234]

mick

problem is i need a gate not a trigger. see i need something that will go low when my note starts to die out

a trigger will just start an envelope, which is great for some purposes, but not the one i am currently working toward.

thanks though

[frequencycentral]

mick

problem is i need a gate not a trigger. see i need something that will go low when my note starts to die out

a trigger will just start an envelope, which is great for some purposes, but not the one i am currently working toward.

thanks though

You need my Roland 100m Modular Gate Delay schematic. it allows you to specify the threshold for triggering, has a hold function and a delay function. Let me dig it out, scan it and post it. It uses two 555's. i built one using a single 7556.

[frequencycentral]

Here is Roland's M-172 module schemo. Four separate circuits (top to bottom):

1. a very cool voltage controlled phaser
2. BBD analogue delay, voltage controlled
3. simple triangular LFO - easy to adapt a square using a comparator
4. gate delay

Don't get hung up on the title 'gate delay', it's actually a gate extender and/or a gate delay. If you don't want to delay the gate, just extend it, you can omit IC9 and associated circuitry, leaving one opamp and one 555. I built the whole circuit about ten years ago using a dual chip (7556). I seem to remember having to add an extra cap to prevent crowbarring the power rail. You need to research that one on the 7556 data sheet!

What the Gate Delay will do: extend any signal at the input (audio or trigger) by whatever VR10 is set to, from 3ms to 6 seconds. The delay feature is obvious - using modular synths it's sometimes nice to trigger a second envelope some ms after the initial one. The Gate Delay generally feeds into an envelope generator's gate input.

I scanned this schemo off an A4 sheet, some of the values are a little hard to read but its pretty obvious, if you get stuck give me a shout!

[moosapotamus]

can anyone recommend a good circuit for turning my guitar into a gate to trigger your circuits?  (would a comparator work?)
thanks

How about this...
http://www.musicfromouterspace.com/analogsynth/signaltogate.html
I'll bet you could run it on +/-9V from  MAX1044, too.

~ Charlie

[loss1234]

funny i built another ray wilson (gate) circuit today, it was similar, called the guitar trigger circuit

the roland schematic looks cool BUT i cant read it when i try to print it or zoom in.
does it need a gate to create a delayed gate? if so, i suppose i could feed it a gate from something else and then it would wait awhile before sending it on?

thanks all