DIY Audio Effect Pedal Part 4 - The Sustain Effect

#93 In this video I take the feedback I've gotten from my viewers and finally build an effect. The circuit is supposed to be a Sustain Effect. I go trough the operating principle of such a circuit, simulate it using LTspice and finally I build something. Just how well it works? well... its a subjective topic.
Schematics:
Mother board: drive.google.com/file/d/1Rf9T...
Sustain: drive.google.com/file/d/1xlzR...
Datasheet used: www.ti.com/lit/ds/symlink/lm1...
Spice model for the LM13700: www.ti.com/lit/zip/snom267
References:
www.hobby-hour.com/electronic...
www.electrosmash.com/mxr-dyna...
Other videos in the series:
Ep1- • DIY Audio Effect Pedal...
Ep2- • DIY Audio Effect Pedal...
Ep3- • DIY Audio Effect Pedal...
Ep4- • DIY Audio Effect Pedal...
Special Thanks to all my supporters on Patreon! Especially @afiskon and Xegomen!
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[@aswincvenu3958]

Why isn't this guy famous like @GreatScott?

[@guilldea]

Awesome! More effects please :D

[@guilldea]

@Dillon Genesis You two like this app? Y'all got so much in common, this app, the creation date on your yt accounts... Amazing

[@horiarizea8258]

Felicitari, ai content misto si video-urile sunt faine si la obiect, deci ca viewer ajungi rapid la informatia de care ai nevoie. Tot asa!

[@FesZElectronics]

Mersi mult!

[@Scrogan]

I’d have used an op-amp ideal-diode based envelope follower, followed by an op-amp differential/instrumentation error amplifier. The ripple in the envelope follower will cause distortion in the output signal if the gain is too high, but the difference in output amplitude will be too great if the gain is too low, so it’s important to be able to tune the error-amp’s gain. The common linear capacitive envelope follower can be a bit ripply or slow depending on the RC constant, and it also has the issue that the frequency of the note will change while this RC constant remains constant, so there are some switching topologies that seek to rectify this. Personally I’m fond of the one that uses two envelope followers (with reset transistors to V-) that are periodically reset out of phase with one another based off triggering from the edges of a square wave derived from the audio wave itself. If that makes sense. Anyhow, good to see this effect pedal coming together nicely, it’s been an important factor in how I’m designing my modular synth.

[@sathyapalreddy2157]

Thanks for the great content I would like to know about the smps feedback circuits .to make a variable output.limitations of duty cycle,frequency etc.. on different topologies.. and its selection range.. Regards Sathyapal

[@alexloktionoff6833]

Do you have experience with OPAMP peak detectors? Could it be more compact to use just one LM358 with two diodes as peak detector? Does this discrete BJT schematics have advantages?

[@p_mouse8676]

I would have a look at THATcorp. They make excellent VCA's like THAT4305, specifically made for audio applications. Or THAT218x series

[@FesZElectronics]

To be honest, while doing research for this project, I did come across products from THATcorp but, they are a bit more difficult to obtain; the "local" supplier I usually buy parts from does not keep them in stock... Thanks for the suggestion though, I might take a closer look at all their products some time, maybe try something specific out.

[@p_mouse8676]

@@FesZElectronics just email them for samples. You can also buy from them directly. Otherwise Mouser or Digikey.

[@capnzilog]

Could you maybe comment a little bit on how this AGC circuit differs from a traditional feedback compressor with the usual set of attack / release / ratio controls & time constant? It seems like you're much of the way there already, and yet this seems so much more straightfoward for the intended purpose of sustain.

[@FesZElectronics]

Well, the design is based on the Boss CS2 (its basically identical but the transconductance amplifier IC is different, and component values are in places changed) - so the same Attack, Level and Sustain controls are present. Attack and release are controlled by the same pot2 - it refers to charging and discharging of C7; If by ratio you mean level, then that's a basic "volume" control, not much different that can be done about that. And the time constant I guess is again related to C7 and the attack pot above it. I'm not sure if this is the answer you are looking for - maybe you can give me an example of a "traditional" feedback compressor.

[@capnzilog]

@@FesZElectronics Standard piece of studio gear, I could point to anything really but here's a famous one: www.sweetwater.com/store/detail/GComp--solid-state-logic-g-comp-stereo-bus-compressor

[@Stable_KDV]

If building part is more simple we can do one for ourselfs.Please try to made simple.

[@FesZElectronics]

I guess complexity is relative... Anyway, because of the effect, there isn't really a way to make it that much simpler. As a starting project in guitar effects I would definitely not recommend this, but rather something like a distortion or fuzz.