Cut off gate

[thomasthebuzzard]

Ok, I have this crazy home made synth that i built and when I run guitar signal into it it sounds crazy! I absolutely love the sound but I need the self oscillation to shut off when I am not playing. Not just a little but instantly and completely. Is there any way to do this simply? I want it to make noise when im playing and completely shut off the output when im not. CAN THIS BE DONE SIMPLY? ALSO I DO NOT WANT TO USE THAT MXR NOISE GATE! IT IS NOT SIMPLE IN MY BOOK AND THAT SEEMS TO BE THE ONE EVERYONE POINTS OUT.
Is there a way i can make a STUPID SIMPLE on/off gate that responds to my guitar? MAYBE WITH A FET OR OPTO?

[mattthegamer463]

Maybe like a diode? Signal drops below forward voltage, stops conducting.  You could use a diode or schmitt trigger to control a FET or something.  I'm not sure on specifics but I'm sure something like that could work. Perhaps an expert around here can fill in my blanks.

[thomasthebuzzard]

That is totally the kind of thing I wanted to hear! Im new to this! More help please!

[R.G.]

There are stupid and simple ways to do gates - but you won't like them. It turns out that getting a gate that listenable is neither stupid nor all that simple, because you are not dealing with signals to make it listenable - you're dealing with the human ear's expectation of what the signal does. That's hard.

What you have to do is either sense the presence of any signal over X voltage and fire the "signal sensed" signal, perhaps with a comparator, then keep that signal going for some reasonable time so that it does not cut off every half cycle. The sensing level has to be above the noise level and that is not always simple to do. You can use diodes or the calculated, resistor-set threshold of a Schmitt trigger to do the sensing, but it will sound bad unless you also account for how it works as the signal decays under the noise level.

Determining the signal that says "un-mute it NOW!" is the hard part. Using a FET, opto, whatever, to mute the signal is the easy part.

[PRR]

> Determining the signal that says "un-mute it NOW!" is the hard part.

Determining the signal that says "MUTE it now!" is, in my experience, another hard part.

> shut off when I am not playing... instantly and completely.

When do you "stop playing"?? When your pick leaves the string? When the note decays a little? Decays a lot?

R.G. and I agree: noise gates -always- nip the heads and tails of sounds. It has to work VERY fast to open on the rise-time of plucked string (worse: spoken words that start with consonants, the "ssssailing" problem). And since music is played with fading note tails, deciding "when it stops" is not easy neither.

I hate noise-gates too but they ARE the best answer possible. In this case where your synth goes nuts, you feed raw gitar into synth AND into gate's control input. Synth output goes to gate signal input. When your pick and string level decays "enough" (a real compromise) it mutes the gate.

[Solidhex]

Check the transistor connected to the emitter of the third transistor on this Maestro fuzz. It acts as a simple noise gate. Current flows through the diode, turns on the 4th transistor in turn allowing current to flow from the emitter of the 3rd transistor to ground. When no current is supplied (guitar isn't being played) both transistors shut off and the 3rd one passes no signal audio signal. Who know if it can be applied to your circuit but it at least illustrates a dead simple style of noise gate. I bet an opto based one would be rad.

[thomasthebuzzard]

Thank you solid hex! That might work. If anybody read my earlier post its kind of a synth pedal and it absolutely destroys the tone (in a good way) so tone is not something im trying to salvage. So a simply brutal cuttoff gate IS what i need. There is no way its going to make it sound worse anyway. How might one go about this shmidt trigger thing? Is it made of simple components?

[DDD]

That WORKS 
The famous Satisfaction solo by The Rolling Stones takes it's specifics just from this circuit.

[thomasthebuzzard]

OKAY THAT WAS ALL MEGA! HELPFUL! THIS IS SUCH AN AWESOME COMMUNITY! THANKS LADYS AND GENTS.
So with that said I went to the breadboard this morning and made a great circuit using two 2n3904. I ran the signal from my synth into the emitter of Q1 and then put a diode between the emitter and base. Q2 is used as the "BAZZ FUZZ" circuit With my bass guitar feeding it. The output of the Bazz Fuzz circuit goes to the bass of Q1. The collector of Q1 goes through a capacitor and then to my amp input. This Effectively gates and blends the two sounds (bazz fuzz and synth). Experimenting with different diodes and output capacitors tends to change the rise and fall time of the synth as well as the overall volume of the synth itself. I will draw this up on a schematic if all of this is right. BUT IF IT IS RIGHT I SMELL A NEW PEDAL! The cool thing is if i can improve apon the design maybe it can use all kinds of synths as modulation effects?

[DDD]

Well, we'll wait for the schematic

[thomasthebuzzard]

Here is my first contribution to the DIY pedals world. This thing totally works and I think because of its simplicity it will be super fun to mod. I have it all boxed up and running like a champ. When i run my synth into the noise gen/lfo input on the trigger pedal it makes for all sorts of gated ring mod love and nice bell sounds. When i plug the audio input of my synth to gen/lfo output on the trigger pedal my bass becomes a full synth with attack,sustain,decay,release. I have built a lot of pedals in the past ten years some great and some yucky but i am kind of exited about the simplicity of this one for such a good sound. TRUTH IT ISN'T BIG BUDGET STUDIO QUALITY but I am running it through a Roland Jazz Chorus and An Ampeg Tube Head with ampeg speaks. That setup makes even the worst stuff sound good.

[thomasthebuzzard]

oops! forgot one thing: the overall volume coming from my synth controls the gating too! Example: when i crank the volume on my synth past 5 or 6 all bets are off and so is the gate. OH WELL! maybe a volume or impedance control at the lfo/noise gen input? also as you can see the second half of the circuit is passive. it would be better if somehow active.(less volume drop). what do you guys think about another NPN or Op Amp gain stage at the end? Too dirty?