Stutter pedal

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alf
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Stutter pedal

Post by alf » Wed Jun 02, 2010 7:30 pm

So I decided to make a pedal to stutter a signal. Basically a tremolo but with a square wave cutoff. Choppy. I figured it would be pretty basic to do if I kept it simple. Grr...

I decided to use a 4093 quad NAND gate as an oscillator to trigger an IR emitter. This is in turn picked up by an IR detector that has the audio signal running through it. I made it happen once no problem. Well, one little one, it popped when it changed states. A cap wouldn't fix it. Not terribly noticeable when audio was running through, but when quiet it was annoying. I heard from a guy that built one that the Radio Shak IR emitter/detectors were b.s. and he had the same problem. He ordered some replacements from Tayda and had no further problems.

So I got my parts from Tayda and swapped out the IR doo dads...without retesting the circuit as it was to ensure proper operation...I know, I know...and now it won't work at all. Well, not quite. It squelches everything badly and doesn't really cut off. When viewed with a 'scope it seems that the audio wave is being cut in half(bottom chopped off) after passing through the detector. Even weirder, it passed a signal from a dry guitar to an amp at first no problem, as well as a signal from a tape player. Now it won't pass the guitar and the tape player is, as mentioned, squelched, doesn't fully cut off, and the wave is cut in half.

And when I try the Rat Shak parts, it does the same thing. I can't even get thje previous poppy operation from them anymore.

I am using a 1Kohm resistor to buffer the IR emitter and a 2.2Kohm resistor on the ground side of the IR detector.

Is there something fundamental I am missing about IR emitter/detectors? It worked the one time, albeit with the popping. I have placed it under a box to isolate it btw. I have torn the circuit down and rebuilt it multiple times now and it's driving me nuts. Any help would be appreciated.

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Post by RickvH » Wed Jun 02, 2010 7:47 pm

I'm pretty sure that most IR detectors are diodes, so when it's turned on it's half-wave rectifying your audio signal.

I think you might have more success using the oscillator to trigger an analog switch, something like a CMOS 4016/4066. Make sure to put some resistance to ground on the output of the analog switch, so it's not floating when the switch is off, to avoid a pop when it switches.
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Post by kslight » Wed Jun 02, 2010 7:49 pm

I can't help with your specific build, but couldn't you just put a momentary foot mswitch in a box and use that for manual stutter like a "kill" switch? Just seems like a simpler situation to achieve the same effect...

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Post by The Scum » Wed Jun 02, 2010 9:24 pm

Any chance at a schematic?

Specifically, what IR parts are you using? Are they light-sensitive resistors? Transistors? FETs?

A couple common causes of popping:
-a DC bias on the signal, so things have to jump a long way when the signal is switched in.
-things switching too quickly...a fast rise time, with a large signal suddenly gated open or closed, produces a transient pop or click.

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Post by chris harris » Wed Jun 02, 2010 11:21 pm

kslight wrote:I can't help with your specific build, but couldn't you just put a momentary foot mswitch in a box and use that for manual stutter like a "kill" switch? Just seems like a simpler situation to achieve the same effect...
Maybe easier to build... but, definitely not the same effect. or, at least not as elegant and useful an implementation of the effect.

You can also get a less square tremolo effect by rapidly turning the volume of your guitar or amp up and down... but, sometimes, it's better to have a tool that does that for you, especially if you want the effect to be consistent and rapid and you want repeatable control of the speed.

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Post by Scodiddly » Thu Jun 03, 2010 5:20 am

Hmmm, wonder where my schematic is... a few years ago I built sort of a building announcement system with an opto-FET chip as a noise gate. Pretty simple implementation.

alf
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Post by alf » Thu Jun 03, 2010 7:28 am

Wow, thanks for the response guys!

I'm using an IR transistor receiver.

@ Kslight : Yeah, I want something to do this automatically as I am not exclusively using it for guitar. I do a lot of noise music and this is a nice addition to the setup. It, when finished, will have 4 channels w/ separate rate controls. Stutter madness!

@ Scum, I will get a schem up in a bit. It's really simple though. Just a feedback loop for the 4093 w/ a cap to ground(10uf) and a pot(1M) to control the rate of oscillation. This feeds the IR emitter through a 1K resistor. The ground side of the IR detector is held with a 2.2K resistor.

@ RickvH : The analog switch thing was something I was kicking around at 1st, I just thought the setup I decided on would work fine and be easier. Especially when I saw this video of a guy using the same setup(the guy that told me about the RS parts picking up on the switching of the 4093). And yeah, I was thinking the same thing. My signal was being 1/2 rectified, but why now as opposed to a week ago? And what's up with dude's video that he gets it to work. Must I build something to rectify the rectification? :lol:

This is what I was trying to do. He gets it, what happened to me?

http://www.youtube.com/watch?v=cgXO9aBim1I

It's weird, it's almost like, in my circuit, the IR detector is acting zener-ish(?) Taking a while to develop a charge, then allowing squashed audio through.

Guess I can try the analog switch thing. Might work out. Just upset to have ordered these parts. I also ordered some 4n35 opto-isolators, haven't tried those yet, but apparently they are noisy too.

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Re: Stutter pedal

Post by JGriffin » Thu Jun 03, 2010 8:34 am

alf wrote:So I decided to make a pedal to stutter a signal. Basically a tremolo but with a square wave cutoff. Choppy. I figured it would be pretty basic to do if I kept it simple. Grr...
My Vox Beatle has an effect like that, and I used to have a Hohner amp that did it. It's cool effect.

I'd think if you can find a schematic for one of those old amps it'd give you some clues.
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Post by RickvH » Thu Jun 03, 2010 9:30 am

Okay, the IR detector is a transistor.

Assuming that the oscillator is oscillating, what's really important is how the transistor connects to the audio input signal. Transistor switches aren't so great at passing audio through them in series. I would instead suggest using it to short out the audio when the transistor switches on.

To do this, connect the emitter of the detector transistor to ground. Then connect the audio input to one end of a resistor (100k perhaps). The other end of the resistor goes to the collector of the transistor. Take the audio output from the collector. This way, the resistor and transistor act as a voltage divider. When the transistor turns on, it acts like a low resistance and the signal should be greatly attenuated.

Hope this makes sense.
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jv
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Post by jv » Thu Jun 03, 2010 10:11 am

The Danelectro Tuna Melt in the "hard" setting does this.
The schematic here might give you some ideas:
http://img185.imageshack.us/f/danotunamelt2li.jpg/
(I think this schematic is not 100% correct- I think if q2 is connected as drawn it wouldn't work, but if you switch collector and base on q2 it would).

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Post by alf » Thu Jun 03, 2010 10:13 am

That does make sense! In fact that makes a lot more sense than what I was originally trying to do now that I have your insight. Thanks! I'll try it today/tonight and let you know how it goes.

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Post by Nate Dort » Thu Jun 03, 2010 10:51 am

I built a Treumulus Lune based on the schematic here:

http://fuzzcentral.ssguitar.com/tremulus.php

It can get really choppy if you want it to, especially with the "ramp" mod shown.

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Post by alf » Thu Jun 03, 2010 5:57 pm

Image



Top is the circuit RickvH suggested.

Bottom is what I had originally.

Going to try the top one this wknd.

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Post by The Scum » Mon Jun 07, 2010 11:45 am

That gives me a couple ideas.

Keep in mind that the emitter of any transistor (even a phototransistor) is a diode. In order for the transistor to conduct from C to E, the signal needs to overcome the forward drop of the emitter diode. This is probably where your half-wave behavior is coming from.

One option would be to AC-couple your in and out, and add some DC bias to the signal.

There's a handful of schems floating around that might be useful, like this one:
http://www.generalguitargadgets.com/dia ... iginal.gif
The 3 resistors and cap on the base of the right-hand transistor do the AC coupling & DC bias.

I've got a paper copy of a similar one credited to Jamie Heilman...but I'm having trouble finding it online right now.

An alternate option would be to use a Vactrol (or homebrew LED/CdS cell arrangement). The resistor on those is truly a resistor, no bias required. The cells have a bit of a memory effect, though...they don't switch very quickly. Maybe worth a try, though.

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Post by alf » Tue Jun 08, 2010 5:52 am

Ok. tried the other way and no go. It won't cut off. I need to tinker w/ it some more I guess and see if I can't get it right. But, re The Scums suggestion I may not be able to make it work.

What bugs the shit outta me is the fact that the circuit worked completely fine the 1st time I put it together(except the popping). And now it won't work the same way, even with the same parts! Electronics is not that random. Something happened. But I don't know what.

@ The Scum : Yeah, I did the vactrol setup, but I want faster chopping times which is why I went with the IR sensors. I know SOMEONE pro has to use this in a design, no?. That schem you linked to is nice, but damn it I was looking for the simple way out. I want 4 separate channels w/ separate fx circuits on each. That would be a heck of a build compared to what I was shooting for.

I am going to email the guy on you tube and see if he'd be nice enough to help point me in the right direction. I'm gonna laugh if his circuit is crazy complicated.

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