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Kill Pedal


tomrulez
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Right, here's one for all you electronic guru's.

I had an idea for a pedal that basically is like a killswitch but automated. Therefore it would have one switch to kill the signal, however I want another switch that when pressed will kill the signal and then let it back through really quickly, many times, kind of like a tremolo but actually killing the signal every time. This would allow the user to do those staccato sounds with general ease. I also wanted a pot that could control how fast or slowly the signal is killed, example being in a low position the signal is killed once a second and in the highest position about thirty times a second.

I thought I could do this with a 555 astable circuit running into a transistor which then kills the signal when no power is going through it and lets the signal through when power is going through it.

I can't work out a way to get this to work though so I though I'd give you lot a try.

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Well...what you are looking for is a square wave tremolo...this will give you a hard on off tremolo effect (can sound like a helicopter). They work as you describe kind of, but you are better not to try to design your own circuit as these things are not that uncommon...you could probably find some that have square, triangle and the softer sine wave tremolo as a switchable option all in one.

The reason not to try it yourself is that anything audio that involves a 555 clock circuit does run the risk of having the clock ticking in the signal. It won't be a difficult circuit, it's the filtering of the clock that might cause a DIY circuit problems.

There have even been tremolo's in pedals before and I suspect that you might find some digital effects...I know one of my cheap ones has tremolo assignable to the expression pedal for speed (not sure if it can do a hard clipped trem though).

You used to get hard clipped trem in cheap pedals of the past (fenders and more traditional tremolo's often used optical circuits to get that smooth sine version, while early transistor ones tended to be clipped)...I remember one that also had white and pink noise generators to make the sound of wind and surf as well!

...

So...a hard clipped (square wave) tremolo circuit is what you want...gives you that "crimson and roses" sound!

Products like the Boss TR2, danelectro's Tuna Melt and EHX pulsar will all do hard clipped tremolo...you may to do a bit of searching to find a circuit but they are out there...might even find some kits in electronic stores...

pete

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I've just found this circuit in a book.

tremhj5.jpg

w681.png

From my understanding I think this circuit does what I want but part of the circuit filters the signal to a more triangular waveform. I think this is done by R4, C4 and R6 but I might be wrong, can someone confirm this or tell me what I need to remove to stop it being filtered and to keep it square-wave.

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I thought I could do this with a 555 astable circuit running into a transistor which then kills the signal when no power is going through it and lets the signal through when power is going through it.

Some sort of astable circuit, yes a 555 can do it, switching a transistor will work. I would try to set up the transistor as a normal gain stage, then use the square wave from the astable circuit, to drag the transistors bias down to where it is cut-off on that half of the wave form. You might need some filtering to "round" the square wave a bit if it is too severe and you hear clicking etc..

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Could you tell me how to do this by modifying the circuit I posted above, thanks for the help.

Filtering a square wave doesn't really give you a triangle wave. If you filter it enough, you get left with the fundamental frequency as a sinewave.

However, it appears that R6/C4 are doing the filtering (time constant about .5 second) I wouldn't remove them, I'd try it as is, then reduce the size of the capacitor until it sounds the way you want it. Maybe 1/10th the size might be good - just a guess.

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I can't speak to that circuit other than what has been mentioned...anytime a clock and audio is mixed there is a risk of it's ticking getting into the signal...

Two places you should check out are...

Aron's Stompbox Forum

and...

DIY Layout Creator

The first is the best stompbox and circuit forum with many experts and hundreds of schematics specifically for guitar effects. Also linked directly to it are many great effect sites of which most are active members...

The second is also related, this layout creation software is free and very easy to use for vero, strip or printed circuit board layouts. It was made in conjunction with that forum and so in the linked page you will see heaps of circuits already laid out by members of the forum for guitar effects...

You can use it to make a layout for a circuit like the one you have proposed, or of another design that might be of interest...modifications are also easy to plan...

In order to see the layouts though, you need to download the software and the circuit. Another benefit is that you can render your circuit as a jpeg file making it easy to post the result for others to look at and admire...or maybe troubleshoot.

...

While "project guitar" is a great site, there are some specialty areas like effects making, amp modifications...even guitar wiring...in which it is covered better and with more expert help. If you really like this circuit, there are people at that forum far more easily able to understand and suggest modifications that will produce the effect you are after...

hope that helps and is an interest to others as well...

pete

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This has been brought up a few times at the Arons stompbox forum - I know because I brought it up one of those times. I think if you search for "stuttering pedal" or something like that you'll find my thread. A search there should turn up some info, as PSW noted. There's other more recent threads since mine, I know for certain. The one I asked this same question in has a few other posters touching on some of the issues inherent with a pedal like this as far as noise concerns go.

Also check out Geofex.com - R.G. Keen is a brilliant fellow, and has been gracious enough to share a lot of info with the community. A lot of it is a bit hard for the novice to make it through, but you'll learn an awful lot if you make the effort to look through it all. If you look on the main page, there's an update from 10/24/03 where he posts a schematic for a variable stuttering pedal, that ought to fit the bill - worth looking at, at least, although I haven't heard of anyone trying it, and as R.G. stated, it's a schematic that hasn't been built yet. (Although R.G. is one I would trust when it comes to designing circuits.)

There may be something simpler on the DIY Stompbox forum, however.

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I found the one over at geofex and although I do have a bit of electronics know-how that schematic goes straight over my head, it's probably simpler than it looks. I'm still waiting for my account to be validated over at arons.

That circuit's not that different, in principle, to the one posted above. The 2 opamps at the bottom do roughly the same thing as the 555 in the first circuit. The other 2 opamps are just input and output buffering, and the FET, when wired in "shunt" mode, works pretty much the same as the FET in the first circuit.

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