Chopper Tremolo Effect

March 8, 2008 – 11:50 pm

I’ve wanted to build this kind of effect for a long time. This was actually the reason I got my 4066 ICs half a year ago, when I visited my electronic components shop.

A Tremolo is an effect unit that modulates the amplitude of the guitar signal, usually in a triangular waveform. This version uses a square waveform, for a more switching, chopping kind of effect. This kind of effect can be heard in the beginning of Plant Telex by Radiohead. Tom Morello of Rage Against the Machine uses this kind of effect too, he, however, uses a “kill switch” on his guitar, which he controls manually.

More after the break…

This is a very simple and low quality circuit, whose problems can be seen in the following video. I built it in about an hour, that’s how simple it is. It is based on a simple NAND oscillator from an LED Chaser circuit that I had built maybe a year ago. Here’s the circuit diagram(proudly drawn in GIMP):

Chooper v1 schematics

Values that I had used in my circuit:

  • Supply Voltage: 5VDC
  • R1 – 1MOhm
  • R2 – 10KOhm
  • C1 – 47uF

The idea behind the circuit is quite simple. The NAND provides a square wave pulse (and there are better places where you can understand how it works, google “NAND oscillator”) that is then hooked up to the 4066 IC. The 4066 is contains 4 analog switches, where each switch is controlled by a single input pin – as seen in the following diagram:

4066

The 4093 NAND IC contains 4 NAND gates, so I used a free one to invert the clock signal.

I used 2 of the 4066 switches. The first one, connects the input signal + and the output signal +, while the second one connects the output signal + and the ground. One switch is controlled by the output of the oscillator, and the other is controlled by the same output, but inverted. The result is that the output signal switches between the input signal, and no signal (ground connected to +).

This is rather primitive, but that’s the whole point behind this simple project !

Here’s a short video showing my prototype and live demo of the effect (grr, I forget my entire English vocabulary when I talk):
You need to a flashplayer enabled browser to view this YouTube video

I will be glad to hear any ideas as to how to improve the circuit. My main goals are:

  • Eliminate the POP noise
  • Allow higher frequencies
  • Add a 4017 counter with 8 switches(representing one bar) that will allow more complex chopping

I have loads of bipolar transistors, maybe I’ll try to use them instead of the 4066…

That’s it ! Please let me know if you build it yourself !

  1. 10 Responses to “Chopper Tremolo Effect”

  2. Hi,

    the popping noise you describe is due to abrupt switching of the signal from some non null value to zero. To remove this, you need to add a zero-crossing circuit to trigger the switching. A number of digital potentiometers have a built-in zero-crossing detector. For example the max5457, which also has a mute input which you could use directly in your circuit.

    By vic on Mar 9, 2008

  3. @vic

    Googled up a bit on Zero-Crossing. Let me see if I understood you correctly. You suggest something like using a comparator to determine a signal zero, and use perhaps a D-type flip flop to latch the clock signal, so that switching will only occur when the input signal is at zero?

    By Ben on Mar 9, 2008

  4. woah, i don’t think you need to take it that far! It’s been a while since I did FX pedals, but i think I remember a really simple solution to the popping – it was to place a small cap (i think it was on order of pFs) across the switch leads (ie, from signal to ground).

    By aaron on Mar 10, 2008

  5. Thank you for your sharing, it would be useful for the others.

    By heri on Aug 19, 2009

  6. i will be very happy if i can be provided with information about chopper circuit, and it’s application as aswitch

    By asare daniel on Nov 18, 2009

  7. Tha u fr sharing this with everyone, I never thought to use a 4066 as the switch… You can get quite high frequencies with a 555 astable instead of you inverter thing. search astable 555 times circuits (wiki has a diagram).

    By Mike on Nov 24, 2009

  8. And… Using two 555′s in series (or a 556) will also give slightly more complex patterns.

    By Mike on Nov 24, 2009

  9. i’m working in a kind of random chopper, which works with two 555 and a 4017, we can work togheter to make it work. Write me and will show you the schematic.

    By Gabriel on Jun 27, 2012

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