The Guitar Phaser/Tremolo Effects Box

I’ve really enjoyed using the LM386 audio amp I built in Hack #5. I’ve used it to demo other audio creations as well and this week I’m using it again in a guitar tremolo effects box.

At the heart of this circuit is an RC filter that acts like a tone control on an audio device. It’s a low pass filter comprised of a .047 uF tantalum capacitor and a photoresistor also known as a photo cell or a LDR (light dependent resistor). The LDR’s resistance is modulated by light from a flashing LED which is controlled by the output from a 555 timer circuit in astable mode. As the resistance in the LDR changes with light intensity it alters the tone of the audio signal and creates a phaser like tremolo effect. The 555 astable circuit has a potentiometer that allows the blink speed of the LED to be speed up or slowed down and the LM386 amp is there to help boost the signal strength as the tremolo effect attenuates it somewhat. There are two other potentiometers on board. One that controls how much of the signal passes through the tremolo circuit and one to control the volume.

This is not only an effect box, it’s also a signal booster and it will brighten up the signal from any passive guitar pickup or microphone. It’s a fairly easy build that should be under $30 in parts. Below you’ll find a parts list, a schematic and a video of the entire build with a demo and explanation of the circuit. Have fun and as always….

Keep on hackin!

Parts List:

1 – LM386 audio amp
1 – 555 timer
1 – BC547 NPN transistor
1 – LDR (photoresistor)
1 – Bright white LED
1 – 1000 uF Electrolytic capacitor
1 – 220 uF Electrolytic capacitor
1 – 100 uF Electrolytic capacitor
1 – 10 uF Electrolytic capacitor
1 – .01 uF Ceramic capacitor
1 – .047 uF Ceramic capacitor
1 – .047 uF Tantalum capacitor
2 – 1K ohm resistor 1/4 watt
1 – 100 ohm resistor 1/4 watt
1 – 470 ohm resistor 1/4 watt
1 – 10 ohm resistor 1/4 watt
1 – SPST power switch
2 – 1/4″ phono jacks
2 – 10K ohm potentiometers
1 – 5K ohm potentiometer
1 – 9 volt battery clip
1 – 9 volt battery
1 – 5mm power jack
1 – Perfboard or make your own PCB.
1 – Plastic or metal enclosure
Some 22-24 ga. hookup wire
Shrink wrap to couple the LED to the LDR

OPTIONAL: One more LED of the same type to mount on the outside of the enclosure as an indicator of power on and tremolo speed.
Wire it in parallel with the other LED with it’s own 470 ohm resistor.

9 thoughts on “The Guitar Phaser/Tremolo Effects Box

  1. hi Dino, thanks for sharing this post. I bread boarded this but it’s not working yet… My problem is… 555 timer based Led part is working(controlling blinking speed), and LM386 based amp is working, but LED/LDR part doesn’t work. it doesn’t produce tremolo effect and dry/wet pot is not working. I don’ have any clue yet. For capacity, I only used Electrolytic. Is it necessary to use Tantalum for LDR part? Also instead of BC547, I used BC548. Can you give me any advice?

  2. how important is it to use the Tantalum .o47 Cap? I’m ordering parts for this build and I can’t seem to find those on Jameco. How would it affect the circuit if I used a Ceramic Disc cap instead?

  3. Hi Dino,
    I am quite new to the 555 timer, which is why I love this quite simple guitar effect. Still I have a few questions regarding your schematic. Wouldn’t it be better for the attenuation of the signal, when the LED/LDR part ist replaced by another transistor, that has a (theoretically) infinite resistance, when the base is “low” as opposed to the finite resistance of the LDR, even when the LED is off. I made a schematic for what I am thinking of:
    http://www.imagebam.com/image/a351b6208719138

    From the left comes Pin 3, from the top comes V+, at the bottom ist signal in, and out. I also added a switch, to use both tremolo modes (both LEDs, as you show in your video). I moved the potentiometer towards the signal, in order to use only one. I didn’t know, what exactly the tantalum cap is good for, so i omitted it. What is it good for?

    I also omitted the LM-circuit, because I don’t see, where the signal could loose strength, when the transistor is open.

    The values of the components are essentially the same as yours, all the transistors are equal. Do you think this will work, or sound extremely different than your version? Unfortunately I don’t have any prototyping possibilities right now, otherwise I would have already tried.

    Thanks for all the Hacks!
    Johanz

  4. Hey Dino,

    Great sounding pedal! I’m just at the breadboard stage, and so far I have it working well, aside from a strange ‘clicking’ when the signal switches on. Any ideas as to what this could be?

    In addition, I want to use this as an effect in my pedalboard, ie I need a locking footswitch. I have a DPDT latching switch that’ll do just the job, but my head is going fuzzy trying to figure out where to wire it in. I’m looking at this schematic taken from Melx’s blog:

    http://4.bp.blogspot.com/_nsvZ1rXQwes/TGiBRyyKIlI/AAAAAAAAAl0/kbfXTeendkY/s1600/2pdt.JPG

    Where on your schematic should I take board I/O and jack I/O from?

    Any help would be much appreciated, long time tinkerer but first time with pedals!

    Cheers, Poley

    • That clicking comes from the 555. Wire the switch in at the positive input and the positive output. Just break those two connections and wire in your switch.

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