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!
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.