Sound reactive LEDs

I’ve spent a lot of time inspecting how could I build up a system, which blinks LED lights in time with sound. Found some plans from the internet, but they all sucked. At first I tried to use a TIP31 -transistor, which in fact works somehow, but needs a lot of a amplification to work. My bass amp’s effect loop’s send’s signal wasn’t strong enough to blink the light. Added MXR’s Microamp to the line, and it worked just barely.  TIp31 needs  at least 0.7 V to conduct, which you don’t have in most cases. So, f**k the TIP31.

Instead, one good solution is a LM358, which is a low power dual operational amplifier. It can be used to amplify the DC signal generated by a microphone and act as a LED driver. It has DC voltage gain of 100db, and runs with DC-power from 3 volts to 32 volts. The circuit is as following:

I usually hate circuits containing connections between two sequential rows in vero board, but this time I tried to squeeze the circuit as small as possible. The driving signal can be almost anything. Signal from microphone, instrument level signal from guitar…
It’s very sensitive, so instead of amplifying the signal even more, we have to brake it down instead. The sensitivity can be adjusted with the value of R1 -resistor in the circuit. To make it easily adjustable, use appropriate potentiometer in place of the resistor. Something like 5K pot is worth to try. Everything below 1K makes the leds crazy even if you breath too loud.

R2 -resistor is for limiting the current going to the LED’s. If you plan to use several leds in your circuit, you can use a jumper instead, and connect appropriate resistors in led rows. How many led lights you can use in series depends on the input voltage used, and the colour of the leds. Blue and white are the brightest, and with 9 volts current you can run only 2 or 3 in series. It’s up to to the forward voltage of the led light, which is around 3 volts with white and blue. But that’s not a problem, just create several parallel led stripes.

In the video below I’ve built this system inside a 1590B -box. The LED stripes are built into mini sized guitar. I removed the pickup, and assembled the LED stripes into small piece of wood which I installed into humbucker frame. My bass amp’s direct out is used for the operating signal. So, basically it’s just instrument level signal, and 5K resistor pot is used for adjusting the sensitivity. This is our band’s on-stage decoration, and it takes its signal from the bass drum.