Smash Drive is a DIY community project by Aron Nelson, who runs the DIYStomboxes.com forum. Smash Drive is a overdrive/distortion built from the LM386. Its simple and easy to work with. you’ll find the 386 in many guitar circuits. its cheap and easy to get.
Projects that use the LM386
- RunOffGroove Ruby
- Earth Quaker Devices Acopulco Gold
- Frantone Peach Fuzz
- Many circuits by Tim Escobedo
- D*A*M Sonic Titan
- and many more
The LM386 is an amplifier in an 8 pin DIP. There are three versions. The different versions designate the max voltage and output. The chips range from 1/4 watt to 1 watt. you can make an amp from one of these chips that can drive your 4×12 cab at enough volume to get you kicked out of your appartment!
For a detailed in depth analysis of the 386 read this article: https://www.electrosmash.com/lm386-analysis
In a nutshell the difference between these chips is the output. They range from roughly 1/2 watt to 1 watt output. One watt from an 8 pin DIP is pretty amazing!
The chip is a really easy to use. Similar to standard op-amps it has an inverting and non-inverting input along with an output. Unlike standard op-amps it doesn’t require a bias voltage at the input. Did I say it was easy to setup?
How does it sound?
The chip makes good sounds. The Smash Drive sounds okay. It could use some work. The gain control in the schematic is 500r I only had a 1k pot on hand. For the first half of the rotation there is not change. From 50% to 75% the adjustment is useful. In the last 25% of he range the circuit begins to oscillate and so isn’t useable.
The While it’s not a great sound on this first pass I can hear some potential for good sounds. Maybe with some experimentation it could be improved.
After a second look at my build I realized I used a 1r instead of 100r resistor for R3! Big mistake! With the 100r in place the oscillation was gone.
The 1K Gain pot was working well. The 500r pot would be better. I didn’t have one of these so I soldered a 1k resistor across pins 1 and 3 of the pot to simulate a 500r pot. This changes the taper of the pot but it made a huge improvement. With those changes in place this was sounding a lot better!
Overall I’d say this was worth building. The 386 is a worth exploring. Plenty of people have done great things with it. The Smash Drive is simple to build and the sound is not bad. There is a deluxe version that adds a Marshall style tone stack which would add some sonic shaping.
Building the Smash Drive
I designed my PCB in Eagle. I had the boards manufactured by PCBWay.com. The service is cheap and easy to use. I’ll be posting this board there on their shared service when I get a build page up for this project.
I designed the board to use 9mm pots. The posts and LED mount to the board. All of the off board wiring is at the bottom of the board. The connections are organized for easily wiring up the switch. This makes for an easy trouble free build.
I designed the graphics in Sketch then I milled a black powder coated enclosure and drilled.