Over the years i made a lot of diy guitar amps but this is the first time i use the LM386. I made transistors and IC based guitar amps but never a DIY LM386 guitar amp, so i ordered some LM386 on ebay and i googled LM386 guitar amp to get some inspiration then i found this awesome website: runoffgroove, i was going to make his circuit but i didn’t have FETs at the time and i didn’t want to wait for them, so i design mine with a 2N3094 instead of a MPF102, and to make it even more cooler i added a drive potentiometer, clipping diodes and a gain booster aka 11 switch ?
Circuit description: The diy LM386 guitar amp has 2 stages the pre-amp (input stage) and the power amp (output stage) like every guitar amp, the pre-amp is just one transistor biased by R1 and R2 ( R1 is the feedback resistor ) its gain is set by the Emitter resistor R3 (the higher R3 the lower the gain), the drive POT is the input resistor it limits the gain ans sets the impedance ( increase its value for more clean control ), C1 is the input coupling capacitor (increase its value for more bass). C3 is a bypass capacitor, the audio/AC signal sees it as low impedance thus increase the gain by using 9v instead of 4.5v, D1 and D2 are the clipping diodes, C2 is a coupling capacitor it forms a high pass filter with the Vol POT (increase C2 for more bass).
The power stage is the LM386 at it’s minimal parts configuration (see the datasheet for more), C4 is another coupling capacitor that prevents the DC voltage of the pin 3 of the LM386 to go back to the clipping diodes (it’s not necessary if there is no clipping diodes), C5 and R4 is a Zobel network, C6 is a coupling capacitor that lets only the amplified AC signal to go to the speaker. C7 is a bypass capacitor it’s not in the LM386 datasheet but i found it to be necessary to prevent the LM386 from motorboating (the closer it is to the lm386 the better).
My Suspect Lm386 Problem Seems To Be Solved
If you’re going to use a plastic case you will need Aluminum tape for shielding/grounding, an alternative to the Aluminum tape is to solder a copper wire to the parts that needs grounding (Pots, switches and the input jack).
I wont put the tools list because every body has different tools, but you can see the tools i used in the picture:
To make the PCB faster and easier i printed the inverted copper side of the PCB and i marked the traces and the components layout on the Protoboard
Lm386 Guitar Amp
After i opened the speaker i put some painters tape on top of it then i marked the holes location and i pre-drilled them with 4mm drill bit
The thing i did not take in concentration before drilling is the mounting holes of the speaker so i had to clear space for the pots and the switches. This is a really simple portable guitar amp project you can complete in an afternoon ; with the parts you need at hand. I used an old surround sound speaker as my enclosure, and used the speaker. The unit also has 5 tone settings to allow you to go from clean to gritty.
NOTE: if you are thinking about building one of these, see my newest addition first based on the 'Little Gem' amplifier, using a few more parts. It sounds much better.
Help Me Understand The Lm386 Chip Amp
The diagram below explains this build in detail. If you want 5-mode distortion, then you simply use the dip switch in place of the SPST switch on the 2.2uf-10uF capacitor. Remember that the speaker you use will make all of the difference in how clean your new portable guitar amp sounds. Mine sounds pretty clean, I achieve this by isolating jacks and components from each other, and I hot glue the audio lines and PCB wiring to avoid leakage.
Enclosure: I used an old surround sound speaker as my enclosure. You could make this unit into a box and use as a 'head' for speakers in mini-cabinets too.
This is a pretty simple PCB for making it all work - I think the power output is a 1/2 a watt. Follow my wiring diagram (photo 2) to put it all together.
Guitar Fuzz Effect
I usually use shielded audio cable for the inputs and outputs to cut down on any feedback / buzz ; and a socket for the LM386 IC (not necessary) - just in case it gets toasted.
Battery location could be internal, but they get ate so I mounted mine externally. A 'Supercap' battery is another idea -- (DIY 9v rechargeable) or some other rechargeable battery as this device runs up to 15v.
You can build this into anything, but I decided an old surround sound speaker enclosure would work best (for being dropped, etc..).A few months ago, Aron Nelson released the Smash Drive. The circuit ingeniously used an LM386 audio power amp chip to produce great distortion sounds. Aron based his work on that of Tim Escobedo. Tim's Stupidity Box was another great sounding unit and beautifully simplistic. The Smokey Amp by Bruce Zinky was another design that used a 386 for some great sounds.
Grace / Big Daddy
Depending on your personal tastes, there may be a potential down side to the 386 designs. The input impedance is listed at 50k, according to the datasheet. This is quite low and causes some loading of the guitar signal. There is some degree of high end signal loss. This may be a favorable thing, again depending on personal preference. I chose to try a high impedance buffer before the 386 to alleviate the loading effect.
A simple Jfet buffer was chosen, due to high input Z and minimal parts count. A high value of 4M7 was chosen as the gate resistor, which helps set the input Z. The J201 fet was used, but any N Channel Jfet could be used with similar results.
The result of the input buffer is easily noticeable. There is increased sparkle in the signal. The signal hits the 386 a little harder, due to more signal reaching the amplification stages of the 386. The buffer adds no gain, but there is a perceived increase. The gain control of the circuit is something else unseen this far with the 386 designs. It is simplistic, but functional. A simple 1k pot was chosen and wired as a variable resistor between pins 1 and 8 of the 386. Looking at the datasheet for the IC, you should notice an internal 1.35k resistor. By connecting the 1k pot between pins 1 and 8, you can effectively vary the gain from near the normal condition of 20X gain to the pins 1/8 connected setting of 200X gain with the 1k pot at minimum resistance.
Sam Technology Professionals: Build A Guitar Amplifier Easily
During the testing of this circuit design, the thought occurred to try a Jfet gain stage before the 386, instead of the buffer. The impedance would still be high and the 386 would see more signal and clip harder. The result is a pleasing grind and responsive big amp-like distortion. The gain control functions in the same way, but the range is higher in gain. Pretty effective, considering that if you want to use a gain stage, you probably don't want the semi-clean settings of the buffered version.
The two circuits are very similar and it may be possible to use a switching system to alternate between the buffer and the gain stage versions.
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