Tag Archives: stereo

Stereo Amplifier

My second attempt at mastering the LM386 Audio Amp IC (still sounds terrible).P1020890

 

Here’s the data sheet for the LM386 IC with some example circuits:
http://eicom.ru/pdf/datasheet/National_Semiconductor_PDFs/LM386/LM386.html

Instructables has a simple how-to:
http://www.instructables.com/id/LM386-Audio-Amplifier/

The schematic used in my project is a variation of this one from:
http://www.rason.org/Projects/icamps/icamps.htm
The only difference is that I added a 100nF from pin 7 to ground.  I think it helps keep the noise down.  There’s also two of everything except R1 and C1.

IMG00001

P1020902 P1020916
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P1020904 P1020914

Wow, my wires are all way too long.  It makes it very hard to get into a tiny box, but it works!

Audio Spectrum Analyzer

There is a great tutorial on how to setup and use a 2×16 LCD on the Arduino website:
http://arduino.cc/en/Tutorial/LiquidCrystal

Here’s a good explanation of FFT theory:
http://www.arduinoos.com/2010/10/fast-fourier-transform-fft/

My pinout is a little different because I wanted to save as many PWM pins to add servo control for the next stage of this project.  I’ve been tinkering with the idea of moving physical objects around based on audio input, instead of just showing levels on a display.

To visualize the frequency levels of the incoming audio signal I use the 8-bit Fast Fourier transform code which is discussed here:
http://forum.arduino.cc/index.php/topic,38153.0.html

Honestly, I’m not convinced that what I’m seeing on the display is an accurate representation of the audio spectrum that I’m listening to, but it looks pretty cool and that’s all I really care about at this point.  There is hardware available that would produce much more accurate results than this software.  There is a “Color Organ” project on the Make website that I’d like to build someday:
http://blog.makezine.com/2010/10/18/circuit-skills-led-color-organ-spon/

Additional Reading:
http://forum.arduino.cc/index.php?topic=38153.0
http://forum.arduino.cc/index.php?topic=182169.0

Code and libraries on GitHub

Stereo Preamp

My roommate found a nice Technics record player in a free box on the street.  It wasn’t working very well so he took it apart and cleaned it out and made some adjustments and got it working perfectly.  He plugged it in to his boom box, popped a record in and was really bummed because the audio was barely audible.  I ambled over and said, “Hey buddy, you need a preamp for a record player.”  He asked if I had one he could use.  I did not but I offered to try to build one, and I did.

P1020896

I found a schematic for a Low Noise Stereo Preamp module for sale that looked fairly reliable:
The module:
http://www.maplin.co.uk/low-noise-stereo-preamp-kit-220053

The schematic:
http://www.maplin.co.uk/media/pdfs/N47FL.pdf

Here is the relevant info from the pdf:

stereoprecomponentsstereoprediagram

I didn’t have the exact capacitors, or even the correct IC to build this… but I did anyway.  For the IC I used TL082CP in place of theNE5532 because that’s what The Shack had.  It seems to work just fine, and I can always swap it out later.

Here is the inside:

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It all just barely fits into the case without bulging:P1020874