DIY Audio Amp

DIY Audio Amp

I was once told every man should do three things in his life; father a child, build a house,  plant a tree.  I have done none of those things.  I did however build a very under-powered audio amp.  We were given an old Technics record player, and me being economically self-reliable (cheap) I thought I'd build the amp to go with it.  What follows is a description of a descent into madness;

This is the amp, model version 1.  Rather than order parts to make a monster amp, I used what I had; an LM386 op amp chip.  This chip is not designed to power large stereos, but why let that stop me?   Using the schematic from;

http://www.circuitbasics.com/build-a-great-sounding-audio-amplifier-with-bass-boost-from-the-lm386/

I built two amps into one device, one for each speaker, effectively doubling the power, from 1 to 2 watts of power.   It was never going to blast down the walls or anything, but for home use it should do.  I spent ages neatly soldering everything into place, 

arranging the wires so they looked smart in their new home.  I added a switch so you could choose between the record player or a jack input, a power indicator LED, and an on/off switch.  Everything had gone well during the build, everything was looking good. A thing of beauty you might say.  Then it was time to try it.  A very faint sound from the record came through the speakers, like a spirit communicating from the netherworld. Also a digital 'tapping' could be heard.  I then spent the next 3 days trying to figure out what was going wrong.  The digital noise, I finally deduced was coming from the power supply capacitor being too close to the input jack.  I'd have to re-make the board and move that away from any inputs, and to be safe, keep the amp circuit away from the power supply as well.  With much sadness I started desoldering all the parts on my beautiful circuit.  Parts stubbornly refused to come out, and as time went on it was thrown in the bin in anger.  To save time on the V2 I decided just to build the amp with one LM386.

This is the new version of the amp.  Gone is the selector switch (if you want to listen to music through your phone you can damn well unplug at the back and connect in).  It's also now in mono.  Basically it's a regression from all the features in the first version.  I'm not sure that's how subsequent models are supposed to work, but whatever.

 




























Everything inside was given distance from any parts that might cause interference.  Ground connections also had an individual ground cable, again to minimise interference.  It came time to switch it on.   My trembling finger started to push down on the power switch, all the while remembering the many hours spent finding the causes to the problems.  With a click the power light came on...  AND THEN THE SAME BLOODY THING HAPPENED!!!!!!!!!!!!!!!!!! 

To say I was annoyed would be an understatement.  Swear words echoed down the nearby streets, neighbours cowered behind curtains, dogs yelped.  Anyway, I mostly laugh about it now.  Especially when I realised the record player needed to have a shared ground to the amp.  When I connected this it made a click and then it worked fine.  Oh how I laughed.  Laughed through tears.

Then I was told we were being given a decent technics amp anyway.

RIP old amp.

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