DIY Audio Preamp for a few euros

Well it took a bit of research for a newbie like me but I eventually found a nice looking circuit diagram in this book:100 circuits audio circuit bench

Basically I was trying to get my cahon mic’ed up and into my live Twitch broadcasts so I could stomp it with my right foot whil I sing and play. The issue was I was using a small amp as a mixer – it worked nicely with the headphone socket as output. However, with the mic and instrument inputs taken, the only one left was a kind of CD/backing track level minijack. And my little dynamic mic didn’t have enough juice to make any noise through it.

After looking at a bunch of checp preamps/mixers (I didn’t want another mixer – I only needed 3 channels and was happy with my lil’ battery amp!) I realised that no matter how cheap behringer made something it always had a bunch of features that I didn’t want and probably sounded a lot worse than something I could build for less than half the price…

Therefore I went looking for circuit diagrams and found the aformentioned one to do the job.

Here are a few pointers that might help someone move from the circuit diagram to getting the right components and soldering them on a board.

  • I found this circuit happily worked on 12V instead of 9V – I used 8 1.2V rechargeable 1.2V AA batteries to power it & it seemingly lasts forever….
  • I put the circuit on a prototyping board first to make sure I’d arranged the components right. Then I just copied that to solder onto my main board.
  • I doubled the mono signal in order to output to the stereo minijack input on my amp/mixer.
  • Film capacitors are apparently better than ceramic for this sort of thing so that’s what I used
  • I used cheap carbon resistors and so far they sound fine – some day I’ll try some real expensive ones.
  • I taped it all up liberally. Much prettier than moulded plastic in a rugged DIY sorta way;)

I’ve tried it on some vocals since building and it really does sound better than any of the cheap built in preamps I’ve found on gear over the years. I think you’d have to start spending proper money on a really well made one to do better. Very impressed…

Now to go back to my DIY mic project and finally get that into usage:)

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