Miniature Guitar Amplifier – Never Expected to have THIS Problem

In my quest to figure everything out myself, instead of just blindly following pre-designed circuits, I’ve come up with a pretty good clean sounding 1/2 watt power amplifier as well as an effect loop and more recently a switching setup for dual channels using a DPDT switch and some nice tone shaping. For the most part, it’s been about 60% research and theory and 40% just trying things out and learning from the resultant epic failures.

This has been a great learning experience. Although I have been playing on-and-off with electronics for the last 25 years, in my mind large parts of the underlying theory were … fuzzy … for a lack of a better word.
I was always getting hung up on the math and things like the task of trying to memorize those little resistor stripes. I never knew what the codes on capacitors meant when you get into values lower than typically found on well labeled electrolytics.

A step back for a moment to the past two years – when I first started building my Prusa Mendel i2 (3D printer) I was very intimidated. There was so much about the project which required skills I thought I might possess but had never directly applied to anything before. It gave me a much needed drive to do something outside of my technical comfort zone (I’d already spent many hundreds of dollars on the necessary parts, I was pretty committed if only to justify the expense). I threw out how I was taught to learn in my youth by the school systems – they didn’t apply here and never worked well with me in the first place. This was/is bleeding edge open source tech – there was no text book. I learned to rely on my strengths and intuition to grasp the concepts that made sense, and then tested, re-evaluated what I knew and then tested again until I had a provable concept and knew I had figured it out.

It sounds simple and naturally has it’s roots in the scientific method which was drilled into my head by my wonderful 2nd grade science teacher, Mr. Hurd. I’ve always been a tinkerer and an autodidact, but the Mendel really taught me how to hone those skills and tackle more complex subject matter. It may have taken me some time, but after I was done I had a 3D printer capable of accurate 100micron prints and then went on to design three other printers from scratch. One of which is currently still in the prototype stage but it is a fully functional delta style printer which can almost match my uber-custom and tuned Mendel in terms of print quality. It needs revisions for most of the parts since assembly itself was quite the pain in the arse – I’ve never had any formal mechanical engineering training, so the actual parts were not designed for ease of assembly per-se, only for function and structure.

I digress … back to the point. After tackling such projects in the 3D printing field, I needed to take a break from the intensive 2 years of learning, hacking, designing and tuning melted plastic delivery systems and trying something new, or at least different. I built an electric guitar pedal board and slapped on some new pedals I’ve recently obtained such as a compressor, wah-wah, chorus and fuzz effects. During the process of looking at DIY pedal boards I came across DIY effects pedals. Some of the circuits seemed down right build-able with scavenged parts I had on hand. I made a footswitch for my Peavey amplifier using some cheap parts and my 3D printer.

Since I like to “hack” things – I learn in part by reading something, applying what I think I learned, re-reading it to find out what I did wrong in my implementation and re-iterating… I didn’t want to subject my expensive amplifiers to a pedal circuit I was testing. Plus it’s hard to get the breadboards close enough to the amps without knocking the components off. 🙂
Out of this was born the miniature amplifier project. I’ve built things with LM386 amplifiers before so the Little Gem/Ruby designs from ROG were just not tickling my fancy – too easy and besides, how do you effectively test a delay pedal without an effects loop, assuming you don’t want to move your dirt pedals from their pedal board to your test area.

So, as my previous posts suggest, this project is starting to show some fruition. Having all the basic bits worked out I sat down for a bit today to work out the dirt portion of the amp, now that I have an effective switching system. I figured for the dirt stage I would include a buffer and an overdriven op amp into a single dual-opamp chip to save on components and wiring effort. Wouldn’t you know it, I can’t for the life of me get that chip to distort today – I’ve been increasing the gain and adding clipping diodes to no avail. This puppy does not want to overdrive for me, it just wants to put out a nice clean signal into the power amp – even to the point of pushing the LM386 to distortion without breaking up itself as I crank up it’s gain.

Never anticipated that I’d be getting too much clean amplification in a circuit. What a problem to have after all the times I couldn’t keep it from distorting before.