Miniature Amplifier – Putting It All Together

Based on my previous posts of some simpler amplifier components, here is a block diagram of the amplifier:

 

The input buffer I used is an NPN transistor circuit I cooked up from various ideas online.  Common wisdom is to use a FET however I did not have one available, but I did have a handful of C945 transistors scavenged from an old tape deck.

I then used the circuit for passive tone as used in Big Muff guitar fuzz pedals.

I have not tried the 2nd buffer labelled “Tone Buffer (Buffer)” in the above diagram – that is part of another set of theories and I have not actually tested it yet.

Here is the full schematic for the whole amplifier I have been testing – I believe this is somewhere between 1/2W. I made some part substitutions for the prototype, I have no doubt that some of the extra distortion I get is from a lower value resistor in the buffer than should be installed – the 510k Ω value in the schematic below is correct however.

 

I have ideas for modifying the gain channel settings to use a click switch to toggle the “channels”.  I want to try building a two transistor NPN-PNP boost after the amplifier to see if I can increase the output volume just a tad.
But first I am investigating using pair of LM386 chips in bridged mode to double the output to nearly 2W.

The goal of this project is to create a small 9v battery powered guitar amplifier with a good late-night practice volume and decent clean tones.  Naturally the quality of the tone is going to be limited by the actual amplification quality of the digital IC.

I have been testing it on a Fender Squire 15 amplifier that I modded to have a 1/4″ jack in the back.  When another amplifier is plugged into this jack it disconnects the internally housed Fender amplifier and uses the input line inside.  This override on the speaker connection prevents accidentally running two power amplifiers into the same speaker and causing damage.

Below is my humble but impressive sounding little hack: