I have been playing with some various circuits to deal with the pre amp stages and effects loops for my miniature guitar amplifier design.  The circuit presented here is a revision of my previous core amplifier schematics. Other than a few component changes, the main difference is that I have added an N-FET transistor (MPF102) buffer to the input stage. This should prevent improper impedance loading on any pedals in the effects loop stage...

Yesterday I discussed using op amps for buffers in the pre amp and effects loop stages of a small LM386 based amplifier.  I had lamented that I had thus far been unsuccessful in working with the MC4558 dual op amp chip which was confusing me since I was having great success with the LN741 single op amp.  I have now resolved those issues, which I believe stemmed from incorrect biasing of the signal due to my own ignorance – the...

Based on my research into using op amps configured as voltage followers, otherwise known as unity gain, I’ve been testing out using one at the return point of the effects loop – this seems like a good idea so far and appears to work OK as well. The idea is the same as using a buffer at the input stage of the amplifier, to prevent loading the effects units on the loop. This is my test circuit as currently breadboarded.  I am...

Following some of my previous work playing around with the LM741 op amp I came up with this alternate design for my previous clean amplifier circuit. I have played with a few variations on fuzz style gain preamp circuits, but I’m still exploring the options, hence the “Work In Progress” section. One thing I learned is that the gain preamp needs to be silenced when running on the clean channel, it will still distort the...

After successfully making a nice clean channel for my amplifier, I set about trying to make a high-gain distortion channel.  This is an approximation of the circuit, which is loosely based on the Marshall MG10 practice amp distortion circuit.  It uses a pair of LEDs as clipping diodes which I thought I would try out.  I’ve seen this method referred to as sounding like a “can of bees” – I can confirm that but would...

The saga continues – this version of the circuit is one I am quite proud of.  There is no dirt or distortion options in this design, I was going for as loud and clean as I could drive the LM386N amplifier while getting a nice rich sound. Schematic   Power & Input Pretty self explanatory.  The power can be a standard 9V battery or it can be a switching jack for AC adapter 9-12V.  The power switch is not shown, but it’s...

Based on last night’s previous ramblings regarding implementing dual channel settings with a bit more control over how it all works together, I started looking at how other amplifiers accomplish this feat.   Looking at some existing solid-state amplifiers, the above diagram seems to represent a simplified version outline of how this might be achieved. I found some op amps in a piece of old audio equipment which I will be using...