LM1875 integrated amplifier - April 2005
I built my first LM1875 amplifier in 1992. This was before all the craze about the 47 Labs amplifier and the flood of DIY copies that followed. I built it when I was a student, and given the total expenditure it was a pretty decent amp.
Earlier this year I needed an amp for a TV+speakers setup and I decided to re-visit the LM1875. I checked out www.diyaudio.com and a few other websites, but really not much had changed in the last twelve years. This time I had some better tools however. I used Eagle to design a PCB for the new amp - rather better than the hand-drawn PCB from 1992! I used one of the cases from my old LM1875 amp to build the new version, but first painted it a nice shiny black.
Toroidal transformers (rated 50VA) mean the whole amp now fits into a small case! The internal wiring is not yet complete. A 12V supply is there to power an RF volume control which is to be retro-fitted when the pot arrives. For now a low-end poorly matched part will have to do.
A closeup of the PCB shows that much of the board is taken up by power supply components. Board layout is critical and attention must be paid to current flow through the ground lines. The National datasheet shows one way to do it, but there is room for improvement!
Not its final resting place, but merely a temporary home for testing. The speakers on the DIY stands are going with the amp to its new owner.