Electronics - Audio amplifiers, preamplifiers, mixers, others

Audio Amplifiers

I've come quite a long way in building power amplifiers. My first amplifiers were rated at about 0.5 WRMS. You'd be surprised, but it was fairly loud. As I got more skilled, I began to build more powerful designs. One of my favorites were the TDA2030 18W IC amplifier. It was small, cheap and powerful. The designs were just basic op-amp designs. That also got me interested in op-amps. I've built several amplifiers rated at 160W (+/-50V supply) using a modified design from Maplin. I also built the original design from the ETI magazine rated at about 100W (+/- 40V supply). The Maplin design was great. I've still got my first amp which I built in 1986 and it sounds as good as ever. I've also built mosfet amplifiers (2SK/2SJ series) and hybrid IC amplifiers (2SK series).

Several things I've learnt from building amplifiers:

1. Use the highest possible voltage for power supplies. There's more headroom and everything sounds cleaner.
2. Don't skimp on power supply ratings. Use overrated transformers - high current, heavy duty. Use large capacitors - I used to get scrapped capacitors from old computer power supplies ranging from 22000microFd to 47000microFd. I'd recommend nothing less than 10,000microFd for a 100W x2 amplifier.
3. Use good wiring techniques. This will minimize hums and earth loops.
4. I generally prefer individual transistors than IC designs or hybrid packs, although some do sound excellent.

Finally, If you do decide to build amplifiers, My advise is to start small then increase to higher powers. It's easy to blow transistors at 100V. That's a costly affair. It's also easy to get electric shocks with high voltages.

Preamplifiers

Although preamplifiers deal with much lower voltages, a lot of the principals remain the same. I do recommend using high quality components here. Since preamplifiers generally have a high gain, any hum or hiss is amplified a great deal. Your wiring techniques are very critical at this stage. In the past, I've found op-amps to be the most versatile. They're also silent and can run on a high voltage (+/-18 V). I like to use TL071, TL072 and TL074 op-amps. I use them for mic amps, DIN amps, bandaxell tone controls, mixers, inverters, buffers, VU meter drivers, headphone amplifiers, graphic equalizers, and anything else which may need amplification or buffering.

Mixers and others

Mixers are fun. It's like putting a jigsaw puzzle together. I first decide what I need. I might need just 2 mics and 2 line inputs for CD players and a headphones output). Then I sketch a block diagram. Next, I draw the schematics for the blocks in. Finally, I build it. Simple. Other devices are pretty similar. Everything is just a block which has been pieced in.

Of course, with modern technology, a lot of it is simply not worth building. You might get a good preamplifier with great features for a fraction of what you'd spend on building it. There are still times when I may prefer to build my own though. My amplifiers age generally better than commercial amplifiers. If it ever happens to break down, I can troubleshoot it in minutes. More often than not, the problem will be due to misuse. People love to trash my amplifiers because they are so powerful. In fact, I've seen my amps run so high that you could fry an egg on the heatsinks. Oh yes, my amps are also noted for blowing speakers! Need I say more?