ETI Amplifier Repairs

ETI 470/4000 Stereo Amplifier

Another blast from my past, the ETI 470 or Audiophile 4000 system amplifier (60w/ch). I decided to have a go at throwing these together, a lot was made of TIM (Transient Intermodulation Distortion). Noticed there was +60mV on the 220µF C4 capacitor so revesred it as the original had the positive to 0V, also I didn't like the BD139\140 transistors so used MJE340\350 (had quite a few of these). Also left several resistors and capacitors off the board as these were only needed for stability which I didn't think were needed, I'm waiting for it to self destruct at several megahertz! The input is very low impedence, so as advised in the article fitted an emitter follower at the input, sounded ok but no great improvement over other amps to my ears, hey ho...

ETI 300 Watt Amplifier

I decided to try my luck with an old ETI amplifier design from around 1980, 300W into 4ohms. I drew the PCB layout freehand, wish the Dalo Resist pens were still available as the ones available now are rubbish. Anyway didn't turn out too bad, had problems with powering up after assembling the parts etc, always make sure resistors are soldered in even if they look as though they are! I had to make some changes to resistor values with the components I used in the temp sense area but powered up OK eventually.

ETI 100 Watt Powertran Kit

This would blow the positive fuse at switch on. The transistors checked out okay. It turned out to be the 100 µF 3 V tantalum in the feedback to 0V was short circuit.