Electronics

I decided to put my little amplifier into a box, since it doesn’t really look very nice all exposed. Further, the transformer has exposed terminals with 120 Volts, and that is none too safe. So I got a smallish plastic box, drilled some holes, and mounted the transformer (which is the only heavy thing about this). I mounted the amplifier in the box, added a fuse holder and switch. The only problem is that the speaker wires connect directly to the circuit board, and those connectors are in from the box edges. So I will add barrier strips to connect the speakers.

I use speakers from a once very nice Sony 5-channel amplifier which I bought to improve the TV sound. But that amplifier grew a bug, and it was so computer-controlled that I could not fix it. But it had nice speakers (I saved the two front speakers and the woofer) and I dragged them from Seattle to Taos.

Now with volume turned up loud the amplifier only draws 7 Watts. The amplifier is a class-D amplifier or switching amplifier — an electronic amplifier in which the amplifying devices (transistors, usually MOSFETs) operate as electronic switches, and not as linear gain devices as in other amplifiers. [Wikipedia]

My speakers have unusual (for me) low impedance: 1.5 ohms. I think this contributed to an occasional bit of noise from the woofer. So I added a 1 Ohm, 5 Watt resistor in series with the woofer wire. This seems to have eliminated that problem.

Over the Christmas weekend a neighbor asked if I knew anyone who could repair an amplifier. I looked at their Marantz tuner and could find nothing wrong — other than a dirty main fuse. After cleaning the contacts, at least the panel lit up, and all the voltages were correct (I was able to find a service manual), and nothing looked fried, but no sound. It is now beyond my experience and toolset.

So I recommend a similar small amplifier as a modern replacement for her old tuner, which was 17 years old, big, and heavy. I bought a 50 Watt version of this one direct from China (for $40) plus a power adapter. She is using it temporarily until she buys her own.