This story starts a few month ago, when I found an amplifier and an FM receiver on the sidewalk while returning from work. At the time, I didn't really have any need for them, but I didn't want them to go to the trash and be crushed and burnt, so I brought them home, where they sat unused and untested.
Now, I have moved to a new flat and I have a different setup, in particular my homeserver which is also my MPD server is not installed anywhere near my computer and its loudspeakers (I was using them for both, just moving the jack plug around as needed). So, I decided to try to use this amplifier to play my MPD music.
This meant finally opening, cleaning and testing this gear. The first problem was quite obvious: someone had spotted this on the sidewalk before me, but they only took the power wire to recycle it for copper. So that was unceremoniously cut at the back of the unit (the FM receiver didn't have a cable at all, it is designed for an unpluggable one).
So, my first task was to reinstall a power cable. I opened the device and found that the remnants of the old cable are connected to the power supply PCB with an easy to unplug connector. I had more trouble with adjusting the grommet, as my replacement cable (itslef salvaged a long time ago from a defective power strip) was larger than the old one. But eventually I managed to pop the grommet out, cut it wider, and install it back.
This amp is from the 1990s, it appears to have nicely designed electronics and a solid design, but also some modern computer assisted features including a remote control. There are even jacks at the back that can be used to drive tape decks from the same remote control. This means some extra stuff like a motor to drive the volume knob, and a rotary encoder for the source selector instead of a mechanical solution. This results in several relays clicking when switching inputs. Unfortunately I don't have the remote, I will look for a compatible one or some other solution with something that has an infrared emitter. It also has controlled power outputs on the back, which means the remote control (and the main switch on the unit) can turn the entire setup on or off.
The FM receiver is a bit older and simpler. Nothing really fancy, a mechanical tuning know, a sliding led to indicate the frequency. No quartz lock, no digital frequency indicator, no RDS, nothing like that. It does receive FM as well as long and medium wave AM. Interestingly, it is not limited to the FM range in EU, and can pick lower and higher frequencies. I guess that allowed to sell exactly the same model in Japan (which uses a different frequency range for public audio FM broadcast). This means I can pick some digital transmissions, possibly from the private digital radio system for the electricity distribution company (how do I know? I used to work on the design of their radio system, and it was in that frequency range). Of course it just results in annoying electronic noises.
Anyway, after the power cable replacement and cleaning a bit of the dust inside, everything powered up just fine and I could confirm that the audio was working at least to the headphones output. Since I previously had no use for this, I also didn't have matching speakers. So I went online and found some. U bought a pair of Technics speakers from the 1900s. I got them from the original owner, who purchased them in a previous life when he was 16 years old, and took good care of them for the next 35 years! He had been using them for a home cinema setup, apparently. I got them for just 10€, and since he was replacing the entire home cinema setup, I also got 3 smaller speakers he was using at the back of the room, for which I have no use now.
Unfortunately, after connecting them to the amplifier I heard... nothing at all! That was surprising since the headphone jack at the front was working just fine (and was confirmed to be able to send full volume audio to the headphones, as this dates back from before any laws preventing such devices to cause permanent hear damage at the slightest mistake). So I grabbed the service manual for the amplifier and started looking into the schematics. The headphone output appears to be pretty much directly connected to the speakers output, except for a switch that allows to turn the speakers on and off. After some more disassembly, I gained access to the PCB where these switches are located. And indeed a quick continuity check revealed that neither of them (there are two outputs) were conducting any electricity. Which is actually good news: it's just a problem with these switches, and the amplifier electronics are otherwise fine.
So I then de-soldered and disassembled the switches. They are quite easy to open with a thin flat screwdriver. Inside, there is a springloaded mechanism to allow to move the switch to on and off positions by pushing it (similar to a retractable ball pen). And more importantly there are two small sliders that are supposed to connect the terminals together. Unfortunately, over time, the grease used to lubricate these gets spread out so evenly that it forms an isolation layer (possibly combined with dust and oxidation). So, these parts went into a bath of claning alcohol, and scrubbing with an old paintbrush.
I managed to fix one of the two switches, unfortunately, while reassembling the second one, I misaligned something and bent the copper sliders. So the switch couldn't work anymore. I also didn't have a replacement in the same shape, but I had smaller ones. I only had to make an adaptation bracket to make it fit. I briefly considered having to 3D model and print something, and then I looked at the parts of the old switch on my table and realized that would make a very good bracket. I attached some longer legs to the switch (recovered from resistors and capacitors installed in other projects). Then I could set it in place inside the casing of the old switch, and solder it to the pins inside the switch (being careful with the pinout, as these switch are not constructed the same internally). And finally I secured it all with hot glue, and soldered the switches back in place. The way the amp is designed, the case of these switches is what attaches the PCB to the front of the amplifier. Which seems the right thing to do, as this means pushing on the switches does not put any stress on the solder joints.
After this fix, I could reassemble everything and finally listen to some music! I didn't get the alignment of the new switch perfectly right, but it's good enough that I can still turn the speakers on and off if needed (I will probably not need it, and won't use these buttons often).
Next I turned my attention to the speakers. While the owner generally took good care of them, there still was some damage specifically to the protection domes at the center of the speakers. This isn't a super important part, it's just here to hide the speaker coil and protect it from dust. Which they did well, but they were still a bit damaged. One I could fix by using a vacuum cleaner (on a low setting, and with the bleed valve open) to straighten it out without having to disassemble anything. The other one was too damaged for that, but it turns out you can buy replacement domes quite easily. So I did that and installed the new dome with a bit of neoprene glue. Now it looks as new!
Now I can listen to the radio and to audio CDs (with a small portable player, that happens to have a line output perfect for use in this setup). But the initial goal was to play music from my MPD server, which is at the other side of my flat. I first looked at FM transmitters, but I didn't find quite what I was looking for. Few of them take input from an audio jack these days, and most except 12V input from a car "cigarette lighter" port. Which my server doesn't have. So I looked for other solution and eventually found 1Mii RTS5066 wireless transmitters (which are actually designed and manufactured by Ankbit, but 1Mii is the name everyone knows. These transmit the audio over 2.4GHz and are super easy to setup. They also seem to be high quality devices, with an external antenna, a nice powe supply, and a metal case. I didn't do any measurement of the latency and output quality, but they sound good, which is all matters to me. So now I can control the music from my phone with an MPD client and listen it on this nice hifi system from the 1990s, isn't that nice?