Friday, September 07, 2012

RG's workshop: Stereo system switchboard

It's been a while since I wrote anything on here, and even longer since I blogged about anything interesting. (Oh crap, I hate it when people start off their blog posts talking about how long it's been since they last blogged. You know what? Strike that first sentence. Let's try at this again.)

I have a relatively small apartment, though it is big enough for me and my stuff. It has enough rooms, including one I use as my workshop.

In the living room of my apartment, I have a stereo system. That is to say, there's a stereo device I found on the curb somewhere, through which I route the audio that accompanies the projector screen (among other uses).

The stereo has two sources of external input, not including the radio/CD/cassette stuff built into it. These inputs consist of one end of an audio cable being plugged into the stereo unit's "AUX INPUT" jack, and the other end of the cable split, one path plugged into the turntable in the bedroom, the other connected to a long cable with a standard mini jack. I can plug the mini jack into my laptop or my Blackberry, and the cable is long enough--and my apartment small enough--that I can bring either device into any room of the house to 'remotely' control the audio.

So for example, I can watch online TV in the kitchen with my laptop on the kitchen table and the audio going through the soundsystem back out to the speakers in the kitchen. I can also use my new Blackberry's FM tuner to listen to the radio (I only started listening to the radio again when I got the new Blackberry last week, and I've thus far tended to listen to the station that has all the ads for hearing aids and funeral service providers). The Blackberry (as with the iPod I briefly owned) needs you to plug in the headphones to listen to the radio, because they act like the antenna, but the stereo jack works just as well.

Anyhow, the stereo sits under this desk which I did not find on the curb. I built it with my own two hands, and a screwdriver and hammer, according to the assembly instructions from the non-Swedish office supply store where I had bought it.

The stereo sits under the desk as does one pair of speakers.

Another pair of speakers goes into the kitchen (which can extend into the bathroom if and when I see fit to have them do so), and as of very recently, a third pair is wired through the wall into the bedroom (which I can extend into the workshop, should I see fit to do that also).

The thing is, I do not want all of the speakers to always be on. I only need the sound in the room(s) which I am occupying. So I need a switch system.

I bought a basic audio switchbox from Radio Shack ("the Source" in modern parlance), which didn't really work. Even after I fixed some bad soldering inside it, there were issues with bleeding between the left and right channels. I also couldn't separately activate the left and right units of a pair of speakers.

So I stuck with my previous scheme of a pair of Y adapters on the stereo output cables and plugged or unplugged the Y ends into the ends of the cables for the desired speakers, all of which I have patched into RCA jacks. I had had the jacks stuffed into the grooves of the CD holder under the desk top (circled in the above photo).

But this did not satisfy me. Functionally, it was not an elegant solution to have cables sticking through a grille. So I decided to build a switchboard (you digital-age kids might not know what a manual switchboard is, but they work very nicely).

The first step was to build a panel that would fit into the space where the grille is. The grille is wedged between two columns that have holes corresponding to bumps on the edge of the plastic grille.

I first bent some paperclips into latches that I inserted into the edge of the thin plywood board at the same intervals as the bumps on the grille. There is a recess underneath them, which allows them to dip out of the way and spring back up to latch the board into place (like on a door). They are tapered so that when you push the board up, they are pushed by the edge of the hole in the cylinder into the recess in the board, releasing the board.

I'd seen this trick done online somewhere months or years ago, but don't remember where. It was probably from a project documented by Rob Cockerham or Matthias Wandel.

Anyhow, it works, and I can put the board into the space, and remove it when I need to by pushing up to release the latches.

The next step was to cut holes for the RCA jacks on the ends of the speaker wires. I needed to get the jack through the board, but I also wanted it to be snug so I could push the Y connector into it without the plug just falling through the board.

To accomplish this, I settled on a keyhole-type shape, with two round holes connected by a channel. One hole was larger than the RCA jack, allowing me to stick it through, and the other was slightly smaller, allowing it to be held snug. The holes were connected by a channel that is wide enough for the cable to pass through. (on the right below is my first attempt, which used a hole that was too small)

After cutting the holes for the four stets of speakers (kitchen, living room, bedroom, and a spare set of holes for future expansion), I painted it black to match the piece of the desk it was replacing. The only black paint I had were a couple of cans of spray paint I found one bountiful day of treasure hunting (a.k.a. curb shopping, dumpster diving, etc.):

My only previous experience using spray paint was indoors, and resulted in everything in the room, including plenty of electronics, being covered with a yellow dust. Thankfully, this room was in somebody else's house, and the electronics were theirs, as was the bright idea of spray painting indoors.

To alleviate this problem, I taped together some newspaper pages into a cube, put the board inside, reached in with the can of spray paint and sprayed it as best as I could with the cube closed. I let the dust settle a bit and reapplied the parts that I missed (the cube filled with spray dust, completely obscuring the workpiece so you couldn't see if you had gotten it all).

The paint job worked well enough for me, for something that would most of the time be in the shadows under the desk top anyway.

The only remaining issue was that the jacks sometimes pulled out of the board when disconnecting the switch cables. This was fixed with that quintessential desktop accessory, the trusty binder clip.

Normally at this point in the blog post I'd go back and review it to make sure it makes sense and doesn't drone on too long, but I'm too tired and I might forget to come back to it if I leave it to another day.

I've built (and photographed the construction of) other things since I last blogged, and I'll maybe hopefully eventually probably get around to blogging those also.

- RG>