Summer 2009
I like to listen to music when I'm in the garage doing woodworking, washing the car on the driveway, or barbecuing. For 8 years I had a portable radio/CD player in the garage as the main source of music. Before finally parting ways with my 1992 Chevy pickup, I uninstalled all of the stereo equipment from it and put it all in the closet. It was old equipment but still in fine shape. Not wanting to leave good equipment sitting idle, I started to wonder if I could use the old components to build a stereo system for the garage.
When I was in college, I worked for a while as a courier and drove a company truck that had no radio. To compensate for this, I assembled an old Sony head unit, amplifier, and two 4x6 speakers in a plywood box. The thing had a rubber radio antenna on it, a gray felt covering, and plugged into the lighter outlet. I sat the thing in the seat next to me while I drove and worked well. I knew a could do something similar, but more sophisticated, for a garage stereo.
Such a project would be enjoyable because it would incorporate the stuff I love doing: Woodworking, electrical work, audio work, and salvaging old electronics. Plus, the end result would be a device that would serve a useful function. If I could throw in some photography and put together a webpage, it would even be more fun.
The original list of equipment, all circa 1992, included:
- Sony XM-4040 amplifier
- Sony XM-2040 amplifier
- Coustic XM 3 active crossover
- Audio Control EQQ 24 band equalizer
- MB Quart 6.5" co-axial door speakers
- JL Audio 10" subwoofer
The MB Quart speakers seemed prone to being damaged while in a cardboard box in my closet, so while working on a different project in early 2009, I built bookshelf speaker-sized cabinets for them from 3/4" cabinet plywood and covered them in black felt. I put these on a shelf in the garage and they sat unused for several months gathering dust, but out of harm's way.
Donated hardware
I had been on the lookout for an old car stereo to serve as the center of the new garage system but kept coming up short. I wanted to avoid buying something. In the summer of 2009 a family member graciously donated two Alpine head units from the late 1980's, an a/d/s PQ10 4 channel amplifier, and other equipment. The a/d/s amp was of particular interest as a friend had a similar model in the early 90's and these amps were known for their quality sound. I cleaned this one up and hoped for the best. The a/d/s was considerably more compact than the Sony and had similar specifications.
First design
I worked up several designs on paper for a wooden cabinet that would house the audio equipment and AC to DC power supply that I had picked up on Ebay. I finally settled on one design, and worked up a final plan with the exact dimensions of all the parts I'd have to fabricate. I just needed to line up a suitable head unit and then find some time to start building the enclosure.
Setbacks
In between other projects, I bench-tested the audio setup to see how it sounded and how it would fit together. I bought a Sandisk Sansa MP3 player from a co-worker for $20. This was far cheaper than an iPod. The Alpine head units pre-dated the era of MP3s, and while they would accept a connection from a CD changer, I was never able to successfully get them to accept an aux input of any kind so that I could connect the MP3 player or anything else. If I couldn't play music from CD or an MP3 player, then the system was much less desireable.
The other problem I ran into was that if this rig was going to work, the car stereo would have to retain its memory even when the 13.8 volt power supply was off. I had no intention of leaving a fan-cooled power supply on all the time when I only needed to hear music on occasion. If the radio lost its memory, that wiped out the radio station presets, tone settings, and everything else. I toyed with the idea of using a wall-wart power supply to feed the sytem when the main supply was off, but that seemed like a crude workaround.
After these setbacks, I decided to scrap the project because it was going to be a lot of work for something that didn't fit all of my goals. Then midway through the summer, the same family member donated some Boston Acoustics 8" subwoofers. If I was going to connect the subwoofers to the system, I'd have to use the Coustic XM3 active crossover that I had also pulled out of the truck. By this time I had also decided that I could load up a long list of MP3s and wouldn't need FM radio as the main source of music which was one less reason to need a head unit.
The future of the project was uncertain but I decided to spend some time tinkering with the subwoofers to see what happened.
Subwoofers
The subwoofers were not perfect. They both had damaged surrounds. I did some research and determined that I could replace those for about $10 each, but since the damage was only a small tear in each speaker, I would try to repair them first. Using super glue I was able to fix the tears. The other problem was that the surrounds were coming unglued from the speaker frames in several places. This appeared to have been caused by improper mounting in which the screw heads had pressed into the surround at sharp angles. I was also able to use super glue to repair this.
The second problem with the subs was the cabinet. Not only was it about about .2 cubic feet too large, it was one single chamber when it should have had a separate chamber for each speaker. It also had no speaker wire terminals and was covered in burgundy carpet which was eaten away at one end. When I pulled this off it left patches of burgundy fur all over the wood.
I decided to work with what I had and use as much of the existing cabinet as possible. Why reinvent the wheel? I decided to rework the cabinet for one woofer and then see how it sounded.
I wanted to stick with a sealed cabinet design to maximize low frequency output. I cut the cabinet into two halves, worked out the volume calculations to achieve the optimum reccommended volume for these particular speakers, and then cut about 3 inches from one half. I then fabricated new end pieces, drilled a 2" hole for speaker terminal, sealed everything, pulled off as much of the remaining burgundy fur as possible, and covered the completed enclosure in gray felt using 3M-90 adhesive.
Success
The final result was fantastic. The repair of the speaker surround held up well, and the speaker sounded great. With the basic equalizer built into my MP3 player and all the adjustments on the XM3, I was able to tune the system to produce a fairly flat response across the spectrum. At this point the MP3 player was feeding the Coustic XM3 which was feeding all 4 channels on the a/d/s amp. Two channels of the amp were connected to the pair of MB quart co-axial speakers, and the other pair of outputs was bridged to drive the single Boston Acoustic subwoofer. The sub had a -3db cutoff of 40 Hz so it didn't produce a great deal of bone-shaking bass, but it did sound great and the system was miles ahead of the old boom box and a fine system considering the environment.
The next day I rebuilt the remainder of the original cabinet for the other woofer, making it identical to the first one.
Moving from bench to box
At this point I still had a system that was sprawled out on the workbench. I needed to design a new case and move all of the equipment into it. I knew I needed to incorporate the following elements:
- a/d/s PQ-10 amplifier
- Coustic XM3 crossover, positioned so it can be adjusted
- 13.8 volt power supply, fan cooled
- Four speaker terminals
- RCA input
- Binding posts for 13.8 volt output for accessories if needed
- Illuminated AC power switch
- Hole for the AC power cord
- Switch to shut down the amplifier before shutting down the AC power
- Cooling fan
- Air intake vent
August 1, 2009
I kept going back and fourth about the basic layout of the box. I couldn't decide it it should be horizonal or verical. A vertical design would be like a shoe box standing on end. A horizontal design would be a shoe box laying flat. The original design (the one with a car stereo head unit) was veritical.
One morning I sat down and sketched out horizonal design. It looked good. I drew the thicknesses of the boards and had the basic 6 sides of the box figured out based on the internal layout of the components, the panel were all the wires would connect, and a small panel where the switches would be.
After taking the design out to the bench to start calculating the measurements, I realized that the whole thing was going to be much more compact that I realized. In fact, the thing wasn't going to be much lager than the boom box it was replacing. I made a few minor changes but kept the basic horizonal layout.
Within a couple of hours I had the 6 sides of the box cut, and the front, rear, left, and right fastened together. Later in the day I had the three main conponents mounted inside, and the holes cut for the wiring panel and the crossover. within the space of one day, I had designed the thing and built the basic structure.
August 2, 2009
Another day yielded a great deal of work. By the evening I had completed the box and started covering it with felt.
All that remained was to complete the panels that would hold the various connectors and switches. After that, the wiring could be soldered and the final assembly completed.
August 3, 2009
It took a couple of hours of work to wire the whole thing. This included lots of soldering and custom lengths of wire. I also mounted the power switches and wired those (one for the power supply and one to turn on the amp and crossover. Because of the compact nature of the box, there is often an order to which things have to be inserted. For example, I can't install the wiring panel without removing the amplifier. Now that there are wires crossing all over the place, it's even harder to work.
Upon firing the system up the first time (listening to Boston's "The Launch", as suggested by my son), the sound output was wrong; only one channel was at full volume, and the woofer was not right. There was also what sounded like a 60 Hz hum or a ground loop. After a few minutes of troubleshooting, I determined had mis-wired the speakers at the 4 terminals on the side of the box so this was easily corrected. I had to tweak the gain levels on the amp and the system sounded fantastic again. I think the hum was caused by all of the AC, DC, line, level, and speaker level wires all being crammed together in a small space, and it seemed to come and go. I should be able to eliminate this when I finish the last few issues and spend some time cleaning up the cabling, which will require disconnecting some of the wires and re-routing them.
What remains is to get some 90 degree RCA angle adapters for the RCA cables going to to the amp. Currently, they're sticking straight up and I can't get the lid on. There is a similar problem with 2 set of RCAs coming out of the crossover.
The other issue is cooling. After much thinking, I will mount a fan on the top lid, and have it blow air into the case. Warm air will exit the case througt power supply and a grill on the front of the case. This is going to take another couple hours of work, and I might have to cut a new lid. Although I wanted to avoid putting anything on the lid, this the trade off for having such a compact case. Out of the blue, my son, ever the thinker, suggested putting a connector on the fan cabling so the lid can be totally removed. Good call! I can get a 2 pin molex connector for this.
The last problem is the lighted 110 VAC power switch. The directions state that pins 1 and 2 are the switched side, but make no mention of how to wire the lighted part. There is only one pin remaining. Given that the light is 12 VDC, I'm not sure how to proceed. I'll have to hit Google. I'm not about to wire the AC neutral to the DC negative.
August 4, 2009
With about 35 hours spent, the project is 99% complete. Here's what you see in the following photo:
- MP3 player sitting on top
- The portion below the switches is just an unfinished hole.
- There are two power switches; the green switch turns on the power supply and cooling fan and the smaller switch turns on the amplifier and crossover.
- There are 4 speaker outputs: Left and right full-range and subs.
- There is a 12 VDC binding post in case one needs that kind of power for anything.
- Cooling fan on top, with air filter.
Here's the wiring panel showing RCA inputs, power cable, aux 12 VDC input/output, and speaker outputs:
Here's a shot of the inside:
I tried to separate the AC wires from everything as much as possible. I bundled the low-amperage 12 volt wires into split loom tubing. Everything else does what it wants.
I picked up some 90 degree RCA angle adapters and managed to make things fit. I had to use the router and shave 2/16" of thickness off part of the lid. Here are the RCAs to the amplifier:
The biggest kludge is where the input RCA cable connects to the crossover. This sits right against the panel that houses the power switches. The photos says it all:
Here's a shot of the ADS. You can barely see the dust on the heatsync fins:
I'm very happy with the project. It sounds fantastic and runs cool. The top fan pumps in enough air (even with the filter) to feed the power supply and the extra air exits the front hole. It has the flexibility to accept any kind of audio input. If no 110 volt power is availble, the thing can be easily wired to a car battery using the binding posts on the wiring panel.
What are my disapointments with the final product? The case is slightly too small. It could be an inch larger in all three dimensions. Because of the compact size, the box is not as flexible as I had envisioned, but the chance I will really need to alter anything major is slim as long as the components keep working.
It's 99% done. What remains? A few things:
- Replace the power cord (My son wants to use a gray one) and install a strain relief
- Install a quieter fan
- find or make a grill for the hole under the switch panel
- Label the speaker terminals
- Install feet on the bottom of the box
- USB port to provide power to USB devices
- Install a large volume knob, wired either at the line-level input, or the speaker level output. Currently, volume is controlled at the MP3 player
- Wire the LED inside the green power switch
Update - Janary 2010
I did install a quieter fan. It makes a big difference. I never did make any of the other modifications. At some unknown point in the future, I will forget which terminals drive which speakers, and I'll have to examine the wiring inside to figure out how the speakers are supposed to connect. Oh well.
From day to day the stereo sounds great and performs well. It was totally worth while! I always look forward to using it.