Matt's DIY audio page

These pages were originally at http://kahuna.sdsu.edu/~tucker/diyaudio/ for many years. They eventually got removed about six years after I graduated. I kept a backup of them and am now re-posting them here. I haven't done any DIY audio projects for awhile. Text in italics is text that I added when I reposted these pages.

It has been awhile since I built any speakers, but I couldn't resist replacing my old subwoofers with my DIY Pillar of Power subwoofer. My wood working skills keep me away from doing too many speakers, but a Sonosub (built from Sonotube) simplifies the building. Sonotube is a thick card board like material that is used to make concrete pillars in bridges and other structures. A cylinder is the next best shape for a speaker. Spheres are best, but very hard to build. In short, you take the sonotube cylinder and add a top and bottom. Mount a speaker, throw in some aesthetics and you are done. The subwoofer is a sealed design using a 15" Tempest subwoofer from Adire Audio. With over 16mm of linear one way x-max, the Tempest can push some air and create some good vibrations. You can find more details and pictures for this project. This subwoofer is one of my projects that still sees active duty. It makes room shaking bass for movies, but is still articulate for music.

the chassis AudioXpress magazine My senior project from '99, a single ended class A amplifier (right), has been completely posted. The article was published in AudioXpress magazine (September 2003). The schematic, board layout, parts placement, parts list, and detailed article are now up. The amplifier was designed using PSPICE and Veribest (an electronic simulation and layout program now owned by Mentor Graphics). Specs. 20 Watts per channel, three stage architecture (differential input, gain stage, output stage). The International Rectifier IRFP140N MOSFET was used for the output transistor and current source. Pictures and more details are available. This was a fun project. It never saw too much time in my stereo rack becasue my "stereo" serves both music and home theater duties. The sound level the amp produced (with reasonably efficient speakers) always surprised younger people who consider 100W/ channel the norm. However, 20W is a little anemic when used for home theaters at "reference levels". It is a very nice sounding amplifier.

VLF receiver My VLF (very low frequency) receiver is a audio/radio project. Many of the "signals" the receiver picks up are created by nature. The sounds are sometimes short clicks caused by lightning somewhere in the world or they may be long decreasing frequency tones.
My receiver is based on the design by Stephen P. McGreevy (BBB-4). Instead of using exclusively discrete components, I have implemented the design using a FET input op-amp, chip audio amplifier, and a high pass filter. The high pass filter increases listening enjoyment in less than ideal conditions. More details and links can be found here
The x-over The completed speaker. A two way speaker project. Pictured is the completed box (right) and the crossover (left). The tweeter is a Vifa D25AG-35. The box is a .43 cubic ft. sealed enclosure. I did not build the box because I didn't want a silicone oozing non-parallel walled mess of a box. I ordered the enclosures from Parts Express. The boxes are very high quality and for $44 each very reasonable. The cabinet is made of .75" MDF and the front panel is 1.75" MDF.I chose a sealed box for ease of construction and since the speakers were made to be used with sub-woofers I didn't need real low f3 (low roll off point). Parts Express offers a kit designed by Vance Dickason that uses the same Audax woofer I used but with a Audax tweeter using a ported box. The Leap passive crossover design came from Madisound.Check out the design details and more pictures of the speakers and crossover. These served as my main speakers for several years. If I had to do it over again, I would probably have chosen a woofer/enclosure that would have given more bass extension. Although the speakers got crossed over at 80Hz (standard THX crossover frequency), they would have improved from a little more low end response. One of these speakers served as a center channel at a friends hoem theater for awhile. Both of them are now serving duty in another friends home theater as the front speakers. Good speakers dont die, they get recycled :)
The opened LD player. New LD players have an AC-3 Dolby Digital RF output on them. Most older LD players don't have the AC-3 RF output jack but have the RF signal inside just looking for a way out. This simple Laser disc player modification adds a buffer circuit to the RF signal inside the player so you can run the signal to a Dolby Digital decoder/receiver/pre amp. My page describes the modification to my Pioneer CLD-1090 but many other Pioneer LD players have similar circuitry. Check out my DIY AC-3 RFoutput modification page for Pioneer laser disc players. For about $2 you can upgrade your older LD player and give it an AC-3 RF (Dolby Digital) output.
How do you know you are getting old.... when you mention laser disk player and people say "you mean DVD?" I enjoyed many movies at near DVD quality using this laserdisc player. Bringing the Dolby Digital soundtrack out made the experience even better. It is not relevant anymore, but I thought I would leave this modification up anyway
center channelHere is my center channel speaker for home theater. It uses dual 4" woofers and a dome tweeter. All the speakers including the crossover were bought from The Sound Clearing House (no longer in business). They just started carrying kits and now have a small variety of speaker kits for sale. The prices are very good. The Sound Clearing House ran out of the woofers for this center channel and are now working on a new and better center speaker. Total cost for my finished speaker was about $50. Check out my construction details and general information.
This was a very inexpensive center channel that did a great job considering it was cheap. The 4" woofers were a little small even with bass management. I think I saw this sitting up in the attic last time I was up there. DIY or not, I recommend a center channel that has a woofer (or at least mid-woof) directly below the tweeter. A sideways sitting M-T-M (mid - tweeter - mid) is one of the worst configurations for a center channel. It tends to beam the sound in and only one person in the home theater has a good spot. Why are 99% of most center channel speakers this way? The norm and convenience. There are a few high end center channels with a vertical tweeter-mid, but they are fairly pricey. An excellent budget minded center speaker is the Aperion Audio 533-VAC.
x-overMy latest electronic project is a 24db/octave Linkwitz-Riley hi/low pass electronic crossover at 85 HZ. It is used as the sub woofer I found the Loudspeaker Design Cookbook by Vance Dickason to be very helpful in choosing the type of crossover for the application. The book has graphs of phase and droll off characteristics of many different x-over configurations.The picture shows the finished crossover. Check out the details and schematic of the crossover as well as a close-up picture of the circuit boards.
This was probably my most popular project on my web page. With home theater receivers that have crossovers built-in, this crossover isn't as relevant. However, if your built-in subwoofer crossover has a shallow slope (18db/octave or less) or the crossover freuqency is high you might want to give this crossover a try. It cleans up the main speakers by pulling the lowest bass away and helps make sure you sub isn't trying to produce higher frequencies that it will muddy up. This is an active crossover so you need amplifiers after it to drive the speakers (or need pre-amp in on your receiver)
A.C. power filterAnother project that I have done is an A.C. power filter. A D.I.Y club in San Diego that no longer meets, featured this as a club project.It uses several Corcom type filters, Metal Oxide Varistors, and a large high voltage capacitor to filter RFI/EMI and voltage spikes floating down from the power line.The six large metal boxes in the picture are the Corcom filters which have coils, capacitors and resistors sealed inside them. The three small red discs towards the front are the M.O.V.'s. The A.C. outlets are along the backside and the power switch and circuit breaker are on the front panel. The black square in the front right hand corner is the high voltage capacitor.You can see the details and the messy wiring diagram of the of the A.C.filter.
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