Audio Amplifiers
From Ryft
LM386 1/2 watt Amp
Background
Having read an article in Make magazine about a $5 "crackerbox amp" I (Jake) decided to attempt to build one as my first electronics project (nothing previous had involved more than a few simple analog circuits). I ended up using the diagram for the "little gem"[1] amplifier found on www.runoffgroove.com along with a a diagram posted on flickr that included the hookups to the potentiometers. As a simple and cheap circuit, it seemed like a good beginning project.
Construction
Without too much difficulty I was able to put together the amp on a breadboard. For the final product myself and Ross (who plays guitar, and would be buying the amp from me if he liked it) hacked an old Sony boom box to pieces so as to retrieve the speakers, and let me say, Sony builds things without disassembly in mind, we couldn't get to all of the screws because they had been screwed in with a small Phillips head screwdriver that must have been at least 14" long. Took us a solid few hours, a large hammer, a chisel, bolt cutters, and a good deal of smashing (by the time we finished with it, you would never have know we acctually just wanted to take it apart). After that, Ross and I took half an hour or so to build a box for it out of some scrap particle board we had laying around the workshop.
Results
Overall it came out rather well, the box itself is somewhat shabby looking, but thats not what matters, the fact that it sounds great is what counts.
TDA7265 25 watt Amplifier
Background
When it was necessary to order some sample SCRs (to act as switches for our high power cap banks) off of [2] I (Jake) was also looking around at their audio amp chips and decided to get a few of their most powerful ones (free samples are beautiful thing). At that time I had no idea how to use them, but after revisiting their website I found that they had published detailed specifications and a few variations of example circuitry[3].
After being thoroughly confused and annoyed by the various split supply builds I realized that they had an example that used a single supply. At this point I ordered both parts for the LM386 amp and for the TDA7265 off of www.bgmicro.com. Soon after I completed the LM386 amp I began to piece together the TDA7265 amp according to ST's diagram on my breadboard. Initially had believed the increase in number of parts, the complexity of this project and my lack of experience with this sort of thing would inhibit me from getting the amp to actually work. Unlike with the LM386 amp where I had PCB layouts and other sorts of things to help me get it all together right, ST provided only their schematic, which was in actuality a good thing, because by the time I had everything on the board, I felt that I actually could read other schems aswell and know exactly what they were saying. After it was all together (using a 9v charger as the PSU), it took a few days of fiddling to realize that I had of course connected the negative V in (the chip was designed for a split supply) pins to the positive rail rather than ground. As soon as that was remedied I of course tried it out on the craptastic 16 ohm mini speaker we had laying around, and lo and behold, it worked!
I brought down one of my smallish, HE 5 ohm speakers from my room and plugged it into one of the loudspeaker terminals I had bought from BG, plugged in my Zen Vision M (Z:VM) and let it rip. The sound is very full, and in my opinion there would be no need to add treble and bass pots because its exactly the way I like it (this is most likely actually because it puts out the sound without any distortion or variation in frequency, and my Z:VM's EQ was set for an increase in the low and high frequency ranges). I found that the sound was comparable, if not better than the amplifier I've been using in my room to drive my Advent towers. I should also note that this thing seems to have consider power, at around 65% of my Z:VM's output and using less half the maximum voltage in (9v, 25v is max) it was pretty darn loud. With the full 25v in, I am sure this thing will have considerable power (25 watts on each channel) which is coincidentally the max power for the speakers I was testing it with. For testing purposes it never ran more than 5 minutes at a time because the heat sink I tossed on it was abysmally small and I'm not keen on frying the chip, even if it was free.
Future
I plan on fiddling around and figure out how to boost the bass and treble (if it's possible to modify that circuitry, if not, I might just have to find some eq circuitry and do more than just adjustable bass and treble, and acctually put in sliders for different frequencies. At the least, I'll need to get a volume pot and then put all the circuitry on a PC board (Sam and I have yet to try our hand at etching PCBs, something we definitely need try in the future), a nice sized heatsink will also be necessary. After its all together an working I'd like to stick it in a nice looking box with a 25v transformer rather than the 9v "battery charger".
