TDA7265 25W stereo amplififer

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[edit] TDA7265 25 watt Amplifier

When it was necessary to order some sample SCRs (to act as switches for our high power cap banks) off of [1] 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[2].

Breadboard layout with small heatsink (and very long screw sticking out)
Breadboard layout with small heatsink (and very long screw sticking out)

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 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!

Playing on one channel from my Z:VM
Playing on one channel from my Z:VM

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.
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".

After learning more about virtual grounds, and acquiring the necessary transformer for this project I decided that I'd like to bridge two of these and use them as a 50W per channel stereo Amplifier. When I went back to look at the schematic, I looked more in depth at the spec charts, and I saw that THD (Total Harmonic Distortion) of the bridged chip approaches 10% at the full 50 watts. Not only is this unacceptable, it is downright terrible! I hadn't noticed this distortion before I'm guessing, because the stereo layout stays below 1% THD until you begin hitting higher wattage (I had refrained from testing it high volume because a. it was underpowered with the transformer I was using, and b. I didn't want to risk overheating the op-amp). In any case, I've decided to switch over to the National Semiconductor LM3886 amplifier chip, and will be constructing a fully functional and high quality amplifier based on those chips. The Progress of the LM3886 amplifier can be viewed here: LM3886 Stereo Amplifier

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