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Cheap-as-Chips (chip amps)
All these circuit builds are gettin me-ol' electronics bone itchin. I've wanted to do an amp build for quite a while. Figured I'd try a cheap "proof of concept" to wet my chops.
LM3886 seems to be the current best chip, but commands a bit higher price. I plan to do a build with that but, first I'll mess around with the cheaper TDA7293. I found a super cheap mono kit to try that encorporates the power supply rectification+filter caps. So no seperate power supply board needed. Caps seem a bit small but that just means room for mods later.
https://amazon.com/dp/B0C6QFH4RT?psc=1&ref=ppx_yo2ov_dt_b_product_details
Transformers seem to be the biggest cost for these builds. In my research I've seen folks use two single phase transformers. So looking around, 24v transformers seems like a standard so they are cheap. That voltage seems to be within the butter zone for these chips. 48va x2 might be a little low for the chip's max capabilities, but I imagine will do fine for normal listening levels.
https://amazon.com/dp/B00B8865AC?psc=1&ref=ppx_yo2ov_dt_b_product_details
The kits don't come with heatsinks. The standard heatsinks that fit these chips are realy chintzy. So I ordered this pack and plan to drill and tap them. Might still be a bit small, but oah well.
https://amazon.com/dp/B08L4MZCHZ?psc=1&ref=ppx_yo2ov_dt_b_product_details
Comments
I might still have some LM3886's laying around, I'll look.
I'm surprised to see Digikey still has them in stock -
https://www.digikey.com/en/products/detail/texas-instruments/LM3886T-NOPB/212684
The kits show 4 "monolithic" caps. Looks like ceramics. 1x 1uF and 3x .1uF. I imagine I should look into replacing those with different design? One or two may be on the power supply side Instead of signal path but I imagine still not great. Will get a better idea once I can look at the pcb in person. Unfortunately some of the pics show a smd version so the board design is different.
For $9 I would guess that the electrolytic caps are junk and I would replace them for safety sake. When a cap expodes its not pretty. As for the rest of it, it may be all counterfeit, but who cares, build it and have fun.
Cool project! Good luck with the build! Be interesting to see how much power output you can get with that transformer and heatsink combo.
I have LM3876T ICs.
I've had all the bits and pieces to build a killer LM3886 gain clone for years but have just been distracted by other projects. If I could bring myself to just building a half butt enclosure the actual amp guts build could be done over a couple weekends. Hmmm? If I could find a really large cigar box...
lol yeah if these don't blow up on me I'll need to figure out a cheap enclosure. I've got a bunch of 1/2" baltic birch ply cutoffs that could make sides, would just need to figure out top and bottom plates.
Looking around and comparing the traces to circuits. It seems a near match to this one. Just the bridge rectifier is added and the 220uf caps are swapped for 2200uf for primary DC filtering.
https://xtronic.org/circuit/amplifier/audio-power-amplifier-with-ic-tda7294-or-tda7293-minimus/
Parts on Mouser are cheap enough I probably will replace most of the caps after initial testing.
I don't intend this to be a super serious build. But if it works out I might give it to my father since the "open box" priced DTA-PRO I gave him finally died. Might work with a bluetooth adapter.
Man I wanted to like the DTA-Pro, but I had 2 die on me, never driven hard.
We've got a cigar store in town with all sorts of cigar boxes for $5 each. I've already scooped up several for small electronic projects. Drop me a line if you can't find what you need.
Interesting power output verses +/- Vcc voltage charts on the xtronic.org link. I wonder if these charts are showing RMS power output at the 0.5% and 10% distortion levels? Or are they showing the "Peak to Peak" power output? Peak to Peak would be 2X the RMS figure (1.4 x 1.4).
Looks like he pulled that graph from the datasheet. I don't see any clarification on the datasheet but the chip is listed 100watt rms max. The graph tops out around there so I'd guess it is rms.
Now that I reread it a few times. He did specify multiplying the amp power by 1.4 to get needed transformer power. So 24v becomes 33v which comes to about 65watt at the .5% line. X1.4 comes to 91watt. So 200va transformer would be about right for stereo at 24v I'd have about half that with the transformers I picked originally. This is why I post and discuss before actually starting the project lol
I can find 16v transformers all day for doorbells. That voltage would calculate to needing about 39watt from the transformer. Much closer. I'll look into that some more.
Remember, you will need two transformers to get +/- Vcc, so you would actually have twice the VA.
Sorry I kept switching back and forth between dual and single secondary ones in my head. Yeah these chips are mono also so need 2x for stereo. So works out 1to1 on the calculations if using two single secondary transformers.
Knowing what I know now. If the voltage is low enough to use a 100va dual secondary one then the antek toroidals are hard to beat on price.
+1 on the Anteks
Yep, Anteks are great for many reasons. However I'm going to build mine on the cheap and I scored a pair of 100 VA, 24Vac transformers out of an old CCTV system we had and scrapped for newer POE cameras. They are not as efficient as the toriod and emmit more noise, but hey they were FREE! I have a bunch of big heatsinks so that's covered. Pretty much comes down to fabbing a decent, cost effective, and not so ugly looking case.
Quess which chip is the real deal:
The top one.. unless this is a trick question and both are counterfeit lol.
Bottom one
It looks like my LM3876's, which I got directly from National Semiconductor.
The markings look a little sloppy and the scuff marks might be an indication of tampering (relabeling or recapping).
Could check the manufacturing codes to see if they track correctly with the data sheets.
Truth is this IC has been around for a long time and I doubt what's being made today looks the same as day one. Without handling the parts or going through the data sheets the bottom one looks the most suspect.
I saw a photo and description somewhere stating the big white lettering that is more centered is the fake one. The slightly smaller but more crisp not white lettering that aligned to the left being genuine.
Top one was directly from National Semiconductor (lazer ingraved). Bottom one is what came with my $14 chip amp kit from Aliexpress (silk screened).
I fairly sure this one is genuine. This is one of the Alesis powered speaker amps from long ago that was being sold as surplus.
Makes me wonder if batches for bulk contracts got subbed out.
I wondered that too. This one isn't the tab isolated version, so it may have been manufactured in a different location.
I changed the thread name. Enjoying the chitchat. Glad to get folks taking about the subject! I find it super interesting.
I've decided I don't need another stereo amp in that power range. I do however need a clean and compact single channel amp for portable speaker testing. That is where I'm going with this side project.
I got mine back when I was in tech school, 94/95. I asked for a couple samples and the sent a stick of them, like 20?? I have 6 left. I really have no plans to use them, hit me up if anyone is interested.