Don’t Buy An Amp, Build One To Suit

In need of an amplifier for his home entertainment system [Afroman] decided to build an amp rather than buying one. If nothing else, doing it himself allowed for a form factor that can’t just go out and buy.

He designed the project on two separate boards, one for the power supply and the other for the amplifier circuit. Both are of his own design, and although he doesn’t share the schematic, we know he’s based his work on a National Semiconductor reference design for the LM4780 audio amplifier chip. There’s a few other clues, like his mention of the toroidal transformer seen at the left in the image above and hi-res photos of the unpopulated board that has component values printed in the silk screen.

The final design allows him to get great performance out of his speakers with a very clean look. You’ll need to be logged to the forum linked above to view all of the images, but we’ve embedded three more of them after the break to whet your appetite.

Oh, and cost? This gets up there, just sneaking past the $500 mark.

[Thanks AB]

22 thoughts on “Don’t Buy An Amp, Build One To Suit

  1. No offense… but if there is no BOM or schematics, it should go in the “and we don’t give a frack” category…

    That’s just some unverified showing off… great, but he can keep it TOTALLY for himself…

  2. Whoaaa. $500 for a chipamp with a 4780? That’s a lot. I’ve used all the overture series chipamps by national semiconductor. My favourite is by far the 3886(2 of these in a 4780). The pitch is wide enough that you can wire it up P2P. It has mute circuitry unlike the 3875 and 1875. Getting rid of startup pops and clicks is nice. For absolute minimal parts count the LM1875 can’t be beat IMO. And the sound quality is great. It might seem like it’s a little low on the power side at 30W into 8 ohms, but realistically this is plenty of power for most applications.

    What I I like the most about chipamps is how compact they are. I have a 4780 shoehorned into a 3″x3″x12″ box with 2 little 2″ peerless drivers. It makes a great ipod speaker. I really doubt a discrete amp of the same quality and power capability could be fit in that confined space.

    But anyways the chips can be had under $10 each and the caps and resistors are well under $5. The power supply can be scavenged. I use 2 24V printer PSUs in series to generate the split rails. For another amp I just use a transformer scavenged from an amp left at the side of the road. I added my own diode bridge and some 15V voltage regulators. That amp probably cost under $20 to build.

    I can see one getting up to $500, but don’t let that price scare you away. You can build a great sounding chipamp for quite cheap.

    Just make sure you get the ground lay out correct. Nobody likes a 60Hz(50Hz elsewhere) hum…Star ground is your friend.

  3. Seconding the whole no schematics, no point posting thing. It’s especially out-of-place if it’s straight from a reference design. There’s certainly nothing wrong with working from the manufacturer’s circuit (the designers probably know best). It’s the practical, pragmatic thing to do, but it is certainly not hacking.

    Afrotech Mods brings back memories though. It was an endless source of entertainment for me back in the day. There’s some seriously awesome stuff on his site which _would_ be appropriate here. One example being
    (not entirely sure where you can buy 128nF 1% tolerance capacitors, though)

  4. I’ve built a few Nat Semi chip amps and housed them in Hammond boxes for ease (the Makezine chipamp based on the LM1875 is very awesome for the price and you can shop 90% of the parts at Radio Shack). But I’ve been eyeing this one…

    I’m not sure if I would go as far as to design my own PCBs when you can get the kit out there for such low price and with a small form factor already designed into it, but to each his own.

  5. newb-type question here…
    the pcb stuff is just to up the professionalism of the build, correct? am i correct in assuming they do nothing to enhance sound quality over a perf-board benchtop solder job?

  6. The PCB stuff makes it flatter (more compact), nicer looking, easier to work with (compact, less wires in the way, whatever excuse you like), and massively repeatable. Usually you’re stuck with what you have unless you are into cutting traces and adding jumpers/wires.

    I have seen some really professional looking point to point wiring jobs on amps before (GIS “vacuum tube amp underside”), so hard to say.

  7. Guys if you need a chipamp you can easily make one P2P, no PCB required. Just use a LM3875 or 3886.
    The LM3875 has less pins, so it’s a bit easier to do up.

    I usually mount my chip to the heatsink, and then hotglue the components in place. Don’t let the parts short to the heatsink.

    All these amps are is high power OP-Amps. Just design them like you would any other op-amp circuit. So there isn’t much need for a schematic, it’s probably pretty standard fare.
    Here is an example of a classic chipamp the ‘gainclone’
    which is a clone of the gaincard amp. IIRC it was quite expensive and was made in Japan or something.

  8. Why are there not more amp building posts? Just about everyone own an amp (or three) in some form, and yet building it yourself you can almost shave a zero off the cost vs performance.

    Which is weird because that’s not what this guy did $500 is a lot too much for that amp. I’m not sure why he paid $168 for the PCB unless he bought from someone who buys clad at Radio Shack and the components don’t seem terribly well matched and he way overspent on caps. (Though with out a BOM it’s hard to tell.)

    But yeah, HAD, if you’re going to link more amp building posts (and please do) link to one that has more meat on it than this project. This guy is simply waving out in the breeze. (Which is no surprise. Its what people in audio forums almost exclusively do.)

  9. Heh… this was meant to be a thing for the forumers – I didn’t expect this to get out there.

    Anyways. Yeah, the amp is massively overengineered. That was intentional. I wanted it to be as high quality as possible, heat up as little as possible, and last me for decades.

    It wasn’t $168 for a PCB, it was $168 for five 4.5×9.65″ PCBs with solder mask on both sides and silkscreen with a 5 day turnaround, in Canada (where milk comes in bags and everything costs 25% more). The main reason I opted to get a proper PCB made was safety – there are mains voltages in there as well as some hefty capacitors and solder mask reduces the chance of a cockroach sneaking inside and getting fried, or me zapping myself during the construction and testing phase. Everything is very sturdy now, so I don’t have to worry if it ever gets knocked over. The other reason for a PCB is it allows for a double sided layout with ideal component placement, lower resistance traces, and less susceptibility to noise. Although I don’t have a point-to-point solution to compare it with, I don’t regret this decision. This is the least noisy amp I have ever heard. It freaks me out a little because without any hiss or hum I forget that it is on. I can also build 4 more of these if I want to very quickly.

    Here’s the BOM
    The PSU doesn’t even get warm at normal volumes, but if I ever needed to crank it past 100W it would still stay pretty cool even though there is no ventilation. No heat means the caps will last for many, many years. I ended up not using the heatsinks on the diodes.

    The main difference between this design and the Natsemi reference design is the use of tighter tolerance components, and the use of massive metalized polypropylene capacitors. They may look expensive, but compared to the ones marketed towards audiophiles they are a fraction of the cost and have a ridiculously low impedance of under 3 milliohms at 10kHz. I’m pretty happy with them.

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