cheapest per watt amplifier design

That is a naive specification, like asking for the cheapest possible car that can go 100, 250, or 500 km/hr. depending on a how big a motor you put in it. You spend peanuts and all you'll get is a poorly performing one that needs constant repairs. Do it properly if you want high power.

You are Right!.

Well, i just have experience with ChipAmps, lm3886 lm4780. I really like how they sound!

But looking something now, something that give me something like 100/200/500 watts and use similar components, Of course with nice sound, if better than chipamps will be great!
Hi Guys

The bulk of expense to build a power amp is in the power transformer, chassis and heat sink. More watts generally equates to bigger PT, bigger heat sink and bigger chassis which equates to more $$$.

The electronics generally does not cost very much.

You can take the basic Lin-Thompson-Blameless front-end and adjust the voltages up and down to make different output signal sizes without changing the transistors if you use MPSA92 and MPSA42 in the respective positions. The current sources and current-mirror provide this inherent adaptability. This front end will cost less than $40 for stereo.

Then you just add on smaller or larger EF2 or EF3 output stages to suit the power required.

Since your experience is chip amp, this circuit topology will sound the same or better even though it is not the best one for extreme hifi.

Have fun
Look in this thread by Apex Audio. His designs sound very good and use similar front ends and drivers with some designs having more and more output stages. The bigger the amp name number, the more stages and more watts. One nice thing with his designs is that they don't require exotic parts, in fact, I source my parts almost exclusively from Aliexpress and they work well.

You get the idea... as the number of transistors is indicative of more power/complexity.
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I agree it's tough to beat $45 LJM class D amp that puts out 300w. However, you can make a decent 50w class AB discrete lateral MOSFET amp (stereo FX8 with heatsinks and all components including custom PCB's but not including PSU) for $30. The sound quality is very nice - among the best I have heard.

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2013-03-11 10:52 am
DIY is very expensive, more so than buying finished products - unless you use scrap parts (you should).

200 - 500 watts is in the realm of ridiculously expensive, and DIY becomes totally unfeasible.

Look into buying some old PA amp instead. These can be had almost for free, and they generally perform quite well. If you get a broken one, you can get it cheaper still, and even get your DIY on.
DIY is very expensive, more so than buying finished products - unless you use scrap parts (you should).

200 - 500 watts is in the realm of ridiculously expensive, and DIY becomes totally unfeasible.

Look into buying some old PA amp instead. These can be had almost for free, and they generally perform quite well. If you get a broken one, you can get it cheaper still, and even get your DIY on.

250 Watts doesn't cost a lot more than 100 watts. A bit more expensive transformer(s) and supply caps and an extra couple output devices in most better designs.
You have said you want to build 2 or 3? I would assume they're for separate systems? Else, you can get a stereo or two stereo amps. Second hand PA is a good idea.

Other options you could explore include using a car audio amplifier. You could get a 2 channel one capable of bridging. You may be able to find second hand or cheap new ones which will do well. You can power them off a cheap PC PSU giving enough current and 12V. A friend of mine is doing this with great success.

You could also look for a class D amplifier kit. These are easy, fairly cheap, and will give you what you're looking for.

Another option would be to bridge two LM3886's into an 8 ohm load. You just need to design for 4 ohms in terms of heatsinking.

Class D is great because it is efficient, so it uses a smaller transformer and heatsink, and these are the two parts which make up the bulk of the cost.

I'm sure you'll come right. Good luck!
Hi Guys

The cheapest amp to build is not necessarily the worst. Doug Self's amp design career has been devoted to building the least expensive design possible for any given power rating, concentrating on the simplest circuit to make stable.

As described previously, the front end of the PA is a total of 10 small-signal BJTs (MPSA42s and MPSA92s in 6 of those positions, and any cheapo NPN and PNP for the other 4). This circuit can be used for any supply up to +/-100V. In this BJT count, two are used for each of the two current sources, so we have REAL current sources that are fast.

Then add a bias spreader (1 or 2 BJTs) and EF2 or EF3 output stage with sufficient devices for the power.

Do you really need 500W in a single channel? Maybe you could bi-amp using an electronic crossover? This eliminates a major source of distortion from the system.

If you could get down to 100W/ch then those cheapo surround sound amps cost very little for the five channels of power. Just bypass all the junk comprising the preamp and surround stuff. An alternative that has been mentioned are class-D PA modules. Personally these are not hifi to me but if you just want raw power they are cheap and do not need large heat sinks.

Power amps do not have to cost a lot of money, at least there is no technical reason for them to. It is easy to over-spend on hyped up components that add little or no benefit to performance. DIY CAN be more expensive than buying prebuilt stuff if only because you do not have the scale of purchasing that a large company does.

Have fun


2016-04-30 12:02 pm
Check out JLM audio's amp kits, he has been coming out with some cool bridgeable kits, based on a 2x60 watt chip design. He's got a 2 channel kit, 8 channel kit (originally designed for Dolby Labs), and a 12 channel kit all bridgeable so you can configure a stereo setup for 60 W/ch all the way up to 390 W/ch. It supports volume and mute switches if you need those too.

At $180 USD for 390 watts x 2 channels and low THD, it seems like the best DIY choice with lots of customization options. You just need to factor in cost of the enclosure, heatsink, bridge rectifiers, and transformer. Joe also provides good support through email and his build threads.
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I don't think DIY has to be more expensive at all. My experience has been that you can make it for significantly less if you want class AB or class H. Class D you are better off buying pre made IRS2092 modules but class AB, DIY designed like this Apex 750w doesn't look expensive at all

DIY isn't more expensive because of the total cost of what you use, it's because you need an initial set of tools:
- Soldering iron
- Multimeter
- Various other tools, including small clippers

You also possibly need tools for making the enclosure.

Then you usually need huge excess of other materials:
- Heat paste
- Solder

It often happens that when doing an amp, you do something wrong, and you end up with a number of failed transistors. Then it happens again, and you've paid for the output 3 times over before finding your mistake.

Without tools for an enclosure, you're already looking at R3000. Depending on how you want to make your enclosure, you're looking at another R500 - R3000 for those tools. This equates to about $200 plus another $15 - $200 for other tools.

Then, everything else is more expensive to buy once off. You're looking at easily 50% more for the cost of components, heatsinks, transformer, etc. Say these would cost about $200 for about 100W stereo. That's a total of $400 - $600 for a stereo amplifier, and that's fairly expensive. If you plan on buying an enclosure, it can get very expensive for single units.

So it's the fun, the reward, and most often the quality that makes DIY worth it. If you have the tools, and you are clever about things, you can DIY for very cheap, especially if you have/find an old, unused but working transformer. But in most cases, it's far cheaper to buy an old amplifier.

This is, indeed, my own opinion, based on my last 12 years (and large amounts of money) I have spent building amplifiers as a hobby.
True the case and trafo are the killers. Tools, soldering iron and DMM's aren't that expensive really. But once you build one amp and get all your tools together, you can build a lot more for less. I always use a 10R 25w safety resistor in series with power rail inputs upon initial startup and adjustment phase. It has saved me many times and have yet to lose an OPS because it limits current and you can turn off in time to debug. Also if you do it for hobby, one power supply and heatsink can be reused over and over with different amps.