Build your own professional-grade audio amp on the sort-of cheap (2018)

https://spectrum.ieee.org/consumer-electronics/audiovideo/build-your-own-professionalgrade-audio-amp-on-the-sort-of-cheap

by Tomte • 6 years ago

176 131 6 years ago

spectrum.ieee.org

pjc507• 6 years ago

If you want TPA3250 amps without having to build your own, they're widely available from the usual cheap vendors for less than $100.

The victory of class D is now total; extremely low distortion numbers can be achieved without heroic board layout or expensive passives made of unobtanium. All available in the tiny packages of AirPods, smartphones etc. And power levels in the tens of watts can be done with a single chip.

Hydraulix9894• 6 years ago

I built this project myself last spring. That 3e-Audio TPA3250 board isn't sold anymore, so I built my own custom variant amplifier using similar parts with a TP3251:

https://photos.app.goo.gl/gPH8VZiaGRiNYWfL6

It sounds MUCH better than my existing cheap vendor Fosi TPA3116 did -- the cheap vendor ones don't use quality components, especially for the power supply, so you're not going to see the expected performance.

That power supply board (diode bridge + filtering caps) was designed with a friend in KiCAD and fabricated by JLCPCB (I have a few boards leftover). The speakers are also DIY -- Hivi 3.1 with cherry wood veneer!

I showed article author Zorpette my work, and he gave it his blessing =)

EDIT: If you do try to build this, be VERY careful around the high-voltage power supply electronics.

bxk1• 6 years ago

There is no way DIY diode bridge and filtering caps on a separate board could make a slightest difference here, in fact high frequency noise from the power supply could only be filtered right near the chip. But leveling up an amplifier, to a 4 times more powerful as you did, would make a significant difference in sound.

tuatoru10• 6 years ago

Very pretty! Thanks for showing it. What I'm going to say I hope will be taken as constructive, for those who are a bit more OCD about their electronics.

Safety: -

The mains safety earth (chassis bolt) should only ever have one lug: the mains input earth. Put a separate bolt an inch or so away from the mains safety earth bolt for the chassis connection of the bridge centre ground. (People have killed themselves doing repairs by ignoring this, and having faulty mains wiring.)

Fuses on the transformer secondaries are recommended if the transformer is expensive. If the bridge rectifier or an amp output stage fails, it'll almost certainly fail short, and the transfomer will heat up until its internal thermal fuse melts -- or if there isn't one, until it catches fire.

Likewise fuses on the DC rails will help protect the expensive smoothing capacitors from amp failure. (Yes, the TPA3251 has built-in protection - but that might also be damaged by the surge that caused the output stage to fail.)

I hope the polyester cap across the transformer secondary is X2 class.

Other points:-

A snubber across the mains switch will reduce arcing on switch-off and prolong the life of the switch. 10R-50R 3W in series with 100nF, X2 class, will do it. (The wattage rating is a proxy for both voltage rating and surge current rating.)

From the scale it looks like the transformer is a 120 or 160VA model. That's seriously undersized for an amp module rated at 350W (circa 550 VA with a traditional mains-frequency transformer). Transformer secondary fuses are strongly indicated.

OTOH, going up to a 500VA toroidal transformer means you'd need a soft-start circuit to prevent your house circuit breakers popping on start-up, from the initial transformer saturation inrush current.

I'm amazed you don't get RF interference with all that length of unshielded wire on the input side. I just have to leave one inch unshielded to be plagued with EMI - unless I use filters on the input terminals (100R / 220pF RC filter).

You don't have DC blocking on your volume control. I guess none of your sources have any DC offset. If not, changing the volume will be scratchy.

References: -

1. Bob Cordell, Designing Audio Power Amplifiers.

2. Doug Self, Audio Power Amplifier Design 6e.

3. Rod Elliott, sound-au.com. "Designing Linear Power Suppplies part 2" https://sound-au.com/power-supplies.htm

4. Idem, "Transformers - The Basics, part 2". https://sound-au.com/xfmr2.htm

2sk21• 6 years ago

Interesting - I didn't realize that AirPods have class-D amps.

tomxor3• 6 years ago

I'm pretty sure everything small and portable uses switching amplifiers, in fact pretty much all modern consumer electronics use class-D from your phone to your TV unless you specifically seek out separates from an audio shop. This is because class-D amps are extremely convenient, they are small, cheap, power efficient and they require little consideration for cooling - audio quality is an area of debate, there are certainly lots of very poor quality class-D amps our there with absurdly high THDs, but there are probably lots of good ones too.

AB would be more likely than A, but I can't imagine finding them even in a large flat screen TV since they are inherently less efficient and require larger power transformers which make them fairly heavy and bulky. You only really find non switching amps these days when people want to sacrifice some of that convenience for some nicer sound.

xnyan2• 6 years ago

The trifecta of outstanding power efficiency, low cost, and nowadays very good performance of a class D amp virtually guaranties that any amplified sound you've head from a mobile device, or any consumer device really, was amplified by a class D.

There's not really a good reason to use non-class D in any mobile application today. As few as 10 years ago I thought Class D = garbage you settle for if you must, I've heard some incredibly good Ds that have made me completely change my mind

8bitsrule• 6 years ago

When my amp/receiver bought the farm a decade ago, I decided to try a 50-watt/channel 12-volt class-D amp after seeing the specs. It cost under $50, and I powered it with a hefty wall-wart (120v-1.5amp to 12v) left over from the 90s. It's been on 24/7 since, never used for over 10 watts/ch. The savings went into a decent pair of near-field speakers ... the most important part of great sound.

SomeoneFromCA4• 6 years ago

I disagree that the "victory is total". First of all, distortion in the upper part of the audio range is not that stellar. Secondly - I personally can tell apart Class-D, Class-AB and Class-A. Class-D has grainy sound, even the best ones, $3000+ I tried; I get fatigued pretty quickly from them.

new_realist• 6 years ago

Silly misread—-deleted.

liquidify2• 6 years ago

How do class D amps sound? In my limited amplifier build history, tubes still win over transistor based amps every time. Mosfet amps sound great in the mids and highs and bipolar sounds great in the lows, but neither of them beat nice tube designs.

W-Stool• 6 years ago

An amplifier shouldn't "sound" like anything - the best possible amplifier would be a wire with gain. Tube amps do have their own sound, primarily due to higher harmonic distortion and the use of output transformers in the signal pasth. Whether this "sound" is agreeable to you varies by the individual, but there is certainly no universal agreement that a tube amplifier sounds "best".

tomxor3• 6 years ago

What sounds neutral also seems to be highly subjective.

I think "colour" of sound is a fitting analogy though - in the same way that our can eyes adjust to color temperature within a certain range i've noticed on the scale of hours/days I can become accustomed to speakers/amps with quite different frequency responses.

liquidify2• 6 years ago

I have built multiple amps of different types and topologies. Each one of them 'sounds' completely different. This is the reality of amplification. There is no perfect distortionless amp at all frequencies for all speakers. The interactions between the circuit and the impedance presented across all audible frequencies by any random speaker are infinitely variable. The sound of an amp is the combination of all factors in the system, which includes physical interactions and their response to the variations in presented impedance.

So yes, an amplifier shouldn't sound like anything, but they always do in reality. Within that reality, we can make judgments about the general qualities of certain types of amplifiers. If you want to comment on my question please do. Otherwise, kindly go away, and keep your comments about your magical fairy tail land where all amplifiers are perfect to yourself.

PretzelFisch• 6 years ago

For a few dollars more there is Nelson Pass's(firstwatt) Do-It-Yourself amp camp. Very nice analog amp. https://diyaudiostore.com/products/amp-camp-amp-kit?variant=...

jeffbee5• 6 years ago

If you're the kind of person who equates harmonic distortion with "warmth" you're in for a big treat with these Nelson Pass designs. On objective measurements these are just about the worst amps you can buy (or build). We're talking about 2nd harmonics at only -50dB. Warm AF.

pjc507• 6 years ago

Bias current of 1.45A (not ma!) means it'll be pretty warm to the touch too.

The only advantage is simplicity for teaching purposes. Doesn't get simpler than class A.

analog313• 6 years ago

This is just a quibble, but most switchmode amplifier chips are analog. Granted the term "digital" has been adopted by the audio community for switchmode amplifiers, but it still raises eyebrows.

de6u99er4• 6 years ago

Want to go audiophile?

Here's my Pre-Amp (apavel Dudek's PA03) and Power Amp (Nelson Pass DCB1) that I built a couple of years ago.

I even went the extra mile and used discrete OpAmps from Burson Audio.

https://www.bursonaudio.com/pa03-gainclone-power-amp-by-pave...

For those who are not afraid to go down a rabbit hole. -> https://www.diyaudio.com/

de6u99er4• 6 years ago

should be: Pavel Dudek

Apologies for the typo

de6u99er4• 6 years ago

Another correction: Pre Amp is based on Nelson Pass's design, and Power Amp on Pavel Dudek's

neolog• 6 years ago

microphone -[XLR]-> interface -[USB]-> computer

(I don't know much about this stuff.) I've been wondering why "audio interfaces" are so expensive. Even the cheapest one is $100. Can you explain what makes these expensive? How much would it cost to DIY one of those?

[1] https://www.amazon.com/PreSonus-AudioBox-USB-Audio-Interface...

barkingcat• 6 years ago

I think for your application, you'll just need to separate the concerns out a bit

You have the mic preamp, which can definitely be diy'able

Then you have the AD/DA converter - this will convert the output from your diy'ed mic preamp into digital signals - this can't be done easily DIY, but you can purchase chips that does this : the ESS Sabre is one of the most popular AD/DA converters that you can probably source from aliexpress, etc - you might need to buy in bulk though otherwise the vendor might not talk to you.

Then you have the usb interface itself, which comes with all the issues about certification, interface types and properly engineering/building a usb interface that works with consumer ports across different platforms is non-trivial for DIY'ers. You might be able to do something like "make a usb work for my specific computer, with a specific motherboard/platform" but for example, making something that adheres to the usb2.0 or 3.0 spec for both mac + pc + anything else that uses usb (for example, your cell phone, etc) - that's a totally different exercise that most diy'ers won't be able to easily do.

Again, you can buy off-the-shelf chips to do this, but at that level, you're doing digital circuitboard design, and I'm not sure how well bread boarding works with things like usb. You might be able to layout a PCB and have someone etch it for you, etc.

After that you'll need to build the output portions of the interface (after coming out of the DA chip). That can be DIY'ed.

If you want to DIY an in-and-out audio interface you'll need to take on all these different aspects all at the same time.

That's why you don't see many DIY projects of this kind.

Rather, the DIY projects being talked about in this thread are one aspect of this chain: you want to drive some speakers, ok! we can build an amp diy. You want to do AD/DA ok you can do that one thing with a homebuilt board, with a chip, etc.

But having all aspects being integrated together is non-trivial for a DIY. You might be able to use a Raspberry Pi zero or something like that for driving the AD/DA - USB portions, etc and that could be a way to go.

In fact, I think using an RPi as a DAC would be a great way to DIY a usb audio interface, at least you've got all the chips integrated already, and you have an audio jack for getting inputs, etc, and you have the power source and usb OTG port[1] already designed, etc. And that's where you start to see $100 isn't all that bad for a usb audio interface.

[1] https://gist.github.com/gbaman/50b6cca61dd1c3f88f41

bluGill2• 6 years ago

Two reasons, first, those who want XLR inputs (and outputs in many cases) want quality sounds so they are willing to pay for something a little more high end. If you there are cheap USB audio interfaces that are pretty good, but the next level up is really several levels up in quality (though I'm not sure if you can objectively tell). Second, the volumes sold need high prices to pay for the engineering.

tuatoru10• 6 years ago

I've been wondering why "audio interfaces" are so expensive.

They're a minority interest. Designing good DACs is a subtle art and the engineer costs are amortised over small production runs.

The design of the ancillary circuits (analogue preamps, headphone monitoring, phantom power, input and output protection), and mechanical design and integration are also time-consuming and tricky (=expensive) to make reliable and within design goals. And marketing costs are probably as large as engineering.

You certainly could do it yourself, but the component cost is the least of your worries. You'll need a fair bit of bench gear - oscilloscope, function generator, various power supplies, DVM, ... but even that's not the problem. You need a lot of knowledge about component selection and circuit design and layout, and a lot of experience with the tools of the trade.

Making something like the Presonus (but probably six or ten times as big, because I can't do an all-in-one circuit board with all those functions on it and have it work in any reasonable timeframe), getting it to a state where I would let an unknown mic or computer be plugged into it, or let someone else use it, would easily take me more than three hundred hours. If you're new to this, multiply by n (n >=3).

bestouff• 6 years ago

Pardon my newbeeness here, but is it possible to build a home cinema amp (say 5.1 hdmi) in the same spirit ?

jeffbee5• 6 years ago

It's effectively impossible to DIY anything with HDMI but if you can get an adequate 6-channel analog output from an HDMI line-level converter then at that point all you need is three 2-channel amps or design one with all 6 channels in one box.

mmastrac2• 6 years ago

Agreed. Aliexpress has some digital-to-6-channel decoders that work pretty well (and even support the more advanced codecs that are usually licensed by regular amps). Some of them even run Linux under the hood. :)

I would suggest using TOSLINK rather than HDMI as you can almost always extract TOSLINK from HDMI. Technically HDMI can carry more audio bandwidth, but I'm not sure where that might get used (if at all).

EDIT: I haven't specifically tested this one, but it's similar to one I've played with: https://www.aliexpress.com/item/1005001491403444.html?spm=a2...

pjc507• 6 years ago

HDMI audio is a huge pain. Optical Toslink should be doable; you might be able to find the right board. But there's a lot more involved in doing the digital 5.1 decode and having more channels.

tuatoru10• 6 years ago

Summarizing what jeffbee says in sibling comments: -

Yes, it is certainly possible. But you need to acquire the prerequisite seven to ten years' experience first for a project of that complexity. When you've got that experience...you'll just buy one.

m0zg• 6 years ago

I understand the DIY allure, I really do (I do some electronics DIY myself - guitar pedals, tube amps, that kind of thing), but if you want to get great sound and save money at the same time, then just get a used QSC amp from Craigslist for $400 or so. It's better than pretty much anything you'll be able to build on your own for "reasonable" money, and it doesn't look "DIY".

fest• 6 years ago

I was under impression that class A amplifiers generally have the best amplifier characteristics (linearity, THD), and class D was mainly used in applications preferring efficiency/size/price over audio quality. Apparently class D has gotten lot better for the majority of applications.

asimpletune• 6 years ago

Yes, I believe the main thing that’s changed over the years is the switching speed. IIRC that’s due to geranium transistors?

pjc507• 6 years ago

Geranium is the plant, germanium is the transistor. But everything is silicon, and has improved for the usual Moore's law reasons.

A class D amp is a closed-loop control system. While it can be done entirely in analogue, having a microprocessor in there lets the designer algorithmically compensate for nonlinearity of the output.

jeffbee5• 6 years ago

Class A architecture's main advantage is it is very easy to achieve high objective performance, while trading away heat and power (and consequently size and mass). You can easily get 3rd harmonic below -80dB and you can eliminate even harmonics entirely. All you have to do it spend a lot on heat sinks and commit to a large power bill.

The problem is going to be reaching really stellar objective performance with the Class A design, because all those space age (not in a good way) power transistors are very slow and hard to drive, and that limits your error correction techniques. That's where these fancy designs are better. Basically they're using lightning-fast transistors and a DSP to bridge a power supply directly into a speaker. Objectively these designs have 3 orders of magnitude less total distortion, unmeasurable 2nd and 3rd harmonics, inaudible (-120dB or better) intermodulation products. The space age designs have simply no chance.

willis936• 6 years ago

By slow do you mean high capacitance between base and emitter? I’m under the impression that even high power BJTs will be good out to 100 kHz. FETs are even better I believe. Adding more components to the signal path degrades the signal slightly at best and introduces additional non-linearities at worst.

hatsunearu6• 6 years ago

It's actually class B that has the best performance. A lot of people say class B is bad because crossover distortion, but what they are actually referring to is class C (the classic picture where a bit of the waveform is conducted by the top one and a bit of the waveform is conducted by the bottom one, with some flat spots in between) Class AB is bad because near the crossover, both top and bottom devices conduct and that actually causes an assload of crossover distortion. Properly biased class B precisely hands over conduction from one side to the other, making crossover distortion practically negligible.

Class A is theoretically the best but you can get good performance, and perhaps even better performance than A with a properly designed class B amplifier.

hakfoo• 6 years ago

I'd always heard the problem with class AB was less that both devices were on, but that when it's switching off one side near the zero point, that action added noise.

There were a lot of branded tricks in the dying moments of "stereo as a status symbol" (early 1980s) which tried to mitigate this. (Technics New Class A, JVC Super-A, etc.)

SomeoneFromCA4• 6 years ago

This is the terminology Douglas Self uses. No one apart of him call class B class C.

davidhyde• 6 years ago

It seems like a lot of money is spent on the power supply. Small Bluetooth speakers draw power from lithium ion batteries which are, in turn, topped up with a cheap external power source. I understand that you can draw very high current from these batteries even if only briefly. Why don’t high end amps use the same trick instead of these giant toroidal coils and smoothing capacitors?

pjc507• 6 years ago

Because then you have to charge the battery.

Terminal voltage matters too; higher voltage is required to deliver more power. 3.7V into 4 ohm limits you to under a watt. So many systems have a boost converter in there too - which is a potential source of electrical noise.

You could certainly have a stack of 18650 cells do the job if you want a portable boombox...

regularfry3• 6 years ago

And, importantly, discharge it. Keeping a battery healthy is a moderately involved task, and the circuitry to do it is another-thing-to-go-wrong that's avoidable complexity with just about any other option. Besides which, no matter what you do the batteries will fail out within a single-digit number of years, even under low usage. It's a good option if you need portability, and pretty terrible by almost any other metric.

analog313• 6 years ago

A dark secret of power amp design is that the power supply is half the battle. Note that this design uses a conventional line frequency transformer rather than a switchmode power supply. Making an all-switchmode amp is actually a bit of a challenge. I've been there. My home stereo is a cheap switchmode power amp board, but the power supply is line frequency, as a concession after I discovered that powering it from a switchmode power supply makes it put out all sort of weird noises.

An extremely nice product are the "IcePower" modules made by Bang and Olufsen, which incorporate both power supply and power amp into a single board. So they've worked out the bugs of making the parts play nicely together. These are now the jellybean power amps in smaller musical instrument amplifiers, of which I own a couple.

de6u99er4• 6 years ago

I guess because batteries while being great for high current operations, are not the most environmentally friendly solution. My DIY power amp requires a +/- 20-40V power supply. That would be quite a lot of batteries. Toroidal transformers are the next best choice, since they are smaller than comparable regular transformers.

Large caps are not only for smoothing but also act as power bank for instantious large current needs.

basicplus22• 6 years ago

Class A amplifiers are "high-end, audiophile quality", class D is about as low as you can go

dsr_• 6 years ago

Sorry, this is completely incorrect. A, B, A/B, and D all refer to the amplifier topology, not to the quality.

basicplus22• 6 years ago

Sorry you are incorrect, Only in Class A is the whole of the signal contained in the operating area of the transistor, thus only class A amplifiers transfer the whole of the original signal on to each successive stage.

Class B C and D chop more and more out of the crossover point out of the signal as it passes through each stage.

phkahler• 6 years ago

That used to be true, but it seems class D has got quite good. This prompted me to look up the old LM12 but I cant find it anywhere but Ebay. Must be out of production.

jordanthoms• 6 years ago

There's plenty of extremely high quality class D amps around now that exceed the performance of Class A, e.g. the Benchmark AHB2 ( https://www.audiosciencereview.com/forum/index.php?threads/r... )

mcwone• 6 years ago

A few years ago I built the lx-mini speaker system and it was a fun project. Foe details see Linkwitzlab.com

HungSu2• 6 years ago

At 84€ just for the plans I will give this a miss, but if you happen to have images and other opinions of the ones you made yourself I'd be very curious

http://www.linkwitzlab.com/LXmini/Introduction.htm

supernova87a• 6 years ago

Forgive me, I'm not an audiophile, but am curious about it.

What is the constraint(s) that makes good audio equipment expensive?

Is it about components that can handle enough power? Is it avoiding distortion? Or both of the above (or other factors) for the price that components are available on the market?

Looking at some of the photos of components in the amplifier, it looks way dumber and less sophisticated than a Raspberry Pi. Why has the cost of an amplifier not come down to say, $100?

And maybe related, why does a "good" pair of noise cancelling headphones cost $300 and not $50? Is there something related?

pjc507• 6 years ago

First the usual consideration of mechanical construction and production runs; stopping the plastic from rattling and making headphones comfortable adds to the cost.

Then there is bulk; the transformer+caps arrangement is large and heavy, incurring cost all the way along the supply chain.

Then you get into arguments about how much distortion is OK; you can never get to zero but you can asymptotically approach it at increasing cost.

Personally I bought a Sabaj A3 for my TV, which is about $120 and has TOSLINK and Bluetooth. No audiophile will ever use bluetooth, but for playing music in the lounge it's completely fine.

coin• 6 years ago

No audiophile will ever use bluetooth

That's because audiophiles are more about the equipment and less about the actual music.

atoav3• 6 years ago

I design audio electronics circuits. I think what makes it is mostly:

* high bandwidth.

* over a high dynamic range.

* with a high sensitivity over directionality and pitch changes.

Our ears are exceptional things, and as social animals they are far more important to decoding extremely subtle cues in our surrounding voices and the voice of those talking to us than we probably are aware of.

The thing with audio is, that in the end you still have to move air. And you have to do so without having your vibrating thing breaking after a week. Mechanical reliability is hard while still maintaining these specs. Audio electronics is sensitive to inaccurate power layouts, trace layouts etc.

Bjartr• 6 years ago

Some of it is the need for precision. Cheap resistors, capacitors etc. can be outside stuff spec by +/- 10%. Which is fine for all kinds of applications, but audio is really sensitive to that kind of variance, so to get the one or two orders of magnitude more precise components you need for it to sound good, you pay a premium.

At least this is what I learned trying to save money by building my own modular synth stuff. You'll save some money (labour costs), but it's still gonna easily cost hundreds for a handful of components.

GuB-42• 6 years ago

People had a lot of success buying cheap amps from AliExpress based on a known chipset, like the TPA3250 mentioned in the article, and change the few components that matter.

Usually, it is about changing the cheap knockoff caps by proper audio-grade ones.

Now you are left with the 90% of the work, that is getting a good power supply ;) The easy way is battery power, but then you need to charge the batteries. Linear power supplies are big, expensive and inefficient, but relatively easy to get right.

Switching power supplies are tricky as they tend to introduce all sorts of noise, in fact, they work almost in the same way as the amplifier itself, so you are basically powering an amplifier with an amplifier, both with their own feedback loops.

woofie11• 6 years ago

Counterargument: The power supply is overrated. You want to start with high-power but lousy switching power supply. You want to position it far and shielded from your amplifier. You want a decent ferrite bead on the cable, and a decent bypass filter in the box (both electrolytic and ceramic). The high-frequency stuff should mostly be gone. You can then use a linear regulator and a pretty basic filter to clean up the rest, and introduce an extra volt-or-so of drop on the output.

It sounds like a lot, but it's not.

widea• 6 years ago

Yes, I built a few headphone amplifiers using a similar setup: switching power supply - EMI filter - rail splitter - amplifier. No noise, just wonderful sound.

captn3m0• 6 years ago

Could you pair a okay-ish power supply with a Jitterbug perhaps?

https://www.headfonia.com/review-audioquest-jitterbug-usb-ma...

Archit3ch• 6 years ago

What about non-audiophile? Are there any similar resources for professional-grade guitar amps?

tuatoru10• 6 years ago

Take a look at Rod Elliott's web site, sound-au.com.[1]

Rod has many years' pro audio experience and his web site is a treasure trove of audio DIY information. He has at least one guitar amp project, and several articles about design traps and pitfalls he has seen... and others about how to do it right.

1. https://sound-au.com/index.html

iainctduncan3• 6 years ago

Class D amps are pretty amazing. the Fender class D bass amps are ridiculously good and light for the price now. like 20% of the weight of their predecessors light. Which, if you've lugged a tube 4x10 around, is pretty awesome.

linsomniac2• 6 years ago

I used to be pretty into audio (I used to have bi-amped Vandersteen 2Cs). I've kind of wanted to build a new setup, speakers following the Tech Ingredients "World's Best Speakers" or "World's Second Best Speakers" at https://www.youtube.com/watch?v=CKIye4RZ-5k&t=18s

I had looked at building this amp to power it, but I realized I really want something that can do HDMI-CEC, where my TV can power the amp on and off and control the volume. You know, how my current Yamaha soundbar works. But I haven't for the life of me been able to find any boards that would allow me to add HDMI-CEC into the project. I did find USB modules that would allow a computer to send CEC commands, but no pre-amp or class-D board that could take CEC input.

Building speakers and a soundbar would be pretty fun though. Been really getting into DIY projects.

jcims• 6 years ago

Tech Ingredients is in my top three favorite YouTube finds of 2020.

rawoke083600• 6 years ago

Came here looking to see who would post about that YouTube Videos (Tech Ingredients). Those two videos are brilliant !

wernerb• 6 years ago

Would something like the SHARC work? https://thenaudio.com/

linsomniac2• 6 years ago

Looks like it should, it does say numerous times that it allows the TV remote to control volume and mute, but it also says line-level output. I had looked at some other similar ones on Amazon last year that wasn't clear could do volume control, but the SHARC sounds like a good option. Thanks!

jtwaleson2• 6 years ago

How good are those DLM speakers? I can't find much about it, but the idea of having very good, completely flat $100 speakers is very appealing.

jtwaleson2• 6 years ago

*DML

latchkey2• 6 years ago

I recently ventured into the Campervan world. A friend gave me a couple of older nice waterproof Polk audio speakers. Mounted them in the back of the van on a custom rubber shock mount I build from random pieces at the hardware store.

I wanted a way to power the speakers and send music via bluetooth 5. All powered off my 12v solar system. Looked around at all the 'commercial' offerings and found nothing attractive. Everything was over priced or just didn't have modern features.

So... I searched around on Amazon for the right keywords. Ended up getting one of these little class D 100w+100w amps with treble and bass knobs off Amazon for $30 [1]. Got a 12v->24v step up for $16 [2] to give the amp a bit more power and less distortion.

Works amazingly well for a fraction of the price of anything else.

[1] https://www.amazon.com/gp/product/B089KVH9J1

[2] https://www.amazon.com/gp/product/B01EFUHFW6

krisoft• 6 years ago

But it looks like there was a commercial offering. You say it yourself that you could find a solution on amazon. Or I’m missunderstand what the quotes around ‘commercial’ mean?

latchkey2• 6 years ago

When I mean 'commercial', I'm talking about something specifically made for car audio by a large name brand manufacturer... something like this...

https://www.amazon.com/Sony-XM-GS6DSP-Channel-Bluetooth-Ampl...

$400 and not even bluetooth 5 (it first came out in 2018 and hasn't been updated since).

jiggawatts• 6 years ago

What I've been looking for is a not-outrageously priced home theatre system that supports all the latest standards, like DTS-X, Dolby Atmos, etc... and has proper, decent speakers, not tiny little tin cans or a soundbar or something.

However, nobody seems to make the "proper" speakers that have the up-firing part needed for Dolby Atmos and are also wireless so I don't have to run cables from the TV to the rear speakers.

The few that I've found so far are crazy expensive.

I think home audio needs an IKEA-type manufacturer to upend the traditional economics of the products.

The expensive part of home theatre audio is that proper wood speakers are big and expensive to ship.

Someone needs to figure out a way to flat-pack full size speakers that consumers can assemble at home, but without requiring soldering irons and power tools.

tuatoru10• 6 years ago

If you want good value for money, Dayton Audio is your best bet. They used to do some kits, IIRC, but their FBU speakers are reasonably priced for what they are.

For kits there's Madisound (high-end[1]), and in Australasia, The Loudspeaker Kit[2] for more moderately priced kits -- often using Dayton drivers.

You can get cabinet makers (kitchen designers and the like) to make up the boxes locally for you if you can supply them plans in a format they can use.

1. "High end": Buy components for a total of $1k, build your own box to the plans, and get the equivalent of a $10k pair of speakers.

2. http://www.theloudspeakerkit.com/

3. Dayton Audio: https://www.daytonaudio.com/

xenocyon• 6 years ago

Since this isn't explicitly clarified in the article, it's worth mentioning that THD (or THD+N for that matter) is not always a helpful spec to compare two amps. You can easily have two amps where the one with the worse THD is actually the superior one because its distortion is in low-order even harmonics, while the nominally lower THD amp has more distortion in odd or higher-order harmonics. The distribution of distortion over harmonics is as important as the raw sum. (For the layperson who doesn't care about the math: this is why tube amps sound good even when their nominal THD spec may be higher than low-end solid-state amps.)

tuatoru10• 6 years ago

This is kind of right, but...

Speaker distortion is in the 1% to 5% range.

If your amplifier's distortion is less than 0.1%, you probably won't hear it, whatever it is.

The main reason people like the sound of tube amps (the "warmth") is due to the fact that most of them can't amplify high audio frequencies very well.

For reference, the frequency range of human hearing is taken to be 20 Hz to 20,000 Hz. Hearing is logarithmic in frequency, i.e. the perceived difference in pitch between 100 Hz and 200 Hz is the same as between 10,000 Hz and 20,000 Hz - an octave.

Tube amps have output transformers. It's difficult to design wideband power transformers (heck, designing any transformer is difficult), so most of them have reduced output in the top octave. (AKA "high frequency rolloff".)

One reason for the bad reputation of transistor amps is this: -

Many early transistor amps (and some still today) were prone to oscillation at MHz frequencies under some circumstances. The oscillation itself is inaudible but it affects the linearity control of the amplifier (negative feedback). Amplifiers were oscillating at MHz frequencies for a millisecond or two and losing control, which had a noticeable effect on the sound.

The oscillation wasn't picked up by the designers (of the early transistor amplifiers), because who needs a 100MHz oscilloscope for designing audio circuits that only go up to 20kHz? That's just silly. (Until, of course, it isn't.) And in those days, 100MHz scopes were expensive.

There are other reasons. For example, tube amps withstand some overload; transistor ones don't. Exceed the output transistors' second breakdown rating for a tenth of a second, and suddenly you have no sound. Your new speakers you just brought home from the store killed your amp. "But they're 8 ohms, same as the old ones!" (Another long story there.)

It took a while to figure out all this stuff and how to protect against it, and in the meantime, reputations were made and lost. Tube good, transistor bad.

HungSu2• 6 years ago

Can anyone recommend a DIY speaker in the same vein as this amp? (Aside from the panel speaker linked elsewhere in these comments)

porknubbins• 6 years ago

I’d be interested in this too but get lost down the rabbit hole every time I try to research speakers. I think the problem is an ideal amplifier is easily described as “a straight wire with gain” while a practical speaker is a much more complicated problem with many tradeoffs based on physical properties of vibrating materials and distances etc.

hatsunearu6• 6 years ago

I tried making my own but it's like 99% woodworking and 1% actual audio engineering (i.e. doing the whole Tiele-Small stuff). Be sure you know what you're getting into haha

klodolph4• 6 years ago

The article covers some of the alternatives below, so take this rant with a grain of salt.

I don't understand the need to connect a massive linear power supply to a class D power amplifier. That seems completely backwards to me. If you're going class D, then why not eliminate what is often one of the biggest and most obvious expenses and replace the linear power supply with a switching power supply?

Typically in these projects you spend some chunk of the BOM cost on a few nice transistors or an amp chip, another big chunk on the transformer, smaller chunks of money on capacitors, then miscellaneous ICs/amps/hardware/etc. There's some variation here between components, but it just seems bonkers to pay for a big hunk of metal for a 1960s era solution for your power supply, when you are already using super fancy high-speed switching circuits in the amp.

There is no reason that these devices should have any appreciable mass beyond the heat sink. If you've got a massive transformer, you're building an amp like you've traveled in time back to the 1980s, before class D amps existed (well, before they were feasible for these applications). Nothing wrong with that, it's just that the linear power supply adds a lot of cost and mass for no reason.

whatshisface2• 6 years ago

Although they are conceptually related, it is harder to engineer switching power supplies than it is to engineer class-D amplifiers, so I could sort of understand a hobbyist drawing up a design that uses 1960s technology to make DC to go in to 1990s technology.

klodolph4• 6 years ago

It's hard to engineer a good class D amplifier, but you don't have to do that, you just buy a chip and read the application notes. Same reason why you don't need to engineer an SMPS, you buy a module (if you are a hobbyist) or buy a chip and read the application notes (if you are making a product).

If you are just gluing modules together, then just get the SMPS module and save yourself the weight. If you think you need a linear power supply, then why do you need a linear power supply if you don't need a linear amplifier? Just seems odd.

p-funk2• 6 years ago

At my last company, we tested tons of combinations of class D modules with various power supplies, and the best sounding results tended to be with linear power supplies. Don't get me wrong, there's tons of tricky stuff when it comes to the subjective side of audio, so it may be at least partially placebo effect. But we pretty consistently found that off the shelf switching PSUs sounded worse subjectively, even if they measured the same on the bench.

I haven't been doing audio for a while, so I don't remember more of the details. But audio signals tend to need all their power in short bursts all at once, when a low frequency bass note hits for example, and so the transient current tends to be much more important than a stable voltage rail. A lot of switching supplies do not optimize for this. Well designed versions can both sound great, but a cheap linear supply is going to sound much better than a cheap switcher. Audio is stuck with 1960s technology for the most part anyway though.

klodolph4• 6 years ago

You could add the massive capacitors if you needed the bursts of energy, it just seems like the mains transformer itself is out of place.

balfirevic• 6 years ago

so it may be at least partially placebo effect

That really sounds like a kind of thing that should be tested blinded.

hatsunearu6• 6 years ago

I don't understand the need to connect a massive linear power supply to a class D power amplifier.

Generally from what I understand, linear, unregulated (gasp) supplies are preferred over anything else. I think the reasoning is that the PSRR is great at lower frequencies so having a bit of 120Hz ripple isn't a big deal.

Though this is a bit of antiquated advice, IMO, since you can get amazing performance out of SMPS supplies with a bit of filtering.

amelius• 6 years ago

Perhaps because you'd have to synchronize the switching of the supply with the switching of the amp to prevent aliasing effects.

dang• 6 years ago

Discussed at the time: https://news.ycombinator.com/item?id=18349396

tuatoru10• 6 years ago

The amp shown is nowhere near "professional grade".

Professional means it does the right thing in unusual circumstances - naughty inputs, naughty outputs, naughty mains power, running at full power on the grass under a pile of coats and scarves, pumping through old and fraying speaker leads lying on the ground, ...

The design is missing all sorts of safety features apart from the most basic (prevent electrocution from broken mains wires touching the chassis).

A 200VA transformer with a 350W amplifier is just asking for a transfomer meltdown (or fire, if the transformer doesn't have a functioning thermal fuse), unless there is a limiter in place to limit the output to 120W or less. (Fuses are also recommended, but in the professional environment you don't want them to blow, ever. Hence, a limiter is mandatory.)

The bridge rectifier is undersized.

In traditional mains-frequency rectification such as shown, the diodes only conduct for about 10% - 20% of the time, so the peak current in them is can be more than 10 times the average. At 36V and 10A output average, the rectifier current peaks are in the neighbourhood of 100A. A BR35 (35A 1000V) will provide a reasonable working life. At up to 36W dissipation, you can probably just bolt it to the chassis with some thermal compound.

The design is also missing speaker protection features and surge/spike protection/EMI prevention, and RF intereference filters on the inputs.

The design is also missing convenience features one expects of a professional amp, such as "power good" and "fault" lamps/circuitry. And handles.

It's nice that there are good inexpensive amplification modules now. But as with software, the difference between a toy example and professional grade is thought, time and money spent on reliability, safety, and usability.

regularfry3• 6 years ago

I do think it's interesting, though, that you could conceivably add all those elements, and you'd still be well under $500 in parts.

roland35• 6 years ago

I remember reading you should shoot for total BOM costs of about 30% sale price though... So that seems more reasonable to me

Hydraulix9894• 6 years ago

The design is also missing speaker protection features and surge/spike protection/EMI prevention, and RF intereference filters on the inputs.

1.) TPA325x have built-in speaker protection circuits.

2.) Do balanced inputs need RF interference filters?

For this project: After blowing the bridge rectifier a few times (for the reason you mentioned above), I ended up replacing the linear supply with a SMPS instead.

mikewarot• 6 years ago

Back in 1980 my Science Fair project was a class-D stereo modulation system.... ah, memories.

lowdose• 6 years ago

On a side note has anyone tried the Devialet Phantom speaker system?

https://www.devialet.com/en-eu/phantom-speaker/phantom-premi...

moepstar• 6 years ago

I wish there was something free/oss from NwAvGuy - i love his Objective2...

Build your own professional-grade audio amp on the sort-of cheap (2018)

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