Build Your Own Professional-Grade Audio Amp on the Sort-Of Cheap • Hacker News Board

Re: Build Your Own Professional-Grade Audio Amp on the Sort-Of Cheap

#231

Post by AnthonBerg » Thu, Nov 01, 2018, 5:16 PM UTC

ballooney wrote: post #221

AnthonBerg wrote: post #210

Earlier quoted context omitted.

I'm going with an understanding similar to what is presented e.g. here: https://www.mwrf.com/components/learn-meaning-amplifier-line... "The term linearity derives from an amplifier's linear relationship of input power to output power which, in an ideal amplifier, would be precisely related by the gain of the amplifier." I see it as matching my argument. Could I ask you to give a definition which clashes? Thanks!

Yes, the definition of linearity is that f(A) + f(B) = f(A+B), which you have contradicted in your GP post. If a transistor is fully on, then doubling the input voltage to it will not double the output, because it's already at maximum. That is very precisely not a linear device. That's why linear amplifiers, like Class A, operate the transistor in a partially switched state, where increasing the input signal (about s…

Thanks but no thanks.

When a transistor is off, it’s off. Then it takes a certain input voltage to get it going. Then there’s a varying curve to full output.

In contrast, fully switching on or off “gets rid of the curve” and tranforms the problem into one of timing, and one of a modulation scheme for a series of on or off states. In that respect I contend that it is an useful thought to consider transistors’ behavior (in an amp) as more linear and controlled if used in only the on or the off state. The output quality of Class-D amps in relation to price, size, complexity, and power, and cost suggests to me that the gains are not only in power efficiency.

Class D amps do leave the operation of transistors in their linear domain on the table, and do gain efficiency by that. Overall linearity as a control mechanism is something I stand by saying is increased. You may present an alternate take of course.

Re: Build Your Own Professional-Grade Audio Amp on the Sort-Of Cheap

#232

Post by ryguytilidie » Thu, Nov 01, 2018, 5:30 PM UTC

S_A_P wrote: post #123

Audiophilia is a study in contradiction. The ask is a flat "uncolored" accurate sound. The gear that sells for ridiculous prices is usually tube gear with limited bandwidth and makes ~15 watts at 5-10% (admittedly usually even order harmonic) thd. Hardly uncolored. That said, and Ive mentioned this before on HN. My (now late) uncle had a bunch of audiophile friends in Dallas. He hung around folks who had spent upward…

I don't think that your first paragraph is an honest assessment of the issue. People who buy tube gear are absolutely not looking for "flat, uncolored sound".

Re: Build Your Own Professional-Grade Audio Amp on the Sort-Of Cheap

#233

Post by mrob » Thu, Nov 01, 2018, 5:34 PM UTC

pps43 wrote: post #219

mrob wrote: post #75

Earlier quoted context omitted.

>Combine that with the very limited bits provided by CDs, preventing any possibility of good playback 16 bits gives you 96dB SNR (and subjectively more with dithering), which is plenty at non-deafening listening volumes. It's more than even the highest quality vinyl ever had. High bit depth is mostly useful so you've got some headroom during editing.

16 bits give you 96 dB SNR only if your signal is one-bit. In a quiet room with decent headphones set to comfortable level I can easily hear one-bit flips in otherwise silent WAV file. Not a problem for popular music that's consistently loud, but a real problem for classical music with wide dynamic range.

I tried it and I couldn't hear it. Are you sure you got the endianness right and it was really a least significant bit?

Re: Build Your Own Professional-Grade Audio Amp on the Sort-Of Cheap

#234

Post by [deleted] » Thu, Nov 01, 2018, 6:02 PM UTC

beat wrote: post #215

Tsiklon wrote: post #194

Earlier quoted context omitted.

I like to look on high end headphones as I would any other luxury item - I'm willing to pay for nice materials of a higher quality or a better experience, if the item is right. That could perhaps explain some of the price - plus I think we're at the point where many of the headphone companies have discovered that there is an ultra-high end market for some of these products. You can see this in the prices of many top…

Some people understand the law of diminishing returns, but have the resources to not care. If a $2000 pair of headphones is no more real financial pain for you than a $200 pair, and they're better despite diminishing returns, then why not get them?

[deleted]

Re: Build Your Own Professional-Grade Audio Amp on the Sort-Of Cheap

#235

Post by beat » Thu, Nov 01, 2018, 6:02 PM UTC

rectang wrote: post #230

beat wrote: post #217

Earlier quoted context omitted.

I feel your pain. I produce and mix records - at an amateur level, but enough to get quite good at it. It makes me want to toss all this "objective", "measurable" bullshit from the skeptics right out the window - the subjective experience is all that matters. But it also makes me want to toss the audiophile voodoo out the same window. "Accurate" reproduction? I just want to show them how records are mixed. My pet exa…

I agree that your high-pass filters are an application of masking principles. It would be challenging, especially for an untrained person but even for someone who is trained, to perceive enabling/disabling of those filters in the context of the full mix. Instead we solo to isolate the track being adjusted so the change is easily audible -- i.e. no longer masked by the other tracks -- and adjust the filtering anticipa…

When I say "objective", it definitely needs air quotes, because the well-meaning skeptics love to toss it around for some decidedly non-objective opinions. My pet example is quoting "THD" as if it were a useful figure. It's not. The advantage of THD isn't that it is meaningful, but rather that it's easy to measure. Run a 1khz sine wave into the front of the amp, tap a resistive load on the back of the amp, measure the difference. Manufacturers like it because it makes for a competitive-sounding spec. But it has approximately zero to do with how an amplifier behaves in the face of complex musical signals, driving complex speaker loads.

When it comes to recording, my "objective" reality is the sound I hear in the room before it ever hits a microphone. But what comes out of the other end of the microphone is already deeply subjective. The objective ability of hi-fi systems to reproduce that subjective, colored microphone signal (plus whatever processing is involved downstream) is about as objective as they get. But the recording itself? Outside the world of purely electronic music, it's a subjective experience.

I play acoustic guitar every day, listen to unamplified singers/musicians (other than me) at least weekly, play electric guitar at least weekly, gig regularly. These direct, objective experiences of the natural sounds of instruments color my interpretation of both magical-thinking audiophiles and pseudo-scientific skeptics. I know intimately what the natural sound is, I know intimately what the recorded/reproduced sound is, and I know how the entire recording process works, from miking to mixing to mastering. Laws and sausages. The audiophiles and skeptics are both missing that perspective.

So, as a recording/mixing engineer, as a producer, I'm looking not to deliver audiophile accuracy, but rather to deliver the intended intellectual and emotional experience of the music. What feeling is the artist trying to convey? How do I manipulate the sonics to emphasize the musician's intent, as expressed through the lyrics, the composition/arrangement, and the natural tones of their instruments? That's the fun part, for me.

(As an aside, I'm currently working on a particular song of my own, destined for my long-delayed solo album. I wrote the song based on a nightmare I had in great distress. A few years back, I suffered an illness that left me nearly unable to speak, much less sing, and my voice is permanently damaged (I have surgery a few times a year on my vocal cords to keep speaking and not die of suffocation). I recorded the song right after writing it, just a couple of weeks before my first surgery, with a near-useless voice. "My broken voice won't fill the air / I know that you don't really care / You may not need my song but I need to sing it anyway". Fitting with the broken voice is the melody repeated on a piano that hasn't been tuned in over 50 years and has been flooded multiple times, so it's, um, colorful. To both the audiophile and objective mindset, neither the voice nor the piano were worth recording at all. But as an artist trying to communicate an emotional experience, they're vital.)

Re: Build Your Own Professional-Grade Audio Amp on the Sort-Of Cheap

#236

Post by blattimwind » Thu, Nov 01, 2018, 6:31 PM UTC

compiler-guy wrote: post #229

blattimwind wrote: post #55

Earlier quoted context omitted.

I guess in technical terms this article is about "making" an amplifier as opposed to "building" an amplifier. "Making" as in "Maker", since the electronics come as pre-made assemblies connected together and put in a case.

"If you wish to make an apple pie from scratch, you must first create the universe." --Carl Sagan

"There are only two colors in the world: black and white." --Ansel Adams

Re: Build Your Own Professional-Grade Audio Amp on the Sort-Of Cheap

#237

Post by [deleted] » Thu, Nov 01, 2018, 6:32 PM UTC

dbrgn wrote: post #98

kazinator wrote: post #71

Earlier quoted context omitted.

If your input is balanced, it will be handled by some op-amp circuit or whatever, which converts to single-ended internal signal, like the "balanced line input module" shown in this page: http://sound.whsites.net/project30a.htm You can easily insert a volume control right after such a stage.

Yeah, but in the context of this article, I'd have to cut some traces on the PCB to get there. Doesn't sound like the ideal solution to me :)

[deleted]

Re: Build Your Own Professional-Grade Audio Amp on the Sort-Of Cheap

#238

Post by pps43 » Thu, Nov 01, 2018, 6:35 PM UTC

mrob wrote: post #233

pps43 wrote: post #219

Earlier quoted context omitted.

16 bits give you 96 dB SNR only if your signal is one-bit. In a quiet room with decent headphones set to comfortable level I can easily hear one-bit flips in otherwise silent WAV file. Not a problem for popular music that's consistently loud, but a real problem for classical music with wide dynamic range.

I tried it and I couldn't hear it. Are you sure you got the endianness right and it was really a least significant bit?

Yes, pretty sure. Had to zoom in a lot in audio editor to even see it. Could hear it nevertheless.

It's important for the room to be quiet, as the sound is very faint and easily masked, but it's there.

It's possible that Bluetooth headphones could lose it because of compression, or cheap DAC in the sound card simply ignores least-significant bits.

Re: Build Your Own Professional-Grade Audio Amp on the Sort-Of Cheap

#239

Post by willtim » Thu, Nov 01, 2018, 6:48 PM UTC

stinos wrote: post #161

willtim wrote: post #36

Earlier quoted context omitted.

Your generalisation is unfair. Most Audiophiles just want to listen to music the way the artists intended. This is not easy in a industry where colouring the sound is even celebrated, e.g. 'Beats by Dre'. I recently tried the latest noise cancelling headphones by Sony (1000XM3). The noise cancelling was excellent, but the bass was +5db overblown, boomy and drowned out most of the mids, the treble was dark to hide the…

The noise cancelling was excellent, but the bass was +5db overblown, boomy and drowned out most of the mids, the treble was dark to hide the NC hiss Had pretty much the exact same experience with some noise-cancelling in-ear pair of Bose. I was actually amazed at how good the noise cancelling was, but sound reproduction even in absence of any outside noise was very sub-par. Now I can't imagine the engineers didn't me…

Yes I'm sure it was done on purpose, just like over-saturated colours on TVs and cameras.

Re: Build Your Own Professional-Grade Audio Amp on the Sort-Of Cheap

#240

Post by kazinator » Thu, Nov 01, 2018, 7:10 PM UTC

dbrgn wrote: post #98

kazinator wrote: post #71

Earlier quoted context omitted.

If your input is balanced, it will be handled by some op-amp circuit or whatever, which converts to single-ended internal signal, like the "balanced line input module" shown in this page: http://sound.whsites.net/project30a.htm You can easily insert a volume control right after such a stage.

Yeah, but in the context of this article, I'd have to cut some traces on the PCB to get there. Doesn't sound like the ideal solution to me :)

Perhaps, perhaps not. The schematics don't seem to be available, but let's imagine there is a stage in there which looks roughly like this:

    |\   C        |\
    | >--||-+-----| > 
    |/      |     |/


If we simply remove/desolder components C and R, we should be able to then install hookup wires for a potentiometer (which includes the C also).It looks like this particular board has tiny SMT components, which make this sort of thing a pain in the but.


    
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