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

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

#261

Post by Junk_Collector »

AnthonBerg wrote: post #231
ballooney wrote: post #221

Earlier quoted context omitted.

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…

I think you are confused. To get a linear amplifier, you operate your output transistors in a state of Saturation. This gives a linear transfer function to the drain based on the Gate to source voltage and you use a method of choice to hold the source constant. This is what a class A amplifier does. An AB amplifier has 2 transistors to extended the range of inputs on the gate for which the output is linear at the cost some distortion when switching between the A and B (hi and low side) transistors.

A class D amplifier uses a smaller amplifier internally (which can be a single transistor or more complicated) that is driven open loop so that it is either hard off or hard on but very fast and efficient. The hard on state is known as full compression because the output power will not change with input power. This is purely non-linear behavior and can be very easily verified by measuring the high IMD components it generates. Class D amplifiers employ significant filtering to suppress these non-linear terms and allow you to recover the signal. Mathematically, they violate the linearity condition of F(ax) = aF(x)

Also you should reread the article you learned from. It directly contradicts you.

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

#262

Post by AnthonBerg »

Junk_Collector wrote: post #261
AnthonBerg wrote: post #231

Earlier quoted context omitted.

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…

I think you are confused. To get a linear amplifier, you operate your output transistors in a state of Saturation. This gives a linear transfer function to the drain based on the Gate to source voltage and you use a method of choice to hold the source constant. This is what a class A amplifier does. An AB amplifier has 2 transistors to extended the range of inputs on the gate for which the output is linear at the cos…

It’s not about me; The “you”-ing is incredibly offputting.

We are simply and obviously applying the word “linear” a little differently. I am aware that it is a specific term for certain behavior / a certain operating mode of transistors. I’m referring to it in another wider context on purpose. As another example “linear” in “linear algebra” isn’t about saturation or gates. I’ve gone through this before in this thread and believe my perspective is now pretty complete and clear here and won’t engage further.

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

#263

Post by rubatuga »

archi42 wrote: post #183
rubatuga wrote: post #33

If you just want the amp without building it, you can get a TPA3116 Class D amplifier. It is only $21 USD from aliexpress (with free shipping of course!). It accepts a supply voltage of up to 24V meaning that you can just dig around for your old laptop power supply (19V). It comes with a nice and sleek aluminum case, and has low enough noise floor that I can't detect it at all unless my ear is right up against the sp…

Oh, that one looks neat. I've got another Ali module with integrated Bluetooth for use in my study room. Theoretically the parts have decent specs, but the module has a high noise level and the speaker makes a loud popping sound with a lot of movement on power on :( Maybe I'll replace it with the amp you linked :)

Yes, you definitely don't want a bluetooth combo. Also, you don't want to buy the 100W version that combines two TPA3116 chips. These models are using a special sync pin/line, but when I bought this model, the manufacturers screwed up the design, it doesn't sync properly, and it's super noisy.

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

#264

Post by sjwright »

egeozcan wrote: post #200
S_A_P wrote: post #179

Earlier quoted context omitted.

You’re absolutely right about that. I didn’t even mention how all of the drywall was replaced strategically with acoustic wall board. The entirety of the living room was gutted and refurbished to be the ultimate listening room, complete with stadium seating. Another recollection I just had is that he had a separate electric circuit run to the house(as in a second set of wires coming off the utility pole) so he could…

> Another recollection I just had is that he had a separate electric circuit run to the house(as in a second set of wires coming off the utility pole) so he could properly condition the power feeding his audio gear In my limited experience, "clean power" (I know nil about this so I'm just repeating what I hear) was the most important difference people would "hear". My uncle used to have a Hi-Fi shop and I helped him…

And yet such impressions conflict with how power supply circuits work and how THD measurement works. Wall power is incredibly noisy and there’s nothing much an electrician can do to change that. If this noise had any meaningful effect on the sound—it doesn’t—you would be able to measure it as a variance in THD.

(Now of course that might be less true for some poorly made vinyl/phono level equipment but if you actually cared about audible distortions you wouldn't be listening to the sound of a needle scratching its way across a fragile plastic groove in the first place...)

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

#265

Post by sjwright »

nerdponx wrote: post #195
sjwright wrote: post #143

Earlier quoted context omitted.

The three critical paths for high end sound reproduction are: loudspeakers, speaker placement, room acoustics. Of course all parts of sound reproduction matter, but those three are the ones that affect real systems in practice. Most other factors are rarely an issue and/or inferior parts have a much lower magnitude of impact on sound quality. Sufficiently good source material (256kbps AAC or better) is widely availab…

Apparently the iPhone 6 has a surprisingly high-quality DAC: https://www.computeraudiophile.com/forums/topic/22843-how-do...

They all do. The idea of bad quality DACs is mostly FUD. That’s not to say that there aren’t bad ones, but the impact on the sound is rarely anything other than its self-noise floor.

That thread contains little to no evidentiary merit and a boatload of technical ignorance.

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

#266

Post by egeozcan »

sjwright wrote: post #264
egeozcan wrote: post #200

Earlier quoted context omitted.

> Another recollection I just had is that he had a separate electric circuit run to the house(as in a second set of wires coming off the utility pole) so he could properly condition the power feeding his audio gear In my limited experience, "clean power" (I know nil about this so I'm just repeating what I hear) was the most important difference people would "hear". My uncle used to have a Hi-Fi shop and I helped him…

And yet such impressions conflict with how power supply circuits work and how THD measurement works. Wall power is incredibly noisy and there’s nothing much an electrician can do to change that. If this noise had any meaningful effect on the sound—it doesn’t—you would be able to measure it as a variance in THD. (Now of course that might be less true for some poorly made vinyl/phono level equipment but if you actually…

Maybe then it was because of the isolation that the audio cables got being away from all the chaos created by the random power cables. I don't know. Most of the time, it was a huge improvement. The next step was to fix/remove anything that caused distortions.

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

#267

Post by airbreather »

egeozcan wrote: post #200
S_A_P wrote: post #179

Earlier quoted context omitted.

You’re absolutely right about that. I didn’t even mention how all of the drywall was replaced strategically with acoustic wall board. The entirety of the living room was gutted and refurbished to be the ultimate listening room, complete with stadium seating. Another recollection I just had is that he had a separate electric circuit run to the house(as in a second set of wires coming off the utility pole) so he could…

> Another recollection I just had is that he had a separate electric circuit run to the house(as in a second set of wires coming off the utility pole) so he could properly condition the power feeding his audio gear In my limited experience, "clean power" (I know nil about this so I'm just repeating what I hear) was the most important difference people would "hear". My uncle used to have a Hi-Fi shop and I helped him…

Would have been way better off with a bunch of car batteries, the internal resistance and cold cranking amps would have pissed on any utility supply regulation and power supply regardless of the capacitors he had.

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

#268

Post by airbreather »

beat wrote: post #213
setquk wrote: post #163

Earlier quoted context omitted.

I’ve heard such things. Two points to note: 1. Decent monitor headphones or speakers sound the same. That’s under $500. Even some Sennheiser HD25’s are literally up there. 2. The equipment used to record such music cost less and was lower quality. Adding $500k doesn’t add anything because there isn’t anything there. Then again I have no problem with people who spend $500k on audio kit. That’s up to them. If it makes…

The original directional cables, sans mythology, are a real thing. Grounding for cable shielding matters a lot, and is plainly audible in many circumstances. "Directional" cables only ground the shield at one end, preventing ground loops and interference from grounding both ends. This is electronics 101. An interesting aside on cables... I play electric guitar a lot, which is far more sensitive to cables than hi-fi g…

The point that most people miss is it is not the cable, it is the connection, copper oxide is a rectifier (diode) and if you put it in the circuit it erodes the quality pretty quickly.

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

#269

Post by airbreather »

beat wrote: post #218
taejo wrote: post #43

Earlier quoted context omitted.

While there are endless debates about manipulation , when it comes to actual capturing of images, the photographic community (in my experience) has a healthy dose of "the best camera is the one you're carrying" and "a great photographer can take great photographs with any camera but even a great camera won't help a lousy photographer take great photographs" to go with its love of gear (who can help but love gear?)

Camera nerds are the worst. They're worse than audiophiles, if that's possible. Good photography requires nothing more than a bit of reason and observable standard practice, applied to aesthetics. You don't have to look hard to find someone with a $5000 camera/lens combo who doesn't know what the Rule of Thirds is or how to apply it. Last weekend, I was in DC, and snapping pictures of the Washington Monument on my ph…

Girl at work has 20k camera with 100k megapixels, but then again Huawei just asked to use her pics for their phone screen savers, so...
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