OT: Class D Amplifier Design

Rubbish.

To the speaker circuit, for example, where Z < Zo, it looks like a pure inductance!

The sign of the reactance of the cable depends on circuit impedance.

Both conditions are true for frequencies much lower than 1/4 wavelength (hence ~km).

Most audio *signal* circuits are in the kohms, so you are correct for those cases.

Tim

--
Seven Transistor Labs, LLC 
Electrical Engineering Consultation and Contract Design 
Website: http://seventransistorlabs.com

I would *love* to see a completely digital connector. Can you provide an example?

:)

Tim

--
Seven Transistor Labs, LLC 
Electrical Engineering Consultation and Contract Design 
Website: http://seventransistorlabs.com

3rd harmonic is a perfect 5th.

Note that the diatonic scale does not permit perfect 5ths (i.e., go up two

5ths, down an octave, etc. and come back to the starting point), because there is no integer solution equating the exponents: a^1.5 - b^0.5 = c^(2^(1/12)) (or something like that)

The 5th harmonic is something oddball but okay, also (an octave less a third, or something). 4 and 6 are combinations of two simple ones, so are also okay. 7th is grotesque, and needs to be avoided.

Tim

--
Seven Transistor Labs, LLC 
Electrical Engineering Consultation and Contract Design 
Website: http://seventransistorlabs.com

Depends on the output impedance of the source used.

NT

That's easy. I've sometimes used my finger to connect hum to an audio input. It's 100% digital.

NT

Toslink?

That is of course a very good point, since any "digital" system is basically analog.

A TTL chip is basically analog, but the black box view is digital, so that a logic designer doesn't have to worry about threshold levels (except fan-out) when interconnecting gates.

In a home or stage audio system, the data rates are a few megabits/s and distance at most a few tens of meters, so a data connection using balanced signaling or multimode fibres can handle this with very good signal to noise ratio and very low probability of bit errors, although at least some kind of parity check would be preferable to handle a rare bit error.

The longer cable you use, the more the signal is attenuated and hence signal/noise ratio is dropped.

For a short cable a single bit error at the receiving end might occur once a year, for a long cable, an error might occur every minute or second. A TOSLINK is basically an analog system, the question is, when does the SNR or error rate becomes too bad, making the system unusable.

Depending on instrument and how it is tuned.

For e.g. a guitar this may be true, for pianos not.

So, a 'completely digital connector' is

I don't see how. If you play an E with a B you get a basic E chord. An A fl at makes it major and a G makes it minor. That's IIRC of course, I seem to be forgetting because I don't play music anymore. When I did though I was p retty decent at making up chords. The thing I found is that it is not so mu ch knowing what to play, it is knowing what NOT to play.

I was quite into it for a time and made it a point to play things on both t he guitar and piano. Of course sometimes it is impossible. Also transposing , like I could play "Simple Man" both in A and E but I had to invent a spec ial B chord for it and it actually sounded good. But I got tired of it. Wan na buy a guitar ?

I seem to remember somewhere, and I mean before the internet, a chart that had the 88 keys of a piano with the frequencies the produced. I don't feel like looking it up so I will just capitulate that 3rd and 5th are not so ba d but above that should probably be avoided. Clipping, which eventually bec omes a square wave does not avoid that and that kind of distortion is somet hing I can't stand. Actually I can on an electric guitar, but not on other instruments or integrated program material. Distort the guitars all you wan t but once it is mixed keep it clean on down the line.

Side note, second harmonic distortion can make the voice more intelligible. The human voice has alot of even order distortion when we form the words a nd it is actually an issue in AM broadcasting and to some CB enthusiasts. T hey pay close attention to the polarity of the microphone because the signa l is apparently stronger one way. In AM, if you modulate down to zero I gue ss you are letting noise in or something. I am not sure. If you have a sing le ended amp which has chiefly second harmonic distortion one polarity of t he microphone will sound better than the other. I wonder if the designers o f AM receivers back in the old days paid attention to that or not. Maybe at Grundig in Germany or something, but did they all ? I seriously doubt it.

look at your keyboard while typing. Ah - 10 completely digital connectors!

It either has a S/N that's acceptable, or it doesn't. Either it works, or it doesn't. Sounds binary (digital) to me.

By that argument, there is no such thing as "digital" (kinda making the argument silly). All communications systems have errors.

Or if you go a step further, it's all digital again.

** It's simple fact - pal.

** Did you miss the word "unterminated" in my post ??

Even after I put asterisks at each end ??

You're blind as well as full of bullshit.

** It depends on the termination of the cable.

Open = capacitive & shorted = inductive.

** You over-snipped & misread my post.

You have done this many other times too.

FOAD d*****ad.

.... Phil

Multi-conductor cable! Nice, though the length is pretty short. :-)

Tim

--
Seven Transistor Labs, LLC 
Electrical Engineering Consultation and Contract Design 
Website: http://seventransistorlabs.com

In fact, it is preferred to use current control around the filter inductor. Why? Because current is how the inductor /works/. The state variable is current as a function of time. Trying to discard the current (because you're only ultimately interested in output voltage) merely ignores the fact that the current is still the primary variable. God is notoriously unforgiving of willfull ignorance. ;-)

Al the best SMPS designs are current mode, most often "peak" or "average" modes.

So how do you get constant voltage? Simple, you add an external feedback loop to set it. The inner current loop circuit is simply a transconductance amplifier, with a cutoff frequency somewhat below the switching frequency (because, dynamics matters, and this is a critical parameter). It's a slow, and noisy, transistor stage. Add another stage around that, and apply feedback, and you're golden.

The downside, for audio amplifiers, is the outer loop must necessarily be slower than the inner loop, and so your loop gain -- and therefore output impedance and distortion reduction factor -- are poor at high frequencies.

Tim

--
Seven Transistor Labs, LLC 
Electrical Engineering Consultation and Contract Design 
Website: http://seventransistorlabs.com

The speaker is a current-mode device too. Why do we focus on the eventual output *voltage* then?

Also, current in the voice-coil translates to *velocity* in the cone (because of back-EMF; it's a linear motor). I have a giant disk-drive voice-coil that demonstrates this well...

Of course there are many mechanical dynamic effects also in play, not just air pressure... but the better a speaker is, the more it's about the air, not the cone & magnetics... so...

Fixed velocity does not accelerate any air. The cone must accelerate to affect the local air pressure (to create pressure waves). So we're out-of-whack here too...

Presumably the microphone that recorded the audio has some inverse transfer function that reverses this last one, but it's not at all clear to me that the end-to-end result is a true *reproduction* of the original sound-waves...

Anyhow, I must be talking s**te because it obviously works, but I'd like to hear a reasoned argument that explains *why* conventional audio systems work as well as they seem to.

Clifford Heath.

Depends on the noise peak to average _amplitude_ ratio.

The noise peak amplitude can be _much_ larger than the average level, but that large noise peak might occur only once a minute or once a day, potentially causing individual bit errors.

"Digital" is just an approximation of the real analog world.