A chip-amp to rival Hi-End - design advice

[uncle_leon]

Of course, there is the matter of subjectivity as well.

But I don't agree with your point.

If I say "It is a fact that a trumpet sounds different from a french horn", and someone else says "They both sound the same to me" - it's not the physical differences in instruments that are in question here. It's the inability of one individual to discern a difference which is plainly obvious to another. That does not, in any way, change the fact that a trumpet IS different from a french horn, and DOES sound differently.

The analogy is clear - if one cable is physically different from another, there has to be a difference in their sounds too. Whether one is able to tell that difference is beside the point. (although whether the difference is significant certainly is of interest)

[Steve Eddy]

Originally Posted by uncle_leon

The analogy is clear - if one cable is physically different from another, there has to be a difference in their sounds too.

No, there doesn't.

se

[uncle_leon]

That's a response worthy of a child, not DIY veteran. You can do better than that.

Besides, out of curiosity - what cables are you using? And why? Have you tried using, say, 20m of neatly coiled bell wire instead? Or do you claim that it would make no difference to the sound anyway?

[Steve Eddy]

Originally Posted by uncle_leon

Besides, out of curiosity - what cables are you using? And why? Have you tried using, say, 20m of neatly coiled bell wire instead? Or do you claim that it would make no difference to the sound anyway?

Certainly one can make a cable bad enough as to alter the signal enough to actually be audible. But not every physical difference will be.

se

[jcx]

64 Kb mp3 clips are sufficient for most to distinguish families of musical instruments

we can easily point to harmonic structure in the waveforms - and compare against masking thresholds to predict that most people will hear those differences


but I don't see cable believers trading clips at any high resolution to demonstrate the differences/flavors they hear in reasonable interconnect - seems like a major missed marketing opportunity - can't you just see it: Cu_pvc.wav, Ag_ptfe.wav, Au_cotton.wav...

after all many subjectivists when faced with objective measurements or engineering calculations showing the effects they are ascribing perceived "audible" difference to are way smaller than other errors of similar character in their signal chain resort to claiming they can "listen through" the other defects

right up to the point they decide to flip-flop to "your system isn't resolving enough" - somewhere around when blind test protocols are introduced to the argument



some choose the informed electrical and psychoacoustic engineering based argument that the inevitable differences between any physically distinct systems, in the case of audio interconnect cables, can be orders of magnitude below worst case estimates of human auditory resolution for technically competent interconnects

and await those (so far missing) properly blinded, controlled listening test reports showing cable differences

[abraxalito]

Originally Posted by UnixMan

I know very well that appeal to authority is NOT a proof. Yet, given no other/better option to judge, to whom should I believe?

Since you're asking here - you shouldn't believe any person. You should look at the arguments only and not pay attention to the person making them at all. Paying attention to the person would mean you're giving weight to authority (or lack of it).

So, when you said:

Until someone will do that - not having enough knoledge and skill on the subject to try and judge myself - I'd rather trust more a paper from a well-known and respected audio researcher (and professor) than some unknown, anonymous and vague critics to it. Wouldn't you?

You were obviously paying attention to the persons of Hawksford and jneutron. That's just intellectual laziness. Your knowledge and skill on a subject are your own responsibility - you're free to put in the effort to increase them. The person you were hoping who would help you would help only by showing where Hawksford made mistakes, and jneutron helpfully does indeed do this. Then its for you with your skill and knowledge to decide if he makes errors in his showing.

At the end of the day, its only a person's knowledge and skill which matters. An intellectually lazy person will trust another's statements of authority and not be overly concerned that that person doesn't show why he's right. So learn to discern the difference between 'showing' and 'telling' - the former is art, the latter, propaganda.

[Steve Eddy]

Originally Posted by jcx

plese quit batting around those strawmen - some of us have allergies

Sorry. Bad habit of mi... SQUIRREL!



se

[abraxalito]

Originally Posted by uncle_leon

The analogy is clear - if one cable is physically different from another, there has to be a difference in their sounds too. Whether one is able to tell that difference is beside the point. (although whether the difference is significant certainly is of interest)

Looks to me like your reasoning is flawed. Sound really does mean perception by the ears. If someone hears no difference between cables, then there really is no difference in the sound of the cables. What a person is able to 'tell' about the sounds he or she hears is quite secondary.

So no, not all cables do sound different, even though they may be physically different (and therefore must measure different).

[abraxalito]

Originally Posted by jcx

but I don't see cable believers trading clips at any high resolution to demonstrate the differences/flavors they hear in reasonable interconnect - seems like a major missed marketing opportunity - can't you just see it: Cu_pvc.wav, Ag_ptfe.wav, Au_cotton.wav...

Its a really cool idea, I'd love to capture the differences I hear between cables (hypothesized to be differences in common mode RF levels at the receiver) in a .wav file. Maybe one day I will be able to post these up online

after all many subjectivists when faced with objective measurements or engineering calculations showing the effects they are ascribing perceived "audible" difference to are way smaller than other errors of similar character in their signal chain resort to claiming they can "listen through" the other defects

Yeah, its because the 'defects' are of quite a different form. Just like amplifier defects are quite different in form to speaker ones. But I'm not of the view these (assuming we are indeed talking about the same things) audible defects are small ones - I can hear them when not even in the same room, I hear them with just one speaker powered and listening around the back of it.

right up to the point they decide to flip-flop to "your system isn't resolving enough" - somewhere around when blind test protocols are introduced to the argument

Its true that if a system is already plagued with RF hash, then small differences in CM RF at one stage are going to be swamped.

[gootee]

Originally Posted by uncle_leon

<snipped>

To be honest, I find it a bit hard to comprehend how can RF noise influence the sound anyway... Logical reasoning would suggest that 1Mhz noise will result in distortion at the same frequency (or its harmonics). So how would this degrade the audible range? Especially that RF noise is usually very low level and wouldn't waste any significant amount of amplifier's power (I think?...).

<snipped>

Sorry for turning back to a previous topic. But I don't think it has been covered well-enough in this thread, yet. And it's fairly important.

The main problem with getting RF into an audio amplifier is not the "mixing" or intermodulation between the RF and the audio frequencies, which would just give sum and difference frequencies, which would still be out of the audible range.

The main problem with RF, in lower-frequency circuits in general, is that it gets rectified by every P-N semiconductor junction that it encounters.

That can manifest itself in lots of ways, none of them good (in non-RF circuits, at least).

Here are just a few quasi-examples:

1) In a discrete transistor circuit, or in an integrated circuit, the DC that results from the rectification can change the carefully-designed "DC Operating Point", in transistor sub-circuits. That can de-optimize a whole range of original design parameters (including linear operating ranges, for example) and basically make the circuit work "not quite right", depending on exactly where the RF has an effect. (At an extreme, with strong-enough RF, opamps' and transistor amps' outputs could even be pegged to one of the power rails.)

2) If the RF is simple AM (amplitude modulation), it is basically demodulated by the rectification, and the lower-frequency signal being carried by the AM might get summed with different currents or voltages at various points in a circuit. Sometimes you can even hear radio stations from the output of an audio amplifier that has no RF filtering. But the effects can be weirder, depending on exactly where in a circuit the RF has an effect.

3) RF can come from many sources. Anything that is narrow in the time domain is wide in the frequency domain (and vice versa). So a simple switch being flipped, or a relay closing, or an arc being struck, which would be very short/narrow events in the time domain, can produce a quite broad (in frequency) RF burst. If such an RF burst enters an audio amplifier, and gets rectified by certain P-N junctions, it can temporarily (burstily?) mess up DC operating points, as described above, and can even result in audible pops and cracks.

This is all more-complicated than it sounds, since ICs can have thousands of transistors, with many different purposes, and the effects are probably not usually profound-enough to be overwhelmingly obvious. And it is all compounded by the fact that for RF, everything is an input, and an antenna.

The best thing to do is have RF filters on all inputs, all outputs, and all power inputs/outputs, and also use shielding. It's all mentioned (with circuit filtering and shielding configuration examples) in ADI - Analog Dialogue | Op Amp Applications Handbook (probably mainly in Chapter 7), and in many other places.

Cheers,

Tom Gootee