some Ted Denney censored words of wisdom he didnn’t wan’t you to read:
atmasphere
10,090 postsA lot of what engineers have labeled as "distortion" is actually rich, full sound.
@jmkrajnik They are usually correct on that matter- ’full, rich sound’ is often caused by a 2nd harmonic, and that is the tonality that the ear assigns to it.
Really? 99% of ‘cases?’ What cases?
Most amps made today are not high end amps so that number is probably pretty close!
The distortion signature is the ’sonic signature’ of any amplifier. If the amp sounds ’thin and dry’, its likely because the 2nd and 3rd harmonics are suppressed, allowing the higher ordered harmonics to be unmasked, IOW audible to the ear; this despite an otherwise very low THD.
Distortion is inescapable. Whether the designer recognizes the significance of that fact is a different matter. The ear uses the higher ordered harmonic to sense sound pressure, and so its keenly sensitive to them as well- and this is also inescapable and also often ignored- witness the last 60 years of bright and harsh solid state amps.
Since distortion is a fact of life, the pragmatic designer will design a circuit which makes the least objectionable distortions- and that will be the 2nd and 3rd harmonics, which is why tube amps often sound smoother and more detailed (in a way that I don’t yet understand, somehow the 2nd and 3rd harmonics assist the ear in winnowing out detail, quite unlike the higher orders) than 99% of all amps out there.
The obvious implication is, if you want a solid state amp or if you want an amp that is significantly lower distortion but is still musically involving, the amp will have to have a distortion signature similar to a tube amplifier while at the same time being considerable lower overall. This means that the lower ordered harmonics will still have to predominate, allowing the higher ordered harmonics to be masked.
IF the amp has a distortion signature of this type it won’t matter if its tube or solid state. This stuff does show up in measurements and you can be completely objective about it- if you cause your hand to move to take the measurements in the first place and you have the test equipment to do so. This sort of stuff rarely shows on the spec sheets!
Alternatively if the test equipment is lacking (for example you can measure the THD but you can’t show the various harmonics) the listening is a less accurate method of ascertaining if the design is working.
Here are two things a successful design will need to sound musical:
1) the distortion signature will be consistent from 20Hz to at least 15KHz. If there is insufficient gain bandwidth product to support the needed feedback to conform to this requirement, then no feedback will be used.
To be clear there is nothing wrong with feedback provided enough of it is present (>35dB at all frequencies). The problem with feedback is you need a lot of it and that means you have to have a lot of gain bandwidth product to support it. Most amp designs in the last 60 years simply don’t have enough of either so they sound bright and harsh.
Put another way, in the bass region most solid state amps have plenty of feedback and so play bass rather well. But when you get to 7-10KHz things are different- the feedback is vastly reduced since the gain bandwidth product won’t support it- and so distortion goes up. You can verify this by graphing distortion vs frequency and its plain to see. Most amp manufacturers avoid publishing this sort of thing...
Feedback will by its very nature bifurcate (double) frequencies due to non-linearities at the feedback node. Thus an amp with feedback will have harmonic and inharmonic information (also due to IMD caused by the feedback node) as its noise floor (this is not new information; Norman Crowhurst was writing about this 60 years ago). IF you can apply enough feedback to the design without introducing stability issues (oscillation) then the design can clean up this bit in the process and its all good.
2) the distortion signature will be benign as I’ve already described.
To be sure there are no successful amps out there for which there was no objective testing. They simply don’t exist. There are successful amps out there for which the testing was quite minimal. But there is always some bench testing.
You can see from my comments above that this is all knowable. Whether one has the intention to know it is a vastly different matter! Since 99% of amps are built to make money it follows that the extra attempt to make the amp sound like music (per the distortion characteristics I outlined) will not be taken.
If that intention is there, cost will not be much of a variable. Intention is what drives high end- not cost. So instead of being built to make money, an amp can also be built to sound like music.