Originally Posted by jcx
Engineering principles can be used to predict some dimensions of "difference" from data sheet specs of differing op amps or tubes - in the case of op amps there are many that should give indistinguishable performance by known psychoacoustic thresholds - I heavily discount the op amp rolling subjective difference reports - most are given in the relative frequency response terminology that strongly suggests lack of level matching - "identical" systems heard at slightly different volumes sound different due to Fletcher-Munson loudness curves - way below the differences that are clearly perceived as loudness changes
I agree that opamps should all sound the same, but dont agree that they do.
I think that this is because very few people use inverting topologies. The good lord came down and told us that non-inverting was the way to do it so that the signal remains in polarity because thats another thing people can hear (not really, but its a common audiophile belief)
Anyways, unless the non-inverting opamp is driven from a 0-ohm source impedance imagineering is about as good as the datasheet the MFR published for various specs. The volume control screws it all up.
Inverting topologies have to deal with the fact that they are inverting (and that matters ) before people will start to look at the (generally) superior performance.
On the OP's other q, regarding tubes: several people have tested a wide selection of tubes for THD, noise, etc. Assuming you have the same buffer you could plug that into there... Try diyaudio for sources.
Originally Posted by Uncle Erik
Interestingly, a client at the office is a cable manufacturer. Not audio stuff, but high power transmission lines and industrial applications. I've had an opportunity to look through some of their work. They very much do use measurements and science to develop cables. All the stuff tha skeptics call for here. Their work is legitimate and they seem to make an excellent product. I can't say more because it's privileged, but it is a good company.
Which leads to an interesting question. If cables can be measured and scientifically developed for certain applications, why do those same methods fail miserably for audio cables?
Audio cables dont behave as transmission lines at the lengths commonly used. the number I have heard is ~4000ft for an audio cable to start to act like a T-line. Good T-line design is extremely important in RF and long distance power transmission lines, where it can mean HUGE differences in system efficiency, but means very little in audio.
The reasons that measurements fail for audio cables is that the start of every cable DBT is an electronic (call it the machine) test to verify similarity without the use of a human.
As has been mentioned elsewhere the threshold of human hearing is only so high, and within certain tolerances the ear is not able to distinguish 2 pieces of gear.
If anyone were foolish enough to run a DBT without the preceding control it would be quite easy to pass using several methods.
Here is a recipe for an easy cable to make that will DBT differently from your standard straight wire:
VERY high capacitance cable (200pf/ft, 6ft long... This would be very easy to make with off-the-shelf starquad) with a 100Kohm source resistor in the "upstream" plug.
If you want to go all technical on me and argue against the 100Kohm resistor, I'l cede defeat on the condition that the cables be driven from the plate of a 12AX7. Some audiophiles consider that appropriate... so lets do it!
Is the cable I described "better"? maybe some will prefer it (I might even prefer it based on my EQ settings!) , but 2 seconds with a resistance meter or oscilloscope and a function generator will identify it as reallllllly obviously different.
Edited by nikongod - 11/28/10 at 9:24am