C’mon folks, apply a little critical reading and thinking skills. Read and see what is clearly between the lines. While I had always admired Ralph and thanked him for his participation here (though disagreeing with his continued insistence that higher cartridge loading is always best unless RFI interferes and that correspondingly, RFI is the chief factor upon which cartridge loading should be chosen), there is clearly a theme here towards promotion of his Class D amps. I have to wonder how a customer of Atma-Sphere who just paid 20K+ for a pair of the MA-1’s a month ago must feel when it’s principal proclaims his own product to be by nature inferior to his new solid state alternative.
And I am also surprised and even angry at myself to only now notice that Ralph is so reliant upon that which can be measured.
:) Critical thinking. I like that: far too little of that going on these days; people have taught themselves to disable their critical thinking. Dietrich Bonhoeffer wrote an interesting paper (which later got him killed) regarding this topic.
Some loudspeakers are not meant to be driven by an amplifier that behaves as a voltage source. ESLs are a good example. For those, tube amps remain the more viable alternative (and just for the record, the last set of MA-1s, which did ship about a month ago, are in use with a set of Sound Labs; something our class D simply can’t make the power to drive because of the impedance. So to my understanding, he feels pretty good.)
Regarding the cartridge RFI thing, that’s easy enough to demonstrate:
http://www.hagtech.com/loading.html
If you have a one meter phono cable, 20pf/foot is typical. find the inductance value of your LOMC cartridge and drop the values into the calculator. You’ll find that the resonant peak is in the RF range. This calculator is based on simple math that comes from electronics 101 in the first week.
Regarding our Class D amplifier, you brought that up, not me. Again, I was addressing the original question, which, again, the answer is that there are semiconductor devices now that didn’t exist 25 years ago, allowing designers to build amps that are actually successful at getting rid of audible distortion (harshness and brightness being an example that might measure quite low on the bench), whereas prior to that time, getting rid of harshness in solid state amps was done with a simple technique called ’lying’.
That lying is why for the last 60 years audiophiles have had to take equipment home to find out if it sounded OK in their system. Its going to take a while to overcome that learned behavior! the first and hardest thing will be to convince people this is all real. As audiophiles we’ve been lied to for so long we take it as rote.
Regarding measurements: One of the problems that many audiophiles have is that the spec sheet seems counterintuitive; amps with lower distortion often sound worse than those with significantly higher distortion. This is because the ear is sensitive to higher ordered harmonics and the harmonics are not ’weighted’ on spec sheets (and the amps with higher distortion are often tube amps with a lot of 2nd and 3rd harmonic). Amps with low distortion figures often have unmasked higher ordered harmonic content at low levels, but the ear is keenly sensitive to these harmonics as it uses them to sense sound pressure, so has a 130dB range to support!
But we can measure what’s important! And reliably predict what the amp will sound like based on those measurements. However most of these measurements rarely if ever show up on spec sheets. Here they are:
1) distortion vs frequency. If rising at all past 1KHz, expect brightness; I explained why earlier.
2) distortion spectra. To mask distortion you have two avenues, either get the distortion product well below -100dB or mask the higher orders with a more prodigious 2nd or 3rd harmonic. SETs use the 2nd harmonic, our OTLs use the 3rd. The distortion spectra should remain consistent at all frequencies, not just 100Hz or 1KHz! FWIW zero feedback tube amps can do this last bit quite well.
3) distortion spectra at -6dB of full power (you never see this one). It should be consistent with the 1 Watt spectra. SETs often fail this test; higher ordered harmonics appear in their output at this level (usually on transients) causing the amplifier to sound ’dynamic’. I’ve found that when audiophiles discuss ’dynamics’, for at least 80% of the time, the word ’distortion’ can be substituted for ’dynamics’ without changing the meaning of the conversation.
If the amplifier is well behaved in these regards it will sound smooth and musical; the lower the distortion the more transparent the amp will be because distortion obscures detail. This is why I don’t like SETs because they often have several orders of magnitude more distortion, causing them to lack detail. Detail does not have to be associated with brightness although it often is because typical solid state amps that are low in distortion are often bright and harsh, although they are at the same time more detailed. You know you’re making progress when the sound is smoother and more detailed both at the same time!
Measurements are really really helpful if the designer understands the how the ear perceives distortion. IOW you can design the amp to work with the human ear rather than to look good on paper; if you really know what you’re doing you can achieve both!
