Secrets Q & A
- Written by John E. Johnson, Jr.
- Published on 02 October 2009
Part 7: THD+N Test Results
OK, so now that we have all the preliminary discussion in place, let's do some measuring.
For these initial tests, I used a McIntosh MCD201 SACD/CD player, McIntosh MT10 Turntable with factory cartridge (made by Clearaudio), and a Manley Steelhead phono stage. I connected the analog output of the MCD201 and the Manley Steelhead directly to our Audio Precision SYS-2122 analytical instrument. I used a CD with test tones recorded at - 5dB and a test LP called the Ultimate Analogue Test LP.
To start, I used 1 kHz sine waves.
Here is a graph of the spectrum generated from the test CD. THD+N was 0.005%. That is very low and very good. Notice that the one distortion peak visible is third order.
At 10 kHz, distortion rose to 0.01%. Again, the one visible peak is third order.
And . . . (drum roll) . . . here is what you have been waiting for: The Vinyl Results.
At 1 kHz, 0 dB, distortion was 7%. "Wow, that's a lot of distortion," you say. You bet it is, but notice that it is nearly all second order. Also, the noise level contributes to this high number. At best, the noise is 70 dB below the signal, whereas with the CD test, it is more than 100 dB lower. We could measure just the THD, but much of the harmonics are buried in the noise, so this would not be a fair estimation of the resulting sound.
For this particular graph, I set the "load" for the cartridge at 25 ohms.
Here is the same test, but with the cartridge load set to 400 ohms. THD+N went up a bit, but in this case, I think the distortion peaks were a bit higher, while the noise floor improved. This is why seeing the spectrum is so important. The numbers indicate the overall sum of everything, while the graph shows you where the numbers are coming from. Notice that the primary distortion peak is second order.
For 10 kHz, I kept the 400 ohm cartridge load. THD+N was a very high 20%, but again, the noise level contributes significantly to the number. Notice that the only visible distortion peak is second order.
So, what can we say at this point? It seems to me - and this is with some of the very best hi-fi components in the world - that one of the most significant reasons vinyl aficionados love the LP sound is that the distortion is very, very much like that in Pure Class A triode single-ended tube amplifiers. There is a lot of distortion, but it is virtually all second order (even-ordered), which is euphonic, meaning that it is pleasing to the ears. Now, keep in mind that the distortion seen here for the CD is from a superb CD player. If you look at various lower cost CD player reviews out there, you will see more higher order distortion peaks, with odd-ordered peaks closer in level to the even-ordered peaks. Bottom line is that CD has much less distortion, but more of it is odd-ordered, while vinyl has more distortion, but it is euphonic second order.