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The Korf Blog
The inside story: our research,
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development and opinions
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The Trap of Mental Experiments
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11 November 2025
More Clues from THD
I got a lot of letters over our last article about THD versus alignment. A big thank you to everyone who found time to write!
Let me start with an important clarification: I am neither the first nor the only one who has done those measurements. Many people have done this before me, and all they received in return was the usual scorn from audio forums. No links, you'll find them if you are interested.
Let me start with an important clarification: I am neither the first nor the only one who has done those measurements. Many people have done this before me, and all they received in return was the usual scorn from audio forums. No links, you'll find them if you are interested.
Why the 1970s Measurements Were Different
A few people pointed me to the 1970s spot measurements that seemed to confirm the Löfgren/Baerwald distortion curves. How could that be?
The scattering of spot THD values is immence. Below is a typical raw data recorded by Virtins Multi Instrument software. This explains how making spot rather than continuous measurements can "prove" any theory—Baerwald, Löfgren, Stevenson, you name it. You can draw any curve you want by picking spot measurements out of it.
The scattering of spot THD values is immence. Below is a typical raw data recorded by Virtins Multi Instrument software. This explains how making spot rather than continuous measurements can "prove" any theory—Baerwald, Löfgren, Stevenson, you name it. You can draw any curve you want by picking spot measurements out of it.
Interestingly, the scattering of THD measurements of a record played at 45 RPM (below) is much lower than of 33 RPM one. Same cartridge, same stylus, same 1000 Hz frequency, the other side of the same test record. Any ideas why?
How About Linear Tracking Tonearms?
Here's a small puzzle for your entertainment. One of the lines on the chart below corresponds to a delightful little linear tracker, Technics SL-7. The other, to a pivoting 9" tonearm, Korf TA-SF9R. In both cases, exactly the same stylus was used—original ATN112EP, mounted on very similar Audio Technica bodies. The only difference is, one is P-mount, the other standard 1/2 inch mount.
Can you guess which one is which? Answers on a postcard (or you can just drop me an email).
Can you guess which one is which? Answers on a postcard (or you can just drop me an email).
Correct answer and explanation to follow in the next blog post.
Stylus Dimensions—The Only Thing That Matters?
In our previous post, we have shown the THD chart for a bonded conical stylus. And, of course, everybody went "come on, this is conical, it's being pinched out of the groove, what did you expect?"
Pinched out? By a 1 kHz sinewave, recorded at a pedestrian 0 dB level? Well then, what about a nude conical of the same size? Should be broadly similar, right?
What you see here is the THD of the bonded stylus (0.6 mil) in green, versus JICO Morita nude conical stylus (0.7 mil) in red. Both were inserted into the very same Shure V15III.
Pinched out? By a 1 kHz sinewave, recorded at a pedestrian 0 dB level? Well then, what about a nude conical of the same size? Should be broadly similar, right?
What you see here is the THD of the bonded stylus (0.6 mil) in green, versus JICO Morita nude conical stylus (0.7 mil) in red. Both were inserted into the very same Shure V15III.
Interesting, isn't it? Not only is the THD performance of the JICO conical stylus a lot better than the noname bonded stylus of the same size. It is superior to bonded elliptical, and to some lesser nude elliptical styli too (not shown). Bravo, JICO.
Limits to THD Measurements
And yet THD measurements, at least of the relatively low frequency 1 kHz signal, are seldom a practical solution for cartridge alignment and diagnostics purposes. Why?
First, there's huge scattering that we started today's post with. Taking a 30-second measurement is not enough. We are looking at whole minutes for every measurement. That is too slow to be useful for anything iterative.
Then, there's dust and dirt. Even a tiny speck on the diamond stylus can worsen the THD performance by a factor of 2-3. Dirt-induced THD degradation is persistent and, unless corrected, can last through the whole measurement.
First, there's huge scattering that we started today's post with. Taking a 30-second measurement is not enough. We are looking at whole minutes for every measurement. That is too slow to be useful for anything iterative.
Then, there's dust and dirt. Even a tiny speck on the diamond stylus can worsen the THD performance by a factor of 2-3. Dirt-induced THD degradation is persistent and, unless corrected, can last through the whole measurement.
A phone conversation near the playback rig ruins the measurement
Another thing that surprised me was cellular phone influence. Having a cell phone ring, or having a phone conversation near the playback rig ruins the measurement completely. I haven't done any experiments to prove it, but it feels like the THD recorded in the presence of a cell phone is heavily modulated by its radiation power.
Below is the THD measurement of Ortofon SPU GM E cartridge, made unusable by the mobile phone call in the next room.
Below is the THD measurement of Ortofon SPU GM E cartridge, made unusable by the mobile phone call in the next room.
The phone starts ringing when the stylus is at 125 mm radius, then there's a short conversation that is over by the time the stylus passes 110 mm. Red is the right channel, left is blue.
There's more on the subject of THD that I want to tell you but—next time! And remember, the linear tracker vs pivoting arm puzzle! I am looking forward to your answers.
There's more on the subject of THD that I want to tell you but—next time! And remember, the linear tracker vs pivoting arm puzzle! I am looking forward to your answers.
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