Tracking Tests on the ELP Laser Turntable

An ELP uses laser beams to pick up the signals (no digitization!) without physically touching the groove surface. One may think the distortion level would be much lower than using a stylus since there's no friction involved, and there would be no tracking issue at all. However, in reality there are other factors involved and the test results could be somewhat unexpected.

Using the eight tracking tests on the Hi-Fi News test record, the results are shown below. Some key observations:

1) Harmonic distortions, especially the 2nd and 3rd-order, are still quite visible on the spectrum analyzer, mostly similar to the case of using a regular stereo cartridge.

2) The strongest test signal in Test#4 leads to very high distortion, as can be seen in the deformed sine wave form. This level of distortion is in fact worse than some of the better tracking cartridges. But the good thing is, there's no skipping like in some cartridges' case.

3) From Test#3 to Test#4, the distortion level increases drastically, even though the difference in signal strength is only 2dB higher. Seems like somewhere between +16 to +18 dB, the threshold of the ELP's tracking capability has been crossed.

4) Tests#5, 6 and 7 corresponds to outer, middle and inner part of the record surface, respectively. The difference among them is smaller than most cartridges, showing the lack of side force interference is an advantage for the ELP.

5) Some unusual spikes in the spectrum are likely from dust particles on the record surface. The ELP cannot push away dirt in the groove like a stylus.


用 ELP 播放 Hi-Fi News 測試唱片的8個循軌測試軌，目前的觀察：

1) 播放時諧波失真也是普遍存在，所以這些失真的來源並非因唱針與溝槽摩擦而產生。觀察 TESTS＃1到4，比起抗滑/側向力調整得好的唱頭/唱臂，失真率並沒有較低。

2）強度高的訊號如 TEST＃4，ELP 也是會有嚴重失真，可見內部的雷射換能機構還是有遲緩的弱點。但優點是完全不會有跳針現象，而且左右波型都還相當平衡。

3）從 TEST＃3 到 ＃4，失真的差異很大，猜測是剛好超跨過了 ELP 循軌能力的 threshold。

4）從 TESTS＃5，6，與7看來，內外圈的差異相當小，較一般支點臂 consistent。

5）頻譜裡有些奇怪的雜訊，應該是唱片表面灰塵造成雷射的反應，判讀時應該將之忽略。

TEST＃1

＃2

＃3

＃4

＃5

＃6

＃7

＃8