Monday, November 18, 2019

AC noise from elevator

AC noise generated from the building's elevator moving, is quite visible from Chart#2 compared to the baseline Chart#1. The so called "EMI Meter" from Green Wave also reports up to 1000mV of noise compared to the baseline's 46mv. Unfortunately, no AC filter including the one from Green Wave, or even an ISO transformer can block such noise.

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Thursday, November 7, 2019

Tracking Ability of an Old Decca Cartridge

(中文在後)The Decca family of cartridges are often said to have poor tracking ability. In fact, with proper anti-skate force, at least in standard tests they track better than many MC cartridges. But when they mis-track, the distortions are more offensive to ears. Here in the first spectrum chart taken when running a typical tracking test, the old SC4E shows the typical Decca-family behavior of having higher 3rd harmonic distortion which is less pleasant than the 2nd. This is just the opposite of most other cartridges. In the second chart, the SC4E is put through the maximum signal strength of +18dB and it still manages to play through the whole track with manageable distortion levels, better than many MC cartridges.
許多人說 Decca系列唱頭循軌不好。其實如果抗滑設定對,至少在標準循軌測試,會比許多MC唱頭的循軌表現好。主要問題是,它們的三次諧波失真比二次高,這與大多數唱頭相反。耳朵會比較容易聽到奇次失真,所以容易察覺它微小的循軌問題。第1個頻譜圖是正常強度的測試,顯示這典型Decca唱頭的失真行為。第2個圖是用最強的+18dB訊號測試,顯示這個老唱頭還可以相當穩定的唱完,而且整體失真還不差,不像一些MC唱頭會出現很不堪的波型。

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