The Perils of Using Tangential Arms -- Follow Up

（中文在後面）
The Perils of Using Tangential Arms -- Follow Up

The owner of the cartridge followed my advice and sent the cartridge to the manufacturer. It has just been returned and, upon inspection, I was shocked to realize how much of the original stylus shank had been worn out (Fig. 1) compared to the newly installed one (Fig. 2). For those "gurus" out there recommending air-bearing arm users tune the air pressure lower to get "fuller bodied" sound, please take a look at the two photos and reconsider your stance on the matter.

Here's the earlier post for reference:
http://bingrungtsai.blogspot.com/…/the-perils-of-using-tang…

唱頭的主人聽了我的建議，將它寄回原廠，現在已經回來了。我在顯微鏡下看了之後才驚嚇地發現，和新的針尖（圖2）對照比較，原先的針尖（圖1）磨損掉的部分，比想像中還大很多。雖然磨損這麼嚴重，當初測試聆聽時，在聽了一個多小時後，才開始察覺到弦樂高頻有些許沙啞感，而且這還是因為我累積了一些這方面的聽感經驗，才會開始懷疑。所以除非用顯微鏡定期檢查，多數人對所用的針尖已經磨損，都很少察覺。而建議將氣浮臂的氣壓調低來得到比較「厚聲」的「達人」們，在看了這兩張照片後，是否要重新考量一下？

先前的背景資料：
http://bingrungtsai.blogspot.com/…/the-perils-of-using-tang…

Instrument-Based Method to Troubleshoot Hum

For years I've been advocating using instruments to aide troubleshooting hum issues, especially in vinyl playback systems. Due the diversity of component designs/implementations, the hum may be from the most unexpected causes/sources, and very often the resolution can only be found by trial-and-errors and step-by-step reductions before reaching the best outcome. Here's another recent example in my system.

After replacing the stock PSU for iPhono2 with a beefed up Acopian unit, I am quite happy with the sonic improvement, but when standing close to the speakers I can hear some humming, more prominent than my other phono stages such as the Avid Pulsare II. Even though no one can hear it at the listening position, I know the issue has to be addressed to reach optimal sonic performance, because the hum is just an indicator of how easily all kinds of unwanted noise can get into the system.

This morning I hooked up the measurement setup, and after trying out various grounding connections, I finally found the solution. Again, the best configuration is quite unexpected, and may not work at all in another system.

Before:

After:

Turns out in the case, it's best NOT to ground the Acopian PSU and the iPhono2 chasis. Using the relative scale, one can easily see the reduction in each step.

Both grounded, the 60Hz component is set as 0dB: 

Disconnecting the ground wire on the Acopian PSU gets about -7dB:

Disconnecting the iPhono2 chassis ground gets roughly another -2dB: