Tuesday, May 1, 2018

"Powerful Bass" of Phono Stages?

When some people/reviewers commented certain phono stage has "powerful bass", it's better to take it with a grain of salt. Unlike pre-amps or power amps which do not have any EQ circuit in their signal paths, a phono stage has a reverse-RIAA EQ built in. And some designers will "cheat" a little by tweaking the EQ curve to achieve the desired "sound" for the device. So when we find a phono stage to have very impressive bass performance, it's likely not from the superior circuit design or strong power supply unit, just a trick of modifying the EQ. 

The three phono stages tested below are all priced at the ~8000 USD range. Using the same cartridge Lyra Kleos (without changing any parameters) to feed the test signal, I measured the high-frequency responses to be virtually identical. Whereas below 5kHz, the 2nd and 3rd devices obviously display higher output levels, ranging from a couple of dB to the extreme case of nearly 5 dB at the lowest end of the spectrum.

Incidentally, the first two are UK brands, and the 3rd one from the USA. In my experience, phono stages made by the US-based brands tend to have boosted bass responses similar to the 3rd device.

前後級擴大機沒有等化線路,而唱頭放大就必須有「反」RIAA等化。低頻很厲害的唱放,其實可能只是在等化曲線上做了些手腳,並非它的線路或電源部分有多特別。如下面3個圖的比較,用同一個唱頭不改變任何參數,得到的高頻響應幾乎完全相同。但 5kHz以下的,就開始出現明顯的差異。這3台的美金定價都在8000左右,前2台是英國牌子,第3台是美國的。

No comments:

Post a Comment