Pass Labs A 類後級放大器 XA25

wildmanhk

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Pass Labs 推出全新純 A 類後級放大器 XA25

來自美國的 Pass Labs，由業界傳奇人物 Nelson Pass 於 1991 年創立，並於 1992 年推出 Aleph 0 ，在市場上得到極大的好評及迴響，尊定了讓廠在純 A 類放大器市場上的地位。這次 PASS LABS 宣布，即將推出純 A 類放大器 XA25，價格約為 USD$4995 美元。

PASS LABS 自 X 系列以來，器材取名十分直接，如 XA 系列後的 A 便代表 A類放大，而機身型號的數字便是輸出的功率，這次推出的 XA25，表明了放大器的功率，為純 A 類 2ch x 25W / 8ohms，當 4ohms 時則為 50W，並在 2ohms 負載時輸出可達 100WA / AB 類輸出。

XA25 除了提供資真價實的 25W A 類輸出外，它的峰值電流為 10A，而阻尼系數為 200，意味具備良好的喇叭控制能力，廠方更致力簡化信號路徑，同時採用經典的“CFA”電壓增益電路，讓放大器獲得低訊噪及高速度等優點。

Pass Labs 創辦人 Nelson Pass 對 A 類放大情有獨鍾，雖然廠商亦有推出 AB 類的放大以迎合市場需要，但設計 A 類放大才是他本人的拿手好戲。XA25 可說成功延續廠方在 A 類放大上的技術及成就，所得出優質的純 A 類  25W 輸出。

詳細規格：
Output power : 2 x 25 Watts Class A @ 8 ohms, 2 x 50 Watts Class A @ 4 ohms, 2 x 100 Watts Class A/AB @ 2 ohms
Distortion : 0.1% @ 25 Watts, 8 ohm, 1 KHz, 0.1% @ 50 Watts, 4 ohms, 1 KHz
Freq. Response : DC to -3 dB @ 200 KHz
Gain : 20 dB gain
Noise : Output 100 uV unweighted 20 to 20 KHz
Damping Factor : 200
Slew : 100 V/uS
Input Impedance : 47 Kohm
Peak Current : 10 Amp output (200 Watts into 2 ohms)
Independent of loudspeaker load phase.
Idle Power draw : 200 Watts total.
Dimensions : 17”W x 17.375”D x 6”H
Weight : approx. 55 lbs

資料來源：https://passlabs.com/amplifier/xa25

sgb

Nelson says the Xa-25 embodies all these attributes and less, and in Nelson-esq that really is an impressive accolade to bestow upon a product.

The lower power application allows for an elegantly simpler "singe ended" front end, with fewer parts in the signal path, improving both speed and stability. The Xa-25 is stable into very low impedance's as well as reactive loads.

The circuit operates with less feedback, deeper into class A. with enhanced thermal stability. There are no DC servos or frequency compensation anywhere in circuit; design details that are strictly in service of the listening experience.

Where the Xa-25 really deviates from our larger wattage amps is the output stage, itself. Rather than requiring many parallel devices, each channel has a single robust industrial FET rated for 700W and 40A of current. This singe device allowing for a direct couple to the speaker without any bias resistors, for the lowest possible distortion figures and the highest possible damping factor. The result is dynamic impact and contrast well beyond what the 25W rating would suggest.

In a world where great specs are often followed by dry and boring, the Xa-25 breathes new life into music. But having said that, it's metrics are pretty stunning, too.

2 X 25 Watts Class A into 8 ohms at 0.1% THD + noise
2 X 50 Watts Class A into 4 ohms at 0.1% THD + noise
At lower wattage output levels the figures are better still, significantly!

Input impedance 47k-ohm
Bandwidth DC to -3dB @ 200 kHz
Gain 20 dB
Damping factor 200
Idle current 200 Watts

Physical size approx 17" x 17" x 6"
weight approx 55 lbs

Projected MSRP of $4995

Courtesy of the post in AudioShark in Dec 2016

It appears to me that Mr Pass has finally put some First Watt-ness into his more commercial designs!

I wonder how much different sonically when compared to the similar XA30.8.

racewong

sgb 發表於 2017-3-4 10:29
Nelson says the Xa-25 embodies all these attributes and less, and in Nelson-esq that really is an im ...

我都係鐘意FIRST WATT.

timmywan

細細部幾靚仔

mahi

2ohm時足100火，這部機足料！加上極簡單結構，有期待

xlarge

靚仔

ccli1996

Spec裡標示2ohm時，係以"A/AB"類工作，功率輸出上，所以唔算叫做足晒料，不過實際應用情況，會用到部得25W/8ohm輸出嘅A類Amp，去推到2ohm嘅喇叭，都唔會係普遍情況掛！

dannyluo

严格来讲是AB类！

racewong

ccli1996 發表於 2017-3-5 09:27
Spec裡標示2ohm時，係以"A/AB"類工作，功率輸出上，所以唔算叫做足晒料，不過實際應用情況，會用到部得25W/ ...

我對屏風咪得囉

ccli1996

racewong 發表於 2017-3-7 12:52
我對屏風咪得囉

板主，正常我諗你係唔會用部得25W嘅Amp去推你對屏風囉！純粹試下會係咩效果就有可能

racewong

ccli1996 發表於 2017-3-7 15:04
板主，正常我諗你係唔會用部得25W嘅Amp去推你對屏風囉！純粹試下會係咩效果就有可能 ...

推對D7相信會正路好多

wildmanhk

racewong 發表於 2017-3-7 15:08
推對D7相信會正路好多

仲未賣喇

racewong

wildmanhk 發表於 2017-3-7 22:17
仲未賣喇

未喎! 我都不知幾滿意

happy_teacher

板主，攪場XA25推對D7/D9派對?

AS881

唔明已有XA30.8, 出多部25 class A 有咩唔同

sgb

AS881 發表於 2017-3-8 10:38
唔明已有XA30.8, 出多部25 class A 有咩唔同

Where the Xa-25 really deviates from our larger wattage amps is the output stage, itself. Rather than requiring many parallel devices, each channel has a single robust industrial FET rated for 700W and 40A of current. This singe device allowing for a direct couple to the speaker without any bias resistors, for the lowest possible distortion figures and the highest possible damping factor. The result is dynamic impact and contrast well beyond what the 25W rating would suggest.

Less transistors in the signal path, therefore, less manipulation and less distortion.

AS881

So that means the model should be derived from First Watt series, rather than those more commercial Passlab products?

sgb

AS881 發表於 2017-3-8 13:02
So that means the model should be derived from First Watt series, rather than those more commercial  ...

I would say it is more of the First Watt design ethos seeping into Pass Labs products. Which I don't think it is a bad thing at all, Pass Labs products has much more aesthetically pleasing case work when compared to FW.

wildmanhk

sgb 發表於 2017-3-8 13:16
I would say it is more of the First Watt design ethos seeping into Pass Labs products. Which I don ...

Agree

mahi

firstwatt的簡單線路加上passlab的overbuild，好期待