曰本SUNAUDIO SV-2A3是一部非常有趣的放大器，它配上一對有初級包含2.5Kohm及3.5Kohm阻抗的輸出牛,而電源牛燈絲組亦有0-2.5V-6.3V的抽頭,故此可以改裝去配用不同的輸出功率管如名管45,300B,KT88,及多種歐洲編號的管子如AD1,RE604等,選擇可說是尋出不窮的。

SUNAUDIO SV-2A3 is a very interesting amplifier having a pair of output transformers with 2.5Kohm and 3.5Kohm on the primary, and the power transformer has taps on the filament windings（0-2.5V-6.3V). Therefore it can be modified to suit various types of tubes including the famous 45,300B,KT88 and other european such as AD1, RE604 tubes etc. The possibility is endless if you try hard enough.

我們收到很多朋友的查詢,笞案如下;

1. SUNAUDIOSV-2A3實際上是一部後級放大器,機箱前面有2個音量諷控器用來控制輸入敏惑度,這裹是頗高的(0.15V)而一般是(0.5-1V)。所以我們可以把它當作只有一個輸入的合併機來使用,筒單而音效不錯。但要充分發揮這件小魔怪的美妙還是要配搭上一個高質數的前級放大器。

2. SV-2A3輸出功率只有3.5W,故此它不適用於低效率的喇叭,我們曾配搭及有不錯效果的喇叭包括PROAC Response 1SC (88db) 及 Ensemble PA1 (90db)。Zu 喇叭雖然沒有用過但應該不錯,我們用來鑑聽的 KLIPSCH LA-SCALA (100db)就十分理想了。

3. 升級其實很容易,只要換上舊款新管便成。RCA 2A3使音色更厚潤，甜美及從容;U52整流管改善圓滑度,質惑及兩端伸延;Sylvania 金屬座6SN7增加分折力,動熊及三維空間。

4. 耍把SV-2A3的內部零件升級是不困難的,因為它是搭棚形式的結構,將舊零件銲出換上新的便可,成效如何要待零件運行至少十小時或更長時間才能知曉。最大問題是名貴材料並不保証一定會令音色更好,在這環節上經驗加上一對金耳朵是更重要的。

We received some enquiries from some friends and the answers are as follows:

1.  SUNAUDIO SV-2A3 is practically  a power amplifier with two volume pots on the front to adjust  the input sensitivity which is quite high (0.15V) compare with other standard  amplifiers  (normal 0.5-1V). You can use it as an integrated amplifier with only one input. It is simple and the sound quality is nice. But the beauty of this small monster will only be fully revealed with a good preamplifier.

2.  Since the output of the SV-2A3 is only 3.5W it should not be used on low efficiency speakers. We have good result on speakers such as Proac Response 1 SC and even better on Ensemble PA-1 (90db). We have not tried on Zu speakers but they should perform well. We use Klipsch La Scala speakers (100db) for all our Audition and the performance is just great.

3.  You can upgrade the SV-2A3 by simply changed the tubes with NOS or better quality tubes. The RCA 2A3 will give you warmer, sweeter and relaxing sound.; the U52 rectifier improves smoothness, texture and extension in both ends; a pair of Sylvanian metal base 6SN7 give you more details, dynamics and 3-dimension scale.

4.  You can also upgrade the parts inside the SV-2A3 since all the components are hard wired. It is a simple job to de-solder the original part and replace it with a new one.   However the outcome is quite uncertain until you have all the parts run in for at least  for several hours and sometimes even longer. Sometimes expensive parts do not definitely give good performance. Experience and a good pair of ears play a very         important role here.

 

SV-2A3是Sunaudio成立於八十年代時最初期的產品,但多年來仍然是最暢銷的型號。日本國內已售出超過三仟台的記錄,而本店由二千年至今亦賣出兩佰多台。本機所採用的全部是從日本Tamura特別訂造的火牛,輸出午尤其足料,可承受10W的功率, 電源牛相對上鉄蕊較小,長時間工作會比較燙手,但由於要保持合理的售價,這方面的省却是可以接受的。全機共重約18kg,可以說是相當有份量的制作。

Sunaudio SV-2A3 is the best selling unit since the 80s. More than 3000 units sold in Japan and 200 plus through our shop since 2000. All the transformers of the unit are specially made by Tamura in Japan. The output transformer is quite big in size with 10W output capacity,. The iron core of the power transformer seems small and it is quite warm in prolong use. However it is quite acceptable due to comparatively low price of the unit. The amplifier is quite heavy with a weight of 18kg.

 schematic 線路圖

 

 wiring underneath 底盤下 配線圖

 all components soldered 全部零件銲好

 

從本機線路圖可以看到,輸出由壹支2A3直熱式灯胆担任,功率管採用自動式偏壓,用一支 750ohm的電阻在工作電壓250V(屏極與陰極間),而屏流為60mA的情況下提供一個45V的負偏壓。屏極負荷為2.5K時,本級工作最大輸出(失真不大過10%)為3.5W左右,而在此時所需要的推動電壓是亦是45V左右。推動級由壹支雙三極6SN7負責,第一級電壓放大與第二級推動放大採用直接方式,而推動2A3功率管採用電容交連。由於6SN7放大牽約15~17倍左右,兩級放大近三佰倍,所以規格上的輸入0.15V即有滿幅度的輸出是合理的。本機的輸入靈敏度頗高,實用上可以直接駁往CD機或其他音源而省却前級放大器的運用,但始終使用一件合適的前級會在操作上更多元化及能有更好的音色。零件方面所有火牛由日本TAMURA特別訂制,因為數量大而公司老闆是該公司退休工程師,所以廠方沒因為做價偏低而降低產品的質數,所以購買SUNAUDIO器材是十分超值的。電阻全部採用美國舊庒AB灰阻(出名好聲),陰極25W線繞電阻是日本制造的,高压电容是特別訂造47mfdx2/500V（曰本制造）,其他都是高質數零件。

From the circuit diagram we can see that the output tube 2A3 is configured in auto-bias connection through a 750 ohms resistor at the cathode to ground. At a plate voltage of 250V (anode to cathode) the plate current is about 60mA and the bias voltage is 750×0.060=-45V – and this is the driving voltage required for maximum output. The plate loading (output transformer) is now 2.5Kohm and the output tube gives an output of 3.5W, The 6SN7 tube is used as the driver. It is direct connected in the first and second stage, and the 2A3 tube is coupled to the 6SN7 through a capacitor. Since the amplification of the 6SN7 is about 15-17, the total amplification is nearly 300 times, and therefore the specification of 0.15V (45/17×17) input to give full output is quite reasonable. Due to the high sensitivity of the amplifier CD players can be directly connected without using any preamplifier, but using a preamplifier gives you more flexibility and better sound.

All the transformers are specially ordered from Tamura in Japan. Sine the owner of Sunaudio is a retired engineer from Tamura and each order is considerable, the quality of these transformers are pretty good despite of the comparatively low price, and therefore Sunaudio products are very cost effective. For the components they use AB resistors and 25W wire wound resistor (made in Japan). The high voltage capacitor is a specially made film type 47mfdx2/500V (made in Japan), and all the others are good quality parts.

 

Update 4-July-2016

There are a lot of improvement or upgrades on the new coming SV-2A3. Telfon tube socket made by Yamamoto in Japan is now the standard installation for 2A3 power tubes. The speaker output terminals are now using heavy and sturdy gold plated parts. The hum balance pots are relocated so that you can adjust the hum to a minimum level on the casing top instead of turning the unit up-side down in order to do the job. Bigger holes are cut on the bottom cover to improve air flow from beneath and even the rubber feet are upgraded to those bigger and much better looking anti vibration feet.

是次新貨發現有不少升級及改良之處。首先2A3管座選用了日本Yamamoto制造的鉄氟龍鍍金脚的名貴品種,喇叺座及輸入插座改用重型鍍金系列,交流調校噐亦重新佈位;現在調整臊音可在機頂進行,不需像以前要把機身翻轉了(痛苦)。底板的透氣孔変多了使散熱更好了,甚至機脚亦轉用了更大更好看的品種。

teflon socket for 2A3 tubes 鐵氟龍管座

Gold plated speaker terminals and RCA sockets 鍍金重型喇叺座及輸入插座

relocation of hum pots at bottom 在機底的交流澡音調教噐换了位置

now you can adjust on top 現在可以在機上調整

old hum adjust method 以前要將機身翻轉,痛苦!

 

來自星加坡－篇不错的報告：关於結構及表現

SUNAUDIO SV-2A3 採用 ‘简單就是美’ 的觀念去設計。机壳是整个灰色,而前面只有左古声道獨立使用的音量控制旋钮及一个上下打動的电源开关掣,中部是刻上商標及机種的铜質銘牌。結構方面有如磚頭般堅固,兩支2A3座於前方,兩支6SN7及5U4G分別位於左右兩方,而四个火牛裝在後方,是－般胆机的做法。這个机種是單端輸出設計,輸出雖然只有3.5W但表现出乎意料的好。SUNAUDIO SV-2A3所用的火牛都是曰本TAMURA所生產,是廣大發燒友公認為最好的火牛廠之一。內部编排十分考究但简潔,看來SUNAUDIO下了不少工夫。电源輸入插是IEC型,方便用家测試不同的电線。

監聽SUNAUDIO SV-2A3是令人沈醉於音樂的經驗,它表達出十分豐厚的音色而沒有任何失真與噪音,在五人合奏中,每件樂器都分辨得清楚。聽交響樂時,聆聽者可以充分了解樂器舆旋律如何交織及互動而结合為－倜美妙的樂章。人声一向是單端放大器的拿手好戲,在這裹也不例外,獨唱及合唱的感染力很強,有置身其境的幻覺,在節奏稍慢時,歌者舆樂器之間的互動增强,感情更彭拜,有如從音樂中倾注而出。－言敝之,高级音响追求者－定要聽一下這件超级好声的SV-2A3。

 

One nicely written review from Singapore, on the construction and performance:

The Sun Audio SV-2A3 is approached with a very minimalist design, which conforms to the “less-is-better” rule of hi-fi. The chassis is clad in an understated shade of grey, with a gold-hued front panel which houses nothing more than two volume control knobs for left and right channels respectively and a flick on-off power switch. In the middle of the fascia is a plate that proudly bears the make and model of the amplifier. Construction-wise, the amplifier is as solid as a brick, and there is a very reassuring feel to the entire rig. The tube complement is mounted towards the front of the amplifier, comprising two 2A3 tubes as power output tubes, with two 6SN7GTs and one 5U4G tubes beside them. Sitting directly behind the tubes are four transformers, which is the norm for tube amplifiers. It is a single-ended design, power output is relatively low at 3.5 watts but performs beyond expectations. The Sun Audio SV-2A3 utilizes Tamura transformers are held in very high regard by audiophiles, and are part of some of the best transformers available. The internal layout is carefully designed and exceptionally neat, a real testament to Sun Audio’s effort. The power cord input is of the usual IEC variety, which gives some room for experimentation of different cords.

Listening to the Sun Audio SV-2A3 is a very immersive experience that draws the listener to the music. It brings out the richness of the sound really well without signs of any hum or distortion. Individual instruments can be easily discerned in a five-piece ensemble. In classical music, the listener can understand how interactions between instruments weave and interlace around the main melody to create pieces of masterfully designed music. It is the nature of a single-ended amplifier to have very good vocal presentation, and this is no exception. Vocals and choral music have a tangible feel, and the sensation that they are in the same room performing is commendable. On slower pieces, there is an increased intimacy with the vocalist and sounds as if their feelings are pouring out from the music. The Sun Audio SV-2A3 is a superbly musical amplifier that must be listened by those who are considering a top quality unit in their hi-fi sets.

Specifications :
Tubes……………………………………..2 x 2A3
……………………………………………..1 x 6SN7GT
……………………………………………..1 x 5U4G
Circuit Design……………………………Single-Ended class “A” operation without negative feedback
Power Output…………………………….3.5W + 3.5W
Input Impedance…………………………100k ohms
Input Sensitivity………………………….150mV
Output Connections……………………..8 or 16 ohms
Frequency Response……………………15-30kHz / -3dB
Noise Level………………………………..Less than 2.5 mV
Power Supply……………………………..100, 120 and 220-240 VAC can be accepted at 50/60Hz (not changeable)
AC Connector……………………………..Equipped built-in noise filter with detachable AC cord
Dimensions(w x d x h)…………………..36 x 28 x 20cm
Weight………………………………………15kg