Sunaudio SV-300BMKII

update 30-6-2024增新

We have just completed the project on making one pair SV-300BMK2 mono power amplifiers using the casing SV-TE/zero. The power and output transformers will be the same as those used on the last project, but we used the Tamura SIT-5KM interstage transformer here instead. We also used the WE417 (5842) as the driver tube since it will give us more higher gain and better frequency response as compare to the 6SN7 tube. We have also added a filament transformer for the two 300B tubes in order to lower the loading on the PT-150B which is barely sufficient to supply all the power consumption, and become quite hot during long time operation. It is also believed that separate filament transformer improves the sound quality and it proves to be true during our audition. You can feel more relaxing sound coming out from the speakers and the power transformer runs cooler than before. No such amps can be re-produced since we cannot find anymore SIT-5KM inter-stage transformers. It is your last chance to get such nice amps at reasonable price. Get them before they are gone. $29800 for the pair with EH300B tubes.

update 5-9-2016 增新

我們剛在最後一對 SV-300BMK2 單聲道後級加了一些改動. 由於在SV-TE /zero 機箱上有多餘的2個可裝管座的孔洞, 我們決定在這上面加裝2個八腳管座並且用接線平行接上用以使用2支6J5(等效於半支6SN7). 而這2支6J5也與6SN7管子的管座平行接上, 這樣我們就可以隨時換用其中一款管子作為推動。6J5這些管子比較易找而價錢不太貴, 但音色可比美最好並價格高昂的6SN7管子。同時我們亦在整流管輸出處換上4mfd/400V的紙質油浸電容, 這些電容提供滑溜細緻的音色而電解質電容是永遠做不到的, 減低了電容量也消除了用舊款整流管如WE274B於起動時損坏的可能性。（已售）

We have done some additional modification on the last pair of SV-300BMK2 mono amps. Since there is two extra holes for tube socket on the SV-TE/zero casing we decided to make use of them. Two tube sockets are mounted and wired to receive two pieces of 6J5 which is a equivalent to half piece of 6SN7. These 6J5 tubes are wired parallel to the 6SN7 tubes so that you can use either of them. The 6J5 tubes are comparatively easy and cheaper to get but they gives wonderful sound comparable to the best 6SN7 tubes at very high price. One 4mfd 400V paper in oil capacitor is also put at the output of the rectifier. It gives a smooth and delicate feel that no electro type capacitor can ever get, and the smaller capacitance also allow the use of vintage tubes like WE274B to be used without the fear of damage during the start up period. (already sold)

update 2-9-2016 增新

我們剛完成仿製一對SV-300BMK2後級放大器, 全部火牛除了輸出牛用 Tamura F-925去取代SOT-5P, 其他都是和原裝的一,機箱選用Tamura SV-TE/zero, 外表與原裝的很接近。我們在機內加裝了一個給2支300B管子用的燈絲牛, 作用是改善音質及降低電源牛的熱量。我們對這套放大器十分滿意,正在示範及運作中。

We have just re-produced one pair SV-300BMK2 using the all the original transformers (except for SOT-5P which is now changed to F-925 with same primary impedance of 5K). One pair SV-TE/zero casing are used for the project. The appearance is similar to the original product. We install one extra filament transformer for the two 300B tubes. It helps to improve sound quality and reduce the heat on the main power transformer. The result is very pleasing and we are burning in this pair for demonstration.

最近知道SUNAUDIO SV-300BMK2這對市面上最好聲的300B推挽放大器已停產,心中很難遇. 其實要仿造一對並不太困難,只要找到適合的火牛就成了(原本的TAMURA火牛是又平宜質數亦是最好的). 機內的零仲只有十多個,你大可以找零件去調這部放大器的音色直至滿意為止.

It is sad to know that Sunaudio had stopped the production of the SV-300BMK2 mono power amplifiers which is suppose to be the best sounding 300B push-pull amplifier that you can find. However they are actually not difficult to re-produce if you can find the transformers (the original Tamura transformers are the best at affordable price). There are only a dozen of components inside the casing and you can use whatever you want to tailor make the tone of your amplifier.

SUNAUDIO 300BMK2 是極筒潔純美的設計,它用交連牛去實現完美的反相及平衡推動電壓來令一對300B管子正常運作. 這部放大器只用一支並聯了的6SN7去提供足夠的推動力及匠配這個高性能的交連牛 (TAMURA SIT-143 10KOhm：1+1）。 10Kohm阻抗以上的高質最交連中是昂貴並難做的. 整流線路是標準的, 而其他零件加起來亦只有14件而已.

SUNAUDIO SV-300MK2 is extremely simple and elegant design with the use of inter-stage transformer to ensure perfect phase splitting and equal driving voltage on the 300B power tubes. The front end is a single piece of 6SN7 connected in parallel to give better driving power and lower down the output impedance in order to match the inter-stage transformer (Tamura SIT-143 10K ohm 1:1+1). An inter-stage transformer more than 10Kohm with wide bank width is expensive and difficult to make. The rectification circuit is standard and the use of other components is reduced to 14 pieces only (including 2 pieccs 1 ohm 10W resistor for the 300B filament ).

我們曾把兩支300B管子的燈絲並聯及接上一個2.5V+2.5V=5VAC的電壓,而把中心經 500 ohm25W(有100MFD160V電容傍路)電阻接地做回路,這樣可以進一步減少零仲及廢除交流諷整器. 效果非常顯著,但要絕對匠配的300B管子才成.

I have tried to connect the filament of both 300B tubes in parallel and put 2.5V+2.5V =5V AC on to it, and with the center tap connected to the ground through a 500 ohm 25W resistor （with 100mfd 160V capacitor bypass）to reduce further the use of components and the omission of the hum pots. The result is promising but you need to find pairs of perfectly matched 300B tubes in order to get minimum hum.

One nice review from the States: 一篇來自美國不錯的報告

這對SV-300BMKII放大器一個月前抵達, 我必須承認先入為主的喜歡它. 它的設計合理: 沒有交連電容, 壹支並聯了的6SN7接到交連牛,去分相及推動輸出級, 增益當然是低的, 但有好的前級就沒有問題了, 這機不設負回輸, 供電級有桅流圈. B+電壓只有320V, 比一般設計的400-450V低很多, 這個工作點決定了放大器的音色, 而輸出管可以長期處於穩定的狀態, 最大輸出是20瓦。全部零件都是高質數的, TAMURA火牛更是超班的, 線路實在一簡無刃簡。我的朋友GIZMO曾說過: “唯一的一部推挽式放大器令我對至高無尚的單端放大器產生疑問……..這是我至今為止聽到的最好的推挽機

。So the SunAudio SV300B MKII amps arrive a couple of months ago. I must admit that I was pre-disposed to like them. The design parameters made sense: no coupling caps, a 6SN7 input tube is connected in parallel to a transformer phase splitter which drives the output stage. As a result, gain is low, but that’s OK if you have a good driving pre-amp. There’s no global feedback, and the power supply has a choke. The 300B B+ voltage is only 320V which is substantially less than the usual 400-450 Volts. This operating point helps define the “tone”, along with allowing the output tubes to practically “idle”, with a maximum output of 20 watts. Parts are high quality, and the Tamura transformers are super high quality. It is very, very simple. I quote Gizmo:

“This the only push/pull amplifier I have ever encountered that is causing me serious doubts about the artistic primacy of single-ended circuits…. This is the best push/pull amplifier that I have ever heard.”

我堂嘗試用不同的6SN7放在推動級, 在這裹Kenrad 6SN7GT (四十代)令人驚嘆 – 這管子在其它系統表現不平衡及低頻太多 – 但在這處恰好。我找了些RCA 5U4G新貨做整流管, 它令音色更從容甜美而不影晌推動力。三個星期後我終於找到2對匠配的SOPHIA 300B 管子去真正完成這次配搭, 而我亦相信已經做到最好。

I tried a variety of 6SN7 types in the driver position, and IN THIS SYSTEM, the KenRad 6SN7GT (mid 40s)is absolutely “stunning” – I always found this tube to be out of balance with too much bass in prior systems – but not here! I sourced some NOS RCA 5U4Gs for rectification, and they sweetened and relaxed the sound without loosing any drive. Then three weeks ago I finally landed two matched pairs of Sophia 300B Mesh Plates and these output tubes truly completed the amps. I’m sure I can make them sound different, I skeptical that I can make them sound any better.

結論在此 : 我曾鑑聽過最好的放大器, 其他的不是這個級數. 它輕微地缺乏單端機所擁有的中頻魔力, 但其他方面表現更出色, 中頻魔力減少了, 但失真也劇減, 場面更澗更清澈. 音色不含糊, 它的高低頻伸展暢順柔美。它似乎與TANNOY喇叭結合得水乳交融, 動態無人能及, 20瓦的翰出可以把最大音壓推至110db而沒有破音, 在任何大音量時也不會覺得不流暢, 它所產生的由高至低同步的音樂如浪潮般充斥整個房間, 我覺得這些表現和單端機不一樣,這比較吸引迷人。最大的好處是無論播什麼樂曲, 我可以很快便投入其中, 我不會再局限於只聽某類型音樂, 它把全部都做對了, 而且做得令人滿意。

So here’s the deal: these are the best sounding amps I’ve ever heard. In my experience, nothing even comes close. They give up a “smidge” of midrange magic to the single ended designs, but in every other area they are superior. While the midrange is not as spooky magic, it is much lower in distortion, wider and clearer. There is no homoginization. They are fabulously extended, both top and bottom. There appears to be a real synergy with the Tannoy loudspeakers, displaying dynamics to die for. 20 watts per channel allows for peaks of 110db without clipping. They never congest at volumes that make me fear for my hearing. They create this coherent musical wave, top to bottom, that energizes the room differently than SE, and in a way that I find more captivating. The biggest deal is that no matter what kind of music I put on, it quickly becomes mesmerizing. The system no longer tends to lead me to certain kinds of music. It’s all available, in spades.