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Raspberry Pi 週刊 第五期

July 04, 2018

Raspberry Pi 週刊 第五期

本週,店主想談談最近客戶對Project ClayX I2S Digital Coaxial Interface Bridge Device的評價。

為什麼店主想生產這個數字同軸產品,而大多數DAC支持USB?

原因是店主正在使用Wadia 2000解碼。它只能接受數字同軸輸入。產品本身是為店主店內使用而設計的。但有一天,有些客戶來拜訪本店。說他有一個非常好的DDC是由香港DIY製作的,話說它是全世界數一數二可以同軸輸入解碼DSD。比較他的新的R2R dac, 仍然非常好聲.

店主說,本身DAC根本不會過時的,他們都聽起來很體面,很有設計感和個性, 仍然非常好聲。店主答應他做一個I2S同軸產品來照顧那些沒有USB接口的DAC的人,但是想要有像Raspberry Pi 3這樣的播放平台來播放或流式傳輸Spotify, Tidal音樂,並且用手機Apps作為控制。

店主說:等待我的好消息,我們將開始思考和建立一個新的I2S數字同軸Bridge介面,可以重新使用沒有USB接口的DAC,並再次使用它。

客戶答復:太好了,我期待著看到這個新的同軸產品, 並再次重新使用我以前的DAC,如果可能的話可以數字同軸輸入播放DSD Signal將是最好的。眾所周知,數字同軸電纜比USB電纜好得多,而且比較容易用不同品牌的同軸電纜來調音。

店主說:產品背後的設計應該是易於使用和適合大多數人的。每個DIYer產品的製作工藝, 應該反映並提供一些與客戶要求的聯繫。

這就是為什麼我們要開發這個產品,這個I2S同軸產品是市場上獨一無二的,具有獨立的I2S電纜和5V DC插頭輸入,使用最好的音頻等級組件,以確保我們滿足優良的音質。

聽感:

店主試用了不同的同軸卡,還有一系列國外不同版本的I2S同軸卡相比。如預期的AfterDark Project ClayX I2S Digital Coaxial  Interface Bridge Device因為我們店主特別用了溫補TCXO 0.1PPM晶振. 除此以外晶振, 音頻隔離變壓器和芯片上我們特別另外增加EMI Shielding. 在音質和細節方面贏很多,高音更加精緻. 

Raspberry Pi 3 同軸卡名單:
1 / HiFiBerry Digi + STANDARD / TRANSFORMER /PRO 
   (削減成本版本,使用低成本的振盪器, 沒有焊接"音頻隔離變壓器", 或者使用低成本的"Pulse"變壓器,Galvanic Isolation 噪音和保護問題)
2 / Allo DigiOne
     (削減成本版本, 使用低成本的振盪器, 沒有焊接"音頻隔離變壓器, 來自用戶的一些評論,這聽起來比USB連接更糟糕)

上述產品他們沒有DC插頭, 提供連接5V DC線性電源. 有些是因為降低了產品成本, 結果是沒有焊接"音頻隔離變壓器". 店主相信為了好聲音為了可靠性, "音頻隔離變壓器" 能夠提供好的數字音頻同時, 保護音頻設備和主卡,  絕不能偷工減料.

店主一直認為樹莓派 Pi 3對外部電源非常敏感,電源供應越好,音質就會越細緻和密度越詳細。正因為如此,所有Project CalyX 產品都可以由店主來(Mod)修改,為他們提供獨立的DC電源插頭。

關於技術的話題: 

我可以避免使用MircroUSB作為Raspberry Pi3的主電源嗎?
答案是肯定的,店主嘗試直接將DC電源線連接到Raspberry Pi 3 GPIO's 端口。 聲音可以得到很大的改善,之後會有更多的細節。 這是因為,這可以繞過所有的功率調節器和樹莓內部電路的保險絲。 這是因為線性穩壓電源已經過濾優化的,是可以直接飛線安裝在Raspberry Pi 3 電路板上.

店主因其他客戶的要求,將量身訂做上述外部導線專用電線...請關注下週AfterDark.新產品發布

什麼是TCXO (Temperature Compensated Crystal Oscillator)?
TCXO 是溫度補償石英晶體振盪器。TCXO 在規定的溫度範圍期間輸出箝制正弦波以提供極低的操作供應電流,建立穩定的參考頻率。TCXO 支援工作電壓、輸出頻率、溫度穩定性及其他功能特性。TCXO 可對環境溫度、電壓或負載環境等變數進行補償。TCXO 具備卓越的相位雜訊效能,是 I2S模組產品應用的最佳選擇。

http://www.radio-electronics.com/info/data/crystals/tcxo.php


Raspberry Pi Weekly Issue no.5

This week, the owner wants to talk about the recent feedback on Project ClayX I2S Digital Coaxial Audio Interface.

Why shop owner want to produce this Coaxial Product while most DAC support USB?

The reason is the shop owner is using Wadia 2000 Decoding Computer. It only can accept Digital Coaxial Input. The product itself is design for my own use. However, one day some client come to visit me. Saying that he  have a very decent DDC which can decode DSD with Digital Coaxial Input made by Hong Kong DIY. Very good sound compared his new R2R dac. 

The shop owner said, the old DAC is not outdate at all, they all sound really decent, with great design. The shop owner promised him tol make a I2S coaxial product to take care of the people who have their vintage famous dac without USB port, but want to have playback platform like Raspberry Pi 3 for access music and used as control point  with mobile Apps. 

The owner said: Wait for my good new, we will start to think and build a new I2S Coaxial Bridge, which can be re-born the vintage DAC and used it again. 

The client reply: Great, I looking forward to see this new apporach to re-use my old DAC which used to be sound great and if possible can playback DSD with digital coaxial input. As you know, the digital coaxial is far better then USB cable and the easy to tune the sound with different famous brand of coaxial cable. 

The owenr said: The show owner believed that the design behind the product should be easy to use and benenfit to the most people. The workmanship on each DIY product should reflect and provide some connection with client's requirement. 

That's why we have to develop this product, this I2S coaxial product is unique to the market, with separate I2S cables, and 5V DC plug input, use the best audio grade component to ensure we satisfy on excellent sound quality.

Shop owner always believe Raspberry Pi 3 is very sensitive to external power supply, the better the power supply, the sound will be more refine with more density details. 

Technical Insight: 
Can I avoid to use microUSB as main power supply to Reaspberry Pi3? 

The answer is yes, the shop owner implement the power cable directly to Raspberry Pi 3 GPIO ports. The sound can be greatly improved, and more details afterwards. It is because, this can bypass all the power regulators and fuse inside the raspberry circuit. The power can directly fit to the circuit with their good linear power supply which was already optimized with filter and regulated with computer control DC circuit etc. 

What is TXCO?
"TCXO, Temperature Compensated Crystal Oscillator
- the TCXO, temperature compensated crystal oscillator is used for providing a much higher levels of temperature stability than are possible with a normal crystal oscillator.

The TCXO, Temperature Compensated Crystal Oscillator (Xtal oscillator) is a form of crystal oscillator used where a precision frequency source is required within a small space and at reasonable cost.

By applying temperature compensation within the crystal oscillator module, it is possible to considerably improve on the basic performance of the oscillator."