The Equipment Needed for This iPhone Adventure

Now, let's talk about the equipment needed for this iPhone Adventure that has brought so much enjoyment to our circle of friends.

First, as a source an iPhone or Android phone is needed. An iPad may also work. About the Android phone, the latest model would be the better in terms of sound quality, and Bluetooth version 5.0 or higher is preferable.

Anyways, in my experiences so far, when using an iPhone there is a vast sound field expression with a sense of volume in the mid-low range, that is very appealing. It provides a surprisingly high quality music listening experience. 

On the other hand, I have used three types of Android phones over the past two years, and I think they are characterized by a clear midrange-based sound image, such as when listening to vocals. Of course, I think this would be also attractive.

Then, we used these mobile phones to access the streaming services, select a favorite music or song, and play it with only a few finger taps.

Well, the core device of our iPhone Adventure is a small and extremely reasonably priced USB DAC with a built-in Bluetooth receiver called the Douk Audio U4 (about $50 USD - Jeff). I have always bought it from Amazon Japan. Sorry, but the product name has already disappeared from the website of the Chinese company, Nobsound.

(The Douk Audio U4 can still be found online, but they are getting harder to find - Jeff)

Our iPhone Adventure uses the Bluetooth connection between the mobile phone and the Douk Audio U4. The U4 receives the headphone/earphone output of the mobile phone and amplifies it to the normal analog audio signal levels.

Here is the manufacturer's description for the features and functions of the U4:

"The Douk Audio U4 is a multi-function HiFi audio device with Bluetooth 5.0 and a USB input, stereo RCA, 3.5mm AUX, and a 3.5mm headphone jack output. It can be used as a Bluetooth receiver, a USB DAC, a headphone amplifier, and also as a preamp for devices such as smartphones, computers, power amplifiers, and active speakers."

"Adopting the classic 6N3 vacuum tube effectively eliminates annoying digital sound and gives a clear, soft, smooth, warm & sweet vacuum tube sound. The sound field is wide, and is especially suitable for vocals, string instruments, light music, classic music, etc."

"High-end Components and Unique Design: Bluetooth 5.0 (QCC3008 chip) supports APT-X, APTX-LL, adds a removable antenna with TDA1543 chip and external high gain to make audio transmission lossless."

"The USB sound card uses a 2704 chip that is compatible with Windows, Mac, and/ Linux systems, and Android smartphones with an OTG function, so no drivers or plug and play required."

"The headphone amplifier uses the MAX9722 decoding chip which can drive most 16-600 ohm headphones with 300 mW output."

"Note: The latest version has been changed to the 2704 chip, and is compatible with up to 16-bit 96 kHz."

"Note: APT-X and APTX-LL in the description are Codecs that are compatible with Bluetooth 5.0 for this device. In order to achieve data communication with Bluetooth, it is necessary to first encode data in a format that is easy to transmit, and then decode the data after receiving it. Codec refers to the technology that performs this encoding and decoding." 

In any case, I have checked the Bluetooth connection, which is an important feature for our iPhone Adventure, with seven Douk Audio U4s over the past 2 years, including the one that I use regularly, and the ones that I got for friends. They all work well without any problems.

Therefore, I judged that at least the Bluetooth section design of this U4, including the selection of parts used, was highly reliable. And this Bluetooth receiver also had higher sensitivity, so the attached antennas were not necessary.

Now, even if you don't use this Bluetooth function, it's a DAC with USB input, so you can use your computer as a sound source and connect it via USB, so you can enjoy computer audio, and also use the headphone output with a volume adjustment function.

Therefore, it has a variety of functions in its small chassis. However, its most distinctive feature may be that one dual triode is adopted in its analog output stage.

It would be a fusion of the latest digital technology and old-fashioned analog audio technology using a tube. It must be an extremely unique design, and therefore I have been very interested in this little Douk Audio U4.

Please go to the next page.