I hope you've had a chance to read through the latest article by Yazaki-san, A New & Exciting Audio Adventure from Yazaki-san: The iPhone Adventure!, where he describes the fun that he and friends have been having with their iPhone Adventure and the "Improved U4" Bluetooth/USB DAC. 

As I mentioned in Yazaki-san's latest article, I was delighted that Yazaki-san invited me to join he and his friends in their iPhone Adventure with the Improved U4.

Today a delightful package containing the Improved U4 arrived from Yazaki-san, as well as a very thoughtful card, and some delicious green tea. 

It seems amazing to me that it's been 9 years already since Yazaki-san and I met while I was writing about the SPEC RSA-M3 EX Real Sound Amplifier for Jeff's Place and Positive Feedback (HERE). 

How time flies!

It has been a true pleasure interacting with Yazaki-san over the years, and he has shared a wealth of information with readers here at Jeff's Place and Positive Feedback.

To see links for the 58 articles with Yazaki-san please go to the Archives page and scroll down to Adventures In 'Real Sound' with Mr. Shirokazu Yazaki HERE. 

It's easy for us audiophiles to get into a rut listening to albums that are targeted at audiophiles.

The same high-fidelity albums from the stereo magnetic era of the recording arts have been remastered, remarketed, and resold to audiophiles many times over the years.

While I appreciate those premium albums, and have quite a few of them myself, after a while they do get boring. 

While I still enjoy listening to those audiophile albums, I've also had a blast exploring digital transfers of 78rpm records from the acoustic and electric eras of the recording arts.

Those 78 transfers from early in the history of the recording arts are catching on with music lovers and audiophiles, and there are a number of record labels that now offer them.

What fun I have been having exploring the music and musicians from early in the history of the recording arts! I highly recommend it to you.

Positive Feedback Editor Dave Clark told me quite sometime ago that the source component that most young people use for their music listening is their iPhone. Not a turntable, and not a CD player. 

One of my favorite demo rooms at the 2023 Pacific Audio Fest was the Cabasse room, where they were demoing their wireless Rialto system. Guess what their source component was? An iPhone, streaming music via Bluetooth. It was one of the most musically natural high-fidelity rooms of the Fest, and I was really impressed with what their relatively inexpensive Rialto system could do. 

Then I started hearing Yazaki-san talk about how much fun he and his friends were having with their iPhone Adventure. 

The idea behind their iPhone Adventure was to introduce more fun into listening by exploring the vast worlds of new and diverse music that are available on streaming platforms like YouTube and Amazon Prime. Often for free. 

Their adventure started with an inexpensive (~$50 USD) Chinese manufactured vacuum tube Bluetooth/USB DAC from Douk Audio, the Douk Audio U4. 

They were surprised at how good the humble U4 sounded streaming YouTube and Amazon Prime music to their hi-fi systems over Bluetooth.

More important than the sound quality was the fun they were having exploring new music to listen to. An adventure in music listening.

What happens when you have two world class audio engineers like Yazaki-san and Honda-san enjoying a humble vacuum tube U4 Bluetooth DAC (above left)? They have to modify it for more performance, of course (above right).

Naturally, first they started trying some NOS vacuum tubes in the U4 to extract more music. 

Upon examining the U4, they admired the, "... excellent circuitry and mechanical design of this mini USB DAC, the Douk Audio U4."

Honda-san, after hearing the U4, commented, “This is only my very first impression, but the Douk Audio U4 is very good! ... In just one listening, I was impressed that it produced a very fresh, three-dimensional sound image. I also felt it has a lot of potential. The feeling that the sound is released without stress must be unique to a DAC that does not undergo digital processing, and it is very good."

Yazaki-san commented, "Furthermore, Honda-san conducted a circuit analysis of the final stage circuit diagram of the Douk Audio U4 for me, and when I had a chance to look at his circuit diagram, I was led on a new adventure into the Improved U4."

In the photo above you can see the modifications to the U4 (for details see Yazaki-san's article): 

(1) Replacement of the coupling capacitor between the plate of tube and the RCA output terminal with the capacitor that seems to be the best at present.

(2) Connect the metal film resistor (10 k ohm, 1 W) in parallel to the existing cathode resistor (chip resistor: 1.5 k ohm) of the tube.

(3) Strengthen the decoupling capacitors for the plate power supply and another circuit.

The result of the modifications is the "Improved douk Audio U4" that you see in the photo above.

Across the front panel - left to right - are the power switch, the selector switch for Bluetooth or USB, and the indicator lights that signal power, USB, or Bluetooth is on. 

Around back - left to right - are the RCA outputs, the USB connector, the Bluetooth antenna connection, and the power supply connector. 

Yazaki-san also sent along a couple of vacuum tubes to try in addition to the stock one.

I installed the Bluetooth antenna on the U4, and am planning on installing the U4 into my audio-visual system based on vintage Altec A5 Voice of the Theatre loudspeakers, powered by the Yazaki-san voiced SPEC RSA-M3 EX Real Sound Amplifier. 

"The Times They Are a-Changin'" album by Bob Dylan was an anthem of societal change.

The times they are a-changin for me too. I've been enjoying spinning stereo magnetic era LPs, then listening to 78 transfers of albums and musicians from antiquity, and now leaping forward into the future by Bluetooth streaming of new music from YouTube and Amazon Prime (to start with) over my iPhone through the Improved U4.  

I shall report back on the results.

As always, thanks for stopping by, and may the tone be with you!