DMP-Z1 ENGINEER INTERVIEW

DMP-Z1: Leaving no stone unturned for the ultimate headphone listening experience

Introducing the DMP-Z1: a personal audio device that's neither a portable player nor a desktop player, but a brand-new concept. This is the culmination of a pursuit for the ultimate in headphone listening, no matter the environment, with a clean power source provided by batteries. The creators speak enthusiastically about the development process for this unparallelled new model.

The all-new audio player that defies categorization

First of all, tell us about the background from which the DMP-Z1 emerged.

Tanaka, Product Planner:
This product is the second part of our Signature Series, which we introduced to the market in 2016 with the aim of delivering the ultimate in personal audio. We sensed that there is an increasing demand for high quality audio when listening with headphones, just as there had been with conventional speaker systems.

Headphones may be strongly associated with outdoor use, but now more and more people around the world are using high end headphones to enjoy music indoors, and seeking the best audio experience when doing so. We designed the DMP-Z1 for those customers, aiming to pack the best listening environment imaginable into a simple form.

V&S Business Division, DMP-Z1 Product Planner Mitsunori Tanaka

Sony Video & Sound Products Inc.
V&S Business Division, DMP-Z1 Product Planner
Mitsunori Tanaka

DMP-Z1 in carrying case
Detail of DMP-Z1 serial number
DMP-Z1 Project Leader Tomoaki Sato

Sony Video & Sound Products Inc.
V&S Business Division, DMP-Z1 Project Leader
Tomoaki Sato

What kind of product is the DMP-Z1?

Tanaka:
The DMP-Z1 is a product in a new category all of its own. Its greatest strength is that while it's geared toward indoor listening, the audio player, amplifier and battery are packaged up together, guaranteeing the quality of the power source and the signal transmission. We're aiming for an ideal headphone-listening environment with no external dependencies.

Given that it's a high quality, battery-powered music player, the design was entrusted to Tomoaki Sato and his team, who developed the high end version of the Walkman®.

Tomoaki Sato, Project Leader:
In 2016, we released the NW-WM1Z/WM1A Walkman® and TA-ZH1ES headphone amplifier as the first part of our Signature Series. It was the experience of demoing these to the media, critics and store staff that drove us to create the DMP-Z1.

The D.A. hybrid amplifier built into the TA-ZH1ES headphone amplifier achieves a high output, producing a high quality sound even from high-impedance headphones. However, it relies on a large (AC) mains power supply. The drawback of this is that mains power often carries considerable noise. There are also many different factors you need to pay attention to if you want to provide the best audio, such as the quality of the USB cable you use to connect; or when the PC is being used as the audio source, its power supply, the playback app it uses and its USB port.

However, our flagship Walkman® NW-WM1Z runs on clean battery power, meaning the audio quality is very high. With this Walkman®, all the components in everything from the playback device to the amplifier are internal and there are absolutely no external elements that will be affected by the power source. As long as it's charged up, you can take it anywhere and enjoy the high audio quality that we've striven to provide. However, the device is limited by its size and can't ensure the large output required for high-impedance headphones.

So, we thought that if we could take a stationary device like the TA-ZH1ES and make it run on clean battery power with no external elements, like the Walkman®, we could create a product that would allow our customers to easily get the full potential out of their headphones.

V&S Business Division DMP-Z1 Acoustic Engineer Leader Hiroaki Sato

Sony Video & Sound Products Inc.
V&S Business Division DMP-Z1 Leader for Sound Quality Design
Hiroaki Sato

How does the built-in battery lead to higher audio quality?

Hiroaki Sato, Sound Quality Designer:
When you get right down to it, the power source is at the root of the sound played back by an audio device. If the power source is impure, you won't get a beautiful sound, no matter how good the audio circuits are. Like if you don't have clean water, you can't make delicious tea.

Tanaka:
In the world of pure audio, there are people who install electrical outlets specially designed for audio, buy large power units and even go so far as to install their own electricity poles in order to cut noise from the power supply. But if you just use battery power (a DC power source) then there's no need for all this effort and investment, and you can eliminate any concerns related to the power supply. Unlike a speaker amp, which requires a large output of tens of watts to drive a speaker, the DMP-Z1 is a device made for headphones, so it can provide high audio quality through battery power. It doesn't need a huge power supply block to convert variable-quality AC into clean DC power. The equipped batteries are separated into three independent blocks, preventing any drop in audio quality caused by interference or conversion circuits.

V&S Business Division DMP-Z1 Electrical and Acoustic Engineer Keika Matsuzaki

Sony Video & Sound Products Inc.
V&S Business Division DMP-Z1 Electrical and Sound Quality Designer
Keika Matsuzaki

What difficulties did you face when implementing a battery-powered system?

Tomo (S):
We'd already realized battery-powered devices with the Walkman®, but products like that don't have the output necessary to drive high-impedance headphones for indoor listening. The S-Master HX digital amplifier, which has been used in the Walkman® since it became compatible with High-Resolution Audio, is an excellent amp that's power-saving, space-saving and achieves high audio quality, but it wasn't designed with high output in mind, for those who want to listen through high-impedance headphones at home. So with the DMP-Z1, we challenged ourselves to make a product unlike any before, by taking an analog amplifier that could withstand high output and making it operate using large-capacity, high-output batteries, for power that could bring out the best from high-impedance headphones.

Hiro (S):
We've designed new power circuits with totally unique specifications. When the amplifier is in operation, there's a high current due to positive- and negative-output batteries with large capacity that are connected in series. It was hard to achieve this without using a DC/DC converter, which brings with it the possibility of slight noise from the negative power source. In particular, the battery designers went to great pains to create a design that uses transistors to cut off from the negative battery and switch to charging when necessary. 

Matsuzaki, Sound Quality Designer: 
The design would be simple if it was only battery powered, but for practicality reasons we had to enable it to be powered by an AC adapter as well. The process involved melding various complicated elements like gain-switching, and the power circuit design and control became extremely complex as a result. Broadly, we anticipated eight systems of operational pattern, and these could be further split into 295 types. This complex pattern arrangement meant that it was a difficult task in terms of sound quality design, being a totally new product concept, but it was worth it to do something that no one had achieved before. 

Tomo (S): 
When you prune away all the extras and simplify things in order to improve the sound, the functionality becomes less and less workable. But the concept here was to allow people to enjoy the best audio in one easy package, so we couldn't afford to compromise on user-friendliness. We embarked on a lot of research during the long development period to investigate how we could achieve great audio without sacrificing the user-friendly aspect. 

Tanaka: 
The result of our efforts was a system where the DMP-Z1 switches power modes automatically based on the playback status and remaining battery. If you set it to battery mode, it will continue to operate in battery mode even when connected to the AC adapter, and won't use the adapter. Then, when the charge is low, it will automatically switch to AC mode (charging mode).

Incidentally, the playback time is roughly nine hours for FLAC and 10 hours for MP3 (with LCD display off). The battery takes roughly four hours to go from empty to fully charged.

Meticulous craftsmanship in pursuit of noiseless audio

Were there any other challenges related to the power supply?

Matsuzaki:
The connection between the power circuit and the ground (earth) that lets the electricity (noise) escape was one area that took a lot of trial and error. The DMP-Z1 is structured with two circuit boards, one above and one below. The upper circuit board has the power circuit, and the digital circuit is positioned next to it. From there you go via the DA converter down to the analog circuit on the lower circuit board, and the sound is amplified by the analog amplifier. If we didn't get the grounding right, noise would be introduced when the device is powered by the AC adapter.

V&S Business Division DMP-Z1 Electrical and Acoustic Engineer Keika Matsuzaki

How did you solve that problem?

Matsuzaki:
We stuck to the most basic of basics: multi-point grounding for the digital and single-point grounding for the analog. If this failed in even one place, noise would be introduced there. To test audio quality, you have to actually create a prototype and trial the audio, then find ways to improve it and create another prototype. This steady process of repetition is very important. With the DMP-Z1, we continued testing the audio quality right up until the final stage, so I think we managed to achieve a sound that we're really happy with.

Tomo (S): 
Sometimes you thought you'd hit on a way of reducing noise, only to find you'd actually made the sound worse. There were ups and downs, that's for sure. 

Matsuzaki: 
If you just fix lots of analog ground points onto the digital side you won't hear any noise, but the energy flowing out will get mixed into the analog sound and make it muddy and weak. We pored over the finest details to eliminate noise without losing out on the audio quality. I don’t know how many times I wished we could just give up on trying to make the device compatible with the AC adapter!

Don't those problems occur when the device is running on battery power?

Matsuzaki:
No, they don't. The power circuit structure for running on battery power at normal gain is very simple, so there's nothing in the power supply that can become a source of noise. However, in high-gain mode, which is used with high-impedance headphones, the voltage is increased. This means that even when the device is in battery power mode and isn't being powered by the AC adapter, the power supply can still be a source of noise to a lesser extent. But to counter that we use high-grade switching controllers—the kind that are used in measuring instruments—so that the effects are minimal.

Tomo (S): 
This power source structure means that the optimum setting for the DMP-Z1 in terms of audio quality is battery-power mode at normal gain. In this mode, the audio circuit with positive and negative power sources is driven by clean, noiseless power from the batteries, without using a DC/DC converter. This power circuit arrangement, unique to the DMP-Z1, enables this special operation mode. Amongst audiophiles there's an urban legend that high gain gives a better sound even with ordinary headphones, but that's certainly not the case with this product, at least.

Does that mean the DMP-Z1 isn't recommended for use with high-impedance headphones?

Tomo (S):
It does not mean that it is not recommended. Normal gain has output high enough to get the most out of ordinary headphones anyway, and with high-impedance headphones both driver efficiency and noise sensitivity are low, so you won't hear noise even in high gain. You can try listening in normal gain with your headphones and then switching to the high-gain setting if you feel the volume isn’t loud enough. Changing the gain setting to suit your headphones' efficiency and sensitivity in this way is an important point when trialling high quality audio.

You mentioned earlier that the DMP-Z1 uses a dual-layer circuit board structure. What kind of consideration went into the frame used for the housing?

Tomo (S):
Actually, when we started out developing the DMP-Z1, we considered a structure that involved one wide, horizontally mounted circuit board. However, that would have had a large footprint and would be less suitable for carrying around. The structure of the chassis also has a big impact on the sound.

With that in mind, we thought about how best to achieve portability, rigidity and sound quality all in one, which led us to a new development: the H-shaped aluminum chassis. We placed the H-shaped chassis, which is strengthened through aluminum milling, between the two circuit boards and connected it directly to them at the shortest possible distance, providing both high rigidity and high sound quality.

Hiro (S):
One of the finer details is that all four leg screw holes are positioned off-centre for each leg. This technique is common in desktop audio devices. Although it increases production time, these are the kinds of details we strive for.

Matsuzaki:
The rubber footpads on the legs are made of Sorbothane, a material used in medical care as well as in the soles of sports shoes. We intentionally took the dual-layer structure one step further to a triple-layer structure, adding improved slip resistance to prevent vibrations from reaching the device.

DMP-Z1 aluminum milled frame
Tomoaki Sato with the aluminum milled frame

Long years of painstaking research culminating in the perfect analog amplifier

Tell us about the amplifier. The DMP-Z1 incorporates the first analog amplifier created by the Walkman® development team in years. Can you tell us how this came about?

Hiro (S):
We'd been using digital amplifiers for a long time up until now, so the fact that we've suddenly used an analog amplifier may appear rather out of place. However, we'd actually been researching a way to combine an analog amplifier and a DAC from another manufacturer for more than five years now.

Tomo (S): 
This research began at the same time the first-generation high-res Walkman® NWZ-ZX1 went on sale in 2013. We called it the Rinjo Project ("rinjo" is the Japanese word for "immersion"), since the goal was to create a feeling of immersion through sound using an analog amplifier.

Matsuzaki: 
The amplifier used in the DMP-Z1 came from the 8th iteration of the Rinjo Project. Now, we're finally able to reveal what we've been working on behind the scenes. This device actually has "R-∞" printed on the circuit boards. The "R" represents "rinjo" and the ∞ represents "8." Although it's in a place the customers will never see, we pestered the circuit board design team to put it in!

Gold-plated circuit board
Circuit board

What kind of features does the analog amplifier have?

Hiro (S):
We use the TPA6120A2 analog amplifier made by Texas Instruments. We considered using various amplifier types and devices, including ones that were discrete and had an internal negative power supply, but the TPA6120A2 provided sufficient performance, both balanced and unbalanced, and we'd grown used to using it after several years of testing. From the point of view of its power consumption, and of course its sound quality compared with other options, it seemed like the perfect IC for this model.

What's more, to get close to the sound quality of digital amps, which have superior separation, we went with a dual DAC structure. Although size reduction was also a focus, it was important to use a dual structure with a certain degree of size and area to it. If you opted for circuit boards or a device that was too small, the distance between the L and R channels would be too narrow and would degrade the stereo separation, which would negate the choice of a dual structure. In other words, it would defeat the purpose of the product.

Texas Instruments TPA6120A2 analog amplifier IC

Texas Instruments TPA6120A2 analog amplifier IC

Texas Instruments TPA6120A2 analog amplifier IC

Asahi Kasei Microdevices AK4497EQ premium DAC

Tomo (S):
We wouldn't be able to outperform a digital amplifier if we used the analog amplifier on a circuit board designed for devices about the same size as the Walkman®. That's why the product is the size it is—to make it worthwhile using the analog amplifier. At first, we really felt the S-Master HX digital amplifier was the best choice for a portable player. It took us a long time to realize that at that size it would be incredibly difficult to produce a sound quality surpassing the Walkman® NW-WM1 Series that we ourselves had designed!

Matsuzaki: 
We also tried many different DAC products before settling on the AK4497EQ from Asahi Kasei Microdevices. It's been very well received in the high end audio community and is a well-known option. The DAC produces a clear and pure sound that perfectly suits the DMP-Z1, which is geared toward enhancing sound.

Aside from that, what points did you focus on to improve the sound quality?

Hiro (S):
We used KIMBER KABLE® for the cables that connect the amplifier circuit board to the headphone jack. This time, they are thicker cables designed for over-ear headphones. Thanks to this, using headphones like the MDR-Z1R from the Signature Series means that the connection from the amplifier base all the way to your ears is via the exact same cable. I consider this kind of thing one of Sony's strong points, since we make everything from players to headphones.

Tomo(S): 
Even after we had designed the NW-WM1Z, we were talking about wanting to use these thick cables. Of course, such thick KIMBER KABLE® cables wouldn't fit in the Walkman®, so that's why we used a thinner version designed for in-ear headphones in the NW-WM1Z.

Hiro (S): 
Now our dreams have finally come true and we've been able to use thick KIMBER KABLE® cables in our product!

Tomo (S): 
There are also the crystal oscillator, audio-grade solder, etc. I could go on forever about all the tiny details and ideas that have gone into this.

Refining the analog volume control, highly praised by audiophiles

Next, please tell us about the large volume control, which also provides a nice touch of style to the outer appearance of the DMP-Z1. What kind of detail went into the design?

Tomo(S):
Volume control was the one big talking point that kept coming up when testing the sound quality of the DMP-Z1. It is designed based on the same concept as models that already incorporate the full digital amplifier used in the Walkman®. However, our design philosophy is to deliver great audio to the users by keeping volume attenuation to a minimum in the digital processing stage and attenuating it directly before it becomes an analog signal, with no loss of information.

Close-up of analog volume control
Someone using the analog volume control

A full digital amplifier uses final stage Pulse Height Volume to convert the output audio signal amplitude to voltage. However, as the DMP-Z1 needs a volume control instead, the performance of the volume control device we used was extremely important.

Nowadays, you would normally use an electronic volume control. However, it takes a lot of power supply to make proper use of the low-noise performance suited to headphone audio, so this was an aspect that didn't fit the concept of high quality, battery-driven audio that we were aiming for with the DMP-Z1. After weighing up various options, we came to the natural conclusion that analog volume was the way to go for this product.

Hiro (S): 
Audio signals travel directly through the volume control, so it plays an essential role. We tested lots of different volume control parts for the DMP-Z1 and were really surprised just how much of a difference volume control makes to sound quality. After trialling various analog volume controls, we chose the Alps Electric RK501, which is highly regarded among audiophiles. Its sound quality was hugely impressive.

Tomo (S): 
I'd heard of it, naturally. But as you can see just by looking at it, it's somewhat on the large side, so I didn't think we'd ever get to use it!

Hiro (S):
When we requested a sample from Alps Electric for use in a prototype, I think they found it strange that the Walkman® development team wanted a volume control as giant as the RK501!

Has the RK501 used in the DMP-Z1 been modified at all?

Tomo (S):
We worked together with Alps Electric on the customized version built into the DMP-Z1. The first thing we tried was swapping the brass casing to aluminum to reduce the weight of the device. In theory, this shouldn't have had any effect on the sound, but when we actually listened, we found that the sound had become very light.

Hiro (S): 
The team from Alps Electric also did listening tests and looked at the internal structure of the volume control with us, to help figure out why sound quality was being affected by the material used in the volume control casing.

Tomo (S): 
As is always the way when testing audio quality, we had to produce prototypes and actually listen to them in order to get to the bottom of it. And so we kept trying out lots of different variations and kept requesting prototypes, without a thought for mass production. We customized it with all kinds of different specifications to try and improve the sound quality, like aluminum casing with gold plating, almite processing, changing part of it back to brass, etc. But for all our trial and error, we couldn't make the sound any better. Eventually we thought the sound quality would improve if we customized the original and gave up on trying to reduce the weight, so we changed the base metal used in the casing back to brass. At long last, when trialling the prototype with a combination of brass plating and gold plating, which is used in the NW-WM1Z from the first part of the Signature Series, we were finally able to create a customized volume control that surpassed the original RK501 in terms of sound quality.

Hiro (S): 
As we'd only asked the Alps Electric team for prototypes up to that point, we weren't sure whether they'd allow us to mass produce it. But when we all listened and compared the sound quality together, they agreed that the sound was indeed different and gave us the green light to take it to mass production. With this customization, the device is able to reproduce a clearer and more transparent high end than the original RK501, as well as incredibly deep and powerful bass in the low end.

Analog volume control process
Tomoaki Sato demonstrating analog volume control

Finally, is there anything you would all like to say to people reading this article?

Tanaka:
We designed this product with the goal of providing a headphone listening environment unrivalled by conventional desktop audio devices. And so, as I've been saying throughout, I'm proud that we've managed to achieve that, thanks to the passion of our engineers. I know this device can deliver a sound to your favourite headphones the likes of which you've never heard before, so I'd like to invite you all to bring your headphones to a Sony store and give it a try. I'd like everyone to come and experience for themselves just how different the sound is.

What's more, it has a lot to offer in terms of signal processing technology, which is something Sony excels at, including the newly developed DSEE HX™, Vinyl Processor and DSD Remastering Engine. With a combination of these functions, it's a product you can enjoy for a long time.

Tomo (S):
At first glance, the DMP-Z1 may look like a desktop device, but it's actually made by the Walkman® team. I think many people will be interested in hearing what kind of sound we have pursued with an analog amplifier, given that the Walkman® team have been a proponent of full digital amplifiers until now.

Analog amplifiers are sometimes said to have a warm, soft tone, but characteristics like these are heavily reliant on the design of the power circuits and audio circuits. In fact, an analog amplifier with a properly made power source won't result in a warm or soft tone. One of the causes of the soft tone on an analog amplifier is not enough power being supplied to the amplifier due to a poor power source, or it may be the case that it has been designed specifically to produce that tone quality. We wanted to bring out the finer sounds in the same way as the S-Master HX, but through an analog amplifier that can offer large output and added punch beyond that of a digital amplifier. I think that by achieving this, we've managed to give the product a touch of its character.

Matsuzaki: 
This product is a culmination of all the techniques and expertise I've built up since joining the Walkman® team many years ago. I can safely say that I've put my all into it. So please, take a trusted pair of headphones and give your favourite music a fresh new listen. If you listen to the DMP-Z1 using headphones with the potential for high quality sound, it's easy to understand. It creates a spatial audio effect never heard in headphones before now, by reproducing not only a wide horizontal sound field, but also a high vertical field, allowing you to feel the spatial audio effect in front of you and behind you as well. I'm certain you'll discover something new.

Hiro (S): 
These past 30 years, every time a new product has come out, there's a CD that I've tested it against, and this time I truly did discover something new. In fact, this product places importance not only on high resolution, but also on accurately bringing out the sound of an audio CD. Through technology that has been honed over many years, the DMP-Z1 is a portable player that lets you hear all the audio packed onto a CD in the most incredible detail. I'm repeating what was said before, but I would encourage you to visit a shop and experience that sound for yourself.