Battery and Power Supply Design
This is a long and technical topic, please go through it with patience, you don't have to understand these technical detail in order to appreciate the N30LE DAP, but it is an interesting read for those who enjoy digging deep into their audio equipment.
High-Quality Power supply is the foundation of High Fidelity Audio. This is a statement that experienced audiophiles will recognize from the bottom of their heart. After all, the game of high-fidelity audio is ultimately the transformation of electrical energy into sound waves.
Maybe I can illustrate my point by briefly summarizing the first 10 years of my audiophile journey into three distinctive stages. Stage 1 was all about features and components, I create my own product comparison tables and study the key components, with my science training background, I tried to track down the raw information from suppliers instead of relying on consumer product reviews, and that was a nightmare back in the 90s when the Internet is not as informative as today. Sooner or later, I notice “implementation” matters, so in stage 2, I focused on circuitry and product design. I spend a lot of time drawing up functional diagrams of the HiFi products I owned. This slowly developed into an addiction and I continued to do this today, with every DAP I represented. By that time, I was a full-time project leader in Home Entertainment product development and a part-time reviewer in a local HiFi magazine. These two roles allow me to try out a lot of high-end products that I couldn’t afford and meet with engineers I had worshipped since my early time as an audiophile, and these exposures lead me to Stage 3: Power supply is the foundation of High Fidelity Audio. When you change (or upgrade as far as most audiophiles are concerned) a component or modified the circuit design, quite often you’ll gain something in due course, but unfortunately, you’ll also lose something in other less prominent areas. The only exception is enhancing your power supply. This is always the most fruitful tweak in the audiophile system. Experienced audiophiles/reviewers will pay a lot of attention to the power supply implementation of the product they are paying for, but this is rarely an important topic in the portable audio community.
So let’s take a look at the power supply requirements of N30LE:
- Hyper Mode: This is by far the most demanding new feature in N30LE in terms of power supply. When we can’t even enable Class A and P+ mode simultaneously in N8ii, the Hyper mode only existed as a dream before N30LE.
- Discrete Headphone amplifier: we have discussed the advantage and technical difficulties to implement a discrete headphone amplifier, but does it occur to you that a discrete circuit will always drain more power and required more caretaking to provide the appropriate power supply to specific components when compared to highly integrated Op-Amp circuits?
- Digital Audio circuit: the AK4499EQ is a very power-hungry chip, more so if we use them in current output mono mode because we need to provide a matching IV converter network in order to drain the maximum performance of these DAC chips.
- Timbre Circuit: while the Classic/Modern Tube timbre circuitry is extremely complicated, it's the new feature to extend the Nutube timber circuit to Line Out and Preamp out that complicated the power supply design. As always, large analog components such as Nutube 6P1 are very sensitive to power supply, therefore power supply design is crucially important when we adopt Nutube in multiple output scenarios. For the record, Cayin remains the only DAP brand that implemented a matched pair of Nutube in DAP.
The N30LE is powered by a piece of custom ordered a piece of 12570mAh 3.8V lithium-ion polymer battery that provides up to 48Wh of power capacity. This is around triple the power capacity of a modern mobile phone. With this enormous power capacity, we can keep the N30LE running continuously for a reasonable time in each charging cycle (around 7.25Hr to 11 Hr). We have also implemented PD2.0 (18W) fast charging to minimize idle time during charging. The lithium-ion polymer battery pack adopts a structure where two cells are connected in series and then parallel after precise matching of parameters such as capacity and internal resistance.
To customize/enhance the power supply to meet various load-carrying and power supply demands across different scenarios, we have added multiple DC/DC converters, LDO, and filtering capacitors as deemed necessary. Among these, the power supply to the discrete headphone amplifier is definitely the most critical section in our overall power supply design. To facilitate (1) and (2) mentioned previously, we added a piece of Murata's DMF series 470mF/5.5V ELDC (Electric Double-Layer Capacitor) ultra-capacitor to make sure the circuit will have all the power it needed and at the time it needed. The ELDC ultra-capacitor has extremely low ESR (equivalent series resistance) and rapid charge-discharge response. It is equivalent to a large reserve of electrical power, making sure the analog circuitry will have ample power supply at all times.
The architecture of the main power supply showcases N30LE's excellent dynamic performance capabilities by providing stable output with abundant load-carrying capability and revealing transient details even at low volume levels. We have pushed the envelope by, for the first time, applying ELDC ultra-capacitor in portable products. The N30LE power supply system is the cornerstone of its superior audio performance, His only drawback is that it increases the size and weight of the DAP.
Power Amplifier Circuit Power Supply
Being fully differential by design, the N30LE features four channels of headphone amplifier circuits (L+, L-, R+, R-), and each channel is powered by a current mode high-current and high-dynamic DC/DC converters (LT8334) separately. Instead of using linear voltage regulator ICs for secondary regulation, which is a conventional practice in power supply design, we adopt an LC-enhanced filtering circuit to provide a direct power supply to the headphone amplifier circuit after secondary filtering. This maximizes the purity of the power supply, reduces internal resistance, and achieves faster response.
DAC Decoding Circuit Power Supply
We have explained our Digital Audio circuit design previously (HERE). The AK4499EQ DAC chipsets are programmed to provide fully balanced current output across all channels (8 channels). We shall connect these outputs in parallel (per 2 channels), and feed into a 2x2 IV converter network (four dual channel op-amp). There are several different options to implement the AK4499EQ in mono mode. For instance, instead of using all eight outputs, you can use only four outputs per chip (i.e., half the outputs only) and you can still be able to achieve a fully balanced DAC circuit. N30LE connects every two outputs in parallel to Increase the load capacity of the DAC circuit. On the other hand, you can program the AK4499EQ as voltage output by using the internal IV converter in the DAC chipset. This will simplify the circuit design and reduce the overall power consumption, but in our experience, a properly designed current output DAC will almost always outperform the voltage output of the same DAC because the internal IV converters are inevitably a bottleneck of the system. The 2x2 IV converter network is a substantial design for portable applications, it will provide an optimized DAC output stage for subsequent audio circuits. The functional diagram of N30LE and the block diagram of AK4499EQ will illustrate this specific dual AK4499EQ implementation.
As per the Level, 1 functional diagram of the Power Supply System of N30LE, the complete digital audio power supply involves 5 subsystems: DAC (Left), DAC (Right), IV Conversion (Left), IV Conversion (Right), and other support circuitry in Digital Audio systems such as I2S, FPGA, and Femtosecond Oscillators.
The AK4499EQ DAC chip uses two completely independent power systems, with each left and right channel DAC having its own separate power system. Each set of DAC power includes 1 set of highly efficient low-noise DC/DC converters and four sets of low-noise LDOs with different current capacities and dynamic ranges, they are adapted to meet the specific need of different functions in the chipset. Our power supply system has exceeded the reference AKM design which is more power efficient for versatile applications. We are determined to power the DAC chipset properly so that its full performance will be unleashed in N30LE. This will be significantly better than running AK4499 in starving conditions (i.e., insufficiently powered).
The FPGA is provided with 3.3V, 1.8V, and 1.2V voltages separately by three separate low-noise LDO regulators; while the dual femtosecond crystal clock circuit operates at a working voltage of 1.8V supplied by an independent low-noise LDO regulator.
Last but not least, we have also used high-quality Panasonic POSCAP tantalum polymer capacitors for filtering in each sub-power supply along with NP0 and X7R capacitors to comprehensively enhance the dynamic performance of the power system.
To conclude, N30LE has optimized its circuit design and power supply design to maximize the performance of the dual AK4499 DAC chipsets.
Last edited:
