R2R decoder: Feiao K11 R2R evaluation/disassembly
R2R decoder: Feiao K11 R2R evaluation/disassembly
AudioTOP
in appearance, the K11 R2R and the first two models cannot be said to be deja vu, but can only be said to be exactly the same. However, it is actually an iconic product for Feiao. Before that, Feiao had not seen R2R type decoder or all-in-one machine, which may mean the beginning of a new track.
is probably for the convenience of local materials. The shell, structure and UI of K11 R2R have all been borrowed from the previous works.
front and rear panel, display, I/O port configuration, exactly the same.
In order to distinguish from other models, the "R2R" mark is marked in a conspicuous position of the casing.
the configuration of accessories. DC port external power adapter, power cord, data cable, transfer plug.
It is reported that the fuselage color in addition to the conventional silver and black, as well as red limited edition. The red looks very striking.
was CS43198, a modern mainstream Delta-& sum; class DAC chip. This time K11 R2R, as the name implies, must be loaded with R2R type decoding.
get a general understanding of R2R and decoding.
decoder, also known as a digital-to-analog converter (DAC), is a bridge between the digital and analog worlds. Although digital music or analog music contains equivalent musical information, so far, the hearing of carbon-based life can only perceive and understand the latter. The digital-to-analog converter therefore acts like a translator.
digital to analog conversion, and the R2R decoder is both direct and ingenious. At the nodes of the R2R resistor network, the weights of adjacent resistors are always twice as different, which is the same as the arrangement of binary numbers. Its structure is the projection of binary numbers on the circuit.
corresponds to a unique right that calibrates the amount of current. A 16-bit decoder has 16 weights. In the case of a 24-bit decoder, there are 24 weights. In the past, R2R was classified as a multi-bit decoder.
in the real world, something much like the R2R decoder is the balance. Each balance comes with a small box containing weights of different sizes in grams, that is, one by one. Although the balance is actually an ADC, it is indeed a multi-bit paradigm, and the law of weight distribution is close to binary.
is also a multi-bit paradigm, and R2R is cleverer than balance. As shown in the figure above, its resistance is very single, only R and 2R resistors. The closer the node to the op amp, the greater the current contribution and the higher the weight. The further away from the op amp, the smaller the current contribution and the lower the weight. I would call it a cyberscale.
also because 2R is actually equal to R R, so in fact it only needs one resistor. Whether using semiconductor technology or discrete circuits, a single resistance value means that it is easy to manufacture.
the example in the figure is a 4-bit deep decoder, that's actually what a 16-bit or 24-bit decoder looks like, but the resistor string is just a little longer.
R2R is simple, so simple that there seems to be no threshold. But not exactly. In reality, its manufactured products are instead associated with high-end and expensive. And that is precisely because of the cost.
power, the greater the responsibility. To the highest MSB, one right is equivalent to the sum of the other ownership. Its error is the most powerful damage to the performance of the entire circuit. Therefore, MSB sometimes has an external trimming resistor to correct the error, which is the reason.
in addition, as the bit depth increases, the demand for resistor accuracy increases retaliatingly. In short, the performance of the R2R decoder has a price to pay for a little bit of climbing.
finished circuit model, look at the real R2R bar. R2R used to have a large supply of chips, which was very popular for a while, but that was all in the past. There are still bits and pieces of R2R chips in the second-hand market, but this is no longer meaningful for the bulk demand of audio manufacturers.
production. TI's premium goods PCM1704 are currently half-dead and still seem to be taking orders, but the price is ugly and very discouraging.
In addition, TI has a PCM56 that is active and is available as you buy it. This is a living fossil with limited talent and a depth of only 16 bits. It is possible to make a CD player, but it is hard to make a decoder.
a few years ago, I bought a plastic bag of PCM56 for archaeology in a fish market. Only spent a little bit of silver, but also pick and pick. At that time, the seller showed me the photos of the inventory, which was less than half a ton. Out of curiosity, I went to official website two days ago to check the quotation of the new product and found that this chicken rib is not only not cheap, but also can't afford to climb high. There is a misunderstanding. It turns out that it is not sold by weight.
In a word, we can make the following argument: R2R chips used in the audio field have all been abandoned and sent. For manufacturers, it is to give up the illusion of chips, roll up their sleeves and rub their hands. Discrete R2R is the only viable operation right now.
's take a look at the dismantling of the K11 R2R.
the same shell and assembly method as the previous one, but K11 R2R is thinner and bigger. Due to the use of an external power supply, the audio board fills the entire cavity.
R2R decoding module is one of the largest parts. Next to it is the heat sink of the earpiece.
with the last K11 disassembly chart. The main difference is the DAC area. The motherboard layout of the two models is basically similar, but the wiring is redesigned.
module is connected to the motherboard through a plurality of banks.
lifted the shield, which is made of phosphor bronze. In addition to blocking electromagnetic interference, the shielding cover also has a certain heat effect.
the whole picture of R2R decoding circuit. Left: FPGA chip, as digital preprocessing. Right side: two operational amplifiers for impedance transformation. The dense array in the middle is the resistor network and electronic switches, which form the R2R network.
usually, a 24-bit stereo R2R decoding consumes 48x 2=96 resistors and 8x 6=48 switches. Since the K11 R2R is a complementary architecture with differential outputs, the number of components is multiplied by 2. Thus, in terms of stacking materials and burning speed, discrete R2R decoding has the potential to swallow gold.
the off-ear area.
USB interface chip: CT7302.
K11 R2R version has an additional 4-channel volume adjustment chip from JRC, NJW1195A.
take a look at the AP test. Let's talk about the overall performance level of this type of decoder R2R. Usually, after the R2R chip is made into a finished decoder, THD N can reach about-90dB, which is regarded as excellent performance. PCM56 can just step on this line, which is better than Philips' red-turning old fried chicken TDA1541. The later chips are like 1702/1704, which can achieve-93dB ~-95dB, which is very excellent.
discrete resistor class is worse than the chip class as a whole. From our past tests, most decoders are scattered in the range of -68 ~-88dB, and a few can reach-90dB. For discrete R2R,-90dB is a "very good" score line.
K11 R2R is-72dB, which is measured when the amplitude of the input digital signal is-6dB. If the input amplitude is greater than-6dB, the THD N will be visually worse. This shows that it is necessary to trim the resistance of the MSB node.
other items such as channel separation, noise level and other indicators, are quite good. The noise level is only two or three μV, which is very low. The output power of the ear amplifier is sufficient, and the maximum value of the balanced port is close to 1300mW. For such a small all-in-one machine, this is a very decent achievement.
Although the new K11 R2R uses decoding cores with different architectures compared with K11, in AB comparison, the sound quality difference between the two models is not as expected, and the situation of HiFi vs HuFi does not appear.
"Flower Heart" II was created from Ryukyu ballads. The original creator, Shinachangji, is the leader of the Japanese blues music industry. Like other Ryukyu songs, "Flower Heart" has a nice melody but tests the singer's range, and the average person will chop off the first sentence of the chorus. Of course, Zhou Huajian is more than capable.
said that this classic song on any terminal, will not feel bad, even on the TV. But different devices to play, there are still high and low. The interpretation of K11 R2R is obviously more infectious, and the texture of human voice is real and waxy. At 1:50, solo of electric guitar has both passion and tenacity.
, I once heard a female DJ on a radio station, while telling a connected story, while circulating the song "The Fruit of Summer" 10 times. The short and brushed prelude leads to a gentle female voice. I'm not saying that the K11 R2R's human voice has no dental sounds, it has dental sounds but has been softened, so it sounds more human.
for the same reason, listening to Nat King Cole's "Perfidia" feels an extra tenderness and affection.
the four seasons "Summer 1" here, I think K11 is better, the timbre of musical instruments is more pure, and the analysis of high-frequency details is better.
after some comparison, my choice is to leave K11 R2R. Its interpretation of pop music is more to my heart. The voice is pleasant, the atmosphere is good, and the analysis is not burnt out at the same time. Although the paper index can not catch up with modern decoders, but the subjective hearing is good.
another factor is that K11 R2R is the only R2R decoder in Feiao so far. I don't know if there will be any subsequent models in the future.
In any case, R2R is an important decoder category, a mountain in front of audio manufacturers. Go around and climb, are over the mountain, but the scenery is not the same. I hope Feiao will continue to make a little effort on the R2R track after that.
K11 basic models are sent out here. I wish everyone good luck.
Author:AudioTOP Audio Network07-18 11:14
web site:R2R decoder: Feiao K11 R2R evaluation/disassembly (weibo.com)
