[Update completed]FiiO K9 Pro R&D Stories
Oct 6, 2021 at 4:55 AM Thread Starter Post #1 of 26

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Chapter 1 Why would the FiiO K9 Pro keep you waiting for such a long time?

Perseverance makes who you are. The K9 Pro, FiiO's latest flagship DAC/Amp, finally entered the market!

It took about 20 months from its first appearance to its final release. For FiiO, one of the strong manufacturers in the HiFi industry in China, it seemed absolutely abnormal.

What was the reason for the repeated delay of such a well-planned product? And what kept our users waiting for so long? Today, I, as FiiO's product manager of the DAC/Amp line, would like to give you a brief explanation.

image001.png


The whole K9 Pro project has taken about 2 years from the start to release. Here is the rough timeline.

--In November 2019, the new desktop DAC/Amp project started, with a tentative model as K7.

--In January 2020, the FiiO forum announced the project information.

--In May 2020, the first draft of the product ID and electronic scheme was completed.

--In June 2020, we decided to re-plan the project as the higher-end K9 Pro with configurations and features upgraded according to user feedback.

--In September 2020, the K9 Pro was first exhibited at the Guangzhou Headphone Exhibition.

--In October 2020, an accidental fire happened to AKM, which resulted in a chip shortage. The whole project went back to the beginning.

--In November 2020, after clearly knowing AKM's inventory and losses, we decided to start an initial K9 Pro version with a single AK4499.

--In December 2020, the wave of chip shortage spread that the supply of the THX 788 amp chip was cut off, so we were forced to select another chip scheme.

--In March 2021, during the reliability test, we found that the balanced output of the THX 788 would be thermally exhausted due to temperature rise. After discussing with THX, we used the alternative scheme.

--In April 2021, we readjusted the parameters after using the alternative scheme.

--In May 2021, the K9 Pro passed the product reliability and function tests.

--In June 2021, the K9 Pro prototype was qualified for trial production.

--In July 2021, we started trial production in a small batch.

--In August 2021, we produced the K9 Pro in a medium batch and started to sell them in China.

From the timeline, we can see how difficult the R&D process of the K9 Pro was. First, it was the plan adjustment, and then three negative changes to the DAC chip, amp chip and amp module. Every success behind these adjustments was quite hard. It was the result of countless experiments and tests by our group members of the K9 Pro project.
image003.png


For example, it took us nearly 2 months to successfully adjust the THX AAA 788+ headphone amp module.

When our quality test team found that the balanced output of the THX module would be heat exhausted in March, we were quite confused. After all, this was not the first time for us to use the THX 788. Unfortunately, after many experiments, the result was still the same. Some of the K9 Pro would even be thermally protected even after working for about ten minutes. We were so frustrated. Was it the circuit design issue, or the module issue?
image006.gif


We discussed it several times. For one thing, we tried to get a prototype device overseas. For another, we kept communicating with the THX R&D crew (they were basically not in the office at that time because of the COVID-19). In a word, it was very difficult.

Unfortunately, both the communication results and the retest of the purchased prototype were basically the same as our previous experiments. That was: the original scheme did not support long-term stable work in high-power mode. And THX also admitted such shortcomings.

It is true that most people will not select the maximum power for a long time when listening to music. So, should we just ignore this problem, or try to figure it out? To do or not to do, that is a question.

As you know, we finally decided to solve this problem, because the K9 Pro is a flagship!

The project team spent 2 months changing 2 PCB schemes while keeping discussing with the THX R&D team. Eventually, we solved the problem. THX thus gave a new name to our module, THX AAA-788+.
image008.gif



This little "+" was really a condensation of lots of our time and effort!
image010.gif


The whole process was full of challenges. Every change and adjustment required repeated tests and experiments. Fortunately, the K9 Pro is now qualified to enter the market. I believe most of you will like it. After all, it embodies the efforts and pursuits of a group of engineers.
01.png
 
Last edited:
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Oct 6, 2021 at 12:07 PM Post #3 of 26
Chapter 1 Why would the FiiO K9 Pro keep you waiting for such a long time?

Perseverance makes who you are. The K9 Pro, FiiO's latest flagship DAC/Amp, finally entered the market!

It took about 20 months from its first appearance to its final release. For FiiO, one of the strong manufacturers in the HiFi industry in China, it seemed absolutely abnormal.

What was the reason for the repeated delay of such a well-planned product? And what kept our users waiting for so long? Today, I, as FiiO's product manager of the DAC/Amp line, would like to give you a brief explanation.



The whole K9 Pro project has taken about 2 years from the start to release. Here is the rough timeline.

--In November 2019, the new desktop DAC/Amp project started, with a tentative model as K7.

--In January 2020, the FiiO forum announced the project information.

--In May 2020, the first draft of the product ID and electronic scheme was completed.

--In June 2020, we decided to re-plan the project as the higher-end K9 Pro with configurations and features upgraded according to user feedback.

--In September 2020, the K9 Pro was first exhibited at the Guangzhou Headphone Exhibition.

--In October 2020, an accidental fire happened to AKM, which resulted in a chip shortage. The whole project went back to the beginning.

--In November 2020, after clearly knowing AKM's inventory and losses, we decided to start an initial K9 Pro version with a single AK4499.

--In December 2020, the wave of chip shortage spread that the supply of the THX 788 amp chip was cut off, so we were forced to select another chip scheme.

--In March 2021, during the reliability test, we found that the balanced output of the THX 788 would be thermally exhausted due to temperature rise. After discussing with THX, we used the alternative scheme.

--In April 2021, we readjusted the parameters after using the alternative scheme.

--In May 2021, the K9 Pro passed the product reliability and function tests.

--In June 2021, the K9 Pro prototype was qualified for trial production.

--In July 2021, we started trial production in a small batch.

--In August 2021, we produced the K9 Pro in a medium batch and started to sell them in China.

From the timeline, we can see how difficult the R&D process of the K9 Pro was. First, it was the plan adjustment, and then three negative changes to the DAC chip, amp chip and amp module. Every success behind these adjustments was quite hard. It was the result of countless experiments and tests by our group members of the K9 Pro project.

For example, it took us nearly 2 months to successfully adjust the THX AAA 788+ headphone amp module.

When our quality test team found that the balanced output of the THX module would be heat exhausted in March, we were quite confused. After all, this was not the first time for us to use the THX 788. Unfortunately, after many experiments, the result was still the same. Some of the K9 Pro would even be thermally protected even after working for about ten minutes. We were so frustrated. Was it the circuit design issue, or the module issue?

We discussed it several times. For one thing, we tried to get a prototype device overseas. For another, we kept communicating with the THX R&D crew (they were basically not in the office at that time because of the COVID-19). In a word, it was very difficult.

Unfortunately, both the communication results and the retest of the purchased prototype were basically the same as our previous experiments. That was: the original scheme did not support long-term stable work in high-power mode. And THX also admitted such shortcomings.

It is true that most people will not select the maximum power for a long time when listening to music. So, should we just ignore this problem, or try to figure it out? To do or not to do, that is a question.

As you know, we finally decided to solve this problem, because the K9 Pro is a flagship!

The project team spent 2 months changing 2 PCB schemes while keeping discussing with the THX R&D team. Eventually, we solved the problem. THX thus gave a new name to our module, THX AAA-788+.



This little "+" was really a condensation of lots of our time and effort!

The whole process was full of challenges. Every change and adjustment required repeated tests and experiments. Fortunately, the K9 Pro is now qualified to enter the market. I believe most of you will like it. After all, it embodies the efforts and pursuits of a group of engineers.
Thanks for the viable information.

Show us some real measurements using the audio analysis equipment you use to measure this,I like Big words and slick marketing but I ain't spending money on that anymore.
 
Oct 7, 2021 at 7:39 PM Post #4 of 26
Chapter 1 Why would the FiiO K9 Pro keep you waiting for such a long time?

Perseverance makes who you are. The K9 Pro, FiiO's latest flagship DAC/Amp, finally entered the market!

It took about 20 months from its first appearance to its final release. For FiiO, one of the strong manufacturers in the HiFi industry in China, it seemed absolutely abnormal.

What was the reason for the repeated delay of such a well-planned product? And what kept our users waiting for so long? Today, I, as FiiO's product manager of the DAC/Amp line, would like to give you a brief explanation.

image001.png

The whole K9 Pro project has taken about 2 years from the start to release. Here is the rough timeline.

--In November 2019, the new desktop DAC/Amp project started, with a tentative model as K7.

--In January 2020, the FiiO forum announced the project information.

--In May 2020, the first draft of the product ID and electronic scheme was completed.

--In June 2020, we decided to re-plan the project as the higher-end K9 Pro with configurations and features upgraded according to user feedback.

--In September 2020, the K9 Pro was first exhibited at the Guangzhou Headphone Exhibition.

--In October 2020, an accidental fire happened to AKM, which resulted in a chip shortage. The whole project went back to the beginning.

--In November 2020, after clearly knowing AKM's inventory and losses, we decided to start an initial K9 Pro version with a single AK4499.

--In December 2020, the wave of chip shortage spread that the supply of the THX 788 amp chip was cut off, so we were forced to select another chip scheme.

--In March 2021, during the reliability test, we found that the balanced output of the THX 788 would be thermally exhausted due to temperature rise. After discussing with THX, we used the alternative scheme.

--In April 2021, we readjusted the parameters after using the alternative scheme.

--In May 2021, the K9 Pro passed the product reliability and function tests.

--In June 2021, the K9 Pro prototype was qualified for trial production.

--In July 2021, we started trial production in a small batch.

--In August 2021, we produced the K9 Pro in a medium batch and started to sell them in China.

From the timeline, we can see how difficult the R&D process of the K9 Pro was. First, it was the plan adjustment, and then three negative changes to the DAC chip, amp chip and amp module. Every success behind these adjustments was quite hard. It was the result of countless experiments and tests by our group members of the K9 Pro project.
image003.png

For example, it took us nearly 2 months to successfully adjust the THX AAA 788+ headphone amp module.

When our quality test team found that the balanced output of the THX module would be heat exhausted in March, we were quite confused. After all, this was not the first time for us to use the THX 788. Unfortunately, after many experiments, the result was still the same. Some of the K9 Pro would even be thermally protected even after working for about ten minutes. We were so frustrated. Was it the circuit design issue, or the module issue?
image006.gif

We discussed it several times. For one thing, we tried to get a prototype device overseas. For another, we kept communicating with the THX R&D crew (they were basically not in the office at that time because of the COVID-19). In a word, it was very difficult.

Unfortunately, both the communication results and the retest of the purchased prototype were basically the same as our previous experiments. That was: the original scheme did not support long-term stable work in high-power mode. And THX also admitted such shortcomings.

It is true that most people will not select the maximum power for a long time when listening to music. So, should we just ignore this problem, or try to figure it out? To do or not to do, that is a question.

As you know, we finally decided to solve this problem, because the K9 Pro is a flagship!

The project team spent 2 months changing 2 PCB schemes while keeping discussing with the THX R&D team. Eventually, we solved the problem. THX thus gave a new name to our module, THX AAA-788+.
image008.gif


This little "+" was really a condensation of lots of our time and effort!
image010.gif

The whole process was full of challenges. Every change and adjustment required repeated tests and experiments. Fortunately, the K9 Pro is now qualified to enter the market. I believe most of you will like it. After all, it embodies the efforts and pursuits of a group of engineers.
01.png
Someone's attended the Jason Stoddard school of product reveal.
 
Oct 8, 2021 at 6:09 AM Post #5 of 26
Chapter 2 Can we make a good product without a display screen?

The K9 Pro has been on the market for a few days, and many users like it very much. But those who are eager to buy one asked me, why does it not come with a display? Is it easy to operate? And some users also questioned how a product can be a flagship without a display screen?

We also struggled for a long time when we were designing it. Today, let's dive deep into the details of the FiiO K9 Pro.

Two years ago, in November 2019, we initiated the K7 project. Some of you may remember we used to post some discussions about the K7 in our forum and on some foreign websites. This was its initial appearance design. Quite attracted, isn't it?
1.jpg


While the final appearance is like this.
2.png


In fact, we would make a lot of designs for each of our products. For example, the following designs were all under our consideration.
3.png


These designs have also been evaluated for feasibility.
The display screen was the most discussed topic in the middle of the K9 Pro's ID design.
4.png


Some thought that a display is intuitive, high-end, and in line with the characteristics of most products. Because many power amplifiers and desktop devices on the market all have a display. In this regard, we specifically conducted a survey, in which we found that more than 93% of similar products have a display screen.
5.png


However, some thought that although the display is intuitive, it is inconvenient to operate with less practicability. Since it comes with remote control.
6.jpg


So, which one would be the right one? We had divergent opinions until we experienced the prototype.
7.jpg


The K9 Pro is a desktop DAC/Amp. If there are two choices- operate it with remote control and view the working states through the display screen, or operate it with physical buttons and view the working states through the indicator light. Which one is more sensible and convenient?

After experiencing it, most people said that it's also ok without a display screen.

Thinking about it now, it was so exciting and funny.

After that, I thought a lot. As the product manager, how can I make an excellent product? Now I understand there is no better way, but to stand where our users stand. Considerate more, explore more.

Back to the K9 Pro itself:
1. Unlike most products, the K9 Pro was positioned as a desktop product. So it should be easily reached even without a display screen.
2. Physical buttons + RGB indicator light + input instructions are also very intuitive.
3. If there are users who really love remote control, it can also be achieved on the FiiO Control App.
4. It is also a consumer cost issue. For a relatively cost-sensitive product like the K9 Pro, if a display screen + remote control are added, the final cost will be mapped to the product price. Especially in a situation with rising raw material costs, this issue will be more obvious.
8.png


This is why the K9 Pro didn't use a display.

But this doesn't mean we FiiO will not use a display screen in our future desktop devices. Because different product forms and products with different positioning have different needs for display screens. Whether and how to use it depends on the final use scenarios.

Therefore, a product without a display screen can also be a good and practical product, right? I hope this article can dispel your doubts about the display screen.

In the end, for those who have already got the K9 Pro, how do you think about its design, good or bad?
 
FiiO Stay updated on FiiO at their sponsor profile on Head-Fi.
 
https://www.facebook.com/FiiOAUDIO https://twitter.com/FiiO_official https://www.instagram.com/fiioofficial/ https://www.fiio.com support@fiio.com
Oct 8, 2021 at 7:51 AM Post #6 of 26
In the dedicated desktop environment within which this product operates l agree a display seems mostly unnecessary. What I hope when I can demo an F9 Pro is that it’s performance with surpass my M15 as a headphone amp.
 
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Oct 9, 2021 at 6:52 PM Post #7 of 26
Is the K9pro a limited edition ? How many will be produced?
 
Oct 9, 2021 at 7:56 PM Post #8 of 26
Chapter 2 Can we make a good product without a display screen?

The K9 Pro has been on the market for a few days, and many users like it very much. But those who are eager to buy one asked me, why does it not come with a display? Is it easy to operate? And some users also questioned how a product can be a flagship without a display screen?

We also struggled for a long time when we were designing it. Today, let's dive deep into the details of the FiiO K9 Pro.

Two years ago, in November 2019, we initiated the K7 project. Some of you may remember we used to post some discussions about the K7 in our forum and on some foreign websites. This was its initial appearance design. Quite attracted, isn't it?
1.jpg

While the final appearance is like this.
2.png

In fact, we would make a lot of designs for each of our products. For example, the following designs were all under our consideration.
3.png

These designs have also been evaluated for feasibility.
The display screen was the most discussed topic in the middle of the K9 Pro's ID design.
4.png

Some thought that a display is intuitive, high-end, and in line with the characteristics of most products. Because many power amplifiers and desktop devices on the market all have a display. In this regard, we specifically conducted a survey, in which we found that more than 93% of similar products have a display screen.
5.png

However, some thought that although the display is intuitive, it is inconvenient to operate with less practicability. Since it comes with remote control.
6.jpg

So, which one would be the right one? We had divergent opinions until we experienced the prototype.
7.jpg

The K9 Pro is a desktop DAC/Amp. If there are two choices- operate it with remote control and view the working states through the display screen, or operate it with physical buttons and view the working states through the indicator light. Which one is more sensible and convenient?

After experiencing it, most people said that it's also ok without a display screen.

Thinking about it now, it was so exciting and funny.

After that, I thought a lot. As the product manager, how can I make an excellent product? Now I understand there is no better way, but to stand where our users stand. Considerate more, explore more.

Back to the K9 Pro itself:
1. Unlike most products, the K9 Pro was positioned as a desktop product. So it should be easily reached even without a display screen.
2. Physical buttons + RGB indicator light + input instructions are also very intuitive.
3. If there are users who really love remote control, it can also be achieved on the FiiO Control App.
4. It is also a consumer cost issue. For a relatively cost-sensitive product like the K9 Pro, if a display screen + remote control are added, the final cost will be mapped to the product price. Especially in a situation with rising raw material costs, this issue will be more obvious.
8.png

This is why the K9 Pro didn't use a display.

But this doesn't mean we FiiO will not use a display screen in our future desktop devices. Because different product forms and products with different positioning have different needs for display screens. Whether and how to use it depends on the final use scenarios.

Therefore, a product without a display screen can also be a good and practical product, right? I hope this article can dispel your doubts about the display screen.

In the end, for those who have already got the K9 Pro, how do you think about its design, good or bad?
I'll say it,when you design globally westerners want a screen,your designer's have to think outside of China,hope y'all can understand that.
 
Oct 10, 2021 at 4:36 AM Post #10 of 26
How does the unit perform as a headphone amplifier compared to similar or more costly products?
Amp ain't even reaching full potential with the thx788,they should have made a flagship dac and Amp and charged $350 to $400 for each,don't fall for the limited akm chip B.S. but if you have to have one get one.
 
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Oct 11, 2021 at 3:48 AM Post #11 of 26
Chapter 3-1 What exactly is the THX AAA-788+ amp module?

Since the release of FiiO's first module AM3C/AM3D using the THX AAA headphone amplifier technology at the end of 2018, it's been 3 years. During these 3 years, we have been using the THX AAA headphone amplifier technology and gradually expanded it to the Q5s, M11 Pro, and Q3. , M11 Plus Ltd and other products.

Many users have become accustomed to the sound performance of THX AAA amps. After the K9 Pro went on the market, almost all users said that the sound was pretty good.

Why is THX AAA amp technology so amazing, and what other black technologies does it contain? Today, I would like to dig them out with you.

Those who know THX AAA probably know its unique signal amplification and error correction technologies. When coupled with the serious op-amp structure, it has strong audio performance and output efficiency, lower distortion and better sound quality.

There is a picture on the THX official website, which vividly introduces the product line of THX AAA headphone amplifiers.
image031.png


As you can see from the picture above, the THX AAA-788 is one of the best amps among the entire THX AAA technology, and it is THX's sub-flagship amp.

It is also clearly marked here, the 788 is specially used in desktop amplifiers.
image033.png


Some users may notice that the above picture does not contain the THX AAA 788+ model used in the K9 Pro. What is the reason?

If you have read my previous articles, you may know the THX AAA technology used in the K9 Pro is an improvement based on the original one.

THX AAA is an amplifier technology, and each of the names is just to distinguish different power consumption and power levels. When applied to specific products, some necessary adjustments will be made according to the actual needs of the products. The AAA 788+ used this time is based on FiiO's previous THX circuit debugging experience and circuit characteristics of the K9 Pro. Therefore, it is an enhanced version based on the THX AAA-788.

The new THX AAA-788+ has lower output impedance, higher heat dissipation efficiency and stronger load capacity. Compared with the original version, its output power is increased by 50%!
image035.jpg


Compared with the original version, the THX AAA-788+ has a more unique design, which also went through some twists and turns.

At first, when we were testing the THX AAA-788, we were pleasantly surprised that it can maintain ultra-low distortion and noise under extremely high swings. As we all know, this feature fits perfectly with desktop devices, because desktop devices have a higher supply voltage and high output power while ordinary amplifiers will show nonlinear high noise floor at such a high gain.

However, as we dived into the product design, we found that the 788 actually has some shortcomings. For example, it can maintain 1.8W output power in the single-ended mode, but when two THX AAA-788 amps were combined for balanced output, the output heat exhaustion will quickly raise due to the temperature rise, and it cannot last for a long time at all.
image037.png


Actually, this problem only occurred in strict test conditions and would not be easily realized by ordinary customers. But it was not permitted in the K9 Pro not only because it was a flagship, but also because of FiiO's strict quality control.

Therefore, we must work with the THX team to find a solution with a stronger load capacity.

After rounds of discussions, back-and-forth email communications, as well as repeated testing and listening experiments by our engineers, we eventually figured out a new rear driver chip, the TPA6120.
image039.jpg


This is an ordinary yet well-known chip. It is ordinary because of his low-key presence in many TI products. The keywords introduced on its official website are:
Current feedback ‖ SNR of 128dB ‖ THD of 112.5dB ‖ 0.9µV at Gain = 1 ‖ 1300V/µs Slew Rate

Although it is very common, it is still an outstanding amp chip featuring high-performance audio specifications.

It is well-known because it was used in tons of famous audio brands, such as Sennheiser HDV, SONY DMP-Z1/PHA, and Klipsch Heritage.
Sennheiser HDV:
image041.jpg

SONY DMP-Z1/PHA:
image043.jpg


Of course, FiiO has also used it on many products, such as the E9 docking amp, the X7 AM5 power-hungry amp module, the K5 Pro, and now the K9 Pro. Experiencing small desktop, portable and large desktop, it has arrived at the fourth generation.

image045.gif

It can be said that we have learned how to make the best use of this chip. You may be confused why there are so many secrets of an amplifier chip?

Indeed, it is. Because the TPA6120 has a current feedback architecture, where a 10Ω resistor is required in series at the output end to prevent self-excitation capacitive loads. However, this output resistance is detrimental to the sound quality of the amp.

In summary, the output impedance of the amplifier will affect the frequency division of multi-driver earphones! We have solved this problem as early as the K5 after research and design improvements on multiple projects. The output impedance of the TPA6120 amplifier is greatly reduced to about 1Ω.
1633938483167.png


Such output performance not only improves the fidelity of multi-driver earphones, but also improves the damping characteristics of the amplifier, which can drive large dynamic driver earphones with ease.

Since the THX AAA-788 can bring such a large power increase by changing the rear amplification, are other performances equally excellent and qualified to be the THX?
image049.gif


The answer is yes. As mentioned above, THX and FiiO participated in this circuit upgrade together, and the circuit change occupies a large proportion in the development process of the K9 Pro.

While maintaining the circuit architecture of the THX AAA, the characteristics of error correction and multi-level excitation are still maintained. In order to guarantee a very high level when dealing with both low-power amplification and large dynamic output, engineers added multi-level hardware gains to the original circuit, which is a combination of both ability and character.
image051.gif


And the "THX AAA-788+" is also a customized model specially given to us by THX. This small "+" embodies the joint efforts and persistence of both of us.

Now you may understand why our new amp model is called "THX AAA-788+". If you want to learn more about THX AAA amp technology, please pay attention to my next chapter.
 
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Oct 11, 2021 at 1:33 PM Post #12 of 26
To be honest, an effective display is a welcome addition to any such device. Drop the MQA (aka: "The FARCE be with You") and instead give us an appropriately applied, high quality display. Or don't.

FiiO makes some great DAPs with useful displays and a DAC/AMP of such quality as is the K9 Pro doesn't need farcical foofoo "tech" like Stuart's Folly. Because MQA is included I am excluding it from my list of desirable products. I just purchased a couple of SMSL THX headphone amps for my son and my brother and they do not have MQA. If they did I would never buy them.

MQA is the "gift" that keeps on giving. To Bob.

By the way, "gift" in German is "poison". Appropriate for MQA. I have no real clue as to why some manufacturers include this "gift" as a feature. I am not alone in my disgust for this Scheme by Stuart. I like FiiO and their products. I loathe MQA for what it is and is not, i.e., The FARCE and NOT worthy of my hard earned money.

ORT
 
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Oct 12, 2021 at 7:00 PM Post #15 of 26
Why are post being deleted?You saying we can't be objective,I paid almost $1000 for the M11 + and I can go on about all the gear I bought from FiiO but I can't be objective,Head Fi supposed to bigger than this, am I wrong.
 
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