cglin222
100+ Head-Fier
- Joined
- Mar 19, 2012
- Posts
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- 98
@FiiO Willson i was wondering the same too and if you have info at 64 ohm or 150 to give me an idea the in between
thanks
FiiO K9 Pro Hi-Fi DeskDop DAC&Bluetooth&Amplifier，XLR/RCA/4.4/Optical/Coaxial interface
- Thread starter FiiO Willson
- Start date
thanks
FiiO K9 Pro R&D Stories-From@FiiO Willson
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.
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.
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%!
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.
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.
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:
SONY DMP-Z1/PHA:
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.
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.
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?
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.
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.
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.
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.
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%!
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.
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.
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:
SONY DMP-Z1/PHA:
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.
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.
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?
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.
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.
Last edited:
OK, so...why do not use the thx888? More expensive? Not suitable for the amp project?FiiO K9 Pro R&D Stories-From@FiiO Willson
Chapter 3-1 What exactly is the THX AAA-78+ 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.
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.
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%!
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.
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.
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:
SONY DMP-Z1/PHA:
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.
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.
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?
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.
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.
@FiiO @FiiO Willson
Fiio app (I'm interested in the IOS version) is able to change the output when I'm using BT and the input is USB?
My K9Pro is coming (
) and I'd like to ask about switching between speakers & headphones. If I can, I'd like to avoid using that front switch usage more times a day (and as far as I know, there is no remote controller).
I know, the physical switch won't follow the output, if the application will change it.
Second question:
The cable (USB c - lighting) which came with my iPhone, will work, or do I need some kind of OTG cable?
Fiio app (I'm interested in the IOS version) is able to change the output when I'm using BT and the input is USB?
My K9Pro is coming (
) and I'd like to ask about switching between speakers & headphones. If I can, I'd like to avoid using that front switch usage more times a day (and as far as I know, there is no remote controller).I know, the physical switch won't follow the output, if the application will change it.
Second question:
The cable (USB c - lighting) which came with my iPhone, will work, or do I need some kind of OTG cable?
Last edited:
Uebelkraehe
500+ Head-Fier
Got mine earlier than expected today. Too early for any serious impressions, but it drives my IEMs and headphones from FD1 to Heddphone ( 
) without running into noise or power limitations. The latter with the volume dial (high gain, balanced) just around 12 o'clock. Pretty impressive start and quite a bit more than i expected on the high power end.
Edit: The bass wobble on James Blake's "Limit to your love" is just delicious with the K9 Pro and the Heddphone. Not at all just 'loud enough' but excellent control and texture.
) without running into noise or power limitations. The latter with the volume dial (high gain, balanced) just around 12 o'clock. Pretty impressive start and quite a bit more than i expected on the high power end.Edit: The bass wobble on James Blake's "Limit to your love" is just delicious with the K9 Pro and the Heddphone. Not at all just 'loud enough' but excellent control and texture.
Last edited:
The K9 Pro is an interesting device in terms of connectivity—especially the 4.4mm balanced input. Vinyl listeners could pair the iFi ZEN Phono with a single 4.4mm cable. In general, the K9 Pro could be a practical hub for listeners who want to combine analog and digital sources, outputting to powered speakers and headphones.
Does anyone know of similar devices featuring 4.4mm balanced analog input, coaxial digital input, balanced preamp output (XLR or TRS), and 4.4mm balanced headphone output?
Does anyone know of similar devices featuring 4.4mm balanced analog input, coaxial digital input, balanced preamp output (XLR or TRS), and 4.4mm balanced headphone output?
Could you try the Fiio apps to change the output? I'd like to change between speakers and headphones, I'm courious could be work or not.Got mine earlier than expected today. Too early for any serious impressions, but it drives my IEMs and headphones from FD1 to Heddphone (
Edit: The bass wobble on James Blake's "Limit to your love" is just delicious with the K9 Pro and the Heddphone. Not at all just 'loud enough' but excellent control and texture.
Uebelkraehe
500+ Head-Fier
I'll take a look at it this evening.
ScubaDrunk
100+ Head-Fier
I just received mine this morning and have tried to hook up my iPhone 13 pro max to it using a Apple USB-C to Lightning cable from the phone into the K9 side USB-C port but nothing plays. K9 is set to USB input and output is set to HP using the 4.4 balanced headphones out on the front of the K9
I'm using Apple music on the iPhone so wondering if the fact that I'm using Apple Music on the iPhone is the issue causing no sound coming out of the K9???
What do you have hooked up to the K9 to get your phone playing music thru the K9 and what music application are you using please?
itsnein
100+ Head-Fier
I am using macbook usb-c out, and android phone usb-c out. Both with Tidal app. Both works great
ScubaDrunk
100+ Head-Fier
Ok so I think the issue is Apple Music on the iPhone when connected to the K9. No sounds comes out of the K9.
Strange when you can use another DAC connected to the iPhone whilst using Apple music and sound comes out all ok. For example a Fiio q1 mk2 plays apple music on the iPhone just fine so why not the K9???
@FiiO any ideas on this please???
Uebelkraehe
500+ Head-Fier
No output change through the app, but considering that there's a physical switch, this is probably not a surprise.
TommyGeenexus
Head-Fier
I've upgraded to the K9 Pro coming from a K5 Pro, and to me (paired with AKG K702s) the listening experience is much improved all around.
Also another big plus is that you can easily build your own K9 control application if you are somewhat familiar with Bluetooth/BLE/QCOM GAIA.
For me the K9 so far has been very much worth the money due to the sheer versatility it provides.
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