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PCB Design and Supported Technologies

The Auzen X-Fi Forte 7.1 has a black PCB with a unique velvety coating I have never seen before. Together with the darkened metal of the mounting bracket and the bright green capacitors, this endows the card with an original and attractive appearance that the photograph fails to convey.

Thanks to its reduced height, the sound card can be installed into slim system cases. The Auzen X-Fi Forte 7.1 is designed like the out-of-production Audiotrak Prodigy 7.1 LT which also used to have an integrated headphones amplifier and a braid with 3.5mm analog connectors. Modern low-profile sound cards come either with fewer outputs (like the Audiotrak Prodigy HD2) or with analog inputs and optical output combined (ASUS Xonar D1) or with nonstandard output connectors (Creative X-Fi XtremeAudio) or with all of that (Creative X-Fi XtremeGamer). And if you need a low-profile PCI Express sound card, your choice is limited to two models only: the ASUS Xonar DX and the Auzen X-Fi Forte 7.1 that I am talking about right now.

The card’s heart is the latest audio processor E-MU 20K2 that is used by Creative in its Titanium series sound cards. It is identical to the E-MU 20K1, the basis of all X-Fi family cards, in terms of sound processing, but features an integrated bus controller optimized for PCI Express and supports DDR memory. As opposed to the Auzen X-Fi Prelude 7.1, the card’s 64 megabytes of buffer memory are represented by a single X-RAM chip, which helped save PCB space.

The high component density is not only due to the specific form-factor. It is also due to the unusually broad range of functions. As I mentioned above, the X-Fi Forte 7.1 seems to trace its origin to the not-yet-released X-Fi Home Theater, but a close examination of the comparative tables reveals one important difference between them: the latter card’s four stereo outputs have identical characteristics whereas the front output of the Forte is based on a separate stereophonic DAC from Asahi Kasei and a higher-quality operation amplifier. Of course, a sound card does not have to have high-quality analog outputs if it is mostly meant to deliver sound via a digital interface (HDMI), but a high-quality DAC makes the HDMI-less model more appealing in the customer’s eyes. Moreover, the combination of AK4396 and LM4562 chips (the latter was later renamed into LME49720) was quite successful on the X-Fi Prelude. Still, I’ve got one question: why AK4396 if it is no better than the CS4382 installed on the other outputs in terms of distortions? Auzentech makes use of the AK4396 in their third sound card model in a row, why not make at least a small step forward? I don’t even mean the newest AK4399 which boasts best-in-class specs. The AK4390 would suffice as it is superior to the AK4396 across most of parameters. I can remind you that ASUS offers better DACs even in the less expensive models of their Xonar family.

Instead of a higher-quality DAC, Auzen engineers have fitted as many as two ADCs, one of which is only responsible for the microphone input on the computer case’s front panel. Neither the WM8782 (SNR -100dB, THD -93dB), nor the WM8775 (SNR -102dB, THD -95dB), which is responsible for the line, microphone and auxiliary inputs, boast high specs. Most of Creative X-Fi series cards come with the same converter and the Auzen X-Fi Forte 7.1 does not make use of two out of the eight channels provided by the CS4382 (the front output and the headphone amplifier are equipped with a dedicated AK4396 DAC), which makes me suspect that Auzentech receives a set of chips from Creative that includes an audio processor, system memory, DAC and ADC chips. Using this chip-set, the company has created an original sound card.

To tell the world how unique the Auzen X-Fi Forte 7.1 is, a special document was issued. It was later published in the Tech Notes section of the manufacturer’s website, describing in detail that the sound card is equipped with a high-precision clock generator, carefully calculated analog filters with minimum phase shift, high-quality components, and a number of exclusive technologies such as balanced power generation system, pointing ground design (using the star topology typical of high-end equipment), a composite headphones amplifier, and a microphone amplifier with balanced input. Unfortunately, I could not find any details about the clock generator and the characteristics of the filters whereas the other technical solutions are covered in the Tech Notes section, so I will only dwell upon a few unobvious points here.

One of the most important innovations implemented by Auzentech is the headphones amplifier. Until now, sound cards that allowed to directly connect headphones used to do with the modest capabilities of opamps installed on the appropriate output. When a load with a few dozen Ohms’ impedance is connected to the output of such an opamp, the latter’s linearity usually worsens and there are some other undesirable effects. Reinforcing the output with a buffer based on the same opamps helps reduce the negative consequences of low-Ohm load but does not eliminate them altogether. One possible solution of this problem has been recently examined in our review of the ASUS Xonar Essence STX sound card where a high-speed operation amplifier with current feedback plays the role of a headphone amplifier. For all advantages of such opamps, the TPA6120A2 model was not particularly good at handling a 32Ohm load while the amplifier’s output resistance could not be close to zero even theoretically because of the need for an output resistor to isolate the opamp from the load capacitance. A special buffer, e.g. an LME49600, might be used, but Auzentech engineers went their own way.

The headphone amplifier of the Auzen X-Fi Forte 7.1 is based on a composite design with an NJM4580 amplifier and a buffer based on eight transistors from an obscure maker. A couple of transistors more can be found on the reverse side of the PCB. Amplifiers based on discrete components have been considered a prerogative of expensive external devices and have not been used on sound cards except for the twin products Audiotrak Prodigy 7.1/Terratec Aureon Space whose 4-transistor buffer was Class B and did not ensure high sound quality. Thus, it is the external DAC called Audiotrak DrDAC 2 that seems to be the most similar product to the amplifier of the Auzen X-Fi Forte 7.1 but it is a few times as expensive as this whole sound card.

The purpose of the Balanced Power Generation System is to convert the +12V voltage from the PCI Express bus into bipolar ±10V power. The key feature of this system is in the symmetric filtering of the converters’ ultrasound noise to ensure that the potentials of the positive and negative buses change concordantly. Theoretically, the level of the virtual ground remains the same across a very wide range of frequencies and power noise cannot seep into the sound card’s output signal.

The Pointing Ground Design means two well-known principles. First, the digital and analog grounds are separate. And second, all ground interconnects of all analog section components converge in a single point (the so-called star). The latter principle is most important for power amplifiers because the voltage drops down in PCB interconnects when high currents are flowing in them, and the ground ceases to perform its role of the reference zero potential. The Auzen X-Fi Forte 7.1 comes with a rather serious headphone amplifier that has an output power of 2x100 milliwatts, so this wiring is quite useful.

One more special feature of the sound card is the support for microphones with symmetric signal. A symmetric transfer of weak signals can improve their protection against noise, and such microphones could only have been connected to studio equipment or professional sound interfaces like the E-MU 1820, which are absolutely incomparable to the Auzen X-Fi Forte 7.1 in terms of price. Coupled with the opportunity to record the line and microphone inputs simultaneously, this sound card might be a good tool for a home recording studio, but there is one hitch: the microphone amplifier with symmetric input is installed on the same analog-to-digital converter that services the line input. That is, you still have to choose either one or another when recording. Moreover, the opportunity to connect a stereophonic microphone mentioned in all the manuals proved to be not true. Only monophonic sound can be recorded from both microphone inputs.

Winding up the description of the sound card’s hardware, I want to note the capacitors and resistors which are often undeservedly disregarded as unimportant. For example, in our ASUS Xonar Essence STX review we saw a considerable difference in the measured characteristics of the right and left channels that did not depend on the opamps and the tested output (line or headphone). Therefore, I was glad to learn that the Auzen X-Fi Forte 7.1 uses 1% tolerance resistors. This should ensure that the characteristics of the different channels coincide.

ASUS emphasized the importance of Nichicon’s FG series electrolytic capacitors in achieving the resulting sound quality of the Xonar Essence. Auzentech uses capacitors from Nichicon, too. These are the eight bright-green Nichicon ES series capacitors installed on the analog outputs. The power supply of the analog circuits is filtered with inexpensive general-purpose capacitors of Sam Young’s SHL series. There are also 14 electrolytic SMD capacitors on the PCB, a couple of film capacitors in the front output filter and nine tantalum AVX capacitors in the power circuits of the DAC and ADC. In the next section I will try to tell you how these variegated components affect the sound quality of the card.

 
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