[iFi audio]

iDAC2: Spilling the Secret Sauce (2/6)

 
Digital section: ‘True Native’ augmented by latest gen Octa-Core Transputer
 
At the heart of AMR/iFI products including the iDAC2 micro is the same Burr-Brown ‘True Native’ chipset which we have explained before in the micro iDSD thread. This particular Burr-Brown chip offers two separate signal pathways for PCM and DSD. What this means is that one chip offers the ‘best of both formats’ as the signal quality remains native.
 
Choosing the right DAC topology significantly effects the final sound. We loved the dynamics and slam of the multi-bit topology (e.g. the legendary Philips TDA1541A), however when a High-Definition signal is used, the Multibit topology (actually no true multi-bit DAC chipset available yet) doesn't have the low-level linearity of the Delta-Sigma topology.
 
So to get the best of both worlds, we need:

1. Multi-bit for dynamics and slam (the higher bits of the PCM data);
2. Delta-Sigma for the low level linearity (the lower bits of the PCM data);

 
So the DAC chip we picked for the micro iDSD has the following topology:

1. Top 6 bit: true multi-bit;
2. Lower bits: Delta-Sigma.

 
 
 

 
 
 
As a result, the iDAC2 micro also supports DXD and DSD up to DSD256^#. Three Digital Filters are included; Bit-Perfect (Non-Oversampling), Minimum Phase and Standard and three selectable analogue filters for DSD.
^# DSD256 is available on Windows via ASIO DSD and with special firmware on OSX, Windows and Linux via DoP DSD
 
Running alongside the Burr-Brown ‘True Native’ chipset is the 8-Core XMOS. But with one essential difference – our own firmware. Such update to the XMOS Design and Firmware introduced by iFi include Star Clocking as first outlined in the iDSD micro.
 
 

 
 
 
 
The IDAC 2 implements Version 4 AMR XMOS Platform and uses the latest generation 8-Core 500MIPS XMOS1 transputer derived main processor. These processors are quite unique in their architecture and are based on a technology that once was considered to have revolutionized computing, the INMOS Transputer: which allows extremely high sample rates, supporting 384kHz/32Bit PCM and 11.2MHz single bit (DSD).
 
¹INMOS transputing to XMOS
 
The ‘Transputer’ (Trans – Com – Puter) was a pioneering microprocessor architecture of the 1980’s, intended for parallel (multi-core) computing. It was designed among others by David May and produced by Inmos, a semiconductor company based in Bristol, United Kingdom.

For some time in the late 1980’s many considered the Transputer to be the next great design for the future of computing. While INMOS themselves ultimately faded from the scene, their pioneering parallel computing platform is echoed in every modern PC running Dual or Quad Core CPU’s and in any Smartphone or Tablet featuring multi-core CPU’s.

XMOS was started among others by David May and modernised the Transputer core architecture. XMOS ‘Transputer’ Chips have since found many applications where their unique architecture outperforms both traditional CPU’s and FPGA systems, not the least in USB Audio.

While the digital section is very extensive and based on fairly unique items that stand out from the crowd, without a commensurate highly dedicated analogue section, the iDAC2 would not be half the DAC it is.
 
Next time – Secret to the ‘Analogueness’ (part 3)


 

 

[hfflt]

  I know it can be extreme, but can someone describe the differences in sound between the stock laptop on-board audio vs this iDAC 2?
Yep, I am sure difference is enormous, but I would like to know exactly how things have changed. Detailed and emotional description would be highly appreciated.

 Anyone? 

 

 

[rafaelpernil]

Considering iDAC2 sounds pretty close to iDSD, which is the one I have, the difference between this DAC and the on-board audio is night and day. Huge difference in dynamics, detail, smoothness, impact, clarity, realism... It's like listening to real music instead of a noise hardly similar to real live music.

I hope I've been helpful, m8.

Have a nice day

 

[iFi audio]

iDAC2: Spilling the Secret Sauce (3/6)

 
Analogue section: Secret to the ‘Analogness’
 
The analogue stage uses a Burr-Brown (by TI) Soundplus® J-Fet integrated amplifier with an added discrete Class A output buffer. The Class A buffer is a unique design combining J-Fets and bipolar transistors in a single-stage and allows the iDAC2 to handle even 600 Ohm Loads without breaking a sweat.
 

The ‘Soundplus®’ integrated amplifier selected for the iDAC2 easily goes up against the ‘ultimate’ audio integrated amplifiers from Burr-Brown (OPA627 and OPA827). Rather than relying on ‘fashion’ and selecting a ‘fashionable’ Op-Amp, we selected a specific Burr-Brown part because of its performance when combined with our unique Class A TubeState® output stage and in our mixed passive/active filter Analogue stage, it goes up right against the most expensive options (both in objective measurements and in listening).
 

 
 
We start from the datasheet specifications in the comparison table below itself which speaks for itself. Using industry benchmarks such as Input Noise and GBWP the BB Soundplus® compares well with both the BB OPA627B and OPA827….
 
 

 
¹ Input Noise, a measure how much noise the Op-Amp produces, lower is better
² Stands for Gain Bandwidth Product, a measure how ‘fast’ the Op-Amp is, higher is generally better
³ Stands for Total Harmonic Distortion & Noise, a measure how linear the Op-Amp is, lower is generally better
 
 
….BUT where we finish is by adding the extra discrete J-Fet + BJT Class A output stage to the iFi selected Burr-Brown, distortion performance is improved beyond that of the OPA627 and OPA827 from an already pretty good 0.00005% to a gobsmacking 0.000017%. This is another instance of where we go beyond the datasheet to wring a higher measured performance level.
The next question is, nice number but can one hear this in the real world?
Our answer would be a resounding ‘yes’ – we compared and we found audibly better dynamism with more difficult loads.
 
Next time, DirectDrive® (part 4)

 

[alvin1118]

since when all of us are like engineers, like to get down to the components level to judge the sound quality of a product? 
Isn't just sit back, enjoy the music is more important?
 
don't get me wrong, i'm just in a dilemma. i'm one of the engineer (technically, i'm an engineer) who likes to dig deep down to the circuit design of hifi gears ! 

 

 

[hfflt]

Considering iDAC2 sounds pretty close to iDSD, which is the one I have, the difference between this DAC and the on-board audio is night and day. Huge difference in dynamics, detail, smoothness, impact, clarity, realism... It's like listening to real music instead of a noise hardly similar to real live music.

I hope I've been helpful, m8.

Have a nice day

 
It's amazing! Hoping one day to get my hands on one. 

 

[iFi audio]

iDAC2: Spilling the Secret Sauce (4/6)
 
DirectDrive^® look mom, no coupling capacitors
 
Commonly, coupling capacitors are employed to ensure the output from the DAC is free from DC (Direct Current). As the signal directly passes through coupling capacitors compared to other components in the system, these have an uncommonly large impact on sound quality. There is an after-market in coupling-capacitors. Take these rather special audiophile capacitors (pictured is the Duelund CAST Copperfoil Capacitor – yours for a cool 2,700 USD EACH). They are huge in size and expensive, sound every bit as good as their price yet a simple straight copper or silver wire invariably ‘impacts’ the signal less.
 

 
 
In the iDAC2 the analogue stage is direct-coupled (read: no coupling capacitors). In the iDAC2 a DC Servo is employed to ensure the output is always DC-free, however the DC Servo is implemented such as to make it effectively ‘invisible’ sonically-speaking, by using the same type integrated amplifier as for the actual signal path to perform the DC servo duties (so the DC servo is of the same level of quality) and the influence of the Servo on the signal becomes 20 times less than that of the main audio path through the circuit design and so completely disappears from measurements as well from the subjective sound quality.
 

 
 
In the iDAC2 we use MELF resistors as well as C0G filter capacitors (these are at least as good as polystyrene and approach Teflon capacitors for performance) for the low-pass filter. Additionally, the filter is a mixed-mode type where a passive filter first removes the unwanted very high frequency noise from the DAC output, which would be detrimental to the integrated amplifier performance before an active filter implements the final roll-off.
 

 
 
 
 
Dual-Mono Headphone section
The headphone amplifier is a non-trivial section either. It is an all-new dual-mono design with 350mW output into 16 Ohm and a maximum of 3.3V output available to drive high impedance headphones (> 100 Ohm). Using Direct Drive® technology it too is fully direct-coupled and MELF resistors are used for the gain setting network.
 
From above....
 

 
 
From below.....
 

 
 
With a well-respected pair of headphones such as the Fostex TL50-RPs, this reasonably-priced ‘plug ‘n play’ combination really shines. It even surprises one or two far more expensive setups.
 
Next time, Active Noise Cancellation® (part 5)

 

[tjw321]

I'm really enjoying these posts giving us an insight into "the secret sauce". My ears tell me that the iDAC2 sounds really good, and now I am getting some idea of how much attention to detail was put into getting it that good.

 

[zachgraz]

My iDAC2 is on the way. For 2 weeks I have been using the iDSD as DAC only and as I need a desktop 100% solution the iDAC2 might suit me more.
 
I have been amazed by how good the iDSD DAC sounds. I have had various DACs, Musical Fidelity V-DAC, Stoner DAC 110 mk2, Musical Fidelity V90, Arcam irDAC (multi award winner !) but sonically the iDSD beats them all especially in terms of refinement and "musicality". Run at 32bit/192khz it sounds exceptionally smooth too.
Only 3 weeks ago I heard/read of the iFi brand for the first time (sorry for not being up 2 date

). In the meantime I have already become a fan.

 

 

[iFi audio]

iDAC2: Spilling the Secret Sauce (5/6)

Active Noise Cancellation® gives >1,000X noise reduction
 
Another new feature used is the Active Noise Cancellation® power supply conditioning.  First seen here in the iDAC2 micro and specially developed for USB-powered devices.  They are not ‘Regulators’ in the classic sense of the word, but instead they only work on noise on the power supply voltage, without actually ‘regulating’ the voltage.
 
The traditional approach (see first graphic) using filters and regulators sees DC voltage lost AND noise is not comprehensively eliminated, there is still a residual level.
 

 
 
However, in comparison to the iFi ANC system, there is no DC voltage lost AND the power is noise-free:
 

 
 
We all know that USB Power from common USB ports is very noisy (usually tens if not 100's of millivolts of noise). So normally, power supply regulation is required to remove this noise. Common regulators use regulation elements in series with the powerline and require at least several 100mV to several Volt to work. In a USB-powered device this loss is not acceptable as we need at least 5V to give sensible levels for line outputs and headphones.
 
The all-new Active Noise Cancellation® avoids the loss of power supply voltage, while achieving similar or better rejection of power line noise as classic regulators. No extra series elements are needed. The Active Noise Cancellation® circuit cleans up the incoming USB power before it is distributed inside the iDAC2. A further such Active Noise Cancellation® circuit is cascaded after the first before supplying the headphone amplifier and analogue stage with power. A third Active Noise Cancellation® circuit is cascaded after this to give the DAC Chip the cleanest possible power source.
 

 
 
This multi-stage cascade achieves a reduction of USB noise by over 60dB (1,000 times) at low frequencies for the headphone amplifier and analogue stage. At higher frequencies where switching noise from switched mode power supplies is found, the noise attenuation is even greater.
 

 
 
At the DAC Chip the noise is reduced by over 90dB (31,600 times) for low frequencies. So even very high noise levels of several 100mV are suppressed below the self-noise of the analogue circuitry and DAC Chip, giving the iDAC 2 micro a Signal/Noise ratio of > 114dB(A) or an equivalent number of bits of > 19 Bits. Many DACs with an extra ‘zero’ on the end of the retail price do not go this far.
 
Next time, Power Supply – with great power come great responsibility (final, part 6)

 

[technobear]

Top stuff! Wondrous indeed.

 

[etoilebiscuit]

anyone tried hd598 with idac2? any impressions?

 

[hfflt]

  anyone tried hd598 with idac2? any impressions?

 
+1! I am interested in that too.

 

[BrainFood]

  My iDAC2 is on the way. For 2 weeks I have been using the iDSD as DAC only and as I need a desktop 100% solution the iDAC2 might suit me more.
 
I have been amazed by how good the iDSD DAC sounds. I have had various DACs, Musical Fidelity V-DAC, Stoner DAC 110 mk2, Musical Fidelity V90, Arcam irDAC (multi award winner !) but sonically the iDSD beats them all especially in terms of refinement and "musicality". Run at 32bit/192khz it sounds exceptionally smooth too.
Only 3 weeks ago I heard/read of the iFi brand for the first time (sorry for not being up 2 date

). In the meantime I have already become a fan.

 

 Any impressions?  

 

[zachgraz]

   Any impressions?  

 
To me, the iDAC2 has the same sound as with the iDSD. Easy to set up, it switches on when I start my computer. As I have a 100% desktop setup I sold my iDSD and kept the iDAC2.
BTW. I am no longer using headphones due to great speakers and amp

so I can't say anything about the headphone amp section.