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The long promised iFi iDSD Signature & NEO iDSD review (Part two) - iDSD Signature


Great expectations, high hopes & the elephant in the room

iFi Audio Micro iDSD Signature & NEO iDSD review

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The Micro iDSD Signature - Great Expectations

Contents Part two:
Signature review
Exhibt 2:  4.4mm balanced output Pentaconn
Exhibit 3: The GTO filter

Signature review

Last November I was kind of surprised when I read the announcement of a Signature edition for the iFi Micro iDSD. Great expectations had been raised instantly about this shiny new gladiator for the pursuit of sound quality in your home system and for portable use cases. The package content  is shown  right here:image.jpeg

This review will look into the details in pursuance of clarity about the Signature’s strengths and weaknesses in comparison with its predecessor the Micro iDSD Black Label edition, which I have reviewed here in 2017. You'll find a head-2-head feature comparisonjust below:


As of IFI Audio’s PR material the Signature edition of the Micro iDSD will be produced in limited quantity, which may qualify for calling it a transitional device, smoothing the transition from the versatile Black Label edition to the new “portable king of the hill” iDSD DIABLO, preparing the iFi customers for a streamlined PCB design, perfected purist sound experience and a whiff of boosted mobility.

The Signature’s form, haptic and technology is very much reminiscent of the Micro iDSD series, the most notable changes are:
- the exciting blue colored surface,
- the additional Pentaconn HP socket for S-balanced output
- plus the separation USB port duties for signal transmission and advanced power supply.

Looking at the spec sheets, not much has changed related to the signal path and the HP output apart from the higher output. The provision of digital inputs via USB and a combined SPDIF/Toslink port (adapter provided) is well known from the iFi micro range. The Signature still uses the BB DSD1793 Dac chip in dual mono configuration and a dual mono analogue & pre amplification stage.
iDSD micro.jpg   iDSD sig.jpg

above the DAC sections of the iDSD micro Black Label and Micro iDSD Signature
thanks @ sandalaudio)

g246IDSDSGN-o_other2 idsd sig.jpgI dsd sig.jpg

However, the additional performance in the power supply and HP section comes at a cost. With the announcement of the recent DAC/Pre/HP amp in the iFi-portfolio the Signature lost the ability of variable RCA output mode and along with that change we notice the evanescence of the analog input and optical output. Consequently, we experience a lack of gain selection and supporting line stage. Connecting the RCA output, the volume control now is bypassed.  Secondary features like loading external devices via USB port and polarity selection have been eschewed for the crusade toward better sound, purist experience and enhanced portability.

On the positive side, IFi Audio has stepped up SQ with the new micro iDSD Signature, accessible under clear defined presets, a success accomplished

especially through changes within the device's power structure and less importantly by enhancements in the output section using the 4.4mm s-balanced output design. The major impact in my view comes from the separation of duties for signal transfer and power provision.

These presets for success were most distinctive to the reviewers' ears after changing back to the iFi Limoncello firmware 5.20 that permits the owner the spotless use of DXD and DSD512. Using the most recent software, both features aren't available and the more sterile sounding GTO filter is dominating the SQ.  Nonetheless, as filters are often suspect to personal taste and experience, I'd suggest taking the challenge to find out for yourself. The manual for upgrading/downgrading firmware had been delivered here and effects - in my ears - were well distinguishable.

The Signature’s SQ over Headphones, be it through the SE 6.3mm output or the 4.4mm S-balanced tuned Pentaconn port, is exciting by design. iFi confirmed to me that the DAC section with the BB 1793DSD double mono configuration was left untouched while the important changes towards SQ were made in the amplification section and through the selection between important and less important features. The selection of unbalanced SE or S-balanced Pentaconn did not make a significant difference for my ears, given the power output of both outputs is equal by design and the first demand of the HE-400i is current, current, current. My amateurish hand measurements with a SPL meter have confirmed my “ear educated” guesswork for that instance. I credit the direct drive HP amplification stage well known from the Black Label, with the responsibility for amplifying the signal that arrived through the dual mono analogue stage in both, single ended and s-balanced mode.

As a matter of consequence, the Signature has lost some features we had learned to love with the older micro iDSD editions. There is no capable line stage that would qualify the unit as a digital preamp providing variable output and analog input anymore, while the device's new power circuit design doesn’t allow uninterrupted usage in your system without connecting it to an external power source. There is, for sure, an advantage inherited with that solution, the SQ enhancement driving the unit solely from battery and no USB bus power interference may inject unwanted noise of all sorts. Thus the Sig is an exquisite sounding device for "more transportable" or desktop use, with or without demanding headphones, however it features a far less complex functionality compared to its predecessor.

Accordingly, with this minor "streamlined" changes the device now leans more toward mobility than the Black Label edition which for many users would do greatly as DAC/PRE in the main system. However, I need to admit that using the BL plus a RPI as endpoint rendered somehow as less comfortable for the limited charging power from the RPI2/3 ports plus the need for recharging after listening. Connected directly to the USB3 ports of my CAPS Zuma it has never asked for battery refill.

The cleaner way of powering the Signature may allow you to use the battery now up to twelve hours, depending on the selected power mode. iFi support indicates no quality loss if the device is charged during playback. I've noticed a certain signal loss the very moment when connecting the device to the power supply and preferred generally to listen without power feed. However, employing a 20maH power bank proved to be a solution to allow nearly unlimited (2days) use when needed.
Having noticed the availability of iFi 5v power plugs with some of the 2020/21 product range I would have saluted an inclusive solution for the
Sig as well.

Depending on what your objectives are, the Micro iDSD
Signature may be exactly the device you are looking for. If you're in for a DAC with preamp functionality in your systems, the Sig won't make you happy with its new configuration and you may rather want to look for the Black Label edition, which is richer in features and not far away in line level sq with identical audiophile heritage, although some caveats regarding component selection are the price to pay for the comfort upgrade, knowing that slightly better SQ can be had with the Signature.


Exhibit 2: 4.4mm balanced output Pentaconn

This is a quick overview about TRS, TRRRS, Pentaconn, Balanced and S-balanced headphone amp output.
There are some things to be understood when it comes to the new wave of so called balanced outputs from headphone amps. I am not an expert in EE, therefore I provide some third party information which I found useful for understanding what’s going on. 

The three contact phone connector standard version called TRS is a Tip-Ring-Sleeve connector that arrives in 2 formats (stereo/mono) and three sizes 6.35, 3.5 and 2.5 mm. The five contact phone connector standard called TRRRS is based on the same concept, providing but was only brought into the ITU-T standard P.382  in 2017 for 2.5 and 3.5 mm phone connector

4.4mm Pentaconn:
The Pentaconn technology was developed by NDICS (Nippon Digital  Information  Communication and Service") in 2015 under the Jeita standard 8141C (only in Japanese), marketed under the name Pentaconn (5-connector) and the website pentaconnglobal.com. Sony was an early adopter and is the most prominent manufacturer to date using this standard. Since last year IFI audio provides this adapter/socket technology as headphone & balanced analog output solution in their devices. With the latest devices the installation is used for balanced signal transmission to XLR connectors.

image.png             image.png


As noted above both units offer a 4,4mm Pentaconn HP output socket, which is by definition only usable with a TRRRS connector.

In my opinion, based on acquired knowledge and experience, I like truly symmetrical signal paths for stereo output and balanced line level connections for offering some solutions and a higher dynamic range. With the Pentaconn balanced output I may enjoy higher power output to my planar headphones which in my reception could make a distinction in perceived sound quality compared to SE / TRS based connection.

With reference to the Benchmark-Paper by John Siau about “Balanced Headphone Amplifiers” I like to list 3 important findings:

  1. Headphone transducers are always balanced devices and agnostic to the way (SE vs. Balanced) current is delivered to them.
  2. Balanced line Level connections are a common solution in regard to ground loop and noise injection problems.
  3. Balanced outputs in HPA can deliver up to 4 times more power for a given power supply voltage . While this proves to be helpful in battery driven devices, it gives no advantage in AC powered devices.

Here are some quotes that offer food for thought why a 4.4mm pentaconn connection might not be completely indispensable:

Fully balanced internal circuitry has been promoted as yielding 3 dB better dynamic range, though at increased cost over single-ended designs.” Wikipedia

“A truly balanced and differential signal path from source to load requires double the circuitry and is thus more expensive to manufacture, but it can yield an audible improvement. This is sometimes referred to as ‘dual-mono’ to indicate that each channel is completely isolated from the other” Headphonesty

Most audio products (recording, public address, etc.) provide differential balanced inputs and outputs, typically via XLR or TRS phone connectors. However, in most cases, a differential balanced input signal is internally converted to a single-ended signal via transformer or electronic amplifier. After internal processing, the single-ended signal is converted back to a differential balanced signal and fed to an output. A small number of audio products have been designed with an entirely differential balanced signal path from input to output; the audio signal never unbalances. This design is achieved by providing identical (mirrored) internal signal paths for both the "non-inverting" and "inverting" audio signals. Wikipedia /Source: http://www.co-bw.com/Audio_balanced_cables_audio.htm

We could think about the Pentaconn as a solution that is looking for a problem in real life, however it works as well as a solution for easy adaption between the smallish TRRRS output and balanced inputs for the signal path outside the headphone environment.





1.pngThe easy solution for your existing cable could have been an adapter from SE 3.5 or 6.3 connectors to 4.4 pentaconn. When starting the review period I've looked at five weeks delivery time for such an useful gadget and decided on ordering a complete balanced cable for my Planar headphones instead - which was expedited in 4 days.

However, b
uying a 4.4mm Pentaconn aftermarket cable could rip some serious cash out of your pocket. I paid about 50$ for the aftermarket cable for my 150$ Hifiman HE-400i 2020, if you are in it for your Meze Empyrean, for example, you may need to shed more than 300$ for a suitable connection.

iFi Audio provides for both devices the timeless 6.3 male to 3.5mm female adapter. For me this exactly feels like they have kind of lost that special touch that made them so unique 5 years ago. In my opinion, you may get a stronger push for Pentaconn if you’d include a suiting adapter for 3.5mm TRRS connectors. Only a percentile of customers may be able to use the strongest unique selling points of the devices straight from the start.  Even the majority of balanced headphone cables can't, because in the past they were XLR, 2.5mm or 3.5mm ....

Late in 2020 - during my research - I found not more than a handful of cans using 4.4mm connectors as standard connectors, given I didn't go to specialist places with low volume output.
My short research in European search engines just before Christmas did only provide 5 recent headphones apart from Sony products featuring 4.4mm Pentaconn connector cabling.  The 25 best headphones endorsements for 2021 for the British HiFi consumer provides just a single pair of Sony cans (2k GPB) with the specific 4.4mm connection. Obviously we are facing the early adopter problem and the solution may find its problem in the years to come.

iFi Audio used the Pentaconn technology with two different designs, the fully balanced design for the Neo and the s-balanced design for the Sig. As noted above, the strongest argument for balanced design for headphones may be the surplus current available for demanding cans, which is not provided for the Signature’s configuration.


Most unfortunate, my new adapter did only work with the Sig’s output, but refused to function 100% with the NEO iDSD'S Pentaconn port, which led me to use it only with the single ended 6.5 TRRS cable/output. The caveat I had to face has been the nominal power output, which is too low to drive the (now more affordable) planars from Hifiman in a satisfying manner. Even with the 1040 mA @32 Ohm aren't sufficient to let the cans sing to me.

A short look on the s-balanced design:


“No second amplifier is used, neither is extra signal nor noise, nor distortion added, perfect for sensitive IEMs. Further including the iEMatch technology extends compatibility with ultra-sensitive IEMs. A dedicated negative wire per channel all the way to each channel’s amplifier’s star-ground makes sure there is no crosstalk between the channels” (iFi Audio)

With the iDSD Nano BL this design permitted the use of both TRS and TRRS connectors without compatibility issues. Using it for the Pentaconn output while having a dual mono output stage in the device seems to be that kind of mystery to me that manufactures won’t like to explain.

Here’s an overview of technology deployed & the output specs for iFi’s headphone amps:


Exhibit 3: Gibbs transient optimized

This GTO is neither a Ferrari nor a Pontiac GTO („Gran Turismo Omologato") of digital filters but a development that had been in the pipeline of the AMR/iFi universe since 2011 when they were in research for optimized organic filter solutions for the AM-777.  Actually its primary aim is to minimize pre-ringing and correct the timing in order for optimizing the transient response.


The introduction of "GTO" was escorted by a "white paper" like 9-page-document available here in 2018 when the GTO filter arrived as an alternative with the iFi iDSD pro. iFi says the GTO is their first choice when only a single filter is in the race. That is the case for example with the Neo iDSD. For their XMOS based legacy products the filter is available since FW 5.30c and substitutes the minimal phase filter. These GTO filters are a collaborative development from IFI Audio / AMR with the MQA Labs.

"We must make clear that GTO is not directly related to filter types used by MQA, it is not “MQA through the backdoor”, but instead what we feel is the optimum solution for the playback of digital audio that has not undergone the MQA process. "

The Gibbs Transients Optimized (GTO) is a set of filters for analog output which has been critically reviewed by mansr at our forum in 2019. Nearly everything written there as subjective support to the objective data provided by the thread starter correlates with my personal experience.

My previous and first experience with the GTO filters came with an exclusive setup in a listening booth in Paris 2019. I recall liking the apodizing filter most then, which was a surprising experience because it was the first and only time I can remember this type of filter being my preference, while I was disinclined with most of the others and especially with the GTO filter that was recommended by the IFI personal at the show. To understand why I was kind of put off from that experience, let me introduce the Paris high quality chain:


Aurender A10 &  IFI Audio iDSD PRO & PrimaLuna EVO 100 with MEZE EMPYREAN or Audeze LCD4.

This may have been the most rewarding headphone system I have ever listened to.

During this review, whether it was comparing the iDSD NEO with no filter selection available against the ALLO Revolution with minimum phase fast roll off FIR filter setting or the different firmware selections 5.20 vs. 5.30c for the Signature, the GTO never worked to my aural satisfaction.

While my overall less enthusiastic impressions about the GTO filter endured, the Sig & Planar combination allowed better SQ than experienced with the NEO, however it was the Sig's (FW 5.20) "bit perfect" processing that remained my go to choice. The GTO compared to bit perfect sounded to me again more sterile (like the opposite of organic), flat, less lively and providing absence of anything I would call PRAT for the ones who use that definition to describe audio performance.

Surely it is called “analytical”- thus unfortunately not transporting the emotional bits to my ears. In a car metaphor I would point out to Toyota Camry or Chevrolet Trax, cars so uninspiring that concentrating on the road traffic is very easy. Some folks may be happy with that, I'll pass on that GTO.



iFi iDSD Sig 06.jpg


Part 1
Part 3
Part 4


This is the 2nd part of the 2021 iFi review. I decided to add it today, when the first installment had reached more than 120 views in less than 24 hours and I felt that the interest seems to be right there . Thank you guys and gals.
PS: If you wonder about the big blue layout for the signature, in the word document it was in a handwriting (Signature) type, but the blog layout didn't provide that extravaganza.



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