Preamble:
Derived from my mixed content German & English review site,
http://kopfhoerer-lounge.blogspot.com/, I'd like to share my review of the iBasso AMP2 module, the first replaceable amplifier module available for the DX200 audio player.
Introduction:
http://kopfhoerer-lounge.blogspot.com/2017/03/iBasso-DX200-Review.html
iBasso Audio’s DX200 flagship audio player was introduced with the feature of having replaceable amplifier modules, and now some time after the player was released, the company has brought the first model of likely more to follow modules to the market, logically calling it AMP2 (since “AMP1” is the name of the module the DX200 already comes with).
The implementation that this exact AMP2 module is using is something you don’t find that often in commercial audio applications – it is called “virtual ground” implementation, also often referred to as “active balanced ground”.
In contrast to a true balanced implementation where the headphone would have to be terminated with four pins (L+, L-; R+, R-), a regular headphone with a three-pin configuration can (and has to) be used with an active balanced ground architecture. However, as opposed to the most commonly found single-ended application where the ground channel is carrying a constant zero-Volts signal, active balanced ground/virtual ground implementations have got extra signal components for the input and output ground, by adding and “subtracting” voltage from the signal (that therefore remains effectively the same in the end), which leads to the total electric charge of the ground wires being zero (, like in a true balanced setup). This is also why the AMP2 module has got five operation amplifiers (left channel, right channel, input ground, output ground, line out).
So with a virtual ground architecture, you get some of the theoretical benefits of a balanced implementation, however your in-ears and headphones don’t have to be re-terminated and can still be used with a three-pole plug. This architecture however also brings difficulties, and the overall implementation is what matters anyway, since normal two-channel architecture amplifiers can perform equally and also better in terms of measurements.
While this sounds very interesting and good on paper and can add the benefit of a perceived separation improvement, it can also add problems such as increased impedance or distortions if not implemented well enough.
How does the AMP2 differ from the AMP1 module the DX200 comes with? Let’s find it out!
Full disclosure:
I was provided with a free sample of the AMP2 module for the
iBassoDX200 that I reviewed some time ago. It was sent to me for giving my honest opinion on it as well as writing an (as usually) unbiased, honest and unpaid review. Before I go on, I would like to take a moment to personally thank iBasso and especially their Paul for the continued generosity and trust.
Technical Specifications:
http://ibasso.com/cp_xq_dy.php?id=5332
MSRP: $159
3.5 mm Headphone Output:
Max. Output: 3.2 V (RMS)
Frequency Response: 20 Hz – 20 kHz (-0.1 dB)
SNR: 117 dB
THD+N: 0.00056%, -105 dB (32 Ohms @ 1.8 V (RMS)), -115 dB @ 3.2 V (unloaded)
DNR: 117 dB
Crosstalk: -109 dB
Line Out:
Frequency Response: 20 Hz – 20 kHz (-0.1 dB)
SNR: 118 dB
THD+N: < 0.00018%, -115 dB
Unboxing & Delivery Content:
The amplifier module arrives in a black cardboard box with a white sleeve around it, reading “iBasso Audio AMP2”. On the back, one can find the amplifier module’s serial number.
Inside, of course except for the module itself, one can find a warranty card as well as instructions on how to change the amplifier modules.
I remember that some slight criticism from my side regarding the DX200’s replaceable amplifier design was that the player doesn’t come with a screwdriver in its retail package and that I would suggest to include one with every sold amplifier module, and this has indeed become true and the AMP2 really does arrive with a small screwdriver.
Therefore you will find everything you need in this black cardboard box that can also be handy for storing the amplifier module that is currently not in use.
PS:
I think it would be a great idea if iBasso offered the option to leave the choice of the amplifier modules to the customer so he/she could choose what module he/she wants to be bundled with the DX200, or alternatively iBasso could sell the DX200 without any module at all (but instead a simple plastic back) and offer all modules (including AMP1) separately for purchase, so the customers could buy whatever module they want
I know this would mean some logistical difficulties and is probably not the most realistic scenario, but would be a very nice idea nonetheless.
Visual Appearance & Build Quality:
The AMP2 module looks just like the AMP1 module, except for the lack of both a balanced 2.5 mm headphone output and the large “Reference DAP” inscription on the back; and of course instead of reading “AMP1”, there is an “AMP2” inscription on the module’s lower right side.
It is also made of black as well as silver metal, feels very solid and is built well.
Changing the modules:
… is a very simple process.
The two screws on the side of the amplifier module that is attached to the DX200 have to be loosened using a screwdriver, for example the one that comes with the AMP2 module. Removing the screws entirely is not required but two or three rotations are already enough to loosen them.
Then, the module can be slid down and lifted off.
After that has been done, the other module can be put on, slid in place and the screws can be tightened (be careful not to overtighten them).
Sound:
Specs compared to AMP1:
Module:
AMP1:
AMP2:
Output Voltage:
3 V RMS
3.2 V RMS
Frequency Response:
20 Hz – 20 kHz (-0.16 dB)
20 Hz – 20 kHz (-0.1 dB)
SNR:
122 dB
117 dB
Crosstalk:
-118 dB
-109 dB
THD+N:
< 0.00032%, -110 dB (32 Ohms @ 1.8 V RMS)
0.00056%, -105 dB (32 Ohms @ 1.8 V RMS)
Frequency Response, Output Impedance:
One of the most basic and fundamental things an audio player should have is a flat unloaded frequency response in the important range of 20 to 20000 Hz. While it is anything but sorcery to achieve this in modern days, some (however mainly inexpensive and rather no-name) audio players still fail to achieve this basic thing.
How does the AMP2 module behave in this regard? Let’s find it out (headphone output, using Digital Filter #4):
As it could be expected, the raw and unloaded frequency response is perfectly flat and therefore just the way it should be, which however is no real surprise to be honest.
- - -
But even when having a flat frequency response without any load at all or with a simple load (such as a headphone that has got the same impedance over its entire frequency response), things are getting much more difficult with most multi-driver in-ears that have got more than just one driver and a crossover circuit that causes the in-ears’ resistance to vary along with their frequency response.
If the audio player’s headphone output doesn’t have a low output impedance, the in-ears’ frequency response and therefore heard tonality will be skewed and they will (depending on the player’s output impedance and the in-ears’ specific impedance response) sound more or less different than when driven by an audio player that has got a low output impedance.
To maintain an unaltered sound even with low impedance multi-driver in-ears, it is therefore best to have an audio player that has got an output impedance of less than 1 Ohm.
This is what the DX200 with the AMP2 module puts out when connecting a critical, low impedance multi-driver in-ear to its single-ended output:
The connected load was my Ultimate Ears Triple.Fi 10, an in-ear that is among the more/most source-picky species of its kind and changes its sound
rapidly as the player’s output impedance climbs.
The measured deviation in combination with the AMP2 module is just very small and can be calculated to be around 0.2 Ohms (official iBasso spec: 0.36 Ohms), which is a really good value and proves that the player can drive any multi-driver in-ear without altering its sound unlike players that have a rather high/higher output impedance.
So is the DX200 with the AMP2 module a multi-driver-friendly audio player with really low output impedance? It certainly is!
Hiss:
I consider myself as someone who is rather sensitive to hearing hiss and have also got some very sensitive in-ears (for example the
Shure SE846 and
Ostry KC06A that are among the more/most hiss-revealing models on the market). So with the right in-ear, I hear hiss to a varying degree with about any digital audio player (in fact out of the players I own and have heard, only the iBasso DX90,
Cowon Plenue 2,
Luxury & Precision L3 and
Luxury &Precision L3 Pro are basically hiss-free, however the latter two do not have the most ideal output impedance for multi-driver in-ears and those with a varying impedance response).
Using the AMP2’s headphone output with my
Shure SE846,
Pai Audio MR3 and the
Ostry KC06A, I am happy to report that the amount of hiss that I am hearing with an empty audio file and in quiet passages of the music is fairly little, however a bit more pronounced compared to the AMP1 module (‘s single-ended output), nonetheless the AMP2 module is still a little quieter in terms of showing hiss with extremely sensitive in-ears compared to my Chord Mojo, that, while it is among the better performers in terms of hissing, shows some audible hiss with super sensitive in-ears.
Using still sensitive, however less “extreme” in-ears with the AMP2 module, such as my
Ultimate Ears Reference Monitors or Triple.Fi 10, the AMP2 module’s background is practically quiet.
Subjective Perception of Transparency, Precision & Soundstage:
Now to the rather subjective part of my review. My opinion and experience regarding the perceived “character” and “transparency” of source devices and amplifiers is this one: there can be an existing audible difference between various devices, but it should definitely not be overrated – simply because the basic character of a headphone won’t be completely changed (if the circuit follows a clean design philosophy and the output is load-stable), but sometimes rather slightly “shaped” and is usually very subtle in many cases, and is (in most cases) just slightly present (if even) and not “huge” or like “totally different classes” or “night and day”.
I am not a fan of exaggerations and hyperboles here because as long as the objectifyable parameters of an audio player are neutral and not too shabby (loaded frequency response, distortion, crosstalk, dynamic range, noise, …), the audible difference, if there is any, will be quite small at best if two devices are compared with proper volume matching that cannot be done by ear but only with instruments, since even small differences in loudness can be perceived as a technical advantage by our ear and brain.
A more detailed, German article written by me concerning the “audible difference between comparable audio devices, if there is any” can be found here:
http://kopfhoerer-lounge.blogspot.de/2016/04/Eigenklang.html
So let’s go on with my subjective impressions and observations of the AMP2 module (for this critical listening, I mainly used my
UERM,
Shure SE846 as well as the
Ostry KC06A and
iBasso IT03. I also used more headphones and in-ears from different price and performance ranges for listening, but more for personal enjoyment than for the sake of critical listening and comparisons):
The sound is generally neutral to my ears (and neutrally measuring, both loaded and unloaded, anyway), with just a pinch of smoothness up top for the highs, especially cymbals, when using sensitive in-ears. I would definitely classify the amount of smoothness a little below the
Chord Mojo and Cowon Plenue 2.
The signal is overall very clean, without any noticeable added colouration or shaping caused by an elevated noise floor, sans the slight amount of smoothness compared to the AMP1 module.
Transparency is flawless, and to my ears identical to the AMP1, Chord Mojo and Cowon Plenue 2.
Sometimes audio players seem to have a slightly soft bass with very sensitive in-ears that perhaps might be caused by some hissing in the lower frequencies. This is also nothing I can hear when using sensitive multi-BA in-ears with the AMP2 – just a tight and controlled attack in the lows, the way it should be, is what I can sense.
While I cannot hear a reproducible difference in terms of soundstage reproduction among various audio sources when using full-sized headphones, there can be a slight difference to my ears when using sensitive in-ears with a three-dimensional soundstage on various sources (that have an output impedance that is low enough so it doesn’t change the in-ears’ frequency response).
And this is where I hear a difference compared to the single-ended output of the AMP1 module. With the AMP2 module, there is a great sense of space with a base that is wide, and has got almost as much spatial depth, although the presentation is a bit more oval than circular to my ears.
What really stands out to me though is that instruments appear a bit more vibrant and stand out somewhat more, giving them a slightly more plastic appearance.
Keep in mind though that all the differences are rather just nuances and definitely not “large” or “night and day” when properly volume-matched and compared.
- - - - - - - - -
Compared with the AMP1 module (single-ended use):
The internal structure of the two amp modules is different (AMP1: single-ended TRS & balanced TRRS dual-mono outputs; AMP2: active balanced ground/virtual ground architecture), but externally they are similar in terms of dimensions and ports (except for the lack of the 2.5 mm TRRS headphone output on the AMP2 module).
When it comes to output power, both modules are almost similar, with the AMP1 module measuring ever so slightly more powerful/louder (only on measurements; irrelevant for real-world use).
Using super sensitive in-ears, both modules are very good in terms of hiss performance and the DX200 is still a pretty quiet digital audio player with the AMP2 module, however AMP1 is ultimately quieter.
Both modules have got a very low output impedance and are therefore highly “multi-BA-friendly”.
In terms of transparency, both are on-par to my ears.
Where they however differ is the overall presentation (AMP2 is slightly “smoother” with cymbal attacks than AMP1 using sensitive IEMs, while I couldn’t detect a difference using full-sized headphones) and soundstage, where AMP2 generates a larger sense of space, with more width, which leads to a slightly more spacious appearance. Instruments also seem to stand out a little more, giving it a slightly more plastic appearance using in-ears.
The borders around spatial elements appear ever so slightly less “precise” when using the AMP2 module though.
In the end, I wouldn’t say any of the two modules is better or worse than the other when looking at all their characteristics, but that it will ultimately come down to personal preferences and tailoring the last nuances to one’s personal needs and tastes.
In my personal opinion, the AMP2 module could be interesting for in-ear users who want a slightly smoother presentation along with a slightly larger, more plastic spatial reproduction compared to the AMP1 module. It could also be interesting for “techies” who want an amplifier module with the active balanced ground architecture in their collection.
For full-sized headphones though, if one already has the AMP1 module, I don’t see any reason to get the AMP2 then, since the nuanced differences will vanish using full-sized headphones.
Conclusion:
The concept of the virtual ground/”active balanced ground” used in the AMP2 module is interesting, and so is its implementation. But does it really add any greater real-world advantage? Measurement-wise, it does not. Sonically, it really depends on one’s individual requirements – if you want a slight difference in terms of perceived soundstage and timbre when using in-ears, the AMP2 module might be worth a consideration. If you are however looking for a
big difference (that cannot be expected anyway as long as an audio implementation and signal follows a metrologically neutral as well as clean philosophy, and that is the case for both the AMP1 as well as AMP2 module, and also true for the vast majority of audio other products that are on the market) or an advantage in terms of output power, the AMP2 module is no necessary purchase even though it also features a very low output impedance along with pretty good hiss performance in combination with very sensitive in-ears (although it is a little less quiet than the AMP1 module).
