Given that there is a clear concept on behalf of SMSL regarding the design of both the DO100 and HO100 and that the two devices were delivered together for this review, we decided most of the listening evaluation be made with the two devices combined, as one who wants a good headphone listening system would do. Part of the listening, however, was carried out with the devices separately, with the DO100 as DAC, replacing the reference d/a converter (Teac Esoteric D70) and the HO100 as a stand-alone headphone amplifier, driven directly by the D70. In all cases, the headphones we used were a Grado RS2 (32Ω) and an AKG K702 (62Ω).
Initial installation of both devices is a simple matter and shows no difficulties. The features provided, even allow their remote connection in a setup that requires, for example, the installation of the DO100 on the rack, near the digital signal sources, and the installation of the HO100 near the listener, at a significant distance. In this case, the converter's remote control and the ability to connect through balanced lines, make the user's life simpler.
The first impression you get by listening to the SMSL pair is that of a -positive- surprise. The system appears to have all the essentials that everyone who uses headphones systematically will appreciate, that is, a very low noise level, a good drive capacity, and the possibility to obtain quite large sound levels (much higher than medically allowed).

Although both RS2 and K702 are neither particularly insensitive nor difficult to drive, HO100 has left serious indications that it would be able to successfully drive headphones that are slightly out of the standard, good, behavior, both on the sensitivity and the impedance aspect. With the ability to output nearly 7.5Vrms (this is more than 20V p-p) the amplifier should be considered a good all-around solution, which becomes excellent if you take its price range into account. The sensitivity adjustment switch even allows the use of very sensitive headphones that tend to make system noise more prominent.
In terms of spectral balance, the D100/HO100 pair comfortably approaches a neutral behavior, letting the headphone sound attributes pass without adding any obvious character. Being open-back, both Grado and AKG usually sound clear and fast, with a very good sense of air, the former having a slightly better presence and the latter being characterized by relative rigor and precision towards the lower part of the audio spectrum. In both cases, listening sessions have accurately highlighted these features, while the much better isolation from the surroundings, offered by the K702, has further highlighted the good dynamics that characterize the SMSL system even at lower sound level settings.
Stereo imaging of the system has shown to have very good potential (for which the very good channel balance, found during the lab evaluation, predisposes). Even during the first moments of listening, one can perceive a very crisp and stable placement of acoustic objects on the horizontal axis, a clear description of the sound source's apparent movement, and good reproduction of the ambience information. Moreover, in the event that binaural recordings are reproduced, a very persuasive sound field is maintained.
As a DAC (that is, driving the Melos Plus Series Line preamplifier and through it, the usual Parasound HCA3500/ATC SCM-50PSL system), the DO100 also achieved very good performance levels. The final result was detailed, with good spectrum homogeneity, good low-frequency extension, and control, and pleasant, warm, high frequencies, being a bit slow on the attack times and somewhat lacking definition on stereo imaging when compared to the reference converter (which is expected, of course, as the price ranges to which they belong to are outrageously different). In any case, DO100 achieved a sound quality level much higher than what you should expect, given its price.

Conclusion

To be honest, I had to confirm from many sources the price of the two devices under review just to be sure there is no error in quoting them here. At €400,- (total for a DO100/HO100 pair, including taxes) the price is more than attractive, given what they offer, both in the level of the features included and their build quality, not to mention their sound performance. If you listen systematically through headphones and want a dedicated system for this purpose, it is -based on what we know- one of the best devices you can buy. They define, without a doubt, a reference level in this price range. Well done!

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