Both devices have simple, clean lines and compact sizes. With a width of 150 mm and a height of less than 40mm, they can be easily placed in small places and create a stack that is easily integrated everywhere. If you want to have a special "corner" to listen to the music through your headphones, their dimensions and design are very close to the ideal. The finish of the two devices is of good quality and certainly much better than their price implies.

The DO100 is the simplest in appearance, including only a small monochrome alphanumeric display and a rotary encoder through which the level is adjusted, the inputs are selected and access to a small menu is controlled. From this menu, the filter and PLL sensitivity are selected (we will discuss the later in the next paragraph), while there is, also, a USB operating mode (v1.1 for connections that do not require a driver and support up to 24/96 sample rates and v2.0 for connections which require a driver and support high sample rates and DSD), as well as a screen brightness adjustment. The fact that SMSL leaves the features offered by the D/A chips to the user distinction, offering him more flexibility, should be highly emphasized and -in my opinion- gives the DO100 significant added value. It is difficult to explain why other manufacturers do not do the same, even in more expensive implementations, while the chip(s) used are the same, or similar. All the features are also accessible through the remote control included with the device, which is quite pleasant to use.
The connectivity provided by the DAC is standard for the price range. In the back panel, the device offers standard digital inputs (coaxial, through RCA, and optical through Toslink), a USB port (with a type-C connector) as well as ad-hoc wireless streaming via Bluetooth v5.0 with LDAC 24/96 and aptX/HD support among other codecs. In terms of sample rates, the user should have no complaints: Through the asynchronous USB port, the device support up to 32-bit/768kHz for PCM encoding and up to DSD512 for DSD encoding, while through its standard inputs it supports streams up to 24/192 (PCM) and DSD64 (DSD/DoP). The analog output is available both in single-ended (RCA) and balanced (XLR) formats.

In designing the HO100, the SMSL followed a slightly different approach and the user interface is based on classic, mechanical switches. Through them, the user can activate the device (a blue LED informs for the "On" condition), select the input, and adjust the gain of the amplifier, depending on the headphones used. This arrangement is made on three levels, with "Mid" corresponding to 0dB and values in "Low" and "High" positions being at -9.5dB and +15.5dB respectively.
There are two outputs to connect your headphones, a standard 6.35mm TRS jack, for single-ended connections and a 4.4mm TRRRS jack, for headphones that support a balanced connection. The front panel is completed by a conventional potentiometer-based attenuator
The HO100 connectivity is, also, fairly standard: A pair of gold-plated RCAs for single-ended lines and a pair of XLRs for balanced lines are what you will see on the back panel. Input selection is through the switch on the front panel.

Inside their chassis, the two devices hide some interesting details. SMSL has chosen, in both cases, to use a switch-mode power supply located inside the device (freeing the user from the -usually- low-quality external power adapter and power cable) but both the D100 and the HO100 use linear local regulators in various parts of their circuit.
As far as the DO100 is concerned, its digital front end is based on an XMOS processor for the USB port and conventional digital inputs and Qualcomm's QCC5125 SoC to manage streaming via Bluetooth. An ES9038Q2M chip, from ESS, per channel, is used to convert the digital signal into analog. This chip features all the standard ESS technologies, including seven different digital filters as well as a digital PLL, whose sensitivity can be adjusted through the menu. The latter, allows the user to select - at nine levels - a balance between a "stiff" (i.e narrow bandwidth) PLL for the benefit of low clock jitter and a more "relaxed" (wider bandwidth) PLL with somewhat worse clock jitter. Good quality sources allow for the former, while moderate or poor quality sources that would probably cause dropouts, can be used with a setting towards the latter. The sound quality differences are, probably, debatable, but the sure thing is that the device can be comfortably connected to anything that has an S/PDIF output, even if it is of poor quality.
At its analog part, the DO100 is based on OPA1612 operational amplifiers, specially designed for high-performance audio applications, with very low noise and distortion. Judging by the circuit layout, SMSL also uses in this converter the two trimmer channel balancing we had encountered in their DO200.
The HO100 is also based on OPA1612 for the input stage, with the power stage being implemented by discrete semiconductors. Signal routing features very good quality relays, the company states, to avoid annoying noises when operating the device. The attenuator is based on a CTR potentiometer.

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