Audio science review of the SMSL H100

Audio science review of the SMSL H100

This is a review and detailed measurements of the SMSL HO100 balanced (input) stereo headphone amplifier. SMSL HO100 Review stereo Headphone Amplifier.jpg

The HO100 matches its companion DO100 DAC. Switches feel nice and so does the volume control. While 4.4mm penticon connector is provided, its output is no more than 1/4 HP jack (so it is for convenience, not power).

What is unusual and welcome at this price point is inclusion of AC adapter and XLR inputs:

SMSL HO100 Review stereo XLR In Headphone Amplifier.jpg

As with other SMSL products I have tested, it comes with regulator and safety certification:

SMSL HO100 Review stereo FCC CE Headphone Amplifier.jpg

SMSL HO100 Measurements
As usual we start with 4 volts in (for XLR input) and adjust the output to get 4 volts out. This meant using medium gain at max volume. Output is the same with either HP connection:

SMSL HO100 Measurements Unbalanced Headphone Amplifier.png

The only artifact visible is at -130 dB (15 dB below threshold of hearing) so definitely transparent to the source. This lands the HO100 in our top 10 best headphone amplifiers ever measured:

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Noise performance is excellent at max level of 4 volts and near that at 50 mv out:

SMSL HO100 Measurements SNR stereo Balanced Headphone Amplifier.png


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I tested the frequency response with the amplifier with 4 volts in/out with load of 600 ohm. This caused an odd muting at 14 Hz:

SMSL HO100 Measurements Frequency Response Balanced Headphone Amplifier.png

I tested it at 2 volts out and it did not do this. I am assuming it is the protection circuit kicking in.

Multitone test shows impressively low intermodulation distortion:

SMSL HO100 Measurements Multitone stereo Balanced Headphone Amplifier.png

Sweeping at all frequencies we likewise get excellent performance:

SMSL HO100 Measurements Frequency vs distortion Balanced Headphone Amplifier.png

Power is one of the most important measurements of the headphone amp so let’s see what we have at 300 ohm:

SMSL HO100 Measurements Power 300 stereo Balanced Headphone Amplifier.png

My minimum requirement for desktop amps is 100 milliwatts and the HO100 clears that mark. It also delivers over 1 watt at 32 ohm:

SMSL HO100 Measurements Power 32 stereo Balanced Headphone Amplifier.png

Notice how the noise penalty is marginal for medium gain yet you get a lot more power than low gain. So that would be the setting I would use instead of low.

Sweeping for a range of loads we get sable and nice performance:

SMSL HO100 Measurements Power vs Load stereo Balanced Headphone Amplifier.png

Finally channel matching is excellent as I adjust the volume but your sample may not be as good:

SMSL HO100 Measurements Channel Balanced Headphone Amplifier.png

SMSL HO100 Listening Tests
I started in reverse order of my usual testing with Dan Clark Stealth. This is a very difficult and power hungry headphone to drive. HO100 could only drive it to medium volume before getting distorted. Switching to Drop Ether CX bettered performance where I could get to ear bleeding levels before I could hear distortion. Best performance was with the Sennheiser HD650 where the HO100 drove it with authority to any volume level you wanted. Dynamic rand and detail was superb as is the case when the amplifier is not the bottleneck.

The SMSL HO100 delivers on three of my favorite features: balanced input, included AC adapter and low cost. Distortion and noise performance are excellent landing near the top of the class at any price. Power output though is good to excellent depending on your headphone impedance, leaving room for pricier offerings from SMSL and others. The only odd thing in the measurements is the muting at subsonic frequencies (which I could not force with music content with very deep bass).

I am happy to give a recommendation to SMSL HO100.

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