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SMSL HO100 Review (Headphone Amp)

Rate this headphone amplifier:

  • 1. Poor (headless panther)

    Votes: 1 0.6%
  • 2. Not terrible (postman panther)

    Votes: 5 3.2%
  • 3. Fine (happy panther

    Votes: 32 20.4%
  • 4. Great (golfing panther)

    Votes: 119 75.8%

  • Total voters
    157

amirm

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This is a review and detailed measurements of the SMSL HO100 balanced (input) stereo headphone amplifier. It was sent to me by Aoshida Audio and costs US $149.
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:

best budget headphone amplifier review.png


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



Most quiet headphone amplifier review.png


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.

Conclusions
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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As always, questions, comments, recommendations, etc. are welcome.

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solderdude

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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

This suggests there is a rather 'quick acting' DC protection in the amp.

A potential benefit of the Pentaconn (aside from convenience) is that with low impedance headphones with long cables there is a chance stereo separation is technically better when a Pentaconn connector is used compared to a TRS jack (when it has a 3-wire connection).

Seems like a technically competent and affordable amp with both balanced and SE inputs. Balanced in could prevent ground loops as the safety ground may well be connected to the signal ground (needs confirmation of close to 0ohm between RCA shield and safety ground pin).
 
Last edited:

dib

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While the HO100 is very good, it's not as flawless as the DO100 and will not be a "perfect" amp for the "perfect" DAC.
Amir pushes these companies that hard that we become so spoiled with great performance on the cheap…
 

Vict0r

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Thanks for the review! The price is what elevates it from good to great, in my opinion. Excellent value. Stack it on top of the DO100 and you're set.
 

Koeitje

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Would love to have seen a bit more power, but if you don't have hard to drive headphones it's excellent. Can't complain much at this price.
 

Lupin

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Bit more power would've been nice of course but at the same time understandable SMSL didn't.. they still need something to push customers to higher end offerings :)
 

JSmith

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So... has anyone listened to it? Sorry... there's always one right? :facepalm: ;) :D

This is a cracking device for the price. Always nice to see a well measuring review @amirm.


JSmith
 

restorer-john

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Excellent review @amirm.

It looks to be a great value (AUD$199 on Amazon) HPA and nicely made if the interior shots on their site are representative.

It could be a decent line level preamp with noise levels that low.
 

solderdude

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While the HO100 is very good, it's not as flawless as the DO100 and will not be a "perfect" amp for the "perfect" DAC.
Amir pushes these companies that hard that we become so spoiled with great performance on the cheap…

Can I ask what you find to be not perfect (enough) ?
What are the (audible) flaws ?
 

Vict0r

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Can I ask what you find to be not perfect (enough) ?
What are the (audible) flaws ?

Screw audible! Anything that doesn't have fancy VU-meters can't ever be perfect. :p
 

solderdude

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Alas this is only a headphone amp and not a pre-amp, unless you use one of the headphone outs as input for active speakers in which case it has volume controlled pre-amp functionality with 2 inputs (balanced or RCA).
 

TNT

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As level increases, Amirs ears first bleed, then starts to distort ;)

//
 

HansHolland

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Alas this is only a headphone amp and not a pre-amp, unless you use one of the headphone outs as input for active speakers in which case it has volume controlled pre-amp functionality with 2 inputs (balanced or RCA).
I also wrote through outputs. You know for connecting an amp. It would be nice to be able to connect everything with XLR, that is not possible when using the matching DO100.
 

beefkabob

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Do you hear subsonic bass on headphones? No. Do you feel them? Maybe as a migraine?

The only real flaw I see here is that there are somewhat more expensive headphones that can drive Dan Clark Stealth and otherwise perform similar.

SMSL really can make excellent gear.

Then again, they have made some crap that I've bought.
 

anphex

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How is such a sharp cutoff at exactly 14 Hz possible?
 

milosz

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So, better than the $3,000 Benchmark HP4A's SINAD for $150....?

How do they do it? And why does Benchmark feel they can ask $3,000?
 
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