This is a review and detailed measurements of the SMSL HO200 balanced headphone amplifier.

I like the feel of the mechanical switches on the HO200:

And in-built power supply:

Notice the USB input for changing firmware that handles protection circuit duty. Nice new trend in this regard.

I focused my testing on the headphone output. I trust he pre-amp outputs are just the same but with higher impedance so should have identical performance.

SMSL HO200 Measurements
With balanced headphone amplifiers, I always start with XLR input and balanced output. Here, I ran into some issues in that regard with my measurements not matching what is published and some variability and sensitivity to cabling. In one case one channel had more distortion which then went away as I changed XLR cables and such. After some testing, I realized that best performance is achieved with unbalanced output, not balanced! This forced me to test a number of variations. So let’s start with the best case which is 1/4 HP Out:

This level of noise+distortion lands HO200 neck and neck with the best of the best:

Switching to RCA input improved performance just a hair more:

When measuring balanced output however, performance drops:

But if we switch to RCA input, we get back up there:

The issue seems to be gain management. With XLR Input, I had to dial back the volume know whereas with RCA, I would have it at maximum. Normally I expect balanced input and unbalanced inputs to produce the same output with 4 and 2 volts input respectively. I don’t like having RCA with the best performance because as you see in the last graph, it lets in mains noise. Best performance should have been XLR input to Balanced output.

Note that we are talking about inaudible differences either way but for the battle to land on top of rankings, this makes a difference.

You can see the same drop in performance in our SNR tests with XLR output:

And the same with 50 mv output but with less difference:

Using the better of the two, HO200 again lands shoulder to shoulder with the best there is:

Frequency response test is usually uneventful but such was not so here. The amplifier went into protection as I swept below 12 Hz:

While content with < 20 Hz may be rare, they do exist and I hope SMSL investigates and provides a firmware update for this.

Power vs distortion+noise is the most important test here so let’s start with 300 ohm load:

Once again we see the superiority of the unbalanced mode in lower noise but as usual, you get more power with balanced output. Same happened with 32 ohm load:

Sweeping full set of loads, we see that RCA mode just clips but the balanced output goes into protection at lower impedances:

Note however that at the onset of protection, you still have a ton of power so I would not take this as a negative. Balanced output has higher gain so gets pushed harder and hence the pull back.

Channel balance was good but as you usual, your mileage will vary:

Listening Tests
I did not get a chance to listen to the HO200. I expect it to perform superbly. There is a lightning storm going on and we just lost power (running on generator) so I want to get this out quickly.

Conclusions
The HO200 is a powerful headphone amplifier with very low noise and distortion. There is however something slightly odd about its design when it comes to balanced I/O. It is not enough to have any audible consequences as sum of distortion+noise is below threshold of hearing. But when it comes to competing with top of the class, I like to see this not be there. As well as the protection against playing sub 12 Hz content.

Overall, I am going to recommend the SMSL HO200.