I recently acquired a Sennheiser HD650 as a gift from a close friend. It is a beauty, and I have been using it for quite some time when the very same friend recommended that I buy a headphone amp for it. As usual, I did what any person living in this century would do: go to the internet for product suggestions, reviews, and comparisons. After going through several amplifiers, I arrived with these three as my top choices.

Best Headphone Amp for Sennheiser HD650 Reviewed

I will still have to choose among them, of course. This is a challenging review, as there are many considerations and technical specs that I am not familiar with at all. I will still be listing them since they may help someone who has more refined technical seeking abilities than I do.

Reviewed by Asksound
Little Dot I+ 6JI X2 Tube Headphone Amp
Little Dot MK II greatly increases sound quality, dynamic range, output impedance, and harmonic distortion

It gains the driver tube-rolling options from the rest of the MK-series with the ability to roll 6JI, WE403A/B, GE5654, M8100, CV4010, EF95, etc at its factory jumper setting, and with jumper pins shorted, EF92, CV131, and all equivalents and drop-in replacements.

This is one terminology that I did not fully understand. Searching the internet, I found that it is an abbreviation for Total Harmonic Distortion plus Noise. It is a test for audio measurement. However, it isn’t the most useful test for a device’s performance. Still, it is a starting point.

The Little Dot I+ is a hybrid transistor-vacuum tube headphone amplifier. This amplifier is 7.08 inches in length, 3.81 inches wide, and 3.93 inches in height. It weighs 1.5 kg. It is available in either 120 or 220 AC volts.

The frequency response for 10HZ ~ 50KHz (minus3 dB) THD+N is as follows:

  1. 0.2 percent: 1Vrms @ 1000Hz
  2. 0.6 percent: 3Vrms @ 1000Hz
  3. 1.0 percent: 5Vrms @ 1000Hz

The Signal to Noise is 92dB. Its suitable headphone impedance is from 8 to 600 ohms, while the input impedance is 50k ohms. The power output at 300 ohms is 150 mW, 300 mW at 120 ohms, and 800 mW at32 ohms. Its user variable gain settings are at 6.5x or 3.25x. Its power consumption is 15VA.

It is a black rectangular box with a black cube sitting on top along with two glass tubes. There is a power indicator next to the audio jack, which is beside the volume knob. The last three components are labeled in white. The light indicator and audio jack are above the logo and brand name of the amplifier.

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#2 Pick
Monolith 133304 Liquid Spark Headphone Amp
Liquid Spark Headphone Amplifier by Alex Cavalli

Provides everything people have come to expect from a Cavalli design. It uses dual 18 V filtered power supply rails to produce wide voltage swings for additional headroom. The Spark offers plenty of power at 1300mW RMS into 50ohms (per channel), with very low distortion, and switchable gain.

The Liquid Spark is 11.1 inches wide, 7.3 inches deep, and 2.8 inches tall. It weighs 9.6 ounces. Its headphone output is an unbalanced stereo .25 inches TRS jack. Its Signal-to-Noise Ratio is 108dB in reference to 1 Vrms input / 2 Vrms output at 1kHz. For its crosstalk, the ratio is –73dB with 1 Vrms input / 2 Vrms output at 10kHz. The output impedance is less than 0.1 ohms, while the gain is +3dB or +6dB. Its two output protection is delay and offset.

The THD+N for both channels are as follows:

  1. 1 Vrms (20mW) – 0.007% THD+N @ 1kHz.
  2. 5 Vrms (530mW) – 0.035% THD+N @ 1kHz.
  3. 10 Vrms (2.12W) – 0.065% THD @ 1kHz.

It is a compact, drinking flask-looking device. The On/Off button could be found on the left-hand side next to the headphones input. The volume knob is on the left-hand side of the device. The front and a few centimeters into the body are painted a silvery grey finish, while the back has a black finish.

The Monolith logo is embossed onto the top of the amp. Behind the amp are four ports and the input for the adapter.

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Our #3 Pick
FiiO K3 Type-C USB DAC Headphone Amp
Compact Portable Headphone Amplifier

Features 2 USB audio modes (USB Audio Class 1 & Audio Class 2), PCM 384 kHz/DSD256 decoding and AKM AK4452 processor with 32-bit Velvet Sound technology.

This amplifier is the smallest of the three, with 2.76 inches in length, 2.28 inches in width, and 0.87 inches in height. Its driveability is 16 to 150 ohms. The output power depending on the headphone plugged are as follows:

3.5mm headphone output: 220mW (16 ohms); 120mW (32 ohms).

2.5mm headphone output: 320mW (16 ohms); 200mW (32 ohms)

Its casing is all aluminum with four ports for different uses. The balanced 2.25 mm jack is found next to the single-ended 3.5 mm port on the front of the device’s left-hand side. The bass and gain buttons are next, with the former on top of the latter. The volume knob protrudes from the right-hand side. The knob has 45-degree notches so that it can be turned with just one finger.

At the back, there is a port for Line, Coaxial, and Optical digital outputs. The USB audio is found between the Line and Coaxial outputs. The button is above the actual port. It is operated by 1 A battery. The light indicator flashes different colors depending on the function being performed. It is not recommended for mobile devices,

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Conclusion

As a matter of preference and aesthetic, I will have to choose the Monolith Liquid Spark. It is small, ergonomic, and pretty straightforward. Granted, it is not portable like the FiiO, but I think I’d instead choose the Liquid Spark design over the Little Dot I+.

FAQ: Frequent questions

🏆 Which is the best?

Little Dot I+ 6JI X2 Tube Standard Hybrid Amp

🔍 How did we test them?

We tested 13 products, researched 12 sources, evaluated 159 reviews and spent 9+ hours on our guide.

🤔 What should you look at before buying?

When choosing it's best to make a decision based on the price/quality, functionality and compatibility with other devices/technologies.