Review: Little Dot MkIII Valve/Tube Headphone Amp

The headphone amplifier does matter. It might seem daft - but a chain is only as good as the weakest link.

With the recent purchase of my AKG K702 reference headphones the limitations of the headphone amplifier I was using became apparent. Driving high end headphones direct from a sound card is pointless, so I did not even try! Instead I drove them from them from the 'phone amplifier on a Behringer Xenyx 502 mini-mixer. That had enough drive but nothing like the clarity and detailing to get the very best from the headphones. 

I found that get a really exciting, full sound I was using my Behringer DSP2024 digital effects unit to perform 'valve' emulation. Without it, modern recordings tend to sound 'dead' or 'dull'. This should give one a clue, valve amplifiers rock. But whay?

The answer to this question is contentious. It seems to me that it should be possible to build solid state amplifiers which behave as well as valve based ones. However, this does not seem to happen. That might be partly just a factor of cost. It is more acceptable to the market to pay a large amount for a valve amplifier which looks so cool and glows and stuff. However, there are a bunch of other reasons.

1) Non linearity in the valve amplifier and output transformer (the latter is not required in a solid state amplifier) causes a soft clipping effect. The peak output of a waveform is lower compare to the centre than would be the case for and unclipped waveform. Below is a totally subjective view of this (done using a valve emulator vst plugin to Audacity):
Here the red valve amplifier signal is 'fatter' than the
original (blue). The excursion near the mid line is greater
than that of the original.

This non linearity produces a 'warm' sound by injecting low harmonics into the sound.

2) I personally think the lack of negative feedback in the circuit is more important. Valve amplifiers do not use much negative feedback because the cannot for phase feedback reasons. Having said that, they don't need as much as valves do not tend to ring as much as solid state devices. The lack of negative feedback means there is much less transient intermodulation distortion. The often noted characteristic of valve amplifiers is the 'open' sound. Transients from say a drum strike do not dampen the adjacent sound of a string pluck. 

So what of the little dot?
It is a really nice valve amp. It does exactly what one wants from an amp. The sound is clear and open and slightly warm. I have found that there is now no need for the valve emulator and indeed using it over-does the effect. Sound is super clear with that characteristic lack of transient inter-modulation distortion. The gain is plenty as is the drive for the AKG 702's 200mW/62ohm configuration.

Visually it is very pretty. You have to like naked valves. I am just old enough to remember when these were considered super ugly and hidden away. Nowadays, they look really lovely with their glowing wires, metalised glass and general non 21st century look. But watch out - they get plenty hot enough to burn you.





In summary:

Positives:

  1. Sounds fantastic.
  2. Very clear, low transient intermodulation distortion.
  3. Plenty of drive for high end headphones.
  4. Looks really good.
  5. Robust construction.
  6. Valves super easy to replace.
  7. Can use jumpers on circuit board to allow support of different valves.
  8. Gold plated connectors.
  9. True valve pre and drive amplifier.
  10. Takes a 'proper' 1/4 inch jack.
  11. Does exactly what you expect from a valve headphone amp.


Negatives:

  1. Gets really hot so don't use around pets or kids.
  2. Colours the sound; yes it is valves, this means it is not a completely linear amp. Love it or hate it.
  3. The jumpers and switches are very hard to get to as they are accessed through slots on the casing.
  4. It is really big - make sure you have room.
  5. Easy to knock the valves.


Conclusions:
I love it and I love the tone. However, at £200 it was a lot of money. This could be viewed as a step into the 'over the top' region of audio technology. It is definitely the case what with the AKGs and this amplifier, the limiting factor to the sound quality is the recordings. If only there was a popular 96/24 bit standard for music rather than the stupid 44.1/16 at which CDs run. It is a shame that DVD audio or downloadable hq flac has not taken hold [I live in hope of the latter]. Hey ho...