My first reaction to reading paul2qute reply was that I am sure people have read enough about my posting on adding another amp, as I really have said enough.
But then I thought - have I posted about all the ways that bloom, or the perception of added weight can be added to an amplifier? This would give the illusion that Chord amps are relatively underpowered (when of course they aren't). And I don't think I have posted about all the ways of how to artificially add to the perception of weight.
So here goes:
1. 2nd harmonic addition. Now I have posted about this before, and it's something that is well known about. The ear is actually pretty poor transducer for bass; the ear is non-linear, and not very good at detecting the pitch of low frequencies (bass). The ear/brain has a number of tricks available to actually let the brain compensate for the ear's poor low frequency performance. One of these tricks is to take the 2nd harmonic, then use the level of the 2nd harmonic, together with some fundamental, to trigger the perception of the fundamental; so when you add 2nd harmonic distortion, it's easier to actually perceive the fundamental - so you hear the bass. Another way that the brain uses to infer or perceive bass is through transients, but that leads onto the WTA filters and another situation.
So adding 2nd harmonic makes you think that you are hearing more fundamental and more bass than there actually is. So having an amp (such as a tube) that creates more 2nd harmonic for bass (and this happens naturally with transformers and tubes) will give an illusion that there is more bass than there actually is.
2. Damping. Headphones and speakers are electro-acoustic systems that have a natural resonance in the bass; this resonance is damped (or controlled) mechanically and electrically; when a bass driver starts flapping out of control (creating more bass and the illusion of more weight) it creates a back EMF in the voice coil; this is controlled by the amp's OP impedance. Listening tests have shown that this is directly audible - a high OP impedance (low damping factor) gives more bass than a low output impedance (high damping factor); but with the high damping factor, although the bass is leaner, it starts and stops much faster and is much more accurate. So bass tightness, rhythm perception and impact improves.
3. AC coupling capacitors. These can add considerable bloom to bass, particularly electrolytic capacitors. There is an effect known as dielectric absorption; with this, the capacitor non-linearly stores charge; then it releases this charge at a time after the bass has finished, and creates a low frequency error that depends upon the previous low frequency amplitude envelope. This sounds like a softness in the bass, and it also increases bass perceived weight (you are actually adding low frequency errors). Moreover, they also add 2nd harmonic distortion too, and only with the bass. Indeed, I see a lot of DAC designers using this trick of having large amounts of 2nd harmonic but only with low frequencies - no names, but examine the 20Hz distortion against 1kHz - some DAC's have 1% THD at 20 Hz, and this is done solely to convince you into thinking the bass has more weight than it really has (this is actually done to try to compensate for a hard and glarying treble). You can fine tune the SQ by selecting the right caps - but all you are doing is balancing one distortion against another to try to fool you.
Now Hugo 2 does not "enjoy" any of these tricks - it has extraordinary low 2nd harmonic distortion (-130dB) and very low OP impedance (25 milli-ohms or 0.025 ohms many headphone amps are a few ohms), and no coupling caps at all (with the digital DC servo). So why don't I use these tricks? Simply because it would destroy transparency - and in particular destroy variability. There are some pieces of music where I want things to sound soft and warm and big; there are some tracks where the bass must be fast and super tight; if you use the above tricks - then everything always sounds the same. And that to me ruins the music.
So what does that mean if your headphone sounds too thin with no weight in the bass? EQ - or more importantly - get better headphones. There are many headphones IMHO that actually are not very good, even though they are very highly regarded in the Head-Fi community... If you plug a distorting headphone into Hugo 2 or Dave, it becomes very apparent and very easy to perceive headphone deficiencies.
