The Yulong A100 is a class A headphone amplifier from the far east. They are not a well known brand in the west but produce some higher end models along with this reasonably priced unit. I have used tube headphone amplifiers in the past and wanted to try a class A solid state. It is a compact well made unit with a brushed black metal chassis, thick aluminium front plate and nice vintage style VU meters. The knob is plastic however but it still looks very good and not particularly plastic looking. Phono sockets are again good quality gold plated but it does not have an audio pass through facility which is an opportunity missed I feel. An audio pass though would make it a little more system friendly since it could be daisy chained with the system main amplifier from the source.
The power supply is built in, so none of those horrid plastic wall plug power supply units you typically get with many cheaper headphone amplifiers, so this is a major plus. As can be seen in the first photo it uses a decent toriod transformer and regulation circuit located at the back of the pcb.
The Yulong A100 does not have any particular sonic signature or colour. It is neither warm nor clinical but close to neutral. Sound is well balanced throughout the frequency range being clean and transparent. Also due to its solid state nature it is accurate and fast so transients are handled very well and not blurred. I cannot really criticise it in any major way since if I think for a moment that it is not particularly musical compared to say a good tube headphone amplifier, this is only because its focus is neutrality and minimal influence on the audio signal. It imparts barely any sonic characteristic on the music. The only demerit I can give the Yulong A100 is that the sound could be a little more fleshed out and have more 'air' but some of these faults can be improved by a capacitor upgrade.
If you look at the front right of PCB in the first photo it is quite obvious Yulong have left some space for larger higher quality capacitors. The small red WIMA caps fitted as standard are surprisingly good considering I have spent a great deal of time and money on caps in the past for various amps. This shows that the amp design and circuit are more important than specialist parts. Sometimes adding expensive and particular brands of caps and resistors are done usually to correct a flaw in the design. For example adding some paper in oil capacitors for a warmer, lusher sound typically helps to correct a slightly bright or thin sounding circuit.
These caps appear to be the audio input caps to block any DC from the source as the tracks route from the RCA input sockets. Technically if your source already has output caps then I guess these could be removed and replaced with a wire link for ultimate quality but please be careful since the amp would no longer have any AC coupling and could not block unwanted DC if connected to a source that leaks DC. This could easily damage your headphones. For me it was not worth the risk so I replaced them with better caps and I recommend you do also. So now when I connect it to my CD player, which I know has big film caps on the output, I now have 2 in series which is not ideal electronically. However if I connect it to my PC sound card which may or may not have output dc blocking then I know I am safe.
The choice of upgrade caps would be best if they have little colouration unless you want to tailor its sonic characteristic. A quality film foil type seems to be ideal and this is what I fitted as can be seen in the photo. They need to be at least 4.7uF 100V. Typically such film caps come in 250V and 600V versions so the 250V would be better due to having thinner insulating film. 100V film caps would be perfect if you can find any.
These upgrade caps really just flesh out the sound and make the amp even more open and transparent, the same but better. They needed a little time to burn in though as most caps seem to, so don't be worried if at first it sounds a little brighter.
This is a worth while mod and not difficult to do. The easiest way to fit these without removing the entire pcb is to unscrew the 4 front hex screws and the board can then be angled up. It is then possible to get to the underside to desolder the original caps completely. A desolder pump is also required to clear the holes on the outer edge of the cap mounting silk screen. These outer holes are intended for the larger cap fitting and this becomes quite obvious once you see the pcb.
This is a great little headphone amp, sounds pure and clean, never gets silly hot like some class A amps. Do the minor cap upgrade and it will put it further up the ranks sonically although not at the top. Costing half that of the Musical Fidelity M1 HPAP this is a good buy for someone on a tighter budget.
Tested with Grado PS500 (L-Cush + G-Cush) and Sennheiser HD800