The HPA-01M has essentially two sound profiles on offer that will suit different tastes. The current drive ouput and the voltage drive output do not sound the same and do not operate at the same volume or gain levels either. They match differently to some gear also with differing responses. It really is a case of two halves as a result. There are some defined commonalities such as that little bit of channel imbalanced prevalent on sensitive cans and earphones and general power capability with planars (their ideal match) but that is about it.
Current Drive Output
With the current drive output, you get more of a reference level and very transparent and natural sound that scales wonderfully well especially with planar headphones. Tonality is neutral, fast, clean and relatively linear right the way throughout. The dynamics and detail is excellent whilst never sounding too tiring or forward. Attack and decay is tight but refined so there is never a hint of anything harsh unless the recording is poor. This is the more revealing of the two outputs and as such the one I would channel my better recordings through and anything complex and articulate.
The current drive output is practically color free. When I mentioned transparency that is not some vague description of detecting quirks in a recording that some amps veil over but rather the fact each source I tried was instantly recognizable in its own right but with the benefit of some quality reference amping. I went through about a ton of different portable sources such as the DX90, AK120, Lotoo’s Paw Gold, Shanling’s M3 and the FiiO X5 and each signature could be clearly detected via the Bakoon’s current drive signal. Some obviously performed better than others – after all this is an analog setup so line outs are critically important with the HPA-01M unless you go for double amping.
The Achilles heel is the relative channel imbalance with sensitive headphones and IEM’s at low levels og output, especially if your source line out is powerful in its own right such as the Paw Gold. At absolute zero the sound was not dead quiet. Not to be confused though with background noise or hiss, not a hint of it, rather just the playback level couldn’t hit zero properly even on low gain. IEM’s such as the VE6X from Vision Ears, Custom Arts Harmony 8 and more midfi UE900s’s all had that low level imbalance. It is really unavoidable given the explanation regarding how current signal works. Push it up a few notches though to regular listening levels and all IEM’s sound perfectly fine with no imbalance. It is slight nitpicking perhaps but something to be aware of.
Voltage Drive Output
In most instances, the voltage drive had a weightier and fuller sound than the current signal. To those coming from traditional amping this signature might seem more familiar and possibly more consumer friendly with that added bass bias, slightly slower decay rate and an elevated hint of warmth to take the edge off on the top end. When I say slightly slower it is still by accounts a relatively speedy signature but compared to the current drive you can feel it take its foot off the gas ever so slightly.
Voltage drive’s slightly slower decay rate and lower levels of separation than current drive might also make the sound a bit more congested, thicker and with less space adding to the sensation of having a weighted lower mid to upper bass signature. It is also not as linear as the current drive output, especially in the bass response, it is more of a fun signature for modern rock and pop genres and more forgiving in general of compressed or lossy recordings.
Whilst my own personal preference veered to the overly neutral and speedy current drive for the likes of say prog rock, orchestral, speed metal and acoustics, I did enjoy switching to voltage drive for EDM, pop and hard rock just to color the response a bit more and elevate the bass ever so slightly.
The HPA-01M’s forte is with planar cans, especially the LCD-2, which sounded positively reborn and the LCD-X which sounded so open, detailed and very coherent. This is what I love about a high end transparent amp; a proper conduit for both the source and the cans to shine.
(Paw Gold line out)
The LCD-2 bass response is coherent, detailed and full sounding when paired with the Bakoon HPA-01M. Vocal presence is clear, natural and engaging and whilst treble on the LCD-2 Rev 2 is never going to be the strength, it does indeed sound very smooth and sibilant free. Granted the LCD-2 is not a soundstage monster but the engaging lush tones and liquid flow of the match with the Bakoon will suck you right in. The Bakoon hides nothing. It simply reinforces, adds some juice and a touch of pace.
The Lotoo Paw Gold DAP may not be the most dynamic of DAPs but amped, line out and running out of that flat neutral and speedy Bakoon current drive output it sounds positively brimming with musicality using the LCD-2 rev 2. The amp in the Paw Gold is one of the stronger ones in the portable range but it is not on the level of the Bakoon. The Paw Gold with a straight connection to the LCD-2 sounds smooth and natural but lower in dynamics and a bit too polite. The Bakoon gives it a nice edge, beefs up the sound considerably but still conveying that smooth and liquid tonality of the Paw Gold.
The LCD-X has zero power issues when matched with the Bakoon (Paw Gold source). It can drive these effortlessly without any clipping or distortion. That elevated and cleaner treble of the LCD-x really shines with the neutral and energetic sound signature of the HPA-01M. The speedy nature of the HPA-01M also matches perfectly with the faster transients of the LCD-X and the quickened decay especially in the midrange and lower treble without a hint of any unwanted glare or sibilance.
Switch over to voltage drive in both the LCD-X and LCD-2 and you get a slightly warmer and greater emphasis on the lower mids and bass weight. The pace drops a bit compared to the current drive but you get a slightly weightier or fuller response. The treble still has great detail but the articulation is a bit slower. For some this might be a welcome change to the more linear speedy current stage and a better match for modern pop and rock.
(DX90/Paw Gold line out)
When paired with the Oppo PM-1 the output in current drive was lean, clear, speedy, bass is a bit more linear than before, speed is much improved and the DX90’s dynamics intact. The smoothness of the PM-1 and clarity of the DX90 mesh well but the power of the Bakoon helps deliver a very detailed and rich sound. The pairing at all times remained sibilant free with excellent control.
In current drive the low end weight of the PM-1 has been pulled back ever so slightly in favor of detail and speed. Combined with the new Oppo PM series leather pads the increase in speed and better treble performance works fantastically with heavy rock and metal. Nile’s “When my wrath is done” steel guitar and chugging riffs intro sounds crisp clear and incredibly well defined on the PM-1. The Paw Gold/PM-1 with the Bakoon was far more impactful than the DX90 pairing and slightly more musical. The PM-1 low end just sounded that bit fuller and vocals more natural. Naturally, given the PM-1 super efficient design, there were no issues on power with both DAP’s but high gain felt the more natural of settings with the Bakoon on current gain even thought the PM-1 is relatively easy to drive.
Page 3: IEM and Source Sound Impressions