(continued from Part 1)
Subjective Listening Impressions
From a distance, the Soul & Oppo sound similar, which is expected for DACs/preamps that are well engineered with excellent measurements. Both are neutral and transparent. However, the degree of similarity surprised me. I had to listen carefully to specific recordings that I know well, to hear reliable differences. Even then, the differences were subtle--but real, as I confirmed with blind tests. The differences were easier for me to hear on speakers. I suspect this is because my speakers are more neutral and resolving than my headphones. Audeze LCD-2 are great headphones but not as resolving as Magnepan 3.6/R. Speakers more resolving than headphones are rare, so most people, especially those with revealing headphones that are harder to drive (like the HD-800), will hear differences more easily on headphones than on speakers.
To characterize the differences is to overstate them. But to summarize:
Detailed Summary of Audible Differences
- Oppo: Earthy, Organic, Airy
- Soul: Pure, Taught, Resolving
- HF: Oppo has a touch more air; Soul has equal extension but less air. The first impression is slightly less HF from the Soul, but on deeper listen it is all there, yet subjectively less emphasized.
- Ultimately, “all there but less emphasized” seems truer to live acoustic music, though different from what is often portrayed as “HiFi”.
- Is “air” a barely perceptible hiss or noise that accentuates detail through stochastic resonance? If so, it’s a double-edged sword.
- NOTE: “air” such as hearing the space in a good cathedral recording, is all there with both Soul & Oppo.
- Treble: they balance the fundamental against harmonics slightly differently; Oppo emphasizes harmonics, Soul emphasizes fundamental. The Soul's treble is so silky smooth it makes the Oppo sound slightly grainy by comparison, though I wouldn't normally say the Oppo has grainy treble. This is a only a subtle variation of difference, both have uncolored voicing, and which sounds most natural depends on the recording.
- Mids: Oppo is earthy and organic, with a touch more presence that adds a sense of extra detail in some recordings, slightly veiling in others. Soul sounds more pure, normally a good thing (especially with voice & piano), though with some recordings, extra purity can sound sterile.
- Voicing aside, the Soul has slightly greater midrange clarity and resolution.
- Bass: Oppo sounds a touch looser, but deeper in the bottom octave (< 30 Hz). This perception was consistent across several musical sources, though it must be a psychoacoustic effect because both Oppo and Soul have flat frequency response to 20 Hz and below. Soul has more bass grip and control with better defined bass timbre and slightly more mid-bass energy.
- Transient response: Oppo has a bit more snap which sounds faster, but it also has a bit more ring. Soul is cleaner, which can sound a bit “dead” at first but on deeper listen it doesn’t seem slower or smeared.
- To avoid confusion, I didn’t try the Soul’s alternative minimum phase AA filter (though I’ve tried these before on other devices; the difference is subtle, but I usually find the linear phase “sharp” filter to sound cleaner).
- Dynamics: Soul is punchier with bigger and more effortless macro-dynamics. Both have excellent micro-dynamics, though the Soul sounds darker between plucks/smacks, which hints at faster decay, lower noise or distortion.
- The Soul had slightly better clarity and detail with some recordings. It was sometimes first to reveal subtle details that I heard on the Oppo only after knowing they were there.
- Regarding preferences:
- Sometimes the Oppo’s earthy airiness added realism and refinement. Other times, it veiled what the Soul made more clear.
- Sometimes the Soul’s tonal purity made the Oppo sound veiled in comparison. Other times, this purity sounded sterile where the Oppo sounded organic.
- At first my preference depended on what I was listening to. But with more listening across a wide variety of music I came to feel the Soul is more transparent and true to the source.
- From an engineering perspective, the Soul has 3 key advantages:
- First: its volume control. It changes the gain rather than attenuating a fixed gain, and it is a stepped attenuator so there is no potentiometer in the signal path.
- Advantage: lower noise and perfect channel balance at all settings.
- Sometimes with a stepped attenuator the perfect volume you want is between clicks. But this never happened with the Soul; its 0.5 dB per click was always fine enough to find the perfect level.
- Second: the Soul’s frequency-shaped internal feedback reduces distortion in the mids and treble where the ear is most sensitive. By analogy, frequency shaped dither is common practice in digital audio. Why not apply the same principle to the amplifier’s negative feedback loop, to shape distortion in the same way? It makes perfect sense, though Meier is the only person I know of who does this in his amps.
- Third: the Soul’s power supply; actually it has 4 switched power supplies with about 70 mF (a lot!) of filter capacitance: 1 for the digital section, 1 for the USB section, and 1 each for the positive and the negative supply lines of the analog stage.
- I suspect these 3 features are the primary contributing factors to the differences I heard.
- These features give the Soul a higher level of attention to engineering detail. It’s the right thing to do if you want the best sound at any cost. As an engineer myself I believe in these kinds of features.
- Yet a music lover asks: does this get me closer to the music leading to greater appreciation and enjoyment? Possibly… yet in general not necessarily. With the Soul, I think it does.
Build Quality, Durability, Support
- The Soul has DSP features: adjustable filters, EQ, channel mixing, etc. It has a notch filter to correct headphones that have a resonance peak in the 6-11 kHz range (like the HD-800). And it has tone controls. These can be useful when listening to the occasional recording that is badly mastered.
- But the Soul's DSP is not designed to handle general frequency response corrections for headphones or rooms. That typically requires a parametric EQ enabling precise frequency, amplitude and Q settings for multiple independent bands.
- I found the Soul's headphone crossfeed useful for music sources that have artificial hard L-R stereo separation. This can be distracting and the crossfeed gives a nice correction. The Soul's crossfeed had a similar overall effect to the crossfeed on my Jazz amp, but the Soul's implementation was more transparent, as expected since it is implemented digitally.
- As mentioned above, the Oppo has more types of inputs and outputs, both digital and analog.
- The Soul is fully balanced only, both inputs and outputs. For unbalanced RCA, you’ll need unbalanced/balanced converters. You’ll need balanced cables for your headphones and XLR cables for your power amp.
Good consumer gear has gotten very good indeed, raising the audio bar. Its measurements can be indistinguishable from the best of the best. Yet even someone with an “engineering-first” attitude (myself included) must admit that even gear whose measurements show all forms of distortion below theoretically audible thresholds, still can sound different. We measure much of what we hear, but we don’t measure everything we hear, and the quirks of perception acuity sometimes surprise us.
- Both have great build quality.
- Both get warm during use, but the Oppo much warmer than the Soul–possible longevity disadvantage?
- Support: Oppo has good support (though the HA-1 is discontinued), but Meier is great. He sets an example for the trade, being so responsive and direct with questions and feedback. I’ve never seen better support.
- The Oppo is built better than most consumer gear, both internal (big toroidal power supply, high quality opamps, etc.) and external (case, knobs, etc.). But the Soul has the edge here as it levels up to professional hand-selected parts and is built by Lake People in Germany.
- Ten years from now, which is more likely to still be running like new? Probably both, but if I had to pick one or the other, no question it’s the Soul.
The Oppo HA-1 is no longer made, so it’s hard to recommend despite being a fine piece of kit. If you can find one on eBay, I don’t think you will find its equal in sound quality anywhere under a kilobuck, and it’s super flexible having many inputs and outputs. However, if you want a DAC, headphone amp and line stage that is among the best available at any price, I recommend contacting Jan Meier and listening to the Soul. Sadly, some expensive high-end gear is audiophile bunkum. The high price is mainly about fancy cases and knobs, low production numbers, and social signalling exclusivity. It's wonderful to see engineers like Meier bust that stereotype, justify the price with unique engineering features and demonstrate that well engineered and built equipment really can sound better and get us closer to the music.