Hyperion vs Krell Reference 64: an owner compares AL4, EL8 and EF14 output stages

One owner who lives with Demograf Audio converters on the Cirrus Logic CS4397, the design now offered as Hyperion, spent 2023 comparing them at length: three units with AL4, EL8 and EF14 tube output stages against a Krell Reference 64, then his own newer unit, which can switch between output stages, against the older ones and against an SQtech Matrix DSC. Below we summarise what he heard, where the CS4397 converters led, where they fell short, and how the output tubes change the sound.

These impressions are summarised and translated from owners’ posts on an audiophile forum. They are the subjective views of their authors, not measurements or claims of Demograf Audio.

Which units he compared

He describes the CS4397 converters as one circuit that differs mainly in the output tubes, AL4, EL8 or EF14, and in the grade of parts. In the August 2023 session three such units, each with one output tube, met a Krell Reference 64, a multibit DAC he regards as a benchmark for bass. The EF14 unit was not at that session, but he had compared it with the other two many times and includes it.

A few weeks later the designer delivered his own new CS4397 converter. It was built so that he can switch between EF14, EL8 and AL4 tubes and a solid-state output, and it has a treble adjustment and an I2S input that detects the I2S format by itself. Today the chip and these output tubes are offered in Hyperion, with a solid-state output stage as standard and the tube stage as an option.

Hyperion vs Krell Reference 64

AL4 output stage

The AL4 unit was built with the simplest parts of the three, yet in the midrange and treble he heard it on a very similar level to the Krell, with a different character:

• The Krell was colder, punchier, more precise and more distant.
• The CS4397 converter was denser, warmer and more saturated, with a more cohesive texture and a noticeably larger stage, even though the Krell separated the midrange more clearly.
• Resolution in the midrange and treble was the same.
• He found the midrange of the CS4397 converter much more pleasant: a cohesive texture and full-bodied tonality, with good dynamics and fine contrast.
• The bass was not close. The Krell went lower and was firmer, more sculpted and more dynamic, and the gap was large.

EL8 output stage

• The EL8 unit was clearly above the AL4 one, and against the Krell the picture changed sharply: he heard it well ahead of the Krell in midrange richness, resolution, the drawing of instruments and timbre. In his words, it is simply a class higher in the midrange and treble.
• Its texture was less cohesive and pleasant than the AL4 unit’s, and the AL4 unit had more punch.
• After the Krell, the EL8 unit lost some energy on percussion in the midrange and seemed to soften the strike slightly in the treble, despite a mild emphasis in the lower and middle treble.
• The bass was almost unchanged from the AL4 unit.

EF14 output stage

• The EF14 unit has no emphasis in the lower and middle treble and plays even more calmly and musically than the EL8 one.
• Its midrange and treble are a touch less detailed than the EL8 unit’s.
• In two comparisons in different systems it surpassed a Rockna Wavedream Signature in the delivery and energy of percussion, despite its full-bodied, musical presentation.

The bass question

All three CS4397 units had much the same bass, and all lost clearly to the Krell in it. He sums up his dilemma: in his experience delta-sigma DACs lack truly good bass, and multibit DACs lack treble. By delta-sigma standards he rates the bass of these converters among the strongest he has heard, but next to the Krell, which he calls the king of bass, he concluded that no one has solved the problem. He decided to stay with his CS4397 converter.

His newer unit: output stages compared

Against the older CS4397 units

He compared his new unit with each older one using the same tubes: EF14 against the EF14 unit, EL8 against the EL8 unit. Both older units sounded more full-bodied and denser, but much less airy and large-scale, simpler in resolution of the upper treble, less dynamic and softer in the bass. The older EF14 unit was also simpler in midrange resolution, while the older EL8 unit, despite its weaker treble and softer, denser sound, slightly surpassed his new unit in that respect. With EF14 tubes, his new unit surpassed the older EL8 unit overall.

EF14, EL8, AL4 or solid-state?

• EF14: the most detailed of the outputs, even more detailed than the solid-state one. His choice for most listening: the airiest, most musical and most delicate variant.
• Solid-state: detailed, but with a less musical and more distant midrange, so he likes it less. One friend preferred it.
• EL8: about as detailed as AL4; it brings the midrange closer and makes it denser, more melodic and richer on vocals. Another friend preferred it.
• AL4: as detailed as EL8, but fatter, punchier and slightly V-shaped. He tried four different AL4 tubes and likes the fattest-sounding of them.

The treble adjustment

The treble control, which he had not asked for, became the feature he values most. He sets it for each pair of headphones. With the Audeze LCD-4z at the brightest setting he heard them become airy, without harsh cymbals. With the Audeze LCD-5 voices sounded a little sharp on sibilants at the third of five positions, and one more step cured it. Even Kennerton headphones that tend to be hard in the treble played properly. He heard no muddiness at the stronger settings.

Dynamics, air and resolution

Beyond the comparisons, he describes dynamics he calls perhaps the strongest he has heard from a DAC: a light, weightless sound that “breathes”. He wondered whether it was too bright, and compared it with a friend’s Krell Studio: his unit was not brighter, only slightly lighter in the bass. The resolution was probably the highest he had heard, but it was the dynamics and air that surprised him. He had asked the designer for hard, massive bass, very high dynamics and resolution, scale and a light warmth in the midrange, and felt the converter delivered the technical side of that request.

vs SQtech Matrix DSC

About a month later he compared his unit with an SQtech Matrix DSC, a DSD-based DAC by another builder, on loudspeakers and on headphones.

• On loudspeakers: the DSC had firmer, more informative and more varied bass, more dynamics, a slightly wider stage and a more transparent, calmer midrange with more information from instruments at the back. His unit had slightly higher resolution in the upper treble, but its more pronounced upper treble made an already bright recording somewhat uncomfortable.
• On headphones: the DSC localised the singer and the instruments far more clearly; his unit presented the music more as one canvas, slightly airier. On metal the DSC had faster, firmer bass and cleaner blast beats, while his unit had more body and richer instruments: “garage”, fat, saturated guitars and a growl with more power. On metal he did not want to go back to the DSC.

His verdict: the two are close, with the DSC perhaps slightly higher in level, but for heavy metal on headphones, his main use, he finds the CS4397 converter more involving.

Summary

In this owner’s comparisons the CS4397 converters matched or surpassed a Krell Reference 64 in the midrange and treble, with the EL8 unit clearly ahead in richness, resolution and timbre, and lost clearly to it in bass. The output tube shapes the character: AL4 fat and punchy, EL8 dense and melodic in the midrange, EF14 calm, airy and the most detailed. His newer unit added air, scale, dynamics and a treble adjustment he now sets for every pair of headphones. An SQtech Matrix DSC beat it in bass and localisation, but not in timbre and body on the music he plays most.

Which Demograf Audio piece fits

• Hyperion is the current converter on the CS4397: S/PDIF coaxial and USB (Amanero) inputs, up to 24-bit / 192 kHz and DSD256 over USB, I2S on request. The stock output stage is solid-state; a tube stage on EF14, EL8, AL4, 6Zh4 or ML6 is an option. Our Hyperion owners’ review collects other owners’ impressions.
• Prometheus, the programmable-logic converter that converts PCM to DSD, is the newer design the same owner went on to hear; see his first impressions of it.

Every converter is made to order by Dmitriy Gubchenko, with a one-year warranty (extra warranty available: +1 or +2 years).