The mhdt Havana is built around the Burr Brown PCM56P 16bit chip. In the Havana circuit, the net output is organic, spacious, musically convincing if you are not judging it by how performed music would sound if you were 8 inches from the instruments, as so much is recorded and mixed today. It's also dynamically energetic and bursty. As others have noted, even though the tube is just an output buffer, there are about a dozen compatible tubes and they allow a range of fine tunings to the Havana's sound.
For those who have noted that Havana is less detailed than DACs built around the ESS 9018, the Havana Balanced is, via its balanced outputs, a significant upgrade in resolution while also delivering more shove and tone density. Yup, it's more expensive, but worth it. Running a Havana Balanced via its single-ended outputs is the same as using a straight Havana, as the Balanced version is comprised electrically of two full Havanas.
These DACs are very receptive to DIY upgrades to caps and power supply, but it's not necessary to get very fine sound. The stock GE 5670 tube is pleasant enough and has no sins of commission, but several of omission, comparatively. It's vanilla, cheap, ubiquitous so I understand why mhdt DACs ship with it. A Tung-Sol or Bendix 2c51 reveals more definition, space, tone and shove. The Bendix 1964-production 6385 yields the most perceived resolution along with a bit of leanness in the midrange. The CBS-Hytron 5670 is a very good compromise of traits. The Western Electric JAN 396A matches well in many systems. And then there are another ten or so tubes you can try.
I got some worthwhile but not dramatic further improvement from upgrades to five capacitors. By far the greatest positive change to the sound of both my Havana Balanced DACs was resting them on Aurios Media Bearings. Those seem hard to find suddenly, but by all means I encourage you to try some sort of bearings solution under mhdt DACs. The effect is almost hard to believe.
Among delta-sigma DACs, I put the Havana Balanced against a Yulong D18, which uses the ESS9018 in a well-thought-out power supply and audio implementation, at an Asian-sourced price like mhdt. The Yulong is a voiced DAC, that also has choice of balanced and SE outputs. Unlike Havana Balanced, where the designer simply gives you Havana sound in balanced circuitry, Yulong actively chose to voice the SE and XLR outputs differently, and that difference is very apparent. He refers to the SE outputs as the "hifi" outs and it's what you expect: ultra-resolving, clean, extended, lean ..... and unforgiving. The XLR outputs are voiced for music lovers and their sound is harmonically richer, warmer, more dimensioned; still extended and clean but with considerably more tonal body up and down the aural range. It's still not nearly as organic as the Havana Balanced nor the Havana SE, but it's a tenable sound for someone looking for that sense of ultimate detail in sigma-delta with a little more tone. More expensive 9018 DACs like Mytek, Benchmark 2 and Resonessence have more finesse than the Yulong of course, and are smoother. But I haven't yet heard a delta-sigma based DAC sound as organic and engaging as a nicely-tubed mhdt Havana Balanced, for 16/44 material.
mhdt no longer makes the Havana, though the Havana Balanced is still available. The Stockholm V2 is the essence of the Havana DAC with a 24/192 receiver chip, though the D-to-A conversion is still done by the 16bit PCM56P. For a true 24/192-capable DAC, mhdt now also has the Steeplechase, which uses the Asahi Kasei AK4396, sometimes referred to as the "miracle dac." mhdt's designer is on record saying buyers should not expect its sound to be as organic and satisfying as Havana and Stockholm, but for anyone needing full 24 bit processing for high-res material, Steeplechase will sound pretty good -- the AK4396 being, in his view, the least objectionable delta-sigma DAC chip available. You still have that output buffer tube socket to fine tune your sound.
Phil
