Digital Processor Reviews

Next, I used Cardas's all-natural Clear Beyond interconnects and speaker cables to connect the Wandla directly to the RCA inputs of the Parasound Halo A 21+ amplifier driving the Heretic AD614 speakers. This is my highest-resolving, most uncompressed amp-speaker combo, and it gave me the feeling I was experiencing the "real" Wandla, which now sounded clear and solid and considerably more color-saturated than it had with the wire-wart supply. In my notes, I wrote "Studio sound with flair!"

The next thing I noticed with the 300W A 21+ powering the 97dB/2.83V/m–sensitive Heretics was deeper, denser bass from the left side of Samson François's keyboard. The effect of this weightier bass was to put all 88 piano keys into a smoother octave-to-octave balance. With the HYPSOS powering the Wandla, voices and instruments displayed a more complete and natural spectral balance.

What stood out with this simple, Ferrum-sourced sound system was how its reportage seemed so straightforward and unadorned. No flavorizing. No luminous wowie-zowie. But just enough glow and punch and focused resolve to be satisfying with all musical genres.

Like Ferrum's OOR headphone amp, the Wandla wears its solid stateness proudly, as a virtue, not something to be suppressed. Respecting that and remembering how much I enjoyed the OOR, I decided to let myself fall into some long listening and enjoy the Ferrum's sound on its own terms. No sooner did I make that decision than I began falling under the Wandla's spell. The more recordings I played, the more the Wandla seemed to come to life.

The older I get, the more I see how audio equipment is like cars: You can't let components sit around getting flat tires. You have to start them up, heat up their oil, and take them for long, high-revving spins. I left the Wandla on 24/7 for the entire month. Every day, it got looser, more athletic, and more right-brain enticing. By the third week, it was Swan Lake enabled. So...

For fun I started my swan-clad ballerina journey with Madness's version of Tchaikovsky's Swan Lake, from the album One Step Beyond (16/44.1 FLAC, Rhino–Warner/Qobuz). There were no "baby ballerinas" from the Ballet Russes—just bass-fueled, speeding rhythms and that "heavy heavy monster sound" of mad Brits pogoing between the Heretics. Exactly what I was hoping for.

Filters and voltages
I followed that with a version of Swan Lake I've been wanting to enjoy but have not yet connected with: Tchaikovsky: Ballet Suites with Mstislav Rostropovich conducting the Berlin Philharmonic Orchestra playing Swan Lake Suite, Op.20a, recorded in 1996 (24/96 FLAC, Deutsche Grammophon/Qobuz). With the Wandla at its default settings (HD, HQ Apodizing filter, 24V DC), it sounded dry and compressed on loud passages—as it usually does. Then I remembered an email from Ferrum importer Roy Feldstein of Vana Ltd.: "Have you tried adjusting the voltage in the HYPSOS to match HQ filters? I'd suggest auditioning the HQ Apodizing filter at 22 to 23 volts. The HQ Gaussian filter works better at 26 volts in my system."

The Wandla arrived with its default HQ Apodizing filter engaged and the HYPSOS outputting 24V DC automatically. So, what the hay? I lowered the HYPSOS to 22 volts and tried that Rostropovich-Tchaikovsky again. Deutsche Grammophon's loud-passage compression was still there, but the overall sound had thinned a bit; there was more space and atmosphere in the quiet passages. At 22V DC, the Ballet Suites sounded just sweet and open enough to keep my mind focused on Rostropovich conducting the Berlin. This was the first time I listened to this album all the way through.

This 2V reduction in the Wandla's rail voltage made albums with two-star sonics sound like they had three-star sonics, which encouraged me to experiment more.

After playing the HQ Apodizing filter at 22V DC, I tried HQ's Gaussian filter at 22V DC (just to see what it would do), whereupon I noticed an increase in vibrancy but also a dullness. At 24V, the sound got brighter (lighting-wise) and more microdynamic. Rostropovich's Swan Lake became bright, tight, and tidy, in an appealing way.

When I upped the voltage to 26V like Roy suggested, the change was more obvious. Swan Lake sounded a half-star better. Vocals became dreamy on João Gilberto (1973) (16/44.1 FLAC, Ipanema/Tidal), and that's how I like João to sound. Right away I thought I like this, but I knew I needed to listen to more records longer and closer.

You see, it doesn't matter which filter or voltage settings I like; what's important for readers to realize is that Tchaikovsky's Ballet Suites, which I found to be a two-star recording at 24V apodizing and a three-star recording at 22V apodizing, became a 3.5-star recording at 26V Gaussian. With the Wandla/HYPSOS/Envy driving my Koss ESP 950 electrostatic headphones, it seemed like a five-star recording.

I asked Max Matuszak, Wandla's hardware engineer/designer, why his DAC needed "filter choices." I decided his answer deserved to be shared. "Filter choices are necessary because they change the final sound signature. There are many tradeoffs in digital interpolation-filter design, which have impact on aliasing rejection or pre- and post-ringing of impulse response. Digital filters are designed to focus on one of those characteristics or to balance between them. Therefore, filter selection allows tuning of the Wandla's final sound signature, depending on personal taste. We have some white papers on those topics, which explain this in detail (footnote 3).

"Right now, we use two HQ filters in Wandla. They are versions of filters from HQPlayer app designed and adapted by Jussi Laako of Signalyst for our SERCE module (which processes filtering). Those filters have much better attenuation in the stopband than ESS filters, so they reject aliasing much better."

I asked Max which of the filters he believed best represented the Ferrum sound aesthetic.

"HQ Apod. is our default filter, so it can be considered as the Ferrum sound aesthetic. Trying different supply voltages from HYPSOS will definitely introduce noticeable changes, but I would consider all of them as part of the family of Ferrum's sound aesthetic."

And what about recommended voltages? "When switching from the wall-wart supply, I suggest starting with 24V on the HYPSOS output, because it is the voltage on the output of the wall-wart supply, so it will be a fair comparison. After this, I suggest tinkering with voltage on the HYPSOS output. You should definitely try Roy's suggestions of supply voltage to specific filter, but I encourage you to experiment further after you try those suggestions. Maybe different values will fit your system and taste better. That's why this function of voltage adjustment in HYPSOS is called SST (Sweet Spot Tuning)."

Listening through the Genelec G Three
The analog output of every digital converter must push through all the wires, amps, and speakers strung in front of it. That's not an easy task, and some converters are better equipped to handle it than others. The best someone like me can do is give a DAC a clean, unfettered path.

With hopes of doing that, I connected the balanced analog output of the Wandla to the balanced input of the Genelec G Three active speakers using AudioQuest's ThunderBird interconnects, which I chose because in my view they put through the most low-level signal, especially at the frequency extremes. In my ever-changing sound systems, these interconnects have a history of making R-2R DACs sound bright and superdynamic—qualities they don't normally exhibit. I use ThunderBird wires with the Denafrips Terminator Plus because the T-Birds make the Terminator sound turbocharged. That is exactly what they did for the Wandla.

One thing this interconnect-induced turbocharging accomplished was to make the Ferrum-AudioQuest-Genelec system whisper for goosebumps. Music at low volumes sparkled and scintillated. Playing João Gilberto (1973), the Wandla seduced with detail and captivated with its transparency. João's famously rich vocal textures were seductively highlighted at low volumes. I auditioned the Wandla with a variety of amp-floorspeaker combos, but this Genelec G Three pairing showed the Wandla's sound at its most transparent and dynamic. I earnestly recommend this Wandla–G Three combo as a possible end-game sound system for audiophiles that value measurements and sweet sound.

In concert, the $1486/pair G Threes, the $2795 Wandla, and the $1195 HYPSOS power supply were the heart of one of the more articulate and seductive sound systems I've assembled in my studio.

Conclusion
The Wandla-HYPSOS combo is a thoroughly, wisely engineered converter that made me look forward to using it and made me smile every time I did. At its best with the HYPSOS, the Wandla danced in the same ballroom as DACs costing over $10,000. Sincerely recommended.

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Footnote 3: See ferrum.audio/digital-filters-in-general, ferrum.audio/wandla-ddf-dynamic-digital-filters, and ferrum.audio/wandla-ddf-dynamic-digital-filtering.