The Euforia Evo is a perfect high-end entry drug into tubes for solid-state fans.
- Excels in detail and ambiance reproduction
- Very little OTL coloration
- Looks gorgeous
- Drives even 32-ohm loads
- Dynamics to die for
- Some coloration in the low-end
- Runs hot and the tube “cage” is more for looks
- The gain can be a bit high with hotter sources
- The ON/OFF switch is on the back panel
- It might not be “tubey” enough for some
Is audio signal amplification a solved problem? Depends on what you’re looking for. A multi-thousand-dollar tube marvel doesn’t do anything electrically more revolutionary than a part of an Apple dongle. The problem is that most standard audio signal electrical measurements aren’t exactly terribly relevant to the heard performance.
Having built tube amps for more than 25 years, the family-owned and operated Feliks Audio are specialists of mainly output-transformer-less (OTL) units. Many argue that ditching the trafo lets one hear more of the actual tubes. At the same time, OTL amps are quite picky in terms of loads they drive with higher impedances being more gentle to more voltage-happy tube output stages.
Read on and join me in the journey where I try to gauge the limitations of an OTL tube amp and where exactly its place is in a forward-thinking audiophile’s system.
One Minute Review Video
Design and Build
Feliks Audio handcrafts all of their amplifiers so they all share a similar degree of quality in their looks and build. The Euforia Evo is currently their highest-tier OTL amplifier and it has the looks to match. Most of the chassis is made from bent sheet steel powder-coated in dark grey.
The front panel is nicely sculpted by CNC machining and houses both the output jacks and the enviably huge volume knob.
The top floor displays a pair of input and power tubes with a shielded power transformer box sitting in the back row. The two pairs of bolts in the very front can hold two very minimalistic tube protector shields which honestly are there more for the looks. I kept them off because they get in the way of getting hypnotized by the bottled fire.
On the back panel, we get two pairs of nice RCA connectors – one for input and the other for preamp output. The preamp out’s sadly don’t get muted when headphones are connected so you need some other way to mute what you’re not listening to.
The power switch is on the IEC panel which can be a pain in some setups but potentially keeps the noise down as AC cabling doesn’t need to go to the front panel. Right by the power switch sits a smaller rocker switch which controls the crossfeed function. I found it handy for hard-panned albums like The Beatles, but it was off for most of my listening.
Under the Hood
Without getting too deep into tube amp topologies, all of them have to grapple with the same problem – they output both the amplified signal and a large DC voltage. Unlike solid-state amps, you can’t really have fully DC-coupled tube amplifiers without resorting to very exotic trickery which brings its own set of drawbacks.
To save your precious headphones from getting cooked by DC offset usually two methods are used – large capacitors and output transformers. Each approach has its own set of zealots and detractors, so really it’s about picking your poison and rolling with the punches. Usually, it’s cheaper to manufacture good-quality capacitors than transformers and in theory, they have less distortion mechanisms intrinsic to them. This should make OTL amps more transparent, right? Maybe. The transformer on the other hand makes the output tube more happy with the load it drives because tubes generally like handling high ohm loads.
For example, you won’t ever see OTL amps using famous tubes like the 300B, 2A3 or 45 because they like being cozy with kiloohm loads presented from fancy transformers and not directly driving your 32, 300, or even 600-ohm headphones. The Euforia Evo uses rugged NOS Svetlana 6N13S tubes in a matched pair which don’t mind the extra work.
The input stage employs a more fancy pair of PsVane CV-181 Mk2 “Gold” tubes. Those looking for more adventure out of their tube journey will be happy to know that the Euforia Evo can take 6N8S, ECC32, 5692, 6F8G as alternatives for the driver tube and 6080, 5998, 6N5P, 6N5S, ECC230, 7236, CV2523 for power tubes.
How Does the Euforia Evo Sound?
Powering on the Euforia Evo is quite the spectacle – the power transformer exudes some hum due to the inrush during which the capacitor banks charge up. All four tubes slowly start up with filaments faintly glowing. You can hear some noises due to heat expansion. Lastly, the anode current relay engages and the amp is ready for you.
The amplifier is completely silent both acoustically and electronically.
One thing that stood out when swapping between the multitude of headphones I had on hand was the high-ish 20dB gain. With my DACs outputting 2.5Vrms from RCA, there was less than usual breathing room on the huge Euforia Evo volume knob. With colder sources like 2Vrms DACs and phono preamps, the extra gain will work better.
Out of curiosity, I tried some of my IEMs with the Feliks Euforia Evo and I was taken aback by how silent the amplifier stage is.
The Simgot EA1000 detected some amp stage noise which wouldn’t change with volume control position. With music, it wasn’t a problem. Less sensitive tribrids like the ThieAudio Monarch MK3 were completely silent but the high output impedance changed their sound too much. With full-size headphones, I get a pitch-black background. A heroic achievement in tube amp design and construction!
Now let’s talk about the actual sound. Feliks Audio recommends burning the amp in for 50h but I couldn’t keep myself from listening. There were small changes but the basic character can be heard almost right away – the Euforia Evo has very little in terms of tube coloration.
I can imagine that some folks will want rounder transients, more wetness in the mids, and other ethereal qualities.
The Euforia Evo offers a very linear frequency response, frighteningly good resolution, great imaging, and absolutely explosive dynamics despite having rather meager power specs. In many respects it’s not too different from the best solid-state amp I’ve ever heard – the mighty KG CFA3.
After doing comparisons with other amps here, one thing that stands out is the bass reproduction of the Euforia Evo. Being an OTL, it has high output impedance which slightly blooms the low end in most dynamic headphones. This means that compared to most zero output impedance amps the bass is less controlled and loses a bit of delineation.
Comparisons
Sorry, I don’t have any high-dollar tube amps from the likes of Eddie Current, Donald North, or Woo Audio. What I can offer is a head-to-head with my current reference amplifier, the objectively perfect beast with 80 opamps – SMSL SH-X.
After a few sweaty nights, I can safely say that the two amps are more similar than different. The most obvious difference is the low end. Solid state just grips those drivers like there’s no tomorrow! Both amplifiers are superbly detailed with the Euforia Evo offering more realistic staging and imaging.
The SH-X sounds equally wide with just about every recording while the OTL amp uncannily morphed depending on the material. The comparison also made me realize how versatile the Euforia Evo is. It can handle death metal or industrial electronica just fine, no need to keep on an Ella-only diet.
Where to Buy
Who Should Buy This?
If you have the cash and want a no-holds-barred OTL amp, this is a great option. I will warn you that this is not an amp for retuning headphones. It won’t keep the HD800 from sounding a bit bright or a Focal from having a bit of a metallic taste. If you have reservations about some headphones, a more colored OTL amp might work better. Or just use EQ…
Final Thoughts
Has Feliks Audio solved the audio amplifier problem? If anything, they’ve shown that it probably has been solved around 80 years ago when tube amps ruled the Earth. The Euforia Evo is the least compromised OTL tube headphone amplifier I’ve heard. Yes, the output impedance and current limits of tubes mean it’s best to hook high-impedance headphones to it.
The real question is whether shelling EUR2700 is worth it. There’s no denying that it’s a luxury high-end item but the performance is very much there. Feliks Audio have the Elise which uses almost identical tubes. And the Echo 2 as an entry model. I have no reason to believe that they will sound less than stellar.
Or maybe get off your butt and build one yourself?
Whatever you choose, tubes can be great fun, and in the case of Euforia Evo, the sound quality is absolutely sublime. It’s neutral enough to work even with multibit DACs and make your favorite headphones bloom into a listening experience that’s no less than euphoric.
What’s in the Box?
- Euforia Evo amp
- 2x PsVane CV-181 Mk2 “Gold” tubes
- 2x NOS Svetlana 6N13S tubes
- IEC power cord
- Manual
- Tube guards (optional)
- Hex key (optional)
Technical Specifications
- Form: Desktop amp
- Topology: OTL tube amplifier
- Driver tubes: matched pair PsVane CV-181 Mk2 “Gold”
- Power tubes: matched pair NOS Svetlana 6N13S
- Input: 1x pair RCA
- Output: 6.35mm jack, unbalanced 4-pin XLR, active preamp RCA outputs
- Input impedance (Ohm): 100kOhm
- Output impedance: suitable for headphones in the 32 – 600ohm range
- Frequency Response (Hz): 7Hz – 80Khz@+/- 3dB (300ohm)
- THD+N: 0.4% (300ohm, 20 mW – around 113dB on an HD650)
- Max power: 260mW
- Dimensions: 31,3 × 20,3 × 19,3cm
- Weight (g): 7000