Review: Zesto Audio Bia 120


Adding Zest-o

I first found the Bia 120 from Zesto Audio in, of all places, a Zesto Audio demo at an audio show. Crazy, right? Okay, maybe not, but that’s okay — that’s how I find most new bits, trolling the shows. Zesto has been on my to-watch list for the last couple of years, ever since I found designer George Counnas, who is rightfully lauded for his spectacular Andros phono preamplifier, driving some brutally revealing loudspeakers from TAD with a solid-state amplifier from GamuT.

I remember asking him about that amp, and I remember George shrugging while saying that while that amp was several generations out of date, it was “really quite good”. He followed that by saying that, until he found something better, it was far more than “good enough”. Hard to argue, given the shockingly great sound George was routinely wringing out of those TAD CR-1 speakers, speakers that I happen to know can be cruel to match anything to.

When George finally did find something better, it hit that rack. And it carried his own label. Natch.

The Good

  • Power. 60 watts is plenty for all but the silliest of loudspeakers, and the number of tubes here is just what’s needed for a fully dual-mono design — and no more.
  • Features. Balanced + SE inputs, and outputs supporting 4Ω, 8Ω and 16Ω, gives a boatload of compatibility. Very few modern amps bother, and it’s nice to see that flexibility here.
  • Sound. This amp has some personality, and while it may deviate from “neutral”, it does so beautifully.
  • Looks. It’s a far cry from the boring exposed-trannie casework plaguing most tube amplifiers, and adds a stylistic flourish that says that someone really gives a damn.

The Bad

  • Cost. This is a harder thing to measure, but almost $13k for an amplifier is a respectable chunk of change. Squarely below Art Dudley’s “I call bullshit” point, but still, significant and significant for this brand.
  • Heat. A quartet of KT88 tubes (with another quartet of smaller tubes) bouncing off that reflective wall on the trannies implies a three-season application, or a serious addiction to sweat.
  • Sound. For those looking for a “wire with gain”, this isn’t your amp. Not sure why you’d be looking at tubes for that, but it’s worth pointing out that you’re still looking. Move along.
  • Looks. While the flourish raises the visual interest, it’s a bit of a risk and not everyone will be taken in. Boring people, for example.


Big Tubes

“There’s something about tubes.”

How many times have you heard that phrase, as an audio enthusiast? It’s usually as bald as that, too — the assumption being that there’s this “thing” that tubes have or do that is, in some way, incomparable.

I find this all a bit Mysterian; any assumption that yesterday’s technology is unsurpassable is offensive to my progressive heart. I want to say that there is absolutely no reason why “that sound” cannot be fully recreated, captured and even improved on without having or needing the insertion of a little glass lightbulb. You can imagine me shrugging diffidently as I say that, too, if it helps.

The fact of the matter is that I’m not qualified to comment on why it is that tube amps sound good. I’m not an engineer. There are, I’m sure, lots of theories as to why listeners have been enthralled with vacuum tube amps. But I’m also not a scientist specializing in psycho-acoustics, either. Like most of us, I have to content myself with the experience of that goodness (or its lack), and my job (such as it is) is to report on that.

Now, I have heard that The Reason that a tube amp sounds better, on average, than a solid state amplifier has entirely to do with the kind of harmonics that the tube amp is said to generate. I have no idea if that’s true or not, but it certainly sounds plausible — and mentally scanning my recollection of John Atkinson’s notes attached to any given tube amplifier’s Measurements Section, I get the feeling that the Esteemed Editor tends to favor this explanation, even (and especially) when his measurements reveal serious concerns. But I do have to wonder if this isn’t some placeholder, awaiting a fuller explanation. Just my two-cents, but these explanations do seem to have the general character of hand-waving. Whatever.

But getting back to measurements: isn’t it almost a maxim that tube amps, to a fault, measure poorly? I mean, compared to their alternatives — even when they nonetheless earn a rave review from the writer in question. The fact that the reason for that enthusiasm routinely fails to be explained by the measurement is, no doubt, a source of perplexity and frustration. I mean, I imagine it must be. That kind of disconnect would bug me. Don’t misunderstand me — tube amps can be and are designed in such a way that they do put up credible numbers on the test bench; all I’m referring to is a perception that, when measured against their alternatives, something is amiss. I can practically hear John scratching his insanely thick thatch of hair (a fact that is, by itself, wildly unfair) and shrugging his own shoulders through his conclusions as he attempts to reconcile numbers he sees with the words he got from his reviewer.

But here’s my experience with tube amps. Assuming that the amp and speaker matches are agreeable, the resulting sound I get with tubes is more engaging. Yes, that’s a gross over-generalization, and one that requires some unpacking, because it’s a sad fact that most speakers are not, in point of fact, a salubrious match for most tube amps. Some care is required. In some cases, a lot of care is required. But the result, when everything aligns (or does so, near enough), is almost always interesting. More strongly, when things tend to go gangbusters with a given system, the introduction of a very good tube amp can have a dramatic and electrifying effect on the overall sound of the system. And then there’s the visual — your stereo is on fire. Heh heh. Yeah, that’s pretty cool.

Anyway, I throw all that out there as part of my own audio exploration. I started my audiophile journey with solid-state amps, like many of us do. I cut my teeth on NAD and moved from there to Plinius. I loved those systems. I have many great memories of many shared hours, enjoying the living tar out of the sound I was able to wring from them. But it wasn’t until I got my first tube amp, a pimped-out, chromed up EL34-based integrated, that I actually fell in love with audio. Tubes, for me, were the key. There’s just something about tubes! I’ve been dabbling ever since.

Back to the review at hand.


Bia 120

Bia, according to Hesiod, was a Titan, one of four children of Pallas and Styx: Nike (Victory), Kratos (Strength), Zelos (Rivalry) and Bia, joined forces with the usurper Zeus in casting down the rule of the Titans and issuing in the Olympian age. Bia was the personification of mighty force, and with her three sibs, they were Zeus’ ever-present bodyguards. It was Bia and her brother Kratos that captured Prometheus and brought him to Hephaestos, to be forever chained and tortured on the mountain. Bia, apparently, was not to be trifled with.

Naming an amplifier after a Titan, especially that Titan, is pretty ballsy.

The Bia 120 is a robust amplifier. At 60+ lbs, it’s not the heaviest I’ve had in-house, but it’s cumbersome and quite large, as well — it’s worth noting that the 20″ of depth to the chassis might cause some spillage off your average audio rack. Kinda like what my middle-aged tummy seems to be doing with my belt. [Cough].

Aesthetically, it’s black and silver, mirrored chrome and glass, and all in all, the whole is very striking. I think it’s snazzy and a far cry from the pedestrian chic that typically adorns tube amplifiers in the sub-$20k price point. Yes, that’s subjective — I had a few people look askance when I mentioned the design in conversation at RMAF last year — but haters gotta hate. Whatevs. I dig it.

The amp has three sets of binding posts, for 4Ω, 8Ω and 16Ω, which is pretty nifty — most “modern” tube amps stick to one, maybe two. I should also note that each tap is a 5-way post, and each tap also carries its own slow-blow fuse, and that’s in addition to the main 5 amp mains fuse. Input impedance on the RCA/single-ended inputs is a very healthy and respectable 100kΩ, so matching with preamplifiers is not a problem.

The amp is an auto bias circuit, with no negative feedback, and fully dual-mono in design. THD is a surprisingly low .22% at 1w into 8Ω. Overall gain is 23dB in a push-pull, pure Class A design. Think: hot.

The tube sockets are ceramic and well-spaced — they’re offset, which means that with the lights low, the visual from the front brings the glow from every tube. That’s cool! The 60 watts per channel output of the Bia 120 comes courtesy of a stock quartet of KT88 tubes from JJ, fed by another quartet of 12AU7 tubes (also from JJ). I will admit that this brand of tubes is not my favorite, but they are cheap. Tube rollers will probably rub their hands at the options — these are very popular tubes, with plenty of options to explore. Generally speaking, the small-signal tubes are exactly the ones to start your fiddling about with, if you’re so inclined. George recommended, as an experiment, that folks try a pair the JJ ECC802-S in position 6 and 8 (to the far right) just to “warm things up” a bit. Check with your tube guy if you’re curious about that or any of your other options — I’ve had good luck with Jim McShane Designs, if that helps.

The casework is bent-metal, aside from the chromed/mirrored “backsplash” behind the tubes. The front/fascia has some distinctive metalwork across the front, reminiscent of waves (to my eye, at least), done in aluminum, and the wave motif is worked into the sides of either side of the housing on the trannies. It’s tasteful and artistic, and relatively low-key, as far as such things go. I could imagine some wishing for more bling at this price point, and I have actually heard that some wished for less. Whatever — you can’t please everyone. Me? I find the aesthetic to be attractive, and quite frankly, I really like the distinctiveness — I can tell, at a glance and across the room, what the brand is without having to see the marque. Score one for branding!

Just so you know, the Tung-Sol KT120 tubes are supported, but I was not able to try this combo out. George says it sounds different but switching brings no more power — the amp would need a higher current voltage rail to extract the most from that tube. I asked George if he’d thought about making some design changes to create a real path for ‘rollers curious about that “mega-tube”, but he got a little hesitant. The sole-source nature of the KT120 (and the newer KT150 variant) he found a little worrisome — what happens if Bad Things Happen? In any event, George feels that the KT88 — in his amp with his circuit — is the more musical approach to take. So, I did.



My “Reference Rig” is actually two systems. The first is a low-power setup, featuring a BorderPatrol S10 EXS amplifier and a Control Unit EXT1 pre, wired into a set of Orangutan O/96 loudspeakers from DeVore Fidelity. The second is fronted by a pair of TIDAL Audio Contriva Diacera SE loudspeakers, fed by a RD-100 Reference Preamplifier and RS-100 stereo amplifier from Vitus Audio. Neither one of these systems is “fixed-in-stone” and the parts tend to flow to and from review systems, but these configurations tend to be the most stable.

For the Bia 120, I started with the second system, simply removing the massive 300wpc RS-100 amplifier and replacing it with the (physically) larger (though not as heavy) Zesto amplifier. Cabling came from the Luminous Edition from Purist Audio Design. For digital-to-analog conversion, my current reference is the extraordinary AURALiC Vega. My computer source was the stunning and subtle Aurender W20.

This arrangement let me take advantage of the balanced input connections on the Bia 120, which George says are to be preferred if for no other reason than for the native noise-rejection that a balanced connection brings. I’ll take him at his word, but I really had no issues driving the amp with its single-ended inputs. In fact, I had more luck matching on these inputs than I did on the balanced.

In a fit of enthusiasm, I’d attempted to use my Berkeley Audio Designs Alpha Series 2 DAC as a preamplifier, that is, using the DAC’s built-in volume attenuator and eliminating the extra box that a pre would add to the signal chain. Connected via the balanced connections, the sound was a bit soft and un-involving. Strung out along a preamp, the DAC regained its audio joy. Given that the this DAC has a relatively high output impedance (over 1kΩ, I’ve been told), perhaps it was not the best match for the 12kΩ balanced input impedance on the amp? Following that logic, I tried the Bricasti M1 DAC, which by way of contrast, has an output impedance of right around 40Ω. No issues there. For most of my listening, however, I lashed the Bia 120 to the Vitus pre (which I used exclusively as a preamplifier, not DAC). Worked a treat — and that configuration let me play the occasional LP.

Anyway, this seems like a good point to jump into my notes, so let’s do that now.



Recycling stereotypes is not a particularly effective way to be novel or imaginative, but that said, it is quick.

So, here’s your sliced-and-diced version — the Bia 120 does not sound like “classic tube amp” nor does it sound like a “modern solid-state amp”. In some very interesting ways, it splits the difference and does so quite delightfully.

I’m pretty sure you’ll already be familiar with the stereotypes here, so I’ll skip lightly. The point — the Bia has a very linear presentation, coherent top-to-bottom, with very robust and realistic extension with a non-fatiguing treble and a solid bass presentation. It sound similar to many KT88-based tube amps I’ve heard from Audio Research and others in that the signature seems more stereotypically solid state than tube. That is, it’s coherent from top to bottom, with no bloom in the bottom or mids, and no exaggerated sense of softness or darkness due to a treble limitation. It’s almost transparent … but not quite. To unpack that, I need a step to the right.

The Pass Labs XA100.5 amplifiers that Mal used in his comparison to the new 100.8 amps had a nifty characteristic that I tend to think of a Class A artifact — everything seems to just sound a little bit better with them. A little warmer — in that it’s more inviting. A little smoother — not sacrificing detail, but everything just sounds a bit more liquid. A little more “lit” — not adding distracting cues, but just “burnishing” the presentation in a very agreeable way. The Bia 120? Yes, it does this too. Hot diggity.

For example, in Blue Swede’s classic cover, “Hooked on a Feeling”, the opening refrain (“Ooga ooga ooga chaka”) provides an unlikely (where ‘unlikely’ = “bizarre”) contrast for Björn Skifs’ ringing vocals, and as he launches full-throat into the first chorus, you’re getting his richly grained voice, hard-hitting drums thwacks, a synths, guitar and a massive brass attack. It’s pretty much all of the 1970’s jammed into a single tune. What’s not to like? Anyway, played through the Bia 120, this sounds far better than it has any right to, and Skifs’ lounge-singer styling is just this side of intolerably cheesy. I absolutely love playing this song at volumes that border irresponsible. My 8 year-old twins, who have yet to see Star Wars much less Guardians of the Galaxy, have since taken this song as something of a cheery anthem and are now known to belt out the chorus at all manner of inappropriate family moments — dinner with the grandparents, church, store parking lots. The car. My face. That’s damn fine parenting, if you ask me.

I say this because I got this soundtrack as a free promo for the Guardians movie, and it’s all in MP3 format. Tidal HiFi was streaming the soundtrack for a while, but that seems to not be an option anymore — that said, the song is in their library and can be streamed at CD-resolution with nothing more than a Google Chrome browser. The difference, played back on my Reference System #2, is apparent but not enormous — it’s a little threadbare sounding on MP3 — but the Bia 120 closes that gap in a very happy way. At first, I thought this warmth was a matter of the amps radically dialing back the resolution, so I made a tedious journey back into the archives for the Cricket Test, and plowed once more into the breach with Chris Jones’ “Roadhouses and Automobiles” (off the Stockfisch CD of the same name, not the Tidal version, sadly). Sure enough, the birds and crickets mixed into that track at well-below-casual-listening-levels were there, tweeting and chirping with the all the authority, placement and relative scale that I was familiar with from my time with the Vitus amplifier, if perhaps not quite to the same level of resolution. Said another way, this was the among the very best resolution I’ve heard from a tube amp, next to my SET from BorderPatrol, itself a detail champ. Color me impressed.

While I had the Chris Jones album queued up on the Aurender, I flipped over into “No Sanctuary Here” and shook a few objects off the mantle. I should note that the mantle is upstairs. I’d say that was a successful test, but what I was hearing was a fulsome and ominous bass threat — this tune is all manner of dark and brooding, underwritten with all the anger and disdain of the dying, as it makes mockery of certain political foolishness that many nations and states are facing around the problem of The Other. Politics aside, this track doesn’t hit lower than Lorde’s Pure Heroine, but it is fuller (especially through the upper-bass) than the mixed-for-the-subterranean tracks on Lorde’s album. In my house, it’s like there’s a sub-bass resonant frequency feedback loop that makes the sheetrock get wiggy. As a result, Chris Jones is only allowed when the family is out and about. Anyway, turning at last to that Lorde album, I can appreciate that the EDM crowd would get a lot of mileage out of this amp. I wouldn’t call it a “bass amp”, though, as that doesn’t really do it justice — I think of it as a balanced amp. In fact, it does pretty much everything well. That’s good news.

If it hasn’t been made abundantly clear at this point, though, I should underscore that the Bia 120 isn’t really voiced like a traditional SET — all mids, all the time — it is going to come across as more linear in that respect. More solid-state like. Again, I’m thinking “modern tube” sound, rather than “vintage tube”. That said, I found that the Bia 120 does present with more depth to the sound stage than many solid state amps, my Vitus amp included, but I’m also obliged that this is yet another stereotypical tube characteristic.

Some issues I had with the amp? Well, I started with the amp plugged into my Silver Circle Tchaik 6 power distribution/conditioner, and that proved to be not optimal. George recommends directly into the wall, and I concur. The amp draws a lot of current; a mediating device will not be as beneficial as a dedicated circuit for your listening room. Second, it is a tube amp, so while the backgrounds are dark, the whole Inky Blackerstein of Blackety-Blackness isn’t really an option, which means matching it to something a bit more in line with its character — think 87dB – 94dB in sensitivity, not 104dB.

Note also that the 60 watts per channel is, perhaps, a bit deceiving — those looking for amps with crushingly high output watts may be completely unprepared for the power that a “mere” 60 watts actually is. To wit: for the 87dB TIDAL Audio Contriva Diacera SE loudspeakers, the Bia 120 was more than able to cause devastation and havoc. Said another way, I got lots of complaints about volume levels. Heh heh.

Distortion was not an issue for anything approaching “normal listening volumes”, and the amp remained admirably planted and unflustered, whether that was with Adrian Boult’s handling of the London Philharmonic through “Mars”, from the 24/96 version of Holst’s The Planets from HD Tracks, or “Carry On Wayward Son”, from The Best of Kansas. And, for the record, I did in point of fact play those two tracks back-to-back because that’s how I roll.

I’ll also note that all of my listening was done in prime tube season — that is, not summer — which brings me to my only serious caution. A double-quartet of tubes may not seem like a big thing, but these guys do manage to heat my listening room quite handily. Don’t get too excited here — I used to own a pair of Joule-Electra OTL monos that burned at temps more commonly found nearer to the center of the Earth and they heated my entire basement accordingly — by comparison, the Zesto amp was a cool drink of water. Got a small room, and forced to sit rather close? I’d hesitate. Big room, with lots of ventilation and sub-optimal blood circulation? No worries — wire up, and conquer.



For me, tubes really kinda “do it”. Whether that’s my romantic bias intruding or some generalization based on “objective experience” (if that’s not blatantly self-contradictory), I have no idea and could frankly care less. I like what I like. And I really like the Bia 120.

The amplifier has more than enough power to drive the snot out of all but the most absurd loudspeakers. Chances are, you’re gonna love the way it sounds. Take that, add a healthy dose of style, and you’ve got yourself something marvelous.

The $10k-$15k price range for tube amplifiers isn’t as replete as I’d like it to be, but in the mix are established brands like Conrad-Johnson, Audio Research, and VTL. That’s a tough bunch to compete with. Pretty much all of them, however, are designed with varying degrees of negative feedback and none of them offer a fully Class A circuit. That is very interesting. On specs alone, the, the Zesto is an unusually strong alternative to those brands’ offerings. Not having them here, I can’t comment on who might be standing after a chance meeting at the OK Corral, but my suspicion is that the duded-up newcomer from Zesto would have a fine old time of it. Time to queue up some Yello — Oh, yeah.

George Counnas is on to to something. With the Bia, Zesto now has an excellent and stylish end-to-end analog package for your prize loudspeakers. An audition is highly recommended.



  • Pure Class A
  • 60 Watts per channel
  • 4, 8 and 16 Ohm output taps
  • 8, 5 and 4 Amp Slow blow fuses for outputs
  • Eight 5 way binding post
  • Non inverting output polarity
  • Push-Pull and Ultra-Linear design


  • Transformer floatingbalancedXLR inputs
    • Left and Right SE inputs with an impedance of 100K Ohms
    • Left and Right BAL inputs (pin 2 hot) with impedance of 12K Ohms
  • Independent ground lift switches on left and right BAL inputs
  • 2 Volts RMS input to reach rated output

Detailed Specs

  • Dual Mono
  • Auto bias
  • No negative feedback
  • Frequency response 20Hz to 50Khz  ~ 1dB
  • Total Harmonic Distortion ~ 0.22% at 1W output into 8 Ohms
  • Gain of 23dB
  • Noise level > 0.2 mV RMS into 8 Ohms with input shorted
  • 1% metal film resisters throughout
  • Polypropylene capacitors throughout the audio path


  • Custom Toroidal power transformer with global mains
  • Choke based power supply design
  • 120 Volts AC mains
  • Optional factory installed 220V, 230V, 240V 50/60Hz
  • Power consumption at rated output 300 Watts
  • On/Off switch conveniently located on front panel
  • 3 pin IEC power connector with fuse

Active Components

  • Matched quad set of four (4) KT88’s vacuum tubes
  • Four (4) Gold pin ECC82s (12AU7) vacuum tubes
  • High quality gold pin ceramic sockets

Other Features

  • Each unit is made by hand
  • 50 hour factory burn in on all circuits and vacuum tubes
  • Dimensions 17″ W X 20″ D X 10 ” H
  • Weight 66 lbs. (30Kg)
  • 16 and 14 gauge Zinc plated steel enclosure
  • Manufacturers Suggested Retail Price $12,500
  • Made in the USA






About Scot Hull 1039 Articles
Scot started all this back in 2009. He is currently the Publisher here at PTA, the Publisher at The Occasional Magazine, and the Executive Producer at The Occasional Podcast. There are way too many words about him over on the Contributors page.

1 Comment

  1. Swear you could write a review of a lightbulb change and make it a hoot!

1 Trackback / Pingback

  1. Zesto Audio Bia 120 Power Amplifier | Ultra High-End Audio and Home Theater Review

Comments are closed.