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Integrated amplifier

Circle Labs

Manufacturer: CIRCLE LABS
Price (when reviewed): 24 000 PLN



Provided for test by: CIRCLE LABS


Text: Wojciech Pacuła
Images: Circle Labs | Wojciech Pacuła
Translation: Marek Dyba

No 198

October 1, 2020

CIRCLE LABS is a Krakow-based company founded in 2007. It was founded by KRZYSZTOF WILCZYŃSKI, also brand’s designer. It specializes in audio amplification systems, i.e. preamplifiers, power amplifiers and integrated amplifiers. We are testing its flagship product, the A200 integrated amplifier.

number of audio companies disappearing from the market is larger than one of the newly founded ones. Mathematically, it is an obvious nonsense, but logically not necessarily so - we all benefit from an excess of audio producers who have been shaping our industry for several decades, establishing hundreds, if not thousands of companies. There are fewer and fewer of them, and although new ones are still being founded, the pool is constantly decreasing. At least I think so…

That is why new companies, or companies established a bit earlier, but only now reaching a wider audience, are so valuable. One of them is the CIRCLE LABS. Its designer and founder is Mr. KRZYSZTOF WILCZYŃSKI, who cooperates with another designer, Mr. KRZYSZTOF LICHON. So in this case there is a combination of technical knowledge and a designer who knows what the product should look like. And that's a rarity.

The gentlemen met several years ago and became friends. What brought them together, above all, was their love of music. As they say, the idea of doing something together was featured in their conversations from the very beginning. They wanted to use their skills to achieve, as I’ve already said, proper level of performance, workmanship and looks because only then, as they say, the result could be we a real high-end audio device.

Mr. Wilczyński has been associated with the electronics industry for years. His core business is specialized research equipment, and audio is his hobby. Tube designs were "obvious" to him, because his first designs in the 1990s were guitar amplifiers - he played bass and guitars in the band. The first design was an OTL amplifier, but the circuit turned out to be "extremely uneconomical". Despite the fact that some twenty years ago he started with tube designs, with time he became, as he told me, when the gentlemen brought the A200 amplifier to me, a fan of transistors.

Formally, the company formed in 2007, but the name Circle Labs was first used for audio components earlier that year. All the layouts used by the company are based on his idea. The most important element is the Circle Power, with a JFET transistor in the input and transistors in the output. The amplification circuit developed in 2013 is - as Mr. Wilczyński says - "simple as a circle", hence the name. Let me add that another important person who participated in the development of the company was Mr. Jacek Kopczyński from the Krakow University of Technology, with whom he consults his ideas. The first commercial device was the A100 integrated amplifier, the smaller "brother" of the A200.

Mr. Krzysztof Lichoń stays a bit aside, but it is him that we owe the appearance of Circle Labs amplifiers to. Appearance, I will add, extraordinary in its quality and aesthetics values. But, ultimately, a person who deals with it professionally took it into his own hands - Mr. Krzysztof runs the Creative Agency KOOBA. During the conversation we had, he mentioned several times that the road to the final appearance of the A100 and A200 was long. It consists of obvious things and tiny details. The front baffle belongs to the former. Mr. Lichoń, from the very beginning, wanted to use glass front, not an acrylic one, a noble material that gives depth, color and reflections unavailable to "plexiglass". Each front panel is hand-made by master-craftsmen, and thus, it is unique. He assumed that the amplifiers should look the same in a year and in ten years.

It took even more time to design the sound wave in which the white LED display and the infrared receiver for the remote control are hidden. As he says, this result was achieved a little "by accident". For the first two months, he believed that it could not be done in a quality, aesthetic way. Until he accidentally drew something that turned out to be exactly what he was looking for. As for the small details, it is worth mentioning the way the top cover is made.

The entire chassis is made of aluminum plates in such a way that you cannot see any screw heads. And the slots at the top are made in such a way that when looking at the amplifier from above, we can see the outline of the front panel of a tube radio from the 1930s - with a grille concealing the speaker and a knob. As the designer says, the "standby" button on the top plate is also a well-thought-out element. And also: “Firstly, it does not disturb the pure form of the front, secondly, it is a very ergonomic solution. It is more convenient to put your hand on the amplifier than to look for the button on the front panel with your finger. "

A few simple words…

KRZYSZTOF WILCZYŃSKI | designer and founder

⸤ Circle Labs crew: KRZYSZTOF WILCZYŃSKI, designer and the originator of the idea for an audio company (on the left) and KRZYSZTOF LICHOŃ, designer (on the right)

For many years, the CIRCLE LABS has been involved in designing and production of specialized devices for scientific research in the field of microbiology. The apparatus bearing our name can be found in leading research centers in the country and around the world.

However, audio equipment has always been of interest to the designer and owner of the company, Krzysztof Wilczyński. Audio products offered by the Circle Labs are a result of 25 years of passion and research put into perfect amplification, resulting from the need to create products that reflect the true beauty of music, harmonious in sound, and at the same time elegant and refined in its form. In 2019, the proprietary technology called Circle Power attracted the attention of one of the leading Polish manufacturers of high-end equipment, which resulted in the development of reference monoblocks. It became an impulse for the dynamic development of the company and for offering our products to a wide audience.

The cooperation with LampizatOr, as that’s the brand we are talking about, is a result of a spontaneous listening session that took place beginning of 2019 - we were testing the early prototypes of Circle Labs amplifiers in Łukasz Fikus's proprietary system. The prototypes auditioned at that time made a great impression on everyone gathered there, as well as on the owner.

The owner of LampizatOr offered us cooperation and the development of a special version that would complement his company's lineup with amplifiers that would be able to drive loudspeakers that are more difficult to drive. The final result exceeded our expectations and the Metamorphosis monoblocks were presented at the Audio Video Show 2019 exhibition. Combined with the words of appreciation we received, it gave us a great motivation to finish our work on proprietary amplifiers, offered under the Circle Labs brand.

| A200

CIRCLE LABS' flagship integrated amplifier is now the A200. It is an integrated amplifier, i.e. with a preamplifier section and a power amplifier in one housing. It is also a hybrid amplifier, with an tube preamplifier section and a solid-state output. This is, let me add, one of the best made and finished amplifiers I know, regardless of a price and country of origin. A glass front with a display featuring LED modules, which presents information on volume level, a great remote control, refined descriptions - all these elements created a highly impressive whole.

The A200 features three line inputs - one balanced XLR and three unbalanced RCAs - as well as an unbalanced preamp output (for subwoofer). An XLR input has been added for convenience - the circuit is not balanced. The technical data show that it should be able to drive most of the loudspeakers available on the market - its factor of 500 is impressive, and the output power at 8 Ω is 100 W and doubled at 4 Ω - this is a very stable current source. Its distinguishing feature is also the proprietary technology called Circle Power.

Preamplifier | A resistor attenuator is used in the device’s input. It is a resistor ladder from the renowned company Khozmo. Resistors with a 0.1% tolerance are switched using high-class relays, which guarantees precision of operation and durability unavailable for traditional potentiometers.

The single-stage preamplifier is built using a tube from the ECC88 family operating with a constant polarity. This solution allows the use of a minimum number of passive elements. In the A200 model, the designer used Siemens NOS tube, which "provides smoothness and resolution combined with musicality and palpability of sound". This circuit is built with the use of a single tube, a resistor and the highest class signal capacitor made of a solid copper foil. The preamplifier features separate tubes and stabilized power supplies for each channel.

Power amplifier| Power amplifiers are built as dual-mono design with separate toroidal transformers and power supplies for each channel with capacitor bank with a total capacity of 200,000 μF. The power amplifier is based on a circuit called Circle Power, which is a proprietary development of Circle Labs. It uses an unbalanced JFET input stage and current drive of bipolar output transistors. The company materials say: "this solution combines the detail and precision characteristic of asymmetrical systems with the efficiency and dynamics of symmetrical systems".

The A200 is delivered in a solid "case", that does not cost customer extra.


HOW WE LISTENED TO IT | Since Krzysztof & Krzysztof brought the amplifier personally, I took the opportunity to listen to the reference system together with them, and then to the A200 amplifier, which replaced the separates system consisting of the Ayon Audio Spheris III preamplifier and the Soulution 710 power amplifier. It was a comparison in which the power cord used to connect my power amplifier was almost twice as expensive as the whole tested amplifier. But only then I can you be sure I hear the product under review, not system errors.

The amplifier was placed on the top shelf of the Finite Elemente Master Reference Pagode Edition rack. As a source I used the Ayon Audio CD-35 HF Edition SACD player connected using the Crystal Cable Ultimate Dream unbalanced (RCA) cable. The reviewed integrated was connected with my loudspeakers with the Siltech Triple Crown cable.


⸤ Frank Sinatra, Sinatra Sings Gershwin, Columbia/Legacy/Sony Music Entertainment 507878 2, CD (2003)
⸤ The Oscar Peterson Trio, We Get Request, Verve/Lasting Impression Music LIM K2HD 032, K2HD Mastering, „24 Gold Direct-from-Master Edition UDM”, Master CD-R (1964/2009)
⸤ Chet Baker, Baker’s Holiday, Verve Records B0003279-16/SUHD 009960, Test Press SACD (1965/2004)
⸤ Perfect, Live, Savitor | Damian Lipiński Pro-Audio Mastering (niepublikowana wersja remasteru), Master CD-R (1983/2017)
⸤ Suzanne Vega, Nine Objects of Desire, A&M Records 540 583 2, CD (1996)
⸤ Laurie Anderson, Homeland, Nonesuch 524055-2, CD + DVD (2010);
⸤ Pink Floyd, Wish You Were Here, EMI Records/Analogue Productions PFR25/19075810342, SACD/CD (1975/2018)

|1| K&K

WOJCIECH PACUŁA: What did surprise you most about our reference system?
KRZYSZTOF LICHOŃ: To be honest, I was surprised to hear the scale of the sound presented by the „High Fidelity’s” reference system. It sounded really cool, I mean it was a classy presentation. I am not good in commenting sound on the spot, I need some time for the impressions to sink in. Yet, I know already that I was truly impressed with the soundstage, with its depth.
KRZYSZTOF WILCZYŃSKI: Agreed, I also liked the same aspect of the Soulution’s presentation – the depth of the soundstage. But equally important was the fact, that the system delivered smooth, quite dark but at the same time detailed performance. In other words it was a combination of highly enjoyable and transparent sound.

KL: Yes, I was surprised by that, because I am more of a „tube” guy, and the Soulution didn’t „bother” me at all. I’d even say, that I could leave with it :)
KW: I also liked the nicely differentiated bass range. It sounded different in every recording.

WP: How did you like Harbeth speakers?
KL: Let me repeat myself - I liked them. That’s another of your components I could easily live with… I’m not very original here :) I like their performance a lot.
KW: To be honest, it wasn’t a „solid-state” sound, but it was complete, full. This system has no problems in terms of timbre, details, pace, and the speakers are incredibly transparent. I liked them a lot.

WP: What changes did you notice after we replaced the amplifier with your A200?
KL: Let me answer – with the A200 when listening to Perfect it was much easier for me to hear the fans singing along and what they sang. Generally speaking, it seems to me that the vocals timbre with our amplifier was more open, I have no idea why, but that’s what I heard.

KW: I noticed that with the Soulution bass was better differentiated. It „varied” , depending on a recording. It seemed to me, that Soulution delivered darker sound, but it was still detailed and smooth. The A200, generally speaking, sounded a bit brighter, but mostly in the upper midrange. It was obvious particularly with older Sinatra’s recordings and on the Welcome To The Machine. There were more details, micro-sounds, also dirt in the performance with it.

WP: Are you happy about the performance of your amplifier in my system?
KL: Yes, definitely. It seems that A200 and Harbeths created quite a synergistic setup.
KW: I liked it too. Although at the very beginning I was worried, because after I heard the Soulution I thought: „OK, lets pack up and go home, we can’t compete with that”. But after plugging Harbeths to A200 I was pleasantly surprised. And considering price gap between your reference system and our amplifier, I am more than happy.

It is also a great experience for me to hear something clearly better than the A200 - so far it was usually the case that the differences, even with much more expensive competition, were minimal, and often even in favor of our amplifier. In the end, I heard the difference between my amplifier and the absolute reference amplification for ten times the price. The other thing is that this system is well-thought-through, everything fits well together and we entered to it an „external” or „foreign” element.

To sum up - it's nice to go head-to-head with an amplifier SUCH AS the Soulution. We are very satisfied, but I also learned a lot. I found things in Soulution performance that I would like to work on in the next Circle Labs models. K&K

|2| WP

The switch from the reference system to the Circle Labs amplifier did not cause any real issue for me, I didn’t have to spend much time thinking about how big was the difference between it and the "High Fidelity’s" reference, let alone see it as a "loser". These are not equivalent devices, that is probably clear. With the A200, however, I heard something that happens every now and then, although not so often: it is an internally complex, rich sound with nothing missing from it, which largely repeats what I know from my own system. And that once again shows that the best designers, completely independently and in different ways, come to similar conclusions about what an audio device should sound like.

The sound of the tested amplifier is dense and full. It has powerful, well extended bass with great control and also a clean treble. But one cannot simply label it a "solid-state amplifier", and neither can it be included in the group of "tube-like" sounding devices. It has its own "sonic identity", I will talk about it in a moment, but this "identity" is integrated into the overall class of the sound and a great balance between its individual elements.

It is an amplifier with open but smooth sound. It is more open than the reference system and - I think that's what Mr. Krzysztof meant - it is also more selective. Details of the recording are shown more clearly with it, such as a rhythmically striking musical instrument - something like a hollow gourd - in the Caramel, a track from the Nine Objects of Desire album by Suzanne Vega, like details of the electronic background in the Laurie Anderson’s Falling from Homeland, or - finally - like details of the door opening in the Welcome To The Machine by Pink Floyd from the Wish You Were Here.

These are things that are presented in a more clearer way than with the reference system. Not because they are not there, but because the role of story telling in my system is taken over by higher resolution, and here they owe their presence to the quick attack and this "plankton" nicely shown between the sounds. That is why the A200 seems to sound so open, without brightening or hardening the sound. I would even say that one could point out a "tube-like" smoothness in its presentation, but I know that it is actually not about the tube, but about a large amount of information that forms this smoothness, and it does not has to simulate it by emphasizing the attack or artificially emphasizing some narrow range of the bandwidth.

It just so happens that it's a very similar approach to the way music should sound like as from my favorite amplifier in this price range, namely the Leben CS600X. Yes, it is a tube amplifier, but also a resolving and selective one, similar to the A200 in these regards. The Polish device goes a bit further in selectivity, it also controls the lower bass better. It also slightly emphasizes its medium range. It does not increase the volume, and in this respect the reference system is unrivaled, but it makes sure that the sound has a proper size and great mass.

In terms of spaciousness, it is one of the best organized solid-state devices in the proce range up to tens of thousands of zlotys. Only expensive Accuphase amplifiers do it just as well. The Leben that I mentioned pays more attention to large planes, while the A200 is able to extract smaller elements from them. Its special feature, however, is bringing the back layers of the soundstage closer to the listener and reducing the distance between us and the foreground. This is why its sound may seem "tube-like" - we gain tangibility, intimacy and - when necessary - a punch, and we pay with a loss of further perspective.

But I do not mean to complain about it. I am talking about it only because I compared the Polish amp head-to-head with an extremely good competition from Japan (Leben) and the reference device. However, you should know about it - it is an amplifier that plays "here and now" rather than "out there". Fills rather than "spreads". However, this does not prevent a very good differentiation that the device offers, as well as showing soundstage layers. The A200 does it primarily by emphasizing a different timbre, different ways of mastering, etc. I have not played an album that would "shock" it and whose poor quality would lead the A200 to over-blow the treble. Although it is also true that this amplifier does slightly brighten the upper midrange.

| Summary

All these features make up a truly high-end sound, which is as close in character to tube amplifiers, including the SET type, as to solid state devices from companies with Accuphase's level reputation. There is an openness to details and smoothness that allows the sounds to "flow". The dynamics is excellent, and the bass presentation - exemplary at this price. The upper treble is a bit rounded, you could say - sweetened, which does not prevent it from being very communicative. You have to get used to the close perspective, not because it is bad, but because that’s how it is - close.

This is one of the best reasonably priced integrated amplifiers I know and one of the best built and best looking audio devices at any price. Bravo!

Fully deserved RED Fingerprint.


The A200 is a hybrid design stereo integrated amplifier, with a tube preamplifier and a solid state power amplifier. Its mechanical design is solid, compact and technologically advanced - though it seems simple. The housing is made of aluminum plates to which heat sinks are bolted, and the whole is bolted to the aluminum bottom and back and tighten with an aluminum top. The amplifier gets quite warm during operation, so one should leave enough space around it for proper ventilation. The amplifier rests on three feet - two in the front and one in the back.

Front and back | The front is made of 15mm glass which looks great. In the center there is a two-element white LED display - its brightness can be adjusted using the remote control. On the sides there is a volume knob and input selector; there are white LEDs around the latter. The main power switch can be found on the rear panel, but on the top, on a brass element, there is a standby switch.

The back looks as good as the front. We can find there great WBT loudspeaker sockets from the Nextgen series and a row of screwed, high quality RCA sockets from the American company CMC from the Super Cu series. The XLR inputs are sourced from Neutrik.

Inside | The layout looks very simple, which usually means there is a complex thought behind it. As Mr. Krzysztof said, initially he multiplied the circuits, correcting everything he could, until he reached 100 (!) transistors. Then he began to simplify everything.

After selecting the active input in the relay, the signal goes to the attenuator. It is a Khozmo system with SMD resistors switched in relays. After attenuation, the signal goes to the PCB of the tube preamplifier. There you will find super interesting, rarely seen tubes, a special version of the ECC88 by E. G. B. (Siemens), model ECC8100, designed to work in cascade systems, with a neutralizing grid, etc. These are tubes with constant bias coming from cells placed next to them. The coupling with the rest of the system is handled by polypropylene capacitors with the Circle Labs logo.

The power amplifiers are bolted to aluminum plates, and heat sinks are also bolted to them. There are only four JFET transistors per channel (!) that control a pair of powerful Sanken bipolar transistors (2SA1295 + 2SC3264) working in push-pull configuration.

However, it is the power supply that occupies the most space inside the chassis. It is based on two toroidal transformers, screwed on top of each other, made by the Polish company Toroid. They feed the output stage. Eight extra-tall Kemet capacitors work together with them. There is a separate power supply for the preamplifier stage featuring a classic EI transformer. Voltage filtering is done by polypropylene capacitors, not electrolytic capacitors; which reminded me solutions used by Ayon Audio and LampizatOr.

Remote | The remote control (custom-made by the Khozmo company) - is made of aluminum, with an acrylic top. You can use it to adjust volume in 1 dB steps from 0 to 63 dB, dim the display or mute the amplifier (mute).

Great design and perfect execution.

Technical specifications (according to the manufacturer)

Nominal output (RMS):100 W/8 Ω | 200 W/4 Ω
Frequency range: 10 Hz-130 kHz (- 3 dB)
Input sensitivity: 0,9 V (@ full output)
Gain: 34 dB
Input impedance: 25 kΩ
Output impedance: 0,016 Ω
Damping factor @ 8 Ω: 500
Power consumption:
• standby <0,1 W
• constant 70 W
• max. 500 W
Dimensions (W x D x H): 430 x 360 x 180 mm
Weight: 20 kg


Reference system 2020

1) Loudspeakers: HARBETH M40.1 |REVIEW|
2) Line preamplifier: AYON AUDIO Spheris III Linestage |REVIEW|
3) Super Audio CD Player: AYON AUDIO CD-35 HF Edition No. 01/50 |REVIEW|
4) Stands (loudspeakers): ACOUSTIC REVIVE (custom) |ABOUT|
5) Power amplifier: SOULUTION 710
6) Loudspeaker filter: SPEC REAL-SOUND PROCESSOR RSP-AZ9EX (prototype) |REVIEW|
7) Hi-Fi rack: FINITE ELEMENTE Pagode Edition |ABOUT|


Analog interconnect SACD Player - Line preamplifier: SILTECH Triple Crown (1 m) |ABOUT|
Analog interconnect Line preamplifier - Power amplifier: ACOUSTIC REVIVE RCA-1.0 Absolute-FM (1 m) |REVIEW|
Speaker cable: SILTECH Triple Crown (2.5 m) |ABOUT|

AC Power

Power cable | Mains Power Distribution Block - SACD Player: SILTECH Triple Crown
Power (2 m) |ARTICLE|
Power cable | Mains Power Distribution Block - Line preamplifier - ACOUSTIC REVIVE
Power Reference Triple-C (2 m) |REVIEW|
Power cable | Mains Power Distribution Block - Power amplifier - ACROLINK Mexcel 7N-PC9500 |ARTICLE|
Power cable | Power Receptacle - Mains Power Distribution Block: ACROLINK Mexcel 7N-PC9500 (2 m) |ARTICLE|
Power Receptacle: Acoustic Revive RTP-4eu ULTIMATE |REVIEW|
Anti-vibration platform under Acoustic Revive RTP-4eu ULTIMATE: Asura QUALITY RECOVERY SYSTEM Level 1 |REVIEW|
Power Supply Conditioner: Acoustic Revive RPC-1 |REVIEW|
Power Supply Conditioner: Acoustic Revive RAS-14 Triple-C |REVIEW|
Passive filter EMI/RFI: VERICTUM Block |REVIEW|


Speaker stands: ACOUSTIC REVIVE (custom)
Hi-Fi rack: FINITE ELEMENTE Pagode Edition |ABOUT|
Anti-vibration platforms: ACOUSTIC REVIVE RAF-48H |ARTICLE|

  • HARMONIX TU-666M "BeauTone" MILLION MAESTRO 20th Anniversary Edition |REVIEW|


Phono preamplifier: Phono cartridges: Tonearm (12"): Reed 3P |REVIEW|

Clamp: PATHE WINGS Titanium PW-Ti 770 | Limited Edition

Record mats:


Headphone amplifier: AYON AUDIO HA-3 |REVIEW|

Headphones: Headphone Cables: Forza AudioWorks NOIR HYBRID HPC