Circle Labs A200

Circle Labs A200 – integrated amplifier with ECC88 preamplifier and Circle Power output stage

The A200 is Circle Labs' flagship — a hybrid integrated from Kraków, Poland, that has collected more serious press endorsements than most amplifiers at twice the price. High Fidelity awarded it the RED Fingerprint distinction and called it one of the best-built and best-looking audio devices regardless of price. Positive Feedback gave it a Choice Award. The engineering behind those reviews is straightforward: a single-stage ECC88 tube preamplifier feeds a proprietary Circle Power transistor output stage, with a Khozmo relay attenuator handling volume. The result is 120 watts into 8 ohms and 200 watts into 4.

Circle Labs A200 integrated amplifier — Khozmo attenuator and ECC88 preamplifier

The Khozmo resistor ladder uses components to 0.1% tolerance, switched by high-end relays. Channel tracking and long-term stability are measurably better than any potentiometer — and the difference is audible at low listening levels where most potentiometers drift. Because the preamplifier stage uses a single ECC88 tube, one resistor and a solid copper film signal capacitor per channel, the passive component count in the direct signal path is as low as it can practically be. Each channel runs from its own stabilised supply with polypropylene capacitors.

Circle Power output stage and dual mono construction

Circle Power is Circle Labs' proprietary output stage topology — an asymmetrical input stage driving current-controlled bipolar output transistors. The asymmetrical input delivers the resolution and inner detail that symmetrical circuits sometimes smooth over; the bipolar output stage adds the dynamics and damping factor that valve output stages cannot match. Separate toroidal transformers and power supplies per channel, with 200,000µF total capacitance, provide the headroom. The low output impedance means the A200 drives difficult loudspeaker loads without strain.

Inputs and connectivity

One balanced XLR input, three RCA inputs and a preamp output cover the usual system configurations. Frequency response extends to 130kHz at –3dB — a consequence of the circuit's bandwidth rather than a specification chased for its own sake. Input sensitivity 0.7V, input impedance 33kΩ, gain 35dB.

Specifications

• Power output: 120W / 8Ω, 200W / 4Ω
• Topology: hybrid — ECC88 tube preamplifier + Circle Power transistor output stage
• Volume control: Khozmo resistor ladder with relay switching (0.1% tolerance)
• Inputs: 1× balanced XLR, 3× RCA
• Preamp output: Yes
• Frequency response: 10Hz – 130kHz (±3dB)
• Input sensitivity: 0.7V
• Input impedance: 33kΩ
• Gain: 35dB
• Construction: dual mono, separate toroidal transformers per channel
• Total capacitance: 200,000µF
• Dimensions: 430 × 376 × 176mm
• Weight: 23kg
• Origin: Poland (Kraków)

Frequently asked questions about the Circle Labs A200

What makes Circle Power different from a conventional hybrid output stage?

Most hybrid designs use a symmetrical push-pull output stage fed from a valve input. Circle Power uses an asymmetrical input stage driving current-controlled bipolar transistors — a topology that preserves the resolution of asymmetrical circuits while delivering the efficiency and damping factor of a solid-state output stage. The combination is why reviewers consistently describe the A200 as sounding like a separate line stage and large power amplifier.

Why does the A200 use a Khozmo attenuator rather than a potentiometer?

Relay-switched resistor ladders maintain channel tracking to 0.1% across the full volume range — potentiometers drift, particularly at low settings where most listening happens. The Khozmo is also more durable; there are no moving contacts to wear.

Is the Circle Labs A200 suitable for difficult loudspeaker loads?

Yes — 200 watts into 4 ohms with a high damping factor handles most loudspeakers without difficulty, including impedance-demanding designs that expose weaker output stages.