Circle Labs AS100 – a Purely Analog Integrated Amplifier

The Circle Labs has introduced the Circle Labs AS100 integrated amplifier. This solid-state model is positioned by its designers as a solution for the most precise and controlled sound: rather than expanding functionality, the focus is placed on sonic purity and neutrality, as well as stable power delivery.

Volume control in the Circle Labs AS100 is implemented using a high-precision resistor attenuator with 63 steps and 0.1% tolerance resistors, controlled by high-quality electromagnetic relays. According to the manufacturer, compared with conventional potentiometers this solution provides better channel balance, long-term stability, and repeatability of settings. The amplifier is built in a “dual-mono” configuration all the way to the power supply – each channel has its own dedicated supply with a separate toroidal transformer.

In the input stage, Circle Labs uses low-noise Burr-Brown J-FET transistors, while the output stage employs bipolar transistors responsible for current delivery and a wide dynamic range. The entire circuitry is based on the proprietary Circle Power technology, which combines characteristics of both balanced and unbalanced designs.

The power supply of the Circle Labs AS100 is also designed with control and stability in mind: the total filter capacitance reaches 200,000 µF, which should provide ample power reserves and low distortion even with difficult loudspeakers and dynamic musical material. The manufacturer specifies a wide frequency response of 3 Hz – 500 kHz (−3 dB) and a damping factor of more than 250 (8 ohms). The amplifier’s output power is 65 W per channel into an 8-ohm load and 110 W into 4 ohms.