M60 MkII

About the M60 MkII

The Atma-Sphere M60 Mk II is a high-end OTL (output transformerless) class-A monoblock tube power amplifier using Atma-Sphere's patented fully balanced differential Circlotron topology with a direct-coupled output stage. It delivers approximately 60 watts per channel into 8 ohms and 45 watts into 4 ohms. Each chassis uses eight 6AS7G output tubes and four 6SN7 driver/input tubes in pure triode operation, and the circuit is designed for minimal global feedback (typically 0-2 dB, hard-wired) to preserve transparency. The M60 Mk II is known for wide bandwidth (roughly 1 Hz-200 kHz at 1 W and power bandwidth 2 Hz-75 kHz at full rated power), fast slew rate, and very low phase shift. It is fully hand-wired point-to-point and supplied as a pair of mono chassis with both RCA and XLR balanced inputs, very high input impedance, and direct speaker connection without output transformers. The later Mk II.2 revision retains the same basic architecture and tube complement but incorporates parts and layout refinements for improved performance and reliability, and is often cited as a strong value among OTL amplifiers for its soundstage and transparency.