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Design seems to be influenced by Eversolo
TOPPING A70PRO Headphone Amplifier
A70PRO fully balanced headphone amplifier Newly developed ultra-low noise input stage further improved the noise performance of balanced input and increased the input impedance to 20kQ thus having better compatibility with incoming devices. A70 Pro uses relays and resistor networks to form R2R...
shenzhenaudio.com
Design seems to be influenced by Eversolo