John Siau writes:
Benchmark has introduced the new HPA4 headphone/line amplifier with four 256-step relay-controlled attenuators and four 16-step relay-controlled boost amplifiers. Together these form two fully-independent, fully-balanced stereo volume controls. One volume control is dedicated to the line output and one is dedicated to the headphone output. Each has a +15 dB to -122 dB range in 0.5 dB steps. The lowest step provides a full mute. The volume controls feature high-precision metal film resistors, gold contact relays, and fully buffered inputs and outputs.
Transparency
Our goal was to produce an analog volume control with the highest achievable transparency. We wanted to be able to place this volume control in front of our AHB2 power amplifier or in front of our THX-888 headphone amplifier board without diminishing the performance of either device. Our volume control would need to have lower distortion and lower noise than either of these amplifiers. Given the extraordinary performance of these THX-AAA amplifiers, this would not be an easy task!
https://benchmarkmedia.com/blogs/application_notes/benchmarks-256-step-relay-controlled-attenuator
