Benchmark has introduced a new 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 metal film resistors, gold contact relays, and fully buffered inputs and outputs.

John Siau, VP and Director of Engineering at Benchmark Media Systems told us “Our goal was to produce an analogue 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”.

“The AHB2 power amplifier and THX-888 headphone amplifier have similar specifications; they are virtually noise free (SNR > 132 dB) and distortion free (THD < -120 dB). Our new analogue-to-analogue volume control would need to exceed these specifications to avoid being a weak link in the audio chain. As we looked at available solutions, it became clear that we would need to design something better”.


Measured from balanced inputs to balanced outputs on the HPA4 Line Amplifier:

THD < -125 dB (0.00006%)

SNR > 135 dB, unweighted, 20-20 kHz

SNR > 137 dB, A-weighted

Frequency Response – 0.003 dB at 10 Hz, -0.001 dB at 20 kHz

– 3 dB Bandwidth exceeds 0.1 Hz to 500 kHz

Output Impedance 60 Ohms

Output Noise < 1.9 uV at Unity Gain, 20-20 kHz

Maximum Input and Output Voltage, 20 Vrms (+28 dBu)

Crosstalk < -133 dB @ 1 kHz, -116 dB @ 10 kHz


HPA4 Features

256-Step Stereo Volume Control – Line Output

256-Step Stereo Volume Control – Headphone Output

Relay Selection of Inputs

Two Stereo Balanced Line Inputs

Two Stereo Unbalanced Line Inputs

One Stereo Balanced Line Output

One Balanced Mono Sum Output

One Balanced THX-888 XLR4 Headphone Output

One Unbalanced THX-888 TRS Headphone Output

Independent Control of Headphone and Line Outputs

Balance Control

IR Remote Control

Colour Touch Screen

Two 12 Volt Trigger Ports



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