ConclusionBenchmark's HPA4 is a headphone amplifier and a preamplifier you just have to try. Chances are you will keep it, because just like the power amplifier AHB2 this little box is able to do the greatest jobs, soundwise that is of course. The HPA4 gets the best out of any headphone no matter what the impedance or sensitivity, and it is a preamplifier where you can connect four analog sources. The volume control of headphones and line output is completely separate. We are, just like on the AHB2, madly in love with the HPA4. At this moment we can only fantasize what the combination of these two Benchmark top models will sound like. What a lovely no-nonsense brand. If you wanna have a good time, try Benchmark!
Specs and volume
The specifications mentioned by Benchmark are serious business. An output power of 6 Watts at 16 Ohm of the headphone output is downright large. We haven’t tried, but it could very well be that a speaker can sound very nice on this headphone output! Then the frequency range on the line output: from 0.1 Hz to 500 kHz. This says something about the speed and timing of the amplifier. We have written it down before; transient information in music determines the experience. Overtones, harmonies and other information are often above the hearing threshold of 20 kHz. Soulution amplifiers, known for their speed, have a frequency range up to 1 GHz..
Then the volume control, which is not only separate in terms of operation, but headphones and line output also have a truly separate volume control. This volume control is something else; Benchmark has done everything possible to eliminate the loss in signal to noise ratio, and to level the balance differences at low volumes. With many preamplifiers, keeping both channels in perfect balance is a challenge at low volumes. We have experienced several times during tests that when carefully opening the volume, the left or right channel sounds louder. This imbalance continues and creates a less precise stereo image. Benchmark solved this by working with relay circuits controlled by an FPGA. This should provide the ideal timing for the 256 steps in the volume control to work seamlessly. For those who want to read more about this, we refer to this Application Note about ‘Relay-Controlled Volume’
Specifications Benchmark HPA4
|Type of device||Pre-amp / Headphone amplifier|
|Inputs||2 x balanced, 2 x unbalanced|
|Outputs||1 x balanced, 1 x unbalanced, 1 x mono sum|
|Dimensions||22 x 10 x 21 (wxhxd)|