Benchmark DAC1 and DAC2 converters are equipped with Benchmark’s HPA2™ headphone power amplifier. This is a high-current design with very low output impedance (less than 0.1 Ohms). It is capable of driving a wide variety of headphones while achieving extraordinarily low distortion. The full rated performance of the DAC1 is achieved at the headphone jack while driving two sets of headphones. THD+N is less than 0.0003% under full load. The HPA2™ may be the quietest and cleanest headphone amplifier available.
The HPA2™ also has sufficient output level to drive any headphone well beyond normal listening levels. For this reason, the HPA2™ in the DAC1 USB is equipped with gain programming jumpers that can be used to reduce the gain by 10 dB. We recommend using the 10 dB attenuation setting with the Sennheiser headphones.
The HPA2™ in the DAC1 PRE, DAC1 HDR, DAC2 HGC, DAC2 D, and DAC2 DX converters has an additional 20 dB attenuation setting. This setting is recommended for high-sensitivity headphones. Headphones having a low input impedance (30 to 60 Ohms) often have high sensitivity and we recommend the 20 dB attenuation setting for these headphones.
The attenuation is inserted before the HPA2™ headphone amplifier. This attenuator location keeps the output impedance of the HPA2™ constant and very near 0 Ohms. External attenuators should never be inserted after a headphone amplifier as this would change the output impedance.
Proper attenuator settings are important for maximizing the SNR of the headphone monitoring system. With proper settings, the full performance of the DAC2 can be delivered to the headphones for critical monitoring tasks, or maximum musical enjoyment.
When the headphone attenuation jumpers are set properly, a normal listening level will be achieved between the 10 o'clock and 2 o'clock volume control positions. If a normal listening level is achieved below a 10 o’clock volume-control position, the headphone gain is too high, and the attenuation should be increased. If the level is too low at a 2 o-clock volumecontrol position, the headphone gain is too low, and the attenuation should be decreased.
The 0-Ohm output impedance provides outstanding control of the headphone drivers. This improves bass damping, reduces distortion, and flattens the frequency response.
DAC1 and DAC2 converter families were designed from the ground up to be headphone amplifiers with line outputs. The large power supplies in the DAC1 and DAC2 converters are necessary to support the demanding power requirements of the HPA2™ headphone power amplifier.
How fast things can change!
It is March 23, 2020 and we are currently battling the worldwide COVID-19 pandemic.
This application note will be a departure from normal. I will make a few observations about the current situation and then look at the nuts and bolts of how we reconstructed our operations in less than 48 hours. Benchmark is 100% operational, but nothing looks the same as it did last week.
- John Siau
As an engineer I like to use "rules of thumb" to make quick estimates that help to explain the physical world around me.
These rules of thumb are easy-to-remember approximations that eliminate the need for complicated and needlessly precise calculations.
If you feel discombobulated by the complexities of high school physics, there is hope! I encourage you to step back and take a fresh approach.
If you learn a few simple rules of thumb, you can unravel mysteries of the physical world, amaze your friends, and yourself.
In this paper I will present 15 simple rules that I find useful when working with music and audio.
- John Siau
The Benchmark AHB2 power amplifier and HPA4 headphone amplifier both feature feed-forward error correction. This correction system is an important subset of the patented THX-AAA™ (Achromatic Audio Amplifier) technology. It is one of the systems that keeps these Benchmark amplifiers virtually distortion free when driving heavy loads. It is also the reason that these amplifiers can support 500 kHz bandwidths without risk of instability when driving reactive loads.
This paper explains the differences between feedback and feed-forward systems. As you read this paper, you will discover that you already understand the benefits of feed-forward correction because you use it instinctively to improve a feedback system commonly found in your automobile. If feed-forward correction can improve your driving experience, it may also improve your listening experience!
- John Siau