Benchmark NL4-XLR4 Headphone Adapter Cable for AHB2 Power Amplifier

This adapter cable turns the AHB2 power amplifier into the ultimate headphone amplifier for driving headphones that require a high drive voltage. The AHB2 will deliver a drive voltage that is 9 to 10 dB higher than that of the very-capable HPA4 headphone amplifier. Cable length is 3 feet.

The AHB2 power amplifier is designed to drive 100 watts per channel into a pair of 8-ohm loudspeakers and for this reason, it delivers 28.28 Vrms on each channel at full output. This is more than enough voltage to let the smoke out of ordinary headphones, not to mention the associated hearing damage. This cable should only be used with headphones similar to those listed below. These headphone all have a voltage sensitivity that is less than 100 dB SPL at 1 V. Do not confuse voltage sensitivity with power sensitivity which is expressed relative to 1 mW instead of relative to 1 V.

Use caution when connecting headphones to a power amplifier. Start with the volume control low and make sure your upstream electronics don't produce loud transients when switching on and off. Lack of caution can damage your headphones and your hearing.

The AHB2 will not produce damaging transient, but it will amplify the transients produced by upstream devices when they turn on or off.

The following precautions may reduce the chances of damage due to transients produced by the devices driving the AHB2:

• Unplug the headphones before turning your system on or off.
• Use 12V trigger control to sequence the system turn on and turn off.
• Turn the volume down before plugging in the headphones.
• Set the levels low before placing the headphones on your head.
• If your preamplifier does not have a trigger, turn the AHB2 on last, and off first.

Recommended Headphone Applications

We recommend this cable for the following headphones when driving them from an AHB2 power amplifier. We assume no responsibility for damage to your headphones or hearing (see the caution above). All of these headphones can be cleanly driven to very loud levels with the HPA4 headphone amplifier and this provides a safer solution than the AHB2. Both amplifiers will provide identical performance, but the AHB2 will have the ability to play louder. This cable is not required for the HPA4 and cannot be used with the HPA4.

The peak SPL for each headphone-amplifier combination is shown below:

HiFiMAN HE6 - (96.5 dB SPL at 1V), peak SPL with AHB2 is 125.5 dB, peak SPL with HPA4 is 117.3 dB

HiFiMAN HE6se - (96.5 dB SPL at 1V), peak SPL with AHB2 is 125.5 dB, peak SPL with HPA4 is 117.3 dB

HiFiMAN Susvara - (95.2 dB at 1V), peak SPL with AHB2 is 124.2 dB, peak SPL with HPA4 is 116.0 dB

Not Recommended for Most Headphones!

The "hard to drive" Sennheiser HD 800 S requires a higher drive voltage than most headphones, but we do not recommend driving it with an AHB2.

The HPA4 can drive the HD 800 S to its maximum rated input power. In contrast, the AHB2 is capable of driving the HD 800 S well beyond its maximum rated output. The AHB2 produces enough voltage to drive the HD 800 S to more than 5 times the rated maximum power. The AHB2 can easily cause damage to the HD 800 S headphones (and most others).

Sennheiser HD 800 S - (102.0 dB at 1V),  peak SPL with HPA4 is 123.2 dB