Balanced Main Inputs; Balanced Main Thru; Stereo Headphone Outputs; Stereo Aux Inputs - Art HeadAmp 6 Pro User Manual

Balanced Main Inputs

These XLR and 1/4-inch TRS jacks are active balanced and are used for line level signals. The gain
sensitivity is identical for both the XLR and 1/4-inch TRS jacks. (NOTE: the front panel DIRECT IN jack
overrides these inputs when it is used.)

Balanced Main Thru

These XLR and 1/4-inch TRS jacks are hardwired in parallel with the corresponding BALANCED MAIN
INPUT jacks. The BALANCED MAIN THRU jacks are useful for daisy chaining multiple HeadAmp 6 Pro units
together.

FIGURE 3 - Rear Panel Headphone Outputs and Aux Inputs

Stereo Headphone Outputs

These stereo TRS jacks are the main outputs for each channel of the headphone amplifier. They are wired in
parallel with the corresponding output jacks on the front panel. Either front panel, rear panel, or both front and
rear panel outputs can be used simultaneously to drive headphones or they can be used as feeds to additional
headphone amplifiers in a distributed audio network. (NOTE: The HeadAmp 6 Pro is optimized to drive typical
headphone load impedances of 32 to 600 Ohms. It is not recommended to drive total impedances lower than
16 Ohms however it can be done and will result in limited maximum output power, and possible clipping
distortion depending on the output level and load. When driving multiple headphones from an individual output
channel of the HeadAmp 6 Pro (paralleling), the available output power is split among the various headphones,
and due to the combined load impedances the output may also become limited by premature clipping of the
output signal. Most modern headphones are mid to high impedance and require only milliwatts to achieve full
acoustic output so this should rarely be a problem. If it is a problem simply lower the total count of headphones
on a particular channel in order to raise to total load impedance as seen by the channel output.)
There is no direct relationship between headphone load impedance and SPL output. The relevant
specification that determines acoustic output is the sensitivity spec of the headphone, i.e. how much SPL it will
put out for a given level of input signal, usually rated at 1 mW. Sensitivity is determined by the overall design
and construction of the transducer. Typically the power required is about 1/1000th of the equivalent amplifier
power required to drive a speaker. Therefore typical headphone amplifiers provide power levels in the 10 to 20
mW range in order to achieve a very reasonable SPL output. Even an 8 Ohm headphone (if you can find one
since they are rare) can be driven to full SPL output by the HeadAmp 6 Pro if it has a high enough sensitivity,
regardless of the fact that the output voltage swing will be limited due to the overload protection circuitry.

Stereo Aux Inputs

These stereo TRS jacks provide a means of inserting a direct stereo signal into an individual headphone
channel. When a plug is inserted into an AUX INPUT jack the BALANCE control for that particular channel
changes function to become a balance (or mix) control adjusting the mix between the signal coming into the
STEREO AUX INPUT and the main signal bus.
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