PoE Series Audio Amplifiers Operations Manual Rev E
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8.1.
Considerations When Using PoE+ Amplifiers
All PoE powered devices (PD’s) have limited power available to them from the switch or mid-span
injector (PSE or Power Sourcing Equipment). More specifically, the current through the category cable is
limited because the twisted pair conductor diameter is so small. The current a Class D audio amplifier
draws from its power supply increases as the audio output power increases. If too much audio power is
drawn into the speakers, the PSE will do the job it is designed to do and shut down DC power from the
port, and thus to the amplifier (PD). This is done for safety reasons and to avoid potential damage to the
category cable. Stewart Audio has configured our low impedance models with a 2-position switch which
limits the output power of the amplifier to avoid shutting down the PoE+ supply. With the constant
voltage PoE models, the user must ensure that the total tapped power for all speakers connected to the
output does not exceed 16W/40W.
While the 802.3at and bt standards specify minimum and maximum voltages, maximum current, and
minimum and maximum power available per port, not all manufacturers adhere strictly to the standard.
Stewart Audio has tested our PoE amplifiers with PoE switches and mid-span injectors from several
manufacturers. Some PoE equipment delivers more power than others. When selecting PoE Power
Sending Equipment, whether a switch or a mid-span injector, make certain it is standard-compliant. Also
note the following switch recommendations from Audinate (developers of the Dante™ transport
protocol).
All Ethernet switches are capable of working with Dante. However, please be aware that there are some features on some
kinds of switches that will allow you to build larger and more reliable Dante networks.
While Gigabit switches are recommended, 100Mbps switches may be used in limited scenarios.
For channel counts of 32 or more, Gigabit switches are essential. QoS is required when using Dante
in networks that have 100Mbps devices. QoS is also recommended for Gigabit switches on
networks that share data with services other than Dante.
For lower channel count (<32) applications, a 100Mbps switch may be used as long as it supports
proper QoS, and QoS is active. The use of 100Mbps switches without QoS is not recommended or
supported.
Dante makes use of standard Voice over IP (VoIP) Quality of Service (QoS) switch features, to prioritize
clock sync and audio traffic over other network traffic. VoIP QoS features are available in a variety of
inexpensive and enterprise Ethernet switches. Any switches with the following features should be
appropriate for use with Dante:
Gigabit ports for inter-switch connections
Quality of Service (QoS) with 4 queues
Diffserv (DSCP) QoS, with strict priority
A managed switch is also recommended, to provide detailed information about the operation of
each network link: port speed, error counters, bandwidth used, etc.
If you find that the PoE power shuts down during loud audio sections, reduce the input signal level or
place a signal processing limiter ahead of the amplifier in the Dante™ chain to prevent overdriving the
amplifier and shutting down the PSE power. If excessive power (for the particular switch or injector
used) is drawn and the supply shuts down, it will automatically restart in 5-7 seconds with no damage to
either the amplifier or the switch/injector. However, this is an indication that the signal level to the
amplifier should be reduced or limited.
Stewart Audio recommends the use of 802.3-compliant switches and mid-span injectors. There are a
number of products on the market that merely place a DC voltage on the category cable. They do not
conform to the standards. With these
passive
PoE switches and injectors, there is no negotiation
