Crown Audio STUDIO AMPLIFIER Odep, Activate its DC / low-frequency protection circuitry

Studio Reference I & II Professional Studio Amplifiers

and transformer thermal protection. These systems will	The amplifier’s overvoltage protection circuitry will
prevent amplifier damage in virtually any situation.	put both channels into standby when excessive AC
4.3.1 ODEP	mains voltage is detected. Studio Reference amplifiers
	should not be operated with an AC mains voltage of
Crown invented ODEP to solve two long-standing	more than 10% over the unit’s rated voltage.
problems in amplifier design: to prevent amplifier shut-	If dangerous subsonic frequencies or direct current
down during demanding operation and to increase the
	(DC) is detected in the amplifier’s output, the unit will
efficiency of output circuitry.
	activate its DC / low-frequency protection circuitry
To do this, Crown established a rigorous program to	and put the affected channels in standby. This protects
measure the safe operating area (SOA) of each output	the loads and prevents oscillations. The amplifier re-
transistor before installing it in an amplifier. Next,	sumes normal operation as soon as it no longer detects
Crown designed intelligent circuitry to simulate the in-	dangerous low-frequency or DC output. Although it is
stantaneous operating conditions of the output transis-	extremely unlikely that you will ever activate the
tors. Its name describes what it does: Output Device	amplifier’s DC / low-frequency protection system, im-
Emulation Protection or ODEP. In addition to simulating	proper source materials such as subsonic square
the operating conditions of the output transistors, it also	waves or input overloads that result in excessively
compares their operation to their known SOA. If ODEP	clipped signals can activate this system.
sees that more power is about to be asked of the output	The amplifier’s fault protection system will put an am-
transistors than they are capable of delivering under
	plifier channel into standby mode in rare situations
the present conditions, ODEP immediately limits the
	where heavy common-mode current is detected in the
drive level until it falls within the SOA. Limiting is pro-
	channel’s output. The amplifier should never output
portional and kept to an absolute minimum—only what
	heavy common-mode current unless its circuitry is
is required to prevent output transistor damage.
	damaged in some way, and putting the channel into
This level of protection enables Crown to increase out-	standby mode helps to prevent further damage.
put efficiency to never-before-achieved levels while	The amplifier’s transformer thermal protection cir-
greatly increasing amplifier reliability.
	cuitry is activated in very unusual circumstances where
The on-board intelligence is monitored two ways. First,	the unit’s transformer temperature rises to unsafe lev-
	els. Under these abnormal conditions, the amplifier will
the amplifier’s ODEP indicators show whether the unit
	put both channels into standby mode. The amplifier will
is functioning correctly or if ODEP is limiting output.
	return to normal operation after the transformer cools to
Second, ODEP data is fed to the amplifier’s internal
	a safe temperature. (For more information on trans-
P.I.P. connector so advanced P.I.P. modules like the
	former thermal protection, refer to the section that fol-
IQ-P.I.P. can use it to monitor and control the amplifier.
	lows.)
This is how ODEP keeps the show going with maxi-
mum power and maximum protection at all times.	4.3.3 Transformer Thermal Protection
4.3.2 Standby Mode	All Studio Reference amplifiers have transformer ther-
	mal protection which protects the power supplies from
An important part of a Studio Reference amplifier’s pro-	damage under rare conditions where the transformer
tection systems is standby mode. Standby protects the	temperature rises too high. A thermal switch embed-
amplifier during potentially catastrophic conditions. It	ded in the transformer removes power to the high-volt-
temporarily removes power from the high-voltage sup-	age power supplies if it detects excessive heat. The
plies to protect the amplifier and its loads. Standby	switch automatically resets itself as soon as the trans-
mode can be identified using the table in Figure 4.2.	former cools to a safe temperature.
Standby mode is activated in five situations. First, when	If your amplifier is operated within rated conditions, it is
you turn on the enable switch, standby mode is acti-	extremely unlikely that you will ever see it activate
vated to provide turn-on protection. This power-up de-	transformer thermal protection. One reason is that
lay lets other system components settle before any	ODEP keeps the amplifier working under very severe
signals are amplified and it provides some power-up	conditions. Even so, higher than rated output levels,
“randomness” for multiple units so the system’s start-up	excessively low-impedance loads and unreasonably
current demands are better distributed over time.	high input signals can generate more heat in the trans-

Page 21