VsL Series Power Amplifiers
Page 5
Models VsL460, VsL900, VsL1500
Protection Features.
Every model in the VsL Series incorporates protection features. Derived from
Crest Audio’s extensive experience with the world’s largest sound rental com-
panies, the group of circuits sets new standards in load and amplifier protec-
tion.
ACL.
(Automatic Clip Limiting). At the amplifier’s full power, or clipping point,
ACL will be activated. This is is indicated by illumination of the ACL LED,
located at the right end of the meter array. The channel gain will automatically
be reduced, guarding the loudspeakers against the damaging high power, con-
tinuous square waves that would otherwise be produced. Situations that may
activate ACL include: uncontrolled feedback, oscillations, or an improper
equipment setting or malfunction upstream from the amplifier. Normal pro-
gram transients will not trigger ACL; only steady or excessive clipping will.
ACL is virtually transparent in operation and full signal bandwidth is main-
tained.
IGM Impedance Sensing.
IGM (Instantaneous Gain Modulation) is an innovative circuit that allows the
amplifier to operate safely into loads as low as 2 ohms. When the amplifier
sees a load that overstresses the output stage, the IGM circuit adjusts the chan-
nel gain to a safe level. Like ACL, the IGM circuit is inaudible in normal use.
In addition, if extreme low impedance is encountered, the amplifier’s output
relay will open.
AutoRamp Protection.
Auto Ramp operates every time the amplifier is turned on or is reactivated
after a protect condition is corrected. This exclusive Crest Audio feature grad-
ually (-80dB to 0dB in 3.0 seconds) increases gain to the attenuator setting
avoiding unnecessary stress on the loudspeakers.
Thermal Protection.
If the heatsink temperature reaches an abnormally high temperature, the ampli-
fier will protect itself by disconnecting loudspeakers and shutting down until
sufficiently cooled. During this time, the Protect LED’s will light. If the power
transformer gets too hot, its thermal sensing circuit will disconnect both chan-
nel outputs. During this time, the Active LED will extinguish, the Protect and
ACL LEDs will stay lit, and the cooling fan will stay running at low speed.
Normal operation will resume automatically once the transformer cools to a
safe level.
Short Circuit.
If an output is shorted (i.e., defective speakers or crossed speaker wires) the
IGM and thermal circuits will automatically protect the amplifier. The IGM
circuit senses the short circuit as an extremely stressful load condition and
attenuates the signal, protecting the channel’s output transistors from overcur-
rent stress. If the short circuit remains, the load will be disconnected by the
thermal protection circuitry
DC Voltage Protection.
If an amplifier channel detects DC voltage at its output terminals, the output
relay will immediately open to prevent loudspeaker damage. The Protect LEDs
will light.
Subsonic Frequencies.
The VsL Series amplifiers have built-in high pass filtering to provide subsonic
frequency protection for each channel. In addition, a relay will open if exces-
sive subsonic energy appears at the output.
Service Information.
To obtain service, contact your nearest Service Center, Distributor, Dealer, or
the Crest Audio Service Department at:
Crest Audio Inc.
100 Eisenhower Drive
Paramus NJ 07652
tel 201.909.8700
fax 201.909.8744
http://www.crestaudio.com
