Peavey CS-400 User Manual

CLIPPING/COMPRESSION LED INDICATOR
The clipping/compression LED (light emitting diode) indicator (1), with the compressor operational, indicates when compression takes place.
As long as gain reduction is occurring, the LED will continue to light thereby giving a valuable indication of this unique compression function. When
the compressor is defeated by pulling out the level control on the associated channel (2), the LED now indicates a condition called "clipping.” This
condition is simply the failure of the amplifier to faithfully reproduce the input signal. Clipping can be caused by low line voltage, shorted speaker
cables, or simply overdriving the amplifier with too much signal. In any event, the LED will light when this occurs and it has a short memory circuit
built in to give the soundman a positive indication. The LED indicator will light during every clipping situation, thereby providing a valuable tool to help
prevent severe distortion of the CS-400 ™ . This type of indicator is more valuable than a conventional VU meter because a VU meter tends to ignore
occasional peaks and only responds to relatively long term signals.
INPUT SENSITIVITY CONTROLS
The CS-400 ™ has the level controls for each channel labeled in a more functional manner replacing the conventional 0 to 10 segmented circle
with the actual input sensitivity ratings of the amp for various settings of this control. In the past, this control has often confused even the most
experienced audio technician as to its purpose and usage. This new change will help to explain its fOnction, the need for these controls and the
significance of the sensitivity rating.
The input sensitivity rating of a power amplifier is the RMS voltage level required at the input to produce full power into the rated load at the
output This voltage then becomes the level at which the associated mixer must operate in order to produce the rated full power output.
Operation at levels above this rating will cause the power amplifier to clip (produce distortion) unless the associated amplifier has a compressor or
limiter to minimize this distortion. Such a system called “DDT®” (U.S. Patent #4,318,053) is available on all Peavey power amplifiers and the
advantages should be obvious...without it the sound engineer must “ride gain” on the mixer in order to prevent the mixer from producing an output
signal level above the input sensitivity rating of the power amplifier which would cause distortion.
Traditionally the input sensitivity rating of a power amplifier receives low “billing” on a typical specification sheet. Usually the power output
levels into various loads and the distortion numbers are first, followed by various other “interesting” specs, such as damping factor, slew rate,
transient intermodulation distortion, and others. Then, in the fine print, one might find the input sensitivity rating...then again, one might not. This
rating, however, must be known to have performance visibility at the mixer. Further, the rated sensitivity is only correct if the power amplifier
level control is set at the full clockwise or maximum setting. Any other setting increases the value. With a numbered circle from 0 to 10 this new
higher value is not indicated. The sensitivity ratings of the CS-400 ™ (and CS-800 ™ ) is to make the sensitivity rating known and to allow it to be
adjusted accurately to higher values if necessary. You will notice that the sensitivity ratings are specified in both RMS voltage levels (usually given in
power amp spec sheets) and the equivalent dBV values (usually listed in typical mixer specs). The dBV values are more useful since most
contemporary mixers employ LED arrays, calibrated in sensitivity rating in dBV, indicating mixer output levels. Knowing the power amplifier
sensitivity rating in dBV will allow the mixer operator to know the status of his power amplifiers (whether they are clipping or not) by noting which LED
on the mixer is “peaking”. Obviously the LED labeled the same or closest to the sensitivity rating will indicate full power output of the system
Operation below that point will indicate how much so called “power amplifier headroom’’ is left. Operation above that point will cause
clipping (or compression if the Peavey DDT ™ system is in use). Perhaps an example will be helpful here. Referring to the CS-400 ™ faceplate
you will notice that with the amplifier “sensitivity for rated power” control set full clockwise, the rating is 1,0V RMS or 0 dBV. The critical LED on the
driving mixer then is the one labeled 0 dBV. It will correlate with the power amplifier clipping /compression LED in that, whenever the 0 dBV LED on
the mixer flashes on peaks, the LED on the power amplifier will also flash indicating full power output is achieved If the CS-400 ™ control were
adjusted to a higher value, then this new value would become the new correlation point on the associated mixer. This, then, is the main reason for
knowing the value of the power amplifier sensitivity.
There is a very simple “rule” regarding the setting of the sensitivity (or level) control on a power amplifier. The “rule” is:
"UNLESS THERE IS A SPECIFIC REASON NOT TO, THE SENSITIVITY CONTROL ON ANY POWER AMPLIFIER SHOULD BE SET
TO THE FULL CLOCKWISE POSITION, RESULTING IN THE MINIMUM VALUE OF SENSITIVITY RATING.”
The exceptions to the full clockwise “rule” involve large systems where it is often necessary to employ several power amplifiers supplying the
same signal to multiple speaker systems to achieve the necessary sound pressure levels or audience coverage. If the various amplifiers have
different sensitivity ratings, it is necessary to adjust them to all have the same value so they all reach full power at the same time A typical example is
using a CS-400 ™ and a CS-800 ™ on the same mixer signal output. The CS-400 ™ is rated at 0 dBV, while the CS-800 ™ is rated at +3 dBV (the CS-
800 ™ has 3 dB more power thus requiring 3 dB more signal input). To achieve simultaneous full power operation, the CS-400 ™ should be adjusted to
+3 dBV. Notice the CS-800 ™ must be set full clockwise. The resulting system will have 15 dB of compression capability. Several competitive power
amplifiers on the market have sensitivity ratings of +6 dBV (2V RMS). If these are employed in multiple systems, obviously the more sensitive power
amps must be adjusted accordingly.
In order to achieve the necessary sound pressure levels required in the typical “rock’n roll” concerts for the sound system, the use of bi-amped
and tri-amped systems has become very popular and necessary. In this case, a crossover system must be employed between the mixer output and
the various power amplifier systems in order to achieve 2 or 3-way operation with the associated loudspeaker components. Often these crossover
systems provide adjustments for the crossover frequencies but have no level adjustments on the various outputs to compensate for differences in
efficiency ratings of the various loudspeaker components. In this case, the sensitivity control can be adjusted upward on the particular amp the
amount necessary to “pad” the associated speaker component in order to achieve a “flat” system. Naturally for optimum compression
performance, the “unpadded” power amplifier should be set full clockwise.
Here at Peavey, we have chosen a unique plug-in crossover system, used in conjunction with our so-called “crossover islands” on the CS-
400 ™ and CS-800 ™ , to achieve bi-amped and tri-amped systems easily and at a low cost to the user. For each of our “bi-ampable” speaker systems
we offer a matching crossover “can” which is specifically designed for that speaker system and contains all the necessary “padding and
equalization to achieve a “maximally flat system. In this case, again, the sensitivity controls on the associated power amplifiers must be set at the
full clockwise setting to achieve optimum performance. We also offer general purpose crossovers for competitive speaker enclosures which do not
contain padding or equalization (referred to as “flat” crossovers) and, in this case, the power amplifier sensitivity controls or some other means must
be employed to accomplish the necessary padding requirements.
One final point on setting power amplifier sensitivity controls...often, especially in small clubs, churches, and studio applications, the full power
output capability of the power amplifier is not needed, or at the very most, there is no requirement for large amounts of compression capability due to
the relatively low signal levels involved. Simultaneously these applications usually require a very low noise system. In this case it is possible to
reduce the overall system noise at the expense of compression capability by increasing the power amplifier sensitivity accordingly In other words if
instead of a sensitivity rating of 0 dBV on the Peavey CS-400 ™ , we adjusted it to a rating of +10 dBV, overall system noise would be improved by 10
dB with the resulting compression capability of 8 dB. In other words, this can be one good reason for increasing the power amplifier sensitivity rating.
Remember, however, once this is done, the mixer operator cannot re-establish full compression performance sitting at the mixer If he wants it back
he has to do it at the power amplifier.
“ON/OFF” SWITCH/PILOT LAMP
The front panel of the CS-400 ™ contains a conventional type “ON /OFF" switch (3) with an internal pilot lamp. When the amplifier is pluqqed into
a suitable power source, activating this switch should light the pilot indicator lamp. Failure of the pilot lamp to come on may indicate the line fuse has
blown or the power source is faulty.
FAN SPEED SWITCH/HIGH TEMP. INDICATOR
The fan speed switch (4) determines the speed of the internal cooling fan with the internal lamp indicating over : t emperature shutdown
conditions. For most applications, low speed operation will provide adequate cooling. However, for sustained high powered applications, manual
selection of high speed operation is recommended to provide maximum cooling, thereby minimizing the possibility of any shutdown of power due to
over temperature conditions. The CS-400 ™ contains an internal thermal sensor that automatically raises the fan speed to high if low speed was
selected when conditions exist which require additional cooling. Even at high speed operation, however, overloads into very low impedances and
inadvertent short circuits could result in very high temperature conditions and the amplifier’s thermal overload circuit may activate. This will be
obvious with the pilot lamp off and the high temperature indicator on. The cooling fan will remain on as long as the unit is plugged in. After the unit has
cooled down sufficiently, the amplifier will automatically cycle back on again. If high ambient temperature conditions exist, such as in a closed area

Peavey CS-400 Specifications

General

Minimum Load Impedance (Stereo)	4 ohms
Input Impedance	20 kOhms
Frequency Response	20 Hz to 20 kHz
Total Harmonic Distortion	Less than 0.1%
Input Sensitivity	1.0V RMS for rated output
Signal to Noise Ratio	>100dB
Power Output	200 Watts RMS per channel at 4 Ohms