Ashly PowerFlex 670 Manual de instruções - Página 13

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10.

DESIGN THEORY

Powerflex 70V amplifiers are based on stereo

driver modules that use digital processing to generate a

spread-spectrum switching pattern between about 200KHz

and 1.5MHz, depending on input signal amplitude and fre-

quency. This overcomes the self-limiting and inherent

weakness in traditional class D fixed-frequency PWM

amplifiers, and produces an output with THD+N numbers

comparable to class A and class AB linear amplifiers. (see

Specification Notes at end of this section)

In Powerflex amplifiers, the input signal is re-

ceived by a single operational amplifier configured as a

difference amplifier to reduce common-mode effects from

sources located at a distance. This difference amplifier has

a gain of 2.74 which allows the use of less gain later in the

system, improving overall system noise performance.

The amplified signal, based on the position of vari-

ous selector switches, either bypasses or is processed by a

two-pole high-pass filter with rolloff at 80Hz, and then

passes through the attenuating potentiometer. The attenu-

ated signal is buffered and passed to the amplifier module

along with a zero-volt reference.

The amplifier module receives the attenuated sig-

nal with a unity gain differential amplifier to eliminate com-

mon-mode interference picked up within the amplifier

chassis. The signal is then added to a small DC offset sig-

nal opposite in polarity to any DC offset on the Powerflex

output bridge and adjusted by the digital processing mod-

ule as described above. The digital processing module,

which also generates FET drive signals, has a voltage gain

of 18.2 for a total system voltage gain of 50. The drive

signals generated by the processing module are fed to a

pair of high-current MOSFET transistors, and the switched

output of these transistors is filtered and applied to the

speaker outputs. Fault conditions such as overvoltage,

undervoltage, and output overcurrent are measured by the

module and therefore affect a stereo pair of channels re-

gardless of whether the fault actually exists on both chan-

nels processed in the module. Since every action applied

to protect the digital processing module affects both chan-

nels being processed, other fault conditions are not sepa-

rated by channel, but rather by amplifier module.

Specification Notes: Due to its spread spectrum out-

put switching pattern, the output signal of a Powerflex

fier

contains significant dynamic frequency content* far outside

the audio band, which makes no difference to audible perfor-

mance, but which makes heavily bandwidth-limited** measure-

ment of amplifier noise and distortion characteristics mandatory.

*variable 200KHz to 1.5MHz

**greater than 48dB/octave above 22kHz

Operating Manual - Powerflex Multi-Channel 70V Power Amplifier

ampli-

11.

TROUBLESHOOTING TIPS

11.1

No Audio Output

1.) Power LED not lit:

Line fuse is blown or power outlet is dead.

IF LINE FUSE IS BLOWN, REPLACE ONLY

WITH SAME TYPE AND RATING FUSE.

2.) Power LED is lit but Protect LEDs stay on:

Amp module is in protect mode. Speakers have

been disconnected from amplifier output and connected to

ground until the protect fault is corrected. See section 8

for a complete explanation of protect fault conditions. Out-

put overcurrent, overvoltage and undervoltage faults will

reset in about eight seconds once the fault condition is re-

moved, while excessive DC offset or high frequency faults

take about 30 seconds to reset.

Speaker Load:

The Powerflex 70V amplifier

may go into self-protect at high output levels if the actual

speaker load power is greater than the specified output

power of the amplifier. Some speaker loads may consume

more power at frequency extremes than their nominal

power rating. Alternatively, too many speaker loads may

be connected in parallel on the 70V line.

3.) Thermal LED and Protect LEDs stay on:

Amp module is in thermal protect mode and needs

to cool. The fan will continue to run while in thermal pro-

tect, and other modules will continue to function. See sec-

tion 8.4 for details.

4.) Power LED lit but no Signal LED activity

There is no input signal applied or input level con-

trols are turned down.

11.2

Distorted Sound

1.) Clip LED is flashing regularly

Amplifier is being overdriven. Turn down the in-

put level control, or reduce the output level from the sig-

nal source.

2.) Clip LED is not flashing at all

Amplifier input signal may be exceeding input

headroom, which is greater than +12dBu, or 3.4V rms

(measured using continuous 1kHz sine wave). Incoming