Akiyama AMD-400 User Manual - Page 6

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Before unwrapping and starting your PowerAmplifier there are a few thinks you should know...

Setting input levels at the mixer:

Gain pot adjusts the input sensibility or so to speak the level of

the input signal inside the mixer. It is paramount to set the right input level on every channel.

Why is so important setting the correct input level?

First, we have to understand the concept of Dynamic Range of an audio signal. The Dynamic

Range of an audio signal is defined as the ratio between the maximum level before distortion and

the minimum audible level. It is measured in decibels and gives us an idea of the amplitude of the

signal.

Dynamic Range

Dynamic range

Ratio: Max. Level vs. Minimum audible level

We want the audio signal to fluctuate away from the

maximum level (distortion begins) and away from the

minimum level (or background level), where some

noise is present due the nature of the ICs used in the

electronic circuit (all ICs induce noise into the audio

signal).

At the draw, we depict this "safe" level within two

discontinue lines.

We have to set the level of input signal so that the signal

peaks do not reach saturation levels and the lower

amplitude parts of the signal are not too near the

background noise level.

We have to acknowledge that a professional audio system

is a serial bounded group of professional audio devices and

that saturation or other signal deterioration present in one

device will appear someway or another at the serial

bounded following devices.

If we deliver saturated signal from the mixer to the power

amplifier we will not be able to get rid of this saturation

whatsoever. The power amplifier will amplify all what is

Pic (Transient)

Electroacoustic Signal

Minimum audible level

Time

SATURA ION

given and if noise is given (saturation at mixer), it will be

amplified. Naturally, that is bad.

Power amplifiers and loudspeakers:

reasonably protected against signal deterioration and excessive levels and shortcuts.

Loudspeakers are not that well protected, hence a rule or some must be devised to use the correct

speakers with a given power amplifier.

Well, that rule is not a straightforward statement but more of an understanding of the principles

and nature of the audio signal. The nature of the audio signal reefer to the type of music you are

playing and more specifically of its Dynamic Range. The bigger the Dynamic Range the bigger

the power amplifier needed. If the Dynamic Range of a give audio signal is big, the difference

between the minimum level and maximum level of this audio signal will be big as well. Therefore,

we will need an oversized power amplifier with enough power to amplify the maximum levels

without reaching the saturation level at the power amplifier (normally, power amplifiers have red

LEDs to let you know when they start saturating).

As a vague rule we can say that Rock and highly compress music require a power amplifier

delivering a power value slightly bigger than the rated maximum power of the speakers. However,

we recommend the power amplifier rated power be 1.5 times bigger than the rated maximum

power of the speakers. Example: if the power amplifier rated power is 200W RMS at 8 , the rated

maximum power of the speakers should be 200x1/1,5=133,4W RMS at 8 .

Using the power amplifier:

amplifier you must watch two things:

1- Set the volume controls in a way that the saturation LED lights up only occasionally (peaks).

2- Feed the power amplifier with an audio signal of the appropriate level. What is the appropriate

level? Professional Power Amplifiers are set for an input level of 4 dBu. Do not panic, it is easy to

get to it. 4 dBu is just a fixed measure of the audio signal that professional audio community uses

as reference level, it can be expressed also in Volts 4dBu equals 1.23 Volt RMS. So to speak, the

Power Amplifier will work at its best if feed with a signal of a level near the 4 dBu or 1.23 Volt

RMS. How do we set this level? Easy, using the mixer appropriately. Incidentally, the nominal

level for a professional audio mixer is also 4dBu. Therefore, if we set the master output level of the

mixer carefully monitoring the output level meters (normally LED bars), we will ensure that the

level of the audio signal fed to the Power Amplifier is near 4dBu because the nominal level of the

mixer is 4dBu and we set correctly the output level or the mixer.

Why we should avoid saturation?

Obvious reasons aside there is a more "material" reason. Saturated signal can damage your

speakers. Although some speakers have overload protection, a highly saturated signal can deliver

D.C. and this phenomenon can easily shatter your speakers.

SIGNAL

NOISE

Current professional power amplifiers are quite

Saturation and input levels. In order to make the most of your power