User Manual

supplies employ what is typically called “hard

switching,” which induces more noise into the DC

output and gives square waveforms rich in high

frequency harmonics, requiring an additional filter to

remove them. “Soft switching” as seen in full resonance

switching on the other hand, produces natural

waveforms that are desirable for music playback.

[ Fig.11 ] Current and voltage of a typical competitor power supply. Visibly

much higher noise content can be observed (circled in red). Voltage

waveform shown in yellow, and current waveform shown in blue.

[ Fig.12 ] Yamaha’s Full-resonance switching power supply. Smooth, natural

waveforms with minimum switching noise. Voltage waveform shown in yellow,

and current waveform shown in blue.

3. Behavior of the amplifier under heavy

load condition

3.1. Importance of stable 2 ohm load capability

Tn and TXn series were developed with the concept of

stable operation under 2 ohm load. We do not

necessarily suggest power amplifiers to be configured

for a 2 ohm load setup. However, we recognize that

stability under extreme low impedance is very important

for professional use power amplifiers. For example, in

the use of dual subwoofers, woofer units with nominal

impedance of about 6 to 8 ohms are typically connected

in parallel, giving the amplifier a load of 3 to 4 ohms.

Line array speakers are also often connected in parallel,

requiring stability at lower impedance. The actual

impedance curve of a speaker unit is complex and its

load varies greatly depending on frequency. A

loudspeaker’s lowest actual impedance is usually lower

than its nominal impedance. Because of this impedance

curve, an operator may unknowingly put extreme stress

to the amplifier with a source that repeatedly hits the

frequencies most demanding (lower impedance) for the

loudspeakers. Because an amplifier is put under

extremely demanding conditions at times, it is important

that there is enough headroom to keep the amplifier

from clipping.

When an amplifier clips, its output signal is distorted

and a rectangular waveform is observed. A rectangular

wave contains very high frequency and this causes voice

coils of the loudspeakers to burn out. Clipping of the

output signal, which may potentially destroy speaker

units in the system, must be prevented in a professional

audio system. An amplifier’s ability to maintain stable

operation at lower impedance is essential as an amplifier

is more likely to clip under lower impedance.