Class D system/ Accurate Speaker Driving

Actual live sound contains very slight signal . When we reproduce a music, those slight signal plays important role for space expression, tone quality of instrument, etc. So, we need to drive speakers accurately. But, as a matter of fact,　it's not so easy to drive a speakers accurately because speakers generate the “Counter-Electromotive Force”. When an amplifier send electrical power through a speaker voice-coil, the voice-coil and cone move. Then a moving speaker also generate electrical power and send it back to the amplifier. This "Counter-Electromotive Force" exerts an adverse effect on accurate speaker driving.　A speaker is also a dynamo.
We can easily see the "Counter-Electromotive Force" striking on the cone.

SPEC focus on Actual Operation State.

Counter-Electromotive Force should be absorbed by output stage of amplifier. For that, the impedance of output stage should be very low.

A conventional analog amplifier controls output voltage varying internal resistance of transistor. As output device is equivalent to variable resistor, those output impedance is not so low as a device itself. Counter-Electromotive Force　is absorbed by feed-back-loop.

ON the other hand, Class D amplifier controls output voltage by switching duration of MOS FET. Because the output device is only a switch, the impedance of output itself is very low (during SW-on). Therefore the output device can absorb a part of Counter-Electromotive Force directly through the ”SWITCH” .This operation reduce a load of feed-back-loop and enables more accurate speaker drive　especially for mid-high range.　The feed-back-loop for mid-high range is difficult to operate ideally.

In addition, Because Class D amplifier send energy from power supply into speakers directly and instantaneously ,
we can reproduce the music signal that rises steeply as it is.
Furthermore, because Class D system is using switching technology, the power stage doesn't generate heat at all.

You can't find any cooling hole on the SPEC amplifiers. Depending on this fact, we can apply "wood" for resonant control. All of SPEC's amplifier is using Class D system and Wooden panel.

Like a musical instrument maker , we select materials, consider mechanism connecting wood with metallic chassis, and combine a different wood. Because an amplifier which has high gain is sensitive to rigidity and vibration, wooden structure provides suitable vibrational damping property. This is why we said the amplifier is a musical instrument.

In addition, SPEC has strong control over screw-tightening torque. This is also for the moderate rigidity and damping property . In some cases, we cut sleeve of electrolytic capacitor so as not to cause a unwanted vibration.

In order to control volume, we are using electronic device. As indicated in the figure below, it is complete analog circuit. The sound level is determined by a resistance ratio.

The mechanical volume device located on the front panel only generates the control signal. Audio signal doesn't go through it. This is important for reproducing a slight signal stably. By this system, the sound quality doesn't change depending on the volume level. You can enjoy good sound even if at small volume level.

SPEC propose NEW Pre and Power amplifier system. All of conventional Pre amplifier transmit Audio signal to Power amplifier by a small level after level control. But it is absolute nonsense because they are more vulnerable to noise and will lose slight signal.

SPEC think the volume control should be laid out close to the power stage because level downed signal is susceptible to noise.

SPEC think class D System will take the place of analog amplifier by prominent drive ability. But, some people has negative image for the Class D system. Class D system itself is an ideal system. But, unfortunately, at the beginning, there was not MOS FET having a good performance. It was difficult to switch large current ideally. We had to wait until completion of the good device for High End Audio.
Now, we have it. And we can offer the sound close to live music using prominent merit of Class D system.

As for the Class D system, there are two methods to drive MOS-FET. One is PULSE WIDTH MODULATION(PWM).
The other is DELTA SIGMA MODULATION.
SPEC adopts PWM. It is an analog processing and the circuit is very simple. SPEC think that the circuit for audio system should be simple .
In addition, PWM method don't digitalize input signal level. PWM don't use A/D converter. We think it “ANALOG AMPRIFIER “ except for 400kHz switching.
You should feel the sound as an analog sound.

The “Real Sound” is the sound close to live music.

Reproducing slight signal carefully
It’s a basic of stereophonic.
Slight signal is also important for natural tone and space expression

The way of volume control is also important for slight signal.

Counter-Electromotive Force disturbs accurate speaker drive. In order to overcome it, we adopt class D.

SPEC focus on Actual Operation State.
It's impossible to dissociate amplifier from speakers.
We don't focus measurement value using pure resistance and signal that does not vary.

Amplifier is the musical instrument.
Therefore, we focus on the vibration and damping characteristic of chassis.
Wooden panel and insulators brings natural and comfortable sound.

As for the circuit or system, Simple is the best.

How the joy of music would grow if the current mainstream speakers with wide range but low efficiency can reproduce higher-dimensional acoustic sound like the old vintage high-efficiency speakers.

In the development of our “Real-Sound” amplifiers,we have tried to make it possible to reproduce a tone that is beautiful, rich and penetrating as if appealing directly to the human emotions, a real three dimensional field, and a musical sound full of dynamism !!

• Changes and Evolution of Audio Amplifier
• Advantages of Class-D Amplifier
• Technology of the top of our lineup the superb “Real-Sound” of RSA-F33EX
• The rich, sweet tone and exceptional powerful “Real-Sound” of RSA-M3EX
• New era of amplifier raises the curtain with our renewed “Real-Sound” of RSA-717EX
• “Real-Sound” Phono Equalizer　REQ-S1EX