Yamaha White Paper Power Amplifiers Reference Guide
Contents
1. Ch1 DC coupling 2 0E1 Vidiv 5 0E 2 s div 2500 points Sample mode Fig 18 An oscilloscope measurement of amplifier model Competitor B 2900w 2 ohms Fig 18 shows that Competitor B rated 400 watts higher than the T5n at two ohms seems to start out well but quickly loses power and its output voltage drops This behavior was observed when the amplifier was driven on both channels Ch1 DC coupling 2 0E1 Vidiv 5 0E 2 s div 2500 points Sample mode Fig 19 Competitor C Rated at 3300W into two ohms this amplifier muted quickly after its limiter kicked in 3300W 2 ohms Fig 19 shows the output signal of amplifier model Competitor C Though this amplifier is rated at 3300W into two ohms and specified to have the highest power of all the amplifiers in this comparison the oscilloscope trace shows contradicting results Its limiter kicked in drastically dropping output voltage Though not apparent on one still image of the measurement it took a few seconds for the output voltage to recover only to have the limiter activated once again shortly afterwards This behavior repeated for the entire duration of this test These results show that different amplifiers behave differently under low impedance operation The results of the comparison also prove that actual performance of an amplifie2. YAMAHA COQ Yamaha Power Amplifier White Paper August 2008 Table of Contents 1a ADOU a ol 9 0 asec ee Meee net cern EE ne ne ene eee tree ee ene mene ner tr 2 CE NON CUO Tiersen careers states E E bnstcedecseeiein cap nnn sueneananteenaaiteaasynngonesemneetaseannente 2 1 2 Explanation of different amplifier topologies 0 0 00 cece ccccccesssessseeseseeseseesseseeseeseeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeseeeeeeeeeeeeeeeeeeees 2 2 gt Yamana COCMNOIOOY sccsenrsseccexc sree rctunectesevoset svar sues sceutoeressvossccusbanessutbiuazessboeacsvesncdavcwenieaatacs 5 Zi Hal MO MO aN ATC r Sucre esiis ne a E aa ae ae iaeia aiae iaer e a iaie iiin 5 22 PFullreson ance switching power Supply asserena ETE E EE 5 3 Behavior of the amplifier under heavy load condition cccscceseeeeeeeeeeeeeeeeeeeneeees 6 zl Tmporta nce of Stable 2 ohm load capability sersicressisisieisrinianaini i era EEE EEN E ENET EEEE ENN 6 3 2 Comparison of amplifiers at lower impedance situations cccceeeseeeesesseessessssssesseeeesssssesssssesssesssasaseaaaaeaaas J 3 3 Explanation of results of listening test USING MUSIC SOUZXCe nnnnnnnnnnnnnnnennnnesseesssrsssesesersrereerrrrrrrrrrreerererereeeeererene 8 YAMAHA COQ 1 About EEEngine 1 1 Introduction Yamaha Power Amplifier Philosophy Our approach to manufacturing power amplifiers 1s simple pure and natural amplification of the input signal Mixed audio is
3. all of which are rated from 2500W to 3000W at 2 ohms Voltage gain and input levels have been carefully measured and adjusted for a fair comparison 0 4sec 1 2sec interval 0 4sec gt 4 F gt lt gt 2 ohm Digital Dummy load Oscilloscope 2 ohm Dummy load 500Hz x 200 cycle i c oO T c D N Fig 14 Set up overview Fig 15 The input signal The same waveform with a higher amplitude is Fig 16 Output of Yamaha s T5n amplifier 2500W 2ohms Output signal desired for the output signal of the amplifier is very true to the input signal YAMAHA COQ j ii Chi BC coupling 2 0E1 Vidiv 5 0E 2 s div 2500 points Sample mode Fig 17 Output signal of an amplifier Competitor A 2500W 2ohms The oscilloscope measurement on Fig 17 shows strong compression like behavior on its output signal The output signal shows no resemblance of the input sine wave This behavior was not seen when the amplifier was driven only on one channel but quickly became unstable when driven on both channels We believe this to be result of overstressing of the one power supply that supplies power for both channels E E i i H i H i i i i j i j i H i H i H i H i i
4. allowing for surprising improvement in efficiency It utilizes Class D operation to provide the power at the final output stage of Class AB operation Almost all of the current energy is output as the audio signal and just a small fraction of the remaining energy is emitted as heat dissipation through the heatsink With the final output stage operating as Class AB the output signal is of remarkably high sound quality There is none of the deterioration of frequency response and damping factor or unwanted EMC as conversion of the audio signal to a PWM signal does not take place Plus EEEngine is designed to operate perfectly while keeping the power amplifier heat generation to a minimum regardless of the load requirements All together EEEngine offers Class AB sound quality with efficiency that matches Class D EEEngine circuitry was uprated for TXn and Tn series amplifiers with a new high efficiency electrical current buffer FET driver circuit to withstand the power and 2 ohm loads that the amplifiers will drive Heat dissipation Voltage Fig 7 EEEngine operational waveform EEEngine vs competitor technology There is one well respected amplifier manufacturer with a proprietary amplifier topology which shares the same concept of combining Class AB amplification and Class D power supply operation Both technologies track the audio signal to always provide the minimum power required for the
5. 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 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 YAMAHA CO 3 2 Comparison of amplifiers at lower impedance situations Below are oscilloscope measurements to visualize differences in behaviors of some of the better known power amplifiers available today The test signal is sine wave 200 cycles of 500 Hz 0 4 sec followed by 1 2 seconds of interval no signal This frequency can be IMPEDANCE AMPLITUDE found in many typical program materials and an interval was set because continuous playback of sine waves is not realistic in actual sound reinforcement applications Fig 13 A typical impedance curve of a bass reflex woofer The nominal This is a comparison of various power amplifiers in the impedance is 4 ohms but the lowest impedance is below 4 ohms market
6. are located on top of it The heatsink itself is fastened to the chassis side panels at numerous strategic points with special insulators that are designed to absorb vibration and chassis resonance that interfere Fig 9 EEEngine s High speed buffer is activated only when Class D power with optimum reproduction supply is not able to keep up with sharp increases in sound This circuitry allows EEEngine to maintain a preferable slew rate without manipulating and degrading the audio signal 2 2 Full resonance switching power supply The power supply plays a crucial role in the quality of 2 Yamaha technology any amplifier Full resonance switching power supplies found on TXn Tn and PCIN series amplifiers processes 2 1 Dual mono amplifier structure two types of switching Zero Voltage Switching and Yamaha power amplifier technology mechanical Zero Current Switching Full resonance power supplies design provide voltage and current waveforms with natural The TXn Tn and PC9SOIN series amplifiers are 2 curves significantly reducing harmonic components from switching noise Typical switch mode power YAMAHA COQ supplies employ what is typically called hard 3 Behavior of the amplifier under heavy switching Waea induces more noise ne ue De load condition output and gives square waveforms rich in high frequency harmonics requiring an additional filter to remove them Soft switching as seen in full resona
7. final output stage Two technologies are different however in its tracking operation methods Signals of higher frequencies require a higher slew rate and are harder to track Slew rate is a measure of the ability of an amplifier to respond to very fast changes in signal voltage To compensate for the inability to keep up with changes in signal voltage this competitor technology adds a delay to the input signal This delay gives the Class D power supply more time to respond to sharp changes in voltage but it must be noted that manipulating the audio signal will inevitably have effect on the final sonic quality Yamaha s EEEngine takes a different approach to compensate for Class D power supply s limitation in keeping up with sharp changes in voltage by adding an auxiliary high speed buffer power supply This high speed power supply circuit is activated only when Class D power supply alone is not able to keep up with the speed This high speed buffer mechanism allows EEEngine to respond to quick voltage changes without manipulating the audio signal and degrading sound quality The elimination of unwanted and excessive components to the audio line is a reflection of Yamaha s philosophy of delivering natural output signal that is faithful to the input signal Slew rate affects the ability of an amplifier to accurately render complex waveforms at high power levels A higher OK YA M A H A CQ commercial audio slew
8. E1 Vidiv 1 0E 2 s div 2500 points Sample mode topology which had been the norm in the industry for Figa f OUPUESIGNAL OF at plear fol pelenanm plier decades offers a simple circuit configuration and superb sound quality Yamaha s older amplifiers such as P2200 released in 1976 and PC2002M released in 1982 were Class AB amplifiers Class AB topology however has a drawback of always requiring its output stage to drive at maximum voltage output resulting in a great deal of heat dissipation This low efficiency is the reason why Class AB amplifiers are comparatively limited in output power considering their unit size and weight When YAMAHA CO driven with typical program material with occasional clipping 1 8 power Class AB topology typically achieves around 20 efficiency meaning that 80 of power drawn is lost as heat Various methods have been developed to overcome this drawback which led to the development of Class H and Class D topologies Efficiency rate within this document refers to overall efficiency of the power amplifier including its mains power supply Efficiency is calculated at 1 8 of rated output power which is a reference of typical program material with occasional clipping Heat dissipation Fig 4 Class AB operation waveform Class H Class H uses a method that switches the power supply voltage level according to the input signal This can vastly improve output stage heat diss
9. d the most headroom among the competitors The amplifier s output did show slight distortion when levels were high but the playback remained musical and had the best performance in this comparison Dummy load 20 Back yard Fig 20 Listening test set up YAMAHA CORPORATION P O BOX 1 Hamamatsu Japan http www yamahaproaudio com
10. dio signal s frequency response distortion and damping factor are affected by the low pass filter High power PWM signals also have the side effect of emitting harmonic electromagnetic EMC waves within the radio frequency range of up to a few megahertz Class D amplifiers may be convenient on the efficiency side but often face difficulties in achieving optimal sonic quality and many manufacturers are attempting to work their way around this problem Pee errr l l Electromagnetic Wave r Hyde TTE et pene eet ee ee et Fig 6 Class D operational waveform YAMAHA CO EEEngine EEEngine combines the sound quality of Class AB circuitry while maintaining the efficiency of Class D circuitry Combining positive aspects of both Class AB and Class D may seem simple by concept but it took years of extensive engineering efforts to achieve this technology on a mass production base EEEngine overcomes problems conventional amplifier topologies while providing advantages in all areas offering a dramatic leap in power amplifier design It realizes efficiency that matches Class D without compromising the sound quality of a Class AB amplifier The patented EEEngine technology is scalable and can be found on a wide range of Yamaha power amplifiers from the value class P series to the flagship TXn series EEEngine tracks the audio signal to always provide the minimum power needed for the final output stage
11. ipation by providing low voltage when the signal level is low However as the signal level increases the system functions in the same way as a Class AB system and efficiency is lost Class H loses efficiency when fed music signals with a wide dynamic range A system that uses a multi step voltage switching method may easily come to mind to overcome this problem but this would create many complications such as increased switch loss making it impractical as a solution Class H amplifiers typically have efficiency of around 30 Yamaha s P5002 amplifier released in 1982 was an early adopter of Class H topology Voltage H dissipation Fig 5 Class H operational waveform Class D Often misunderstood as an abbreviation for digital Class D utilizes PWM or Pulse Width Modulation First a PWM signal is created from the input audio signal The power supply voltage is then switched according to the pulse width creating a high power PWM signal to drive the loudspeaker The elements used for the switching operation require only a minimum of voltage allowing vast improvements in efficiency compared to previous amplifier topologies Class D amplifiers typically have efficiency of around 60 However to convert the audio signal to a rectangular wave PWM signal a high power consuming low pass filter must be used at the output stage to eliminate pulse or the original audio signal cannot be recovered The au
12. nce 3 1 Importance of stable 2 ohm load capability switching on the other hand produces natural Tn and TXn series were developed with the concept of waveforms that are desirable for music playback 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 Fig 11 Current and voltage of a typical competitor power supply Visibly to the amplifier with a source that repeatedly hits the much higher noise content can be observed circled in red Voltage waveform shown in yellow and current waveform shown in blue 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
13. r cannot always be predicted from its catalog specifications Because there are no industry standards for amplifier specifications paper comparison of figures such as output power is not very practical 3 3 Explanation of results of listening test using music source We conducted the above experiment using a music source To replicate a more realistic setup we replaced the dummy load on one channel with four loudspeakers connected in parallel To reduce interference between the four loudspeakers and also to reduce stress on our ears we verified our results from one reference loudspeaker the remaining three loudspeakers were placed in a remote location The results of this listening test were basically YAMAHA COQ reproductions of the oscilloscope measurements The kick drums on Competitor A were heavily distorted extremely harsh on the ears and harmful to the loudspeakers as well Its playback level fluctuated after the kick drum as was observed in the oscilloscope measurement Competitor B s output was considerably distorted when louder notes were repeated The amplifier s limiter kicked in on Competitor C after the kick drum beat Sound source CD The amplifier muted for a few seconds before returning This limiter may protect the amplifier from damage but this behavior is unacceptable in a live situation Yamaha s T5n showed positive results in this test The T5n showed minimal limiting and ha
14. rate is however preferable only toa point A higher slew channel amplifiers incorporating a symmetrical dual rate will give the amplifier a wider bandwidth and when in l rae aie mono amplifier design with each mono amplifier excess it will ultimately result in amplification of signals even in the radio frequency range This will waste energy create having its own power supply Dual mono amp structure distortion and also put undesirable stress on the speaker unit plays an important role in achieving separation between the two channels Having a dedicated power supply on each mono amplifier minimizes interference between the channels preventing powerful bass notes on one channel from taking power away from the other channel for example The two power supplies operate in opposite phases synchronizing to cancel noise and lowering electromagnetic interference Fig 8 Circuit of a competitor amplifier To allow Class D power supply more time to respond to quick changes in voltage requirements all audio goes through a delay Effect on sonic quality cannot be avoided with this manipulation of the audio signal Fig 10 Dual mono amp structure Each channel has a dedicated power supply The amplifiers are also carefully designed to suppress internal vibration within the amplifier that could have a negative impact on sound quality The top surface of the heatsink is reinforced to reduce vibration to the power transistors that
15. sent to the amplifier from the mixing console to be amplified before final coloring or flavoring through the loudspeakers The role of Chi BC coupling 1 0E1 V div 1 0E 2 s div 2500 points Sample mode amplifiers in a sound system should not be to add its Fig 3 Output signal of Yamaha T5n amplifier Natural and true to the input own color but to be faithful to the input signal to give ou maximum control over the final sonic performance er y P Reliability is another important feature of Yamaha amplifiers All Yamaha products are also tested under severe conditions and must comply with Yamaha s strict quality assurance standards Read more about Yamaha s quality assurance testing and standards at http www yamahaproaudio com topics leading technol ogy quality_control index html 1 2 Explanation of different amplifier topologies There are many different amplifier topologies or circuit design principles that are used in professional power amplifiers The majority of the high power amplifiers seen in the professional audio industry today can be classified as derivatives of three major technologies Class H Class D or a hybrid of Class AB and Class D such as Yamaha s EEEngine Energy Efficient Engine Class AB Class AB technology is the foundation of professional amplification Even to this day Class AB amplifiers can be found in many professional audio applications This Ch1 BC coupling 1 0
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