Accuphase-A30-pwr-sm维修电路原理图.pdf

m Pure Class A operation delivers quality power: 30 watts 2 into 8 ohmsm Power MOS-FET output stage features triple parallel push-pullconfiguration m Instrumentation amplifier principle m Further improved MCS+circuit topology m Current feedback combines operation stability withoutstanding sound m Bridged mode allows upgrading to true monophonicamplifier m Massive transformer rated for 400 VA m 4-step gain controlRadioFans.CN 收音机爱 好者资料库Pure Class A power amplifier using power MOS-FET devices Fullybalanced signal paths as found in high-quality instrumentationamplifiers. Further refined MCS+ topology and current feedback designresult in even better S/N ratio, distortion, and other performanceparameters. Robust power supply and power MOS-FET devices in tripleparallel push-pull configuration sustain an amazing 150 watts perchannel into ultra-low 1-ohm impedance loads (with music signals).Pure Class A power amplifiers from Accuphasehave long been blending the purity of class Aoperation with the superior performance of powerMOS-FETs. While building a string of outstandingamplifiers, Accuphase has accumulated a storeof technical know-how that is second to none. Thelatest in this series, the A-30 is a pure class Astereo power amplifier based on the advancedtechnology of the model A-60.The A-30 employs the so-called instrumentationamplifier principle throughout. The signal handlingstages feature further improved MCS+ topologyand the renowned current feedback approach. Thishas resulted in electrical characteristics thatsurpass even the demanding standards set by itspredecessors. Employing only highest gradematerials and strictly selected parts, the A-30pursues the two most important goals of anamplifier: very low output impedance (Note 1) andconstant drive voltage (Note 2).The output stage of the A-30 features power MOS-FET devices renowned for their excellent soundand superior reliability. Because they have negativethermal characteristics, there is no danger ofthermal “runaway” as exists with bipolar transistors.Operation remains totally stable even when theamplifier is running hot. Driving these devices inpure class A assures high-definition sound thatbrings out the finest nuances in the music.In pure class A operation, the power supply deliversa steady current, regardless of the presence orabsence of a musical signal. This means that theamplifier remains unaffected by fluctuations involtage and other external influences. On the otherhand, it also means that the output stage generatesconsiderable thermal energy. In the A-30, this isdissipated effectively by large heat sinks whichprovide ample capacity to remove the heatproduced by the internal circuitry.The heavy-duty power supply easily sustainsoutput levels of 120 watts into 2 ohms, 60 wattsinto 4 ohms, or 30 watts into 8 ohms (per channel).This linear progression demonstrates that theamplifier will be capable to drive even speakerswith very low impedance ratings or withpronounced impedance fluctuations. Stabilityremains excellent at all times. The amplifier alsohas the necessary reserves to handle musicaltransients that require considerable power in aninstant. If even higher power is required, bridgedmode turns the A-30 into a high-outputmonophonic power amp.Output current (A)Output voltage (V)OUTPUT+ B3 B3INPUT+INPUTNFBNETWORKNFBNETWORKGAIN CONTROLCIRCUIT+REGULATORREGULATOR+ B1 B1 B2+ B2Q1Q3Q2Q4Q8Q6Q7Q5Q9Q17Q19Q18Q20Q21Q22Q23Q24Q25Q26Q13Q11Q15Q10Q14Q12Q16NFBNETWORKMCS+Multiple CircuitSumming( )Bias stabilizercircuitBias stabilizercircuitBias stabilizercircuitBias stabilizercircuitBias stabilizercircuitFig. 1 Circuit diagram of amplifier section (one channel)Note 1:Low amplifier output impedanceThe load of a power amplifier, namely the loudspeaker, generates acounterelectromotive force that can flow back into the amplifier via theNF loop. This phenomenon is influenced by fluctuations in speakerimpedance and interferes with the drive performance of the amplifier.The output impedance of a power amplifier should therefore be madeas low as possible by using output devices with high current capability.This absorbs the counterelectromotive force generated by the voice coiland prevents the occurrence of intermodulation distortion.Note 2:Constant drive voltage principleEven in the presence of a load with wildly fluctuating impedance, theideal power amplifier should deliver a constant voltage signal to theload. Figure 2 shows the results of actual output voltage/output currentmeasurements at different load impedances for the A-30. It can be clearlyseen that output voltage is virtually constant at various loads, whichmeans that current increases in a linear fashion. Actual measurementsof clipping power have yielded the following figures, which impressivelydemonstrate the more than ample performance of the A-30: 1 ohm: 175watts, 2 ohms: 142 watts, 4 ohms: 94 watts, 8 ohms: 58 watts.1-ohm rating is for music signals only.Fig. 2 Load impedance vs. output power(Output voltage/output current)Instrumentation amp configuration allows fullybalanced signal pathsThe A-30 features a new “instrumentation amplifier”principle whereby all signal paths from the inputs tothe power amp stage are fully balanced. This resultsin excellent CMRR (Common Mode Rejection Ratio)and minimal distortion. Another significant advantageis that external noise and other external influencesare virtually shut out. The result is a drasticimprovement in operation stability and reliability.Further refined MCS+ topology for even lowernoiseAccuphases original MCS (Multiple Circuit Summing)+INPUTNFBNETWORK GAIN CONTROLCIRCUITNFBNETWORK OUTPUT+INPUT+Signal input stagePower amplifier stageInstrumentation amplifier configurationprinciple uses a number of identical circuitsconnected in parallel to achieve superior performancecharacteristics. MCS+ is a further refined version ofthis approach. Improvements in the bias circuitry ofthe input-stage buffer amplifier result in greaterstability. This in turn makes itpossible to extend the paralleloperation approach to the class Adrive stage of the current/voltageconverter, thereby further loweringthe noise floor.Power MOS-FET output stagewith triple parallel push-pullpower units delivers 120 wattsinto 2 ohms, 60 watts into 4 ohms,or 30 watts into 8 ohms withoutstanding linearityThe output stage (Figure 1) usespower MOS-FETs. Three pairs ofthese devices are arranged in aparallel push-pull configuration foreach channel. The result is stableoperation with ideal power linearityeven down to ultra-low impedances.The maximum power dissipation ofone MOS-FET is 130 watts, but theactual power load per pair is muchRadioFans.CN 收音机爱 好者资料库lower, so that each device is driven only in its low-power range where linearity is excellent.A music signal consists of a continuous successionof pulse waveforms. To prevent clipping on occasionalmomentary high-level pulses, the maximum clippinglevel of the A-30 is set to 50 watts per channel into 8ohms (sine wave output).Current feedback circuit topology assuresexcellent phase characteristics in high rangeIn the A-30, the signal current rather than the moreconventionally used voltage is used for feedback.Since the impedance at the current feedback point(current adder in Figure 3) is very low, there is almostBufferCurrent adderI-VconverterTrans-impedanceamplifierAmplifierOutputCurrent NFBnetwork InputBuffer+ InputGain(Large)(High)Frequencyno phase shift. Phase compensationtherefore can be kept at aminimum. A minimal amount ofNFB results in maximumimprovement of circuitparameters. The result isexcellent transientresponse and superbsonic transparency,coupled withutterly naturale n e r g yb a l a n c e .Figure 4 showsf r e q u e n c yresponse fordifferent gainsettings of thec u r r e n tfeedback amplifier. The graphs demonstrate thatresponse remains uniform over a wide range.Robust power supply with large powertransformer and high filtering capacityIn any amplifier, the power supply plays a vital rolesince it acts as the original source for the outputdelivered to the speaker. The A-30 employs a largeand highly efficient 400 VA power transformer. It ishoused in anenclosure filled witha material thattransmits heat andabsorbs vibrations.This completelyprevents anyadverse influenceson other circuitparts.Two aluminume l e c t r o l y t i ccapacitors rated for47,000 F eachserve to smooth outthe pulsating directcurrent from therectifier, providingmore than amplefiltering capacity.Fig. 3 Principle of current feedback amplifierFig. 4 Frequency response with current feedback(Response remains uniform also when gain changes)n Power amplifier assembly with threeparallel push-pull power MOS-FETpairs per channel mounted directlyto large heat sink, MCS+ circuitry,and current feedback amplifierRadioFans.CN 收音机爱 好者资料库Instrumentation amp type gain control minimizesresidual noiseThe gain control switches gain in the first amplificationstage that uses aninstrumentation ampdesign. Four settings areavailable (MAX, 3 dB,6 dB, 12 dB). With thisapproach, reducing gainalso results in reducednoise. This is especiallybeneficial when using highly efficient speakersystems where the noise floor could be a problem.Bridged connection allows upgrading to a truemonophonic amplifier with 300 watts into 2 ohms(music signals only), 240 watts into 4 ohms, and120 watts into 8 ohmsOperation in bridged mode results in a monophonicamplifier with four times the power output than duringstereo operation. This gives effortless dynamicpower. Specifications and design subject to change without notice for improvements.K0405Y PRINTED IN JAPAN 851-0139-00 (AD1)http:/ n n n n Front paneln n n n n Rear panelGUARANTEED SPECIFICATIONSn Supplied accessories: AC power cordn n n n n Easy switching between dual mono/stereo/bridgedmodeIn the dual mono position of themode selector, the left-channelsignal is supplied to both speakerterminals, which can be used for bi-amping with dedicated low-rangeand high-range drivers.n n n n n Oversize speaker terminals also accept Y lugs andbanana plugsThe sturdy terminals canhandle even very largegauge speaker cable.The connectors aremade of extruded high-purity brass material andare gold-plated for ut-most reliability and mini-mum contact resistance.Y lugs and banana plugs can also be used.n n n n n Large analog power metersn n n n n Balanced connection prevents induced noisen n n n n PCB copper foil and all major signal path componentsare gold-platedn n n n n Buttons for meter on/off, meter sensitivity, and inputselectionGuaranteed specifications are measured according to EIA standard RS-490.m m m m m Continuous Average Output Power (20 - 20,000 Hz)Stereo operation150 watts per channel into 1 ohm ()(both channels driven)120 watts per channel into 2 ohms60 watts per channel into 4 ohms30 watts per channel into 8 ohmsMonophonic operation300 watts into 2 ohms ()(bridged connection)240 watts into 4 ohms120 watts into 8 ohmsNote: Load ratings marked () apply only to operation with music signals.m Total Harmonic DistortionStereo operation (both channels driven)0.05%, with 2-ohm load0.03%, with 4 to 16-ohm loadMonophonic operation (bridged connection)0.05%, with 4 to 16-ohm loadm Intermodulation Distortion 0.005%m Frequency ResponseAt rated output:2020,000 Hz +0, 0.2 dBAt 1 watt output:0.5160,000 Hz +0, 3.0 dBm Gain28.0 dB (GAIN selector in MAX position)(stereo and monophonic operation)m Gain SettingsMAX, 3 dB, 6 dB, 12 dBm Output Load ImpedanceStereo operation:2 to 16 ohmsMonophonic operation: 4 to 16 ohms With music signals, load impedances of 1 (stereo) or 2 (mono) can be driven.m Damping Factor150m Input Sensitivity (with 8-ohm load, GAIN selector in MAX position)Stereo operation:0.57 V for rated continuous average output of 30 W0.11V for 1 watt outputMonophonic operation: 1.14Vfor rated continuous average output of 120 W0.11V for 1 watt outputm Input ImpedanceBalanced: 40 kilohmsUnbalanced: 20 kilohmsm Signal-to-Noise Ratio111 dB (GAIN selector in MAX position)(A-weighted, input shorted)118 dB (GAIN selector in 12 dB position) at rated outputm Output Level Meters40 dB to +3 dB (dB/% scale)Logarithmic scale, with switching capability for meter operation and sensitivitym Power RequirementsAC 120 V/230 V (Voltage as indicated on rear panel) 50/60 Hzm Power Consumption170 watts idle260 watts accordance with IEC 60065m Maximum DimensionsWidth465 mm(18-5/16”)Height170 mm(6-11/16”)Depth425 mm(16-3/4”)m Mass21.5 kg (47.4 lbs) net26.0 kg (57.3 lbs) in shipping cartonUnbalanced and balanced input connectorsProtection and meter circuit assemblyHigh-quality, high-reliability partsARight/left-channel output power meters (dB and % scale)BFunction indicatorsMETER, 20 dB, UNBALANCED, BALANCED, BRIDGECMeter operation/illumination switchONOFFDMeter sensitivity selector button (20 dB)EInput selector buttonUNBALANCEDBALANCEDFPower switchGGain selectorMAX3 dB6 dB12 dBHUnbalanced inputsIBalanced inputsa: Groundb: Inverted ()c: Non-inverted (+)JMode selectorDUAL MONONORMALBRIDGEKRight/left-channel speaker output terminalsLAC power supply connectorRemarksThis product is available in versions for 120/230 V AC. Make sure that the voltage shown on therear panel matches the AC line voltage in your area.The shape of the AC inlet and plug of the supplied power cord depends on the voltage rating anddestination country.RadioFans.CN 收音机爱 好者资料库