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M&D® A-400

Power Amplification System


♁ Introduction:
Most inexpensive amplifiers on the market, especially AV amplifiers, can not properly drive the Mark & Daniel® speakers due to their insufficient current drive and high internal resistance. Because of the high sound resolution ability of M&D® speakers, unsatisfactory performance and distortion, especially in bass reproduction under higher SPL (sound pressure level) operation, becomes readily apparent to most audiophiles who use ordinary AV amplification to drive M&D speakers.
The M&D® A-400 amplifier was developed to precisely match every critical demand of M&D® speakers with true hi-fi sound quality, outstanding spatial clarity, and high dynamic reproduction. The A-400 is a high-end amplifier able to match and drive all critical speakers on the market with the best C/P value available to the customer.
Power amplification providing 100W output at 8 Ohms, 200W output at 4 Ohms, and with 400W output down to 2 Ohms load per channel; such an ※ideal§ amplifier is required by M&D® for designing the A-400 to perfectly match his own speaker systems.
Based on the ※Current Pond§ concept, the A-400 holds a tremendous amount of energy in reserve. This powering reserve assists the low-resistive power transistor arrays of the amplification system. A swift and infinite current is therefore supplied to the speaker system even under extreme load conditions. The A-400 therefore, acts as an instantaneous constant-voltage source which exactly follows every detail of the input music, without degradation due to impedance variations throughout the complete audio spectrum under high output conditions.
The A-400 amplifier has also been designed with great versatility. It may be used as an integrated amplifier with pre-amp stage and volume control, or with the option to by-pass the volume controlㄛconnected as a pure power amplifier. The A-400 also has balanced input which allows it to be converted as a very high power mono amplifier with a combined total of over 700 W output capability!
A ※memory§ function has been built into the A-400 to avoid the unnecessary redundancy of resetting the system to one*s preferred levels and parameters every time the power switch is turned on. The precision 80-steps volume control and 6 input-mode selection both remain at their prior setting held before the last power-off condition. The A-400 amplifier can also be both manually or remotely controlled.
The A-400 has a very tough chassis with large heat sinks built into the structure; each amplifier weights to 33Kg (73 lb). Internally, a heavy shield is placed in between the power transformers and the main PCBs for isolation of the two chambers. The front panel, back panel, and the cabinet cover are both unusual; they are made with the CAM (Compound Artificial Marble) to prevent unnecessary resonance and electric-magnetic interference.
Every detail has been painstaking attention in the A-400 to achieve the creation of the optimal power amplification system.
The A-400 Amplifier
Power Supply Section:
A-400 has a built-in ※current pond§ to power the system in order to achieve the qualities and characteristics of an ideal power amplifier. This virtually guarantees a negligible signal loss during music reproduction even under extreme, heavy-loaded high output conditions.
Two independent transformers, rectifiers, and power systems, with a total 1200VA capacity, incorporated with the large audio-grade 140,000米F/63V capacitor banks are built into the A-400 in order to produce 100 Watts output at 8 Ohms, 200 Watts at 4 Ohms, and 400 Watts at 2 Ohms load to each channel. This prodigious power output helps the M&D®*s A-400 meet the rigid design criteria established for this extraordinary power amplification system.
Amplification Section:
A-400 has a three-stage current amplifications design; the final stage employs 4 pairs of Motorola MJL21193/21194 (200W) or the equivalent high quality power transistor arrays, which are capable to delivering a total 60A peak current to the load with minimized internal resistance.
The high-speed voltage amplification stages are quite complicated with precise parameters to control and finesse every detail. Combined with the current amplification stage, the A-400 yields a fast system slew rate of up to 220V/us, with frequency response from 5Hz-150KHz (-3dB) and ‹0.1% THD at 80% rated output.
A-400 employs both voltage and current feedback controls to optimize the system performance. There is also a local-stage feedback in every voltage amplification stage to optimize the open-loop gain, plus advanced current feedback is employed to effectively isolate the unwanted counter-signal derived from the connected speaker system.
The two-sided, 2 OZ thick-copper PCB have been used to each amplification circuitry and all susceptible parts on the PCB have been protected with the copper shields.
The volume control of the A-400 provides 80-steps adjustment through the relay array using precision resistors with 0.3%variation. The volume setting and the 6-channel input mode are built internally with a memory function and can either be manually or remotely controlled.
System Protection:
Multi-protection systems, including output short-circuit protection, DC output protection, and power-on delay protection, are provided with the A-400 amplifier to ensure the system safety and to prevent misuse.
Once the protection circuit is activated, the VFD indicator will flash to indicate system status. Turn off the power, check for any possible reason for the activation of the protection circuit, then to reset the system back to the normal operation.
Structure and Chassis:
The A-400 system sizes W480x D452x H160mm (19§x 18§x 6.3§) and weights to 33Kg (73 lb). It is a very heavy steel chassis with the large heat sinks built into the structure. Internally, a 2mm thick steel shield is placed in between the power transformers and the main PCBs for isolation of the two chambers.
CAM (Compound Artificial Marble) material is used for making the front panel, back panel, and the cabinet cover of the A-400 amplifier. This provides you with not only for a stylish design; CAM can also effectively cut down cabinet resonance and induced stray current interference from the parts of the amplifier.
Complete A-400 amplifiers are assembled, adjusted, tested, and furnished, with all works done by the mastering technicians, a rare hand-made product created by skilled craftsmen rather than thru mass production.
Front/Back Panel and Remote Control:
Front Panelㄩ
K VFD Panel:
A large sized VFD indication panel is provided with both input selection (CH1 to CH6) and volume control level (-80 to 0) indications.
The infrared sensor is also installed in this panel, just point to the panel while using the supplied remote controller.
L Power Switch:
Push in to turn on the power; push in again to turn off the power of the A-400 amplifier.
M Input Selector:
A step switch is used to select the 6 input channels. CH2 to CH5 is for the integrated amplifier adjusted through the volume control;
CH1 is the pure amplifier mode; the volume control is by-passed on this channel in order to connect with the bi-amp applications or the other pre-amplification systems such as the multi-channel AV decoder, the audio mixing console, and so forth;
CH6 is the mono amplifier with the balanced input mode, and is used to connect the balanced amplification system with high output capability.
N Volume Control:
A step-in switch is used, matching with the relay array and resistors in 0.3% precision in order to provide 80-steps precise volume control for the A-400 amplifier.
Back Panelㄩ

O AC Input Plug:
Check your area AC voltage (120, 240V, or other) and make sure it matches the indicated voltage on the back panel of your unit before plugging in the power cord. A fuse-holder is included with this plug. A minimum 10A fuse is used in the 120V AC system; and a minimum 5A fuse is used for 240V AC system.
P Speaker TerminalsㄗRightㄘ:
Two pairs of parallel right-channel speaker terminals are provided for true bi-wire connections.
Q Speaker Terminals (Left):
Two pairs of parallel left-channel speaker terminals are provided for true bi-wire connections.
R Input Panel:
CH2 to CH5 are used to connect ordinary play-back equipment while volume control is needed for such audio systems as CDs, DVDs, TV, the Tuner, Phono amplifier, and so forth; CH1 is the direct input where the volume control is not needed; CH6 is used to connect with the balanced amplification system as a high power mono amplifier.
Remote Controller:
- Point towards the VFD indication panelK while using the remote controller.
- The remote controller provides the volume up (+)/down (-), input (+/-) selection, and mute (on/off) functions.
System Functional Summery:
Functional Description   Volume       Input        Input     VFD Indication
                                    Control    Sensitivity  Impedance
Input CH1 (Dirㄘ             no          0.775V    15K Ohm      1 ignore
Input CH2                      yes          0.3V        47K Ohm      2 80 每 0
Input CH3                      yes          0.3V        47K Ohm      3 80 每 0
Input CH4                      yes          0.3V        47K Ohm      4 80 每 0
Input CH5                      yes          0.3V        47K Ohm      5 80 每 0
Input CH6 (Bal)               no          1.55V      15K Ohm      6  ignore
Output Short Protection                                                        flash
Output DC Protection                                                           flash
Power-on Protection                                                             ignore
Mute (on)                                                                            flash
Application Notes and Safety:
1ㄘBefore turning on the A-400 Amplifier for the first time, please check the back panel to see whether or not the indicated AC Input Voltage matches with your area voltage. Incorrect powering will cause either serious damage or out-of-function to the equipment!
2ㄘWhen first time turn your A-400 Amplifier to power on, each channel*s volume may randomly sit at different level. First step to do, is turning down the volume level to -80.0 indication, form CH1 to CH6; then set up preferable volume setting to each channel, depending on the connected play-back equipment (CDs/ DVDs/ Phono amp/ Tuner, and so forth) and the proper volume to you.
3ㄘThe A-400 has no self-maintenance parts inside to the customer. Please do not try to open the amplifier in order to prevent the possibility of damage and electric shock!
4ㄘMake sure the power cord is properly grounded.
5ㄘDo not place A-400 near any wet environment; it could cause serious damage if any liquid gets into the amplifier! If this does happen, turn off the power immediately and send to qualify personnel to fix the problem.
6ㄘThe A-400 amplifier must be placed adjacent to good ventilation and located in a relatively dust-free environment in order to prevent the over-heating damage.
7ㄘDo not plug/unplug the input cable and speaker cable while the speakers are connected to the A-400 in a power-on condition; otherwise, you may damage your speakers.
8ㄘEven though the A-400 has high power output capability; always turn down the volume if you are not familiar with a particular music selection; also, remember to turn down the volume before you turn off the power switch.
Exercising caution with regards to your volume control is a good habit to get into in order to protect your costly hi-fi equipment.
9ㄘSince the A-400 is a DC-coupling amplification system designed for the best sound performance. You must be cautious to verify that all connected play-back equipments (CDs/DVDs/Phono amp/Tuner, and so forth) shall have no DC content to the outputs. The DC voltage may be amplified through the A-400 to activate the DC protection circuit, causing unstable operations, or even damage to the amplifier and/or your speaker system.
A-400 Specifications
Product Name:  A-400 Amplifier
2-ch Output Power: 100W @ 8次; 200W @4次
                        400W @2次; per channel
Mono Output Power:  ˇ700W @4次
Frequency Response:  5Hz - 150K Hz (-3dB)
Harmonic Distortion:  ˉ0.1% at 80% of rated output
Input Sensitivity:  CH2 to CH5, 0.3V/47K次
                             CH1 (dir) 0.775V/15K次
                             CH6 (Bal) 1.55V/15K次
Slew Rate:  ˇ 220 V/米S
S/N Ratio:  ˇ 115 dB (input shorted)
Input AC power:  AC120V, 240V, or the other
Power Consumption:  1200 Watts, maximum
Size (WxDxH):  480x452x160mm  (18.9§x17.8§x6.3§)
Weight:  33 Kg (73 lb)
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