Audio Database

Model 500
Commentary

As a high-power machine, this stereo power amplifier was developed in pursuit of how to suppress the distortion factor in the high frequency range at full power and how to eliminate distortion at mini power.

The power transistor is the one jointly developed by Marantz and Motorola, and SJ is attached to the model number after M.
In addition, specially ordered resistors and switches are adopted.

The circuit configuration consists of the SEPP direct-coupled preamp section with a differential-amplifier circuit, followed by the power amplifier section of the normal all-stage direct-coupled pure complimentary service OCL.
NF is doubly applied from the end of the preamplifier section and from the output section of the power amplifier section.
This is the first time in the world that the power amplifier section has been fully push-pull from the inlet to the outlet. Therefore, even the top differential circuit is prepared with completely separate upper and lower components. Up to the final stage of pure complimentary service, the upper and lower components are amplified completely independently to obtain perfect symmetry and dynamic characteristics.

The power stage consists of 8 single-channel 4-parallel stones and 3-Darlington (4-parallel stones are counted as 1 stone). This power transistor is operated in class AB by supplying sufficient idling current to suppress the notching distortion characteristic of transistor class B amplification.

The protection circuit uses a 2-stone configuration that stops current at the drive stage and prevents excess current from flowing into the power transistor when some abnormal operation occurs.
The limiter circuit for 500W/300W/100W power switching uses part of this protection circuit, and the operation principle is also the same.
In the speaker protection circuit, when a DC voltage appears at the speaker terminal of a 3-chip amplifier, the output of the speaker terminal and the power amplifier is cut off by a relay. This also functions as muting.
There are three relays in total. One is used to prevent the rush current when the power supply is turned on, and the other two are used to prevent direct current at the muting and speaker terminals.

A forced-air cooling fan is installed inside.

Model Rating
Type Stereo power amplifier
Output 8 Ω (Rated Output, Both Channels, 20 Hz to 20 kHz) : 500W (250W + 250W), Typically 600W
Total harmonic distortion factor 0.05% or Less (20 Hz to 20000 Hz, both channels, at Rated Output)
Cross modulation distortion factor 0.05% or Less (at Rated Output, both channels, SMPTE)
Frequency characteristic 20 Hz to 20 kHz ± 0.1 dB
Power Band With (IHF) 5 Hz ~ 45000 Hz (THD 0.1%)
Input sensitivity 2.25 v for 250W into 8 Ω load with Gain Controls fully clockwise.
Input impedance 33k Ω with Gain Controls fully clockwise.
Damping factor 400 or higher
Total Noise Better than 106 dB below 250W Power (8 ohm Load)
<General>
Voltage Conversion Special tapped primary allows easy conversion to 110VAC or 220 VAC operation
Controls Independent front panel Gain Controls and Power Level Selector Switch
External dimensions Width 425x Height 171x Depth 435 mm
Weight 37.6kg