The Model 510 is one
of marantz's newest amplifiers in the medium to high power range, continuing
their 500 series, and its styling is typical of recent products from this
company. The front panel of the basic model contains two level controls, a
power switch, and peak indicators; included in the "M" version we
tested are two large, illuminated meters and a meter range switch.
The unit is well
made and very compact, with a large encapsulated power transformer, two filter
capacitors, and the cooling tunnel occupying the majority of the chassis
interior. Inside the tunnel are 16 output transistors, each having a small
staggered-fin radiator, across which cooling air is drawn from a
temperature-controlled two-speed fan. Mounted on either side of the tunnel are
the amplifier boards, which allows the transistor pins to solder directly to
the printed conductors, thereby saving both space and considerable chassis
wiring. The top cover is perforated and has a foam air filter mounted to its
underside to keep dust and other debris from being drawn into the box. Marantz
recommends periodic cleaning; this is easily accomplished by vacuuming the top
surface of the amplifier. Mounting and installation of the unit is
straightforward, widh details in the owner's manual.
Several inches
should be allowed atop the amplifier installation for it to draw cool air, and
an opening is similarly required behind the fan for warm air exhaust. All
connections are made to the rear panel. Speaker jacks are the five-way binding
post type, and inputs are 1/4-inch phone plugs. provided with the amplifier are
adaptors to convert the inputs to the more common RCA jacks.
Marantz tells us
their design intent on the peak load indication system was to indicate the
approach of clipping on peak transients, rather than an actual clipping
situation. Thus, the system should not be considered as indicating an overdrive
situation, as the LEDs will light up before actual clipping. the system tracks
the power supply voltage so it will always give the same warning margin that
clipping is approaching, regardless of the AC power line variations. While the
circuit turns on in microseconds, the "hold" portion of the circuit
keeps the LEDs lit long enough so they can be seen by the eye. The system
indicates an actual overload condition by staying on more or less continually.
Thus, 510 users should consider
occasional flashing of the LEDs as full use of the normal operating range.
Circuit Description
Suitably attenuated input signals are a.c.
coupled to the unity gain buffer amplifier, which uses Q301 and Q302 in a
circuit often called an amplifier emitter follower. This stage exhibits a high
input impedance which minimizes the the loading on the gain control and the
preamplifier. Minimum input impedance for the 501 is approximately 31 kilohms,
so preamp manufactures' specifications should be checked to ensure
compatibility, especially if vacuum tube preamp models are used.
Capacitor C307
couples the buffer amplifier to the noninverting input of the differential
amplifier Q304 and Q306, and feedback is applied as usual to the inverting
input. Marantz has used an uncommon but simple circuit to combine both phases
of output signal from the input stage, while also getting the ability to pull
the driver stage hard in either the positive or negative direction. Transistor
Q307 is the key to this circuit; it is connected as a common emitter amplifier
to get the necessary signal inversion and voltage translocation, but
degenerated to a gain slightly less than 1, in order to match its
characteristics to its mate, Q308, conected as an emitter follower. It can be
shown that the driving signal at the collectors of Q309 and Q310 will be
relatively free of even harmonics by nature, if the transistors are chosen
carefully and the resistors involved are properly balanced.
The output stage and
its drivers are straightforward, being similar in design to those of other high
quality amplifiers currently in production. Eight output transistors are used
per channel in a complimentary, series-parallel arrangement. Such a design allows
the use of low voltage expitaxial base devices, giving the composite stage a very good safe operating area
(especially important with reactive loads such as electrostatic speakers) and
good current linearity as well.
V-1 limiting is
employed for protection, but its action is not instantaneous, so short duration
transient will not trigger unnecessary limiting. Capacitors C315 and C316 are
used to accomplish this effect
Specifications
Power Output:
256 continuous
average watts per channel, into 8 ohms from 20 Hz to 20
kHz with 0,05% THD.
350 average watts
per channel, with similar conditions except 4 ohm loads with 0,10% THD
140 average watts
per channel with similar conditions except 16 ohm loads with 0,10% THD
Intermodulation
Distortion: less than 0,1% at or below
rated power using SMPTE method
One-Watt Frequency
Response: -3 dB at 2 Hz and 120 kHz
Input
Sensitivity: 2,26V RMS for 256 W into 8
ohms
Input
Impedance: 25 kohms, not afected by gain
control setting
Slew
Rate: ±15 V/μS.
Hum and Noise: -110 dB below rated output, 8 ohms
Damping Factor: Greater than 100 at 1 kHz, 8 ohm load.
Phase Shift: leading 9 degrees at 20 Hz, lagging 10
degrees at 20 kHz
Dimensions
(W x H x D): 390,4 x 155,5 x 355,6 mm
(15⅜ x 6⅛ x 14 inch)
Weight: 20,7 kg (46 lbs)