Nakamichi 620 User manual

‘= 620
Power
Amplifier
Operating
Instructio

WARNING
TO PREVENT FIRE OR SHOCK
HAZARD, DO NOT EXPOSE THIS
APPLIANCE TO RAIN OR MOISTURE
Please record the Model Number and
Serial Number in the space provided
below and retain these numbers.
Model Number and Serial Number are
located on the rear panel of the unit.
Model Number : Nakamichi 620
Serial Number :
CONTENTS:
Control FUNCTIONS —..-.-.eecsceeececereeeees 1,2
PrECAUtIONS
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2
CONNECTIONS vsere-seeseeeeeeereeetereescrreeeenenscees 3
Using
the
620
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4
Block
Diagrams
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5
Troubleshooting
Chart
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6
Performance
Data
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7
Specifications, Accessories +--+ 8

We thank and congratulate you for purchasing
this Nakamichi 620 Power Amplifier.
lf you are a previous Nakamichi customer,
it will be no surprise to you that you own
one of the very best power amplifiers
available now and for many years to come.
If the 620 is your first Nakamichi,
we hope it wil! lead you to an understanding of
our underlying philosophy:
to create only those products
that only Nakamichi can create.
To ensure that you fully realize the capabilities of your 620,
we ask that you carefully read
this manual in its entirety before attempting operation.
NAKAMICHI RESEARCH, INC.

Control Functions
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———. PRIMARY FUSE -
——— AC POWER CORD
Precautions
Since the 620 is capable of delivering
momentary power levels of up to 250
watts per channel into 8 ohm Loud-
speakers, it is strongly advised that you
observe the following precautions:
1. Make sure that the AC Power to the
620 is “off” before attempting any of
the interconnections.
2. The 620 has been designed with a
power supply of tremendous energy
storage capacity for superb low fre-
quency performance. The power
supply, therefore, may continue to
energize the 620’s amplification cir-
cuits for as long as five minutes after
the power has been turned off. If in-
put connections to the 620 are to be
altered immediately after turning off
the power, disconnect the loud-
speakers first.
3. Although the 620 is fully protected
against short-circuited outputs, take
care to avoid shorting the output
wires. A prolonged short circuit will
cause excessive heat dissipation.

Connections
1. Preamplifier or Control
Amplifier
Using a standard phono plug type stereo
connecting cable, connect the preampli-
fier output to the Input jacks on the rear
panel of the 620. If the 620 is to be used
with the Nakamichi 610 Control Pre-
amplifier, utilize the “Monitor Out”
jacks on the 610. ,
2. Loudspeakers
Connect the left and right loudspeakers
to the appropriate terminals on the rear
panel of the 620.
NOTE:
(1) Observe the polarity at the power
amplifier and loudspeaker termi-
nals. Both loudspeakers should be
connected in the exactly same man-
ner.
(2) Although the 620 is virtually unaf-
fected by small capacitances and/or
DC resistances at its outputs, overall
loudspeaker performance may be
slightly degraded by the use of light
gauge speaker wire. Heavy duty
speaker wire is highly recommended.
3. RM-610 Remote Control Unit
Remote selection of up to three loud-
speaker pairs becomes possible when the
620 is used in conjunction with the Naka-
michi 610 Control Preamplifier and the
RM-610 remote control unit. Refer to the
610’s Operating Instructions.
Caution: The 620 has been designed to
operate into load impedances
of 4 ohms or greater. Make
sure that the loudspeaker im-
pedance, or the combined
equivalent impedance of any
loudspeaker combination for
either channel, is 4 ohms or
higher.
RM-610 Remote Control Unit
Nakamichi 620
4. AC Power
The AC Power Cord of the 620 may be
plugged into the switched outlet on the
preamplifier or control amplifier in use.
In this manner, by leaving the power
switch of the 620 “‘on’”’ the AC Power to
the 620 will be controlled by the Power
Switch on the preamplifier. Make sure
that the switched outlet on the preamplli-
- fier is rated at 300 VA or higher (the 620
may be connected to one of the auxiliary
outlets of the 610).:
Nakamichi 610
Loudspeaker System
Loudspeaker System 1
Loudspeaker System 2
Loudspeaker System 3
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Nakamichi 610
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There are no controls that need to be
adjusted on the 620. In normal use all
adjustments, such as listening level or
channel balance, are made with the con-
trols of the preamplifier or control
amplifier. The only features on the front
panel of the 620 are indicator lamps
inset into the heat sink fins. The pilot
lamp to the right will glow orange when
the power to the 620 is turned on. The
two Peak Power Indicating Lamps to the
left will glow green and red to show that
certain output power levels have beer re-
ached. The power points at which these
lamps will glow can be preset using the
Power Indicator Threshold Selector
Switches on the rear panel of the 620.
The switch marked “Low” sets the point
at which the lamps will glow green. The
choices are 1, 5 and 25 Watts (ref. 8 ohm
load).. The switch marked “High” sets the
red indication for 25, 50 or ““Max’’ Watts
(ref. 8 ohm load). When the latter switch
is set for “Max”, the red will indicate
amplifier clipping, which will occur at
110 to 130 Watts per channel with an 8
ohm load. If both switches are set for 25
Watts, the Peak Power Indicator Lamps
will glow red only at that power point.
Set the “Low” and “‘High’’ Threshold
Selector Switches as required for normal
listening levels. For example, red may be
set to show a power level which most
closely approximates the peak power
handling capacity of the loudspeakers.
Green can be set to indicate an inter-
mediate power level that is frequently
reached in normal listening.
NOTE:
(1)
(2)
The power level indications on the
Threshold Selector Switches are ac-
curate only for an 8 ohm load. If a
16 ohm loudspeaker is to be used,
divide the indicated power levels by
two. Load impedances between 4
and 8 ohms will also require minor
correction of the indications in that
the actual power levels will be slight-
ly higher than the preset indications.
The Peak Power Indicating Lamps
are extremely fast in responding to
transient signals. A 0.1. millisecond
power pulse will cause the peak in-
dicator to light and stay “on” for
0.3 second so that the peak can be
readily observed. These lamps are
Using the 620
capable of responding to power
“spikes’’ that escape measurement
on the best peak reading meters. Do
not be surprised, therefore, if the
Red Clipping Indicator (i.e. when
the ‘“‘High’’ threshold switch is set for
Max") comes on more frequently
than expected. Momentary clipping
of this nature does the amplifier and
loudspeakers no harm. The 620’s
overload characteristics. are such,
furthermore, that transient clipping
is impossible to detect by ear with
the vast majority of program materi-
al. This is why the Peak Power Indi-
cator Lamps were designed into the
620.

Block Diagram
output
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(5A) 100W 80hm
volt power
select. supply

Condition
Troubleshooting Chart
Probable Cause
Remedy
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No power.
1. Power switch is off.
2. Fuse is blown.
1. Make sure rear panel Power
Switch is on.
2. Replace primary fuse with fast
acting 5 A fuse (3 A for 220/240 V
use).
i
No output.
1. Poor input connections.
2. Poor loudspeaker connections.
1. Check all connections from
preamplifier.
2. Check all speaker wire termina-
tions.
A
Channels reversed or one channel dead.
1. Improper input connections.
2. Improper loudspeaker wiring.
1. Correct input wiring.
2. Correct loudspeaker wiring.
i
No peak power indications.
Inappropriate threshold settings.
Reset Threshold Selector Switches.
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Note:
The 620 is equipped with a thermal
protection circuit which protects the unit
from damage caused by excessively high
operating temperatures. The circuit will
‘disconnect the power to the amplifier
when the output transistors reach an
operating temperature of 80°C (176°F).
“This rarely occurs under normal use with
loudspeakers rated at 4 ohms or higher, but
an accidental short circuit, for example,
may cause the protection circuit to shut
down the amplifier. In the event that the
protection circuit is activated, turn down
the volume control, and turn off the
power switch. Check all wiring to make
sure there are no short circuits. The
protection circuit will automatically reset
once the amplifier has cooled to a safe
temperature.
SERVICE INFORMATION
Please read all Notices and/or Warranty
Cards included with this unit.
Although it is unlikely that your 620 will
require repair, should servicing ever be-
come necessary, please refer all such work
to qualified personnel. As there are no
user serviceable parts inside the unit,
please do not attempt your own repairs.
Thank you for your confidence in Naka-
michi products.

Performance Data
Output vs Total Harmonic
Distortion
1kHz
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|
1OKHZ
Frequency
vs
Total
Harmonic
Load imp: 8 ohms Distortion
400Hz H.P. Output: 100 Watts Constant
80kHz L.P. Load Imp: 8 ohms
RO *
HHH
nd
° ij
LTH
tH—t-H
=
Total Harmonic Distortion (%)
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Total Harmonic Distortion (%)
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4
6
10
4
6
100
ik
2.
4
6
10k
Output
Power
(Watts,
Frequency
(Hz)
Output vs Harmonic Distortion
Frequency:
1kHz
Output
Power
vs
1M
Distortion
Load Imp: 8 ohms 60Hz : 7kHz (4: 1)
Distortion (%)}
IM Distortion (%)
2 4610 2 4 6 100
Output Power (Watts)
The distortion data immediately above was obtained with the aid of
a Bruel & Kjaer 3348 Real Time Analyzer. These measurements cannot Tr
be made with conventional distortion analyzers because of noise
factors.
46 10 2 4 6 100 2 4
Output Power (Watts)

Specifications
3
Power SOULCE --sseseseeseeererenreereeeeees
Power Consumption ----e-eeeeeeeee
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IHF Power Bandwidth «....--
(both channels driven)
Damping
Factor
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Total
Harmonic
Distortion
+--+
Intermodulation Distortion ++
Frequency
Response
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Input
Impedance
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Residual Noise Level --+resrseees
Signal-to-Noise Ratio srr
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Peak Power Indicators srr:
Specifications, Accessories
100/120/220/240 V AC, 50/60 Hz
50 VA at idling
700 VA with both channels driven to
clipping into 8 ohm loads
100 Watts per channel minimum contin-
uous sine wave ("RMS") at 8 ohms,
5—20,000 Hz with less than 0.01% THD
50 Watts per channel at 16 ohms
5—50,000 Hz for less than 0.1% THD
5--20,000 Hz for less than 0.01% THD
5—10,000 Hz for less than 0.005% THD
Greater than 100 (1 KHz, 8 ohms)
Less than 0.002% @ 1 KHz or below
Less than 0.005% @ 10 KHz or below
Less than 0.002% (60 Hz: 7 KHz,
4:1, 8 ohm load, 100 W output)
5 — 100,000 Hz +0, -1 dB
10 K ohms
Less than 0.05 mV (IHF A Network)
Less than 0.1 mV (linear)
Better than 120 dB at rated output
(IHF A, input shorted)
Better than -70 dB @ 1 KHz
Green at 1 W, 5 W, 25 W, setectable
Red at 25 W, 50 W, Maximum (110—130 W)
selectable (Response time: responds to 0.1 ms
pulse — off after 0.3 sec)
Integrated Circuits: 3
Transistors: 46
Diodes: 41
15.75" (W) x 7.44"(H) x 9.76'(D)
400 mm(W) x189 mm(H) x 248 mm(D)
27.6 Ib (12.5 kg)
© Specifications and appearance design are subject to change for further
improvement without notice.
Dimensions
1)
j-______.4a0( 1894”)
i
+ !89( 776") +
7
Bridging Adaptor BA-100
Permits the use of he Nakamichi 620 as a
Balanced Transformerless (BTL) monau-
ral power amplifier delivering a minimum
of 350 watts continuous sine wave into 8
ohms with otherwise no change in perfor-
mance specifications. For use with loud-
speaker systems rated at 8 ohms or higher
only.
OPTIONAL ACCESSORIES
NAKAMICHI SYSTEM ONE
(Custom Rack Mounted 600 Series Com-
ponents)
With the introduction of the 620 Power
Amplifier, Nakamichi offers a custom
rack mount for the 600 Series Compo-
nents. The SYSTEM ONE module con-
sists of the Nakamichi 600 Cassette Con-
sole, the 610 Control Preamplifier, the
620 Power Amplifier, and a unique mul!ti-
function digital program timer.
Digital Timer
600B
Black Version
610B
Black Version
248(9%")