NKI1480B DAX60 and DAX120 Amplifiers—Installation
Page 15 of 18 (Jul-98)
Input and preamplifier circuits: Resistor R1 and Capacitors Cl and C507 filter
Radio Frequency Interference (RFI). RV1 is the input LEVEL control
(potentiometer), which controls the signal that is applied to the preamplifier
circuits. Capacitors C2 and C9 govern the low-frequency response of the input
signal, to protect horn-type speakers. Transistor Qi is a common-emitter amplifier
that provides the preamplifier gain. It is also a common-base inverter for the
feedback entering its emitter. Q2 is an emitter follower.
Power-amplifier circuits: Transistor Q3 is a high-voltage-gain amplifier that drives
Transistors Q5 and Q6. The latter, operating as phase splitters in a unity-gain
configuration, provide the drive for Transistors Q505 and Q506. Q505 and Q506
are the drivers for the output transistors (Q501-Q504). Diode D503 is a negative-
temperature-coefficient device mounted on the heat sink. This diode controls the
DC bias for the driver and output transistors. Transistors Q501 through Q504 are
push-pull power amplifiers that drive the output transformer. Capacitor C505
blocks DC from the output transformer and limits he low-frequency output to
protect horn-type speakers.
Protective circuits: There are several protections against excessive current.
Transistors Q4 and Q7 are current limiters. If a short occurs across the audio
output, the following sequence of events will occur: (1) the DC voltage across
Resistors R29 and R32 will drop; (2) this drop will drive Transistors Q4 and Q7
into conduction; (3) the output of Q4 and Q7 will limit the drive to Transistors Q5
and Q6; and (4) the reduced output from Q5 and Q6 to the power transistors will
reduce the overall gain (and, thereby, the total power) of the amplifier. An
excessive current surge will cause the fuse to open. In the 28-VDC supply, a short
circuit on the DC output or a DC load that draws significantly more current than
1.2 Amperes will cause Thermal Breaker CB2 to open within 70 seconds. It will try
to reset within 15 seconds, then continue opening and closing until the short or the
excessive load is removed, at which time it will remain closed for normal
operation. A more serious problem will cause CB1 to open; it must be reset
manually.
Specifications
DAX6O: 60 watts RMS
Rated Power Output
DAX12O: 120 watts RMS
Frequency Response
+-1.5 dB from 40 Hz to 15 kHz at -3 dB from RPO.
Harmonic Distortion
Less than 3% from 60 Hz to 15 kHz
Noise Level
84 dB with LEVEL control at maximum setting 90dB
with LEVEL control at minimum setting
Input Impedance
13 kilohms
Input Sensitivity for Rated
Power Output
0.3 V
Power Requirements
DAX6O: 105-130 VAC, 60 Hz, 935 watts
(including the AC and DC outputs)
DAX12O: 105-130 VAC, 60 Hz, 1105 watts (including
the AC and DC outputs)
Auxiliary DC Output
Supplies 1.2 Amperes at 28 VDC
DAX60
DAX120
No Signal
12 Watts
12 Watts
AC Power Consumption
(28 VDC Auxiliary Output
Disconnected)
1/3 RPO
105 Watts
210 Watts
