NTE823 データシートの表示（PDF） - NTE Electronics
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NTE823 Datasheet PDF : 3 Pages
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Application Hints:
To make the NTE823 a more versatile amplifier, two pins (Pin1 and Pin8) are provided for gain control.
With Pin1 and Pin8 open the 1.35kΩ resistor sets the gain at 20 (26dB). If a capacitor is put from Pin1
to Pin8, bypassing the 1.35kΩ resistor, the gain will go up to 200 (46dB). If a resistor is placed in series
with the capacitor, the gain can be set to any value from 20 to 200. Gain control can also be done
by capacitively coupling a resistor (or FET) from Pin1 to GND.
Additional external components can be placed in parallel with the internal feedback resistors to tailor
the gain and frequency response for individual applications. For example, we can compensate poor
speaker bass response by frequency shaping the feedback path. This is done with a series RC from
Pin1 to Pin5 (paralleling the internal 15kΩ resistor). For 6dB effective bass boost: R ≅ 15kΩ, the low-
est value for good stable operation is R = 10kΩ if Pin8 is open. If Pin1 and Pin8 are bypassed then
R as low as 2kΩ can be used. This restriction is because the amplifier is only compensated for closed–
loop gains than 9V/V.
Input Biasing:
Pin2 and Pin3 of the NTE823 are biased to GND with a 50kΩ resistor. The base current of the input
transistors is about 250nA, so the inputs are at about 12.5mV when left open. If the DC source resis-
tance driving the NTE823 is higher than 250kΩ it will contribute very little additional offset (about
2.5mV at the input, 50mV at the output). If the DC source resistance is less than 10kΩ, then shorting
the unused input to GND will keep the offset low (about 2.5mV at the input, 50mV at the output). For
DC source resistances between these values we can eliminate excess offset by putting a resistor
from the unused input to ground, equal in value to the DC source resistance. Of course all offset prob-
lems are eliminated if the input is capacitively coupled.
When using the NTE823 with higher gains (bypassing the 1.35kΩ resistor between Pin1 and Pin8)
it is necessary to bypass the unused input, preventing degradation of gain and possible instabilities.
This is done with a 0.1µF capacitor or a short to GND depending on the DC source resistance on the
driven input.
Pin Connection Diagram
Gain 1
(–) Input 2
(+) Input 3
GND 4
8 Gain
7 Bypass
6 VS
5 Vout
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