National Semiconductor's
LM833: a new dual low
noise operational amplifier
National Semiconductor describe the LM833 as a
"dual general purpose operational amplifier with
particular emphasis on performance in audio
systems". It is largely responsible for the
outstanding performance of our Studio 200 stereo
control unit.
By LEO SIMPSON
Although not strictly new, the
LM833 is a new device to most
audio enthusiasts and the latest
available data (1988 edition) on it
from National Semiconductor is
still classed as preliminary; so it is
new. However, it is already being
used in large numbers, in the audio
output stages of several compact
disc players sourced from Japan.
National Semiconductor claim
that the IC uses new circuit and
processing techniques to deliver
low noise, high speed and wide
bandwidth, without increasing external components or decreasing
stability. It is therefore ideal for use
in the preamplifier and high level
audio stages of hifi equipment.
As shown in the schematic
diagram, the LM833 is a bipolar input op amp (as shown by the PNP
bipolar differential input stage). Its
input bias currents are actually
higher than with run-of-the-mill op
amps (such as the 741), being 500
nanoamps (typical) and lmA (maximum). It has low input offset
voltage (0.3mV) and low input offset
current (20nA). Its open-loop
voltage gain is typically 11 0dB and
it is intended for operation from the
usual ± 15V supplies.
The internal 15pF capacitor compensates it for all closed loop gains
(presumably down to unity gain) but
it has a relatively high slew rate of
7 volts per microsecond which is
more than ten times that of the 741.
Its gain bandwidth product is
+Vcc-----1-------------8
Fig.1: the schematic diagram, showing one op amp in the LM833 package.
50
SILICON CHIP
Fig.2: the pinout diagram for the
LM833 dual op amp package.
typically 15MHz (10MHz minimum)
while its power bandwidth is
120kHz.
Its outstanding parameter is its
low input noise voltage which is
typically 4.5nV/root Hz. This compares very favourably with the
familiar Signetics 5534 low noise op
amp with an input noise voltage of
4nV/root Hz (the 5534A input noise
voltage is typically 3.5nV/root Hz).
As a further comparison of specs,
the LM833 is slightly better than
the Signetics 5532 dual low noise op
amp and slightly inferior to the
5534 single op amp.
Just in case we seem to be making
unfair comparisons with the 5534
and its kin, the LM833 does not
have the 5534's ability to drive a
6000 load. Instead, its performance
is characterised for the more usual
minimum load of 2k0.
Other parameters which are
significant in making the LM833 an
important newcomer to audio
equipment are its high power supply rejection ratio (PSRR) of 100dB
and also its common-mode rejection
ratio (CMRR) of to0dB. Again, these
are typical figures. Crosstalk between the two op amps in the
package is quoted as - 120dB from
20 to 20kHz, which is excellent.
Harmonic distortion is quoted as
.002 % , from 20Hz to 20kHz. Our
DC Electrical Characteristics (TA=
Symbol
25•c. vs = ±15vJ
Parameter
Conditions
Min
Vos
Input Offset Voltage
los
Input Offset Current
Is
Input Bias Current
Av
Voltage Gain
RL = 2 kn, Vo = ± 10V
VoM
Output Voltage Swing
RL = 10kD.
RL = 2 kD.
Typ
Rs = 10D.
Max
Units
0.3
5
mV
10
200
nA
500
1000
nA
90
110
dB
±12
±10
±13.5
± 13.4
V
V
VcM
Input Common-Mode Range
±12
±14.0
V
CMRR
Common-Mode Rejection Ratio
V1N = ±12V
80
100
dB
PSRR
Power Supply Rejection Ratio
Vs = 15-5V, -15- -5V
80
100
dB
la
Supply Current
Vo = 0V, Both Amps
AC Electrical Characteristics (TA =
Symbol
8
mA
25•c, vs = ± 15v, RL = 2 kn)
Conditions
Parameter
5
Min
Typ
Max
Units
SR
Slew Rate
RL = 2 kD.
5
7
V/µs
GBW
Gain Bandwidth Product
f = 100kHz
10
15
MHz
Design Electrical Characteristics (TA =
25•c, vs = ± 15VJ
The following parameters are not tested or guaranteed.
Conditions
Symbol
Parameter
t:.Vos/t:.T
Average Temperature Coefficient
of Input Offset Voltage
THD
Distortion
RL = 2 kD., f = 20 - 20 kHz
VouT = 3 Vrms, Av = 1
en
Input Referred Noise Voltage
Rs = 100n, f = 1 kHz
Typ
Units
2
µVl°C
0.002
%
4.5
nV/,/Hz
pA/,/Hz
in
Input Referred Noise Current
f = 1 kHz
0.7
PBW
Power Bandwidth
Vo= 27Vpp, RL = 2kD., THD,;; 1%
120
kHz
fu
Unity Gain Frequency
Open Loop
9
MHz
60
deg
-120
dB
</>M
Phase Margin
Open Loop
Input Referred Cross Talk
f = 20-20 kHz
Note 1: If supply voltage is less than ± 1SV, it is equal to supply voltage.
Note 2: This is the permissible value at TA
experience with the Studio 200 indicates that typical devices easily
meet these specs and we would not
be surprised to find that, when National Semiconductor finalises its
data on the device, it will be effectively upgraded.
Fig.3 shows National Semiconductor's RIAA preamp application
circuit for the LM833 and it is very
close to that used in the Studio 200.
Our performance results were also
very close to those claimed by
National.
The main difference in the Studio
200 circuit (presented last month) is
in the RF suppression components
at the input and the manner of provision of the 50k0 load for the cartridge (using a 100k0 resistor either
side of the bipolar input capacitor).
National's LM833 is not the
s::
85°C.
10 µF
·i1
1"100µF
Fig.3: National Semiconductor's suggested circuit for a phono
preamplifier with standard RIAA equalisation. Voltage gain is 35dB at
1kHz and claimed signal-to-noise ratio is 90dB A-weighted with
respect ot 10mV input at 1kHz.
quietest, fastest, lowest distortion
or most stable op amp released in
recent times but considering its
overall performance, it must stack
up as one of the best value op amp
packages available. We predict
that it will become extremely
popular.
~
JULY
1988
51
