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AN142

AN142, ►Elektronika, ►Aplikacje
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INTEGRATED CIRCUITS
AN142
Audio circuits using the NE5532/3/4
author
1984 Oct
Philips Semiconductors
Application note
Audio circuits using the NE5532/3/4
AN142
AUDIO CIRCUITS USING THE NE5532/33/34
The following will explain some of Philips Semiconductors low noise
op amps and show their use in some audio applications.
actually five individual active filters with the same feedback design
for all five. The main difference in all five stages is the values of C5
and C6, which are responsible for setting the center frequency of
each stage. Linear pots are recommended for R9. To simplify use of
this circuit, a component value table is provided, which lists center
frequencies and their associated capacitor values. Notice that C5
equals (10) C6, and that the Value of R8 and R10 are related to R9
by a factor of 10 as well. The values listed in the table are common
and easily found standard values.
DESCRIPTION
The 5532 is a dual high-performance low noise operational amplifier.
Compared to most of the standard operational amplifiers, such as
the 1458, it shows better noise performance, improved output drive
capability and considerably higher small-signal and power
bandwidths.
This makes the device especially suitable for application in high
quality and professional audio equipment, instrumentation and
control circuits, and telephone channel amplifiers. The op amp is
internally-compensated for gains equal to one. If very low noise is of
prime importance, it is recommended that the 5532A version be
used which has guaranteed noise voltage specifications.
RIAA EQUALIZATION AUDIO PREAMPLIFIER
USING NE5532A
With the onset of new recording techniques with sophisticated
playback equipment, a new breed of low noise operational amplifiers
was developed to complement the state-of-the-art in audio
reproduction. The first ultra-low noise op amp introduced by Philips
Semiconductors was called the NE5534A. This is a single
operational amplifier with less than 4nV/
/
Hz input noise voltage. The
NE5534A is internally-compensated at a gain of three. This device
has been used in many audio preamp and equalizer (active filter)
applications since its introduction early last year.
Many of the amplifiers that are being designed today are
DC-coupled. This means that very low frequencies (2-15Hz) are
being amplified. These low frequencies are common to turntables
because of rumble and tone arm resonances. Since the amplifiers
can reproduce these sub-audible tones, they become quite
objectionable because the speakers try to reproduce these tones.
This causes non-linearities when the actual recorded material is
amplified and converted to sound waves.
The RIAA has proposed a change in its standard playback response
curve in order to alleviate some of the problems that were previously
discussed. The changes occur primarily at the low frequency range
with a slight modification to the high frequency range (See Figure
2). Note that the response peak for the bass section of the playback
curve now occurs at 31.5Hz and begins to roll off below that
frequency. The roll-off occurs by introducing a fourth RC network
with a 7950
m
s time constant to the three existing networks that
make up the equalization circuit. The high end of the equalization
curve is extended to 20kHz, because recordings at these
frequencies are achievable on many current discs.
APPLICATIONS
The Philips Semiconductors 5532 High-Performance Op Amp is an
ideal amplifier for use in high quality and professional audio
equipment which requires low noise and low distortion.
The circuit included in this application note has been assembled on
a PC board, and tested with actual audio input devices (Tuner and
Turntable). It consists of an RIAA (Recording Industry Association of
America) preamp, input buffer, 5-band equalizer, and mixer.
Although the circuit design is not new, its performance using the
5532 has been improved.
The RIAA preamp section is a standard compensation configuration
with low frequency boost provided by the Magnetic cartridge and the
RC network in the op amp feedback loop. Cartridge loading is
accomplished via R1. 47k was chosen as a typical value, and may
differ from cartridge to cartridge.
The Equalizer section consists of an input buffer, 5 active variable
band pass/notch (depending on R9’s setting) filters, and an output
summing amplifier. The input buffer is a standard unity gain design
providing impedance matching between the preamplifier and the
equalizer section. Because the 5532 is internally-compensated, no
external compensation is required. The 5-band active filter section is
C5
Equ In
5
RIAA Out
+
RIAA
C1
3
7
R7
R8
R7
+
1/2 5532
1
R5
6

1/2 5532
R1
2

R5
R9
C6
R9
R11
R2
R3
2

1/2 5532
+
C7
1
R10
6
FLAT
C2
C3

1/2 5532
TO VOL./
BAL AMP
3
7
+
5
+
EQUALIZE
R4
C4
REPEAT ABOVE CIRCUIT
FOR DESIRE NO. OF
STAGES.
R12
SL00850
Figure 1. RIAA - Equalizer Schematic
1984 Oct
2
August 1988 Rev: 2
Philips Semiconductors
Application note
Audio circuits using the NE5532/3/4
AN142
COMPONENT VALUES FOR FIGURE 1
R8=25k
R7=2.4k R9=240k
R8=50k
R7=5.1k R9=510k
R8=100k
R7=10k R9=1meg
f
O
C5
C6
f
O
C5
C6
f
O
C5
C6
23Hz
1
m
F
0.1
m
F
25Hz
0.47
m
F
0.047
m
F
12Hz
0.47
m
F
0.047
m
F
50Hz
0.47
m
F
0.047
m
F
36Hz
0.33
m
F
0.033
m
F
18Hz
0.33
m
F
0.033
m
F
72Hz
0.33
m
F
0.033
m
F
54Hz
0.22
m
F
0.022
m
F
27Hz
0.22
m
F
0.022
m
F
108Hz
0.22
m
F
0.022
m
F
79Hz
0.15
m
F
0.015
m
F
39Hz
0.15
m
F
0.015
m
F
158Hz
0.15
m
F
0.015
m
F
119Hz
0.1
m
F
0.01
m
F
59Hz
0.1
m
F
0.01
m
F
238Hz
0.1
m
F
0.01
m
F
145Hz
0.082
m
F
0.0082
m
F
72Hz
0.082
m
F
0.0082
m
F
290Hz
0.082
m
F
0.0082
m
F
175Hz
0.068
m
F
0.0068
m
F
87Hz
0.068
m
F
0.0068
m
F
350Hz
0.068
m
F
0.0068
m
F
212Hz
0.056
m
F
0.0056
m
F
106Hz
0.056
m
F
0.0056
m
F
425Hz
0.056
m
F
0.0056
m
F
253Hz
0.047
m
F
0.0047
m
F
126Hz
0.047
m
F
0.0047
m
F
506Hz
0.047
m
F
0.0047
m
F
360Hz
0.033
m
F
0.0033
m
F
180Hz
0.033
m
F
0.0033
m
F
721Hz
0.033
m
F
0.0033
m
F
541Hz
0.022
m
F
0.0022
m
F
270Hz
0.022
m
F
0.0022
m
F
1082Hz
0.022
m
F
0.0022
m
F
794Hz
0.015
m
F
0.0015
m
F
397Hz
0.015
m
F
0.0015
m
F
1588Hz
0.015
m
F
0.0015
m
F
1191Hz
0.01
m
F
0.001
m
F
595Hz
0.01
m
F
0.001
m
F
2382Hz
0.01
m
F
0.001
m
F
1452Hz
0.0082
m
F
820pF
726Hz
0.0082
m
F
820pF
2904Hz
0.0082
m
F
820pF
1751Hz
0.0068
m
F
680pF
875Hz
0.0068
m
F
680pF
3502Hz
0.0068
m
F
680pF
2126Hz
0.0056
m
F
560pF
1063Hz
0.0056
m
F
560pF
4253Hz
0.0056
m
F
560pF
2534Hz
0.0047
m
F
470pF
1267Hz
0.0047
m
F
470pF
5068Hz
0.0047
m
F
470pF
3609Hz
0.0033
m
F
330pF
1804Hz
0.0033
m
F
330pF
7218Hz
0.0033
m
F
330pF
5413Hz
0.0022
m
F
220pF
2706Hz
0.0022
m
F
220pF
10827Hz
0.0022
m
F
220pF
7940Hz
0.0015
m
F
150pF
3970Hz
0.0015
m
F
150pF
15880Hz
0.0015
m
F
150pF
11910Hz
0.001
m
F
100pF
5955Hz
0.001
m
F
100pF
23820Hz
0.001
m
F
100pF
14524Hz
820pF
82pF
7262Hz
820pF
82pF
17514Hz
680pF
68pF
8757Hz
680pF
68pF
21267Hz
560pF
56pF
10633Hz
560pF
56pF
12670Hz
470pF
47pF
18045Hz
330pF
33pF
–25
–20
OLD RIAA
–15
–10
–5
NEW RIAA
0
(db)
5
10
15
20
25
30
1
10
100
(HZ)
1K
10K
100K
SL00851
Figure 2. Proposed RIAA Playback Equalization
1984 Oct
3
Philips Semiconductors
Application note
Audio circuits using the NE5532/3/4
AN142
–15V
.1
m
F
.27
m
F

INPUT
+
3
8
TO LOAD
47K
NE5532A
1
2
4
+

.1
m
F
–15V
49.9K
+
SL00853
49.9
Figure 4.
Assume a signal input square wave with dV/dt of 250V/
m
s and 2V
peak amplitude as shown. If a 22pF compensation capacitor is
inserted and the R
1
C
1
circuit deleted, the device slew rate falls to
approximately 7V/
m
s. The input waveform will reach 2V/250V/
m
s or
8ns, while the output will have changed (8
×
10
-3
) only 56mV. The
differential input signal is then (V
IN
-V
O
) R
I
/R
I
+R
F
or approximately
1V.
The diode limiter will definitely be active and output distortion will
occur; therefore, V
IN
<1V as indicated.
Next, a sine wave input is used with a similar circuit.
The slew rate of the input waveform now depends on frequency and
the exact expression is
dv
dt
2 cos t
.056
m
F
4.99K
47
m
F
.015
m
F
NOTE:
All resistors are 1% metal film.
SL00852
Figure 3. RIAA Phonograph Preamplifier Using
the NE5532A
NE5533/34 DESCRIPTION
the 5533/5534 are dual and single high-performance low noise
operational amplifiers. Compared to other operational amplifiers,
such as TL083, they show better noise performance, improved
output drive capability and considerably higher small-signal and
power bandwidths.
This makes the devices especially suitable for application in high
quality and professional audio equipment, instrumentation and
control circuits, and telephone channel amplifiers.
The op amps are internally-compensated for gain equal to, or higher
than, three. The frequency response can be optimized with an
external compensation capacitor for various applications (unity gain
amplifier, capacitive load, slew rate, low overshoot, etc.) If very low
noise is of prime importance, it is recommended that the
5533A/5534A version be used which has guaranteed noise
specifications.
The upper limit before slew rate distortion occurs for small-signal
(V
IN
<100mV) conditions is found by setting the slew rate to 7V/
m
s.
That is:
7 x 10
6
V
s
2
cos
t
at
w
t = 0
LIMIT
7x10
6
2
3.5x10
6
rad
s
f
LIMIT
3.5x10
6
2
560kHz
APPLICATIONS
Diode Protection of Input
The input leads of the device are protected from differential
transients above
±
0.6V by internal back-to-back diodes. Their
presence imposes certain limitations on the amplifier dynamic
characteristics related to closed-loop gain and slew rate.
Consider the unity gain follower as an example:
1984 Oct
4
Philips Semiconductors
Application note
Audio circuits using the NE5532/3/4
AN142
dV/dt
External Compensation Network Improves
Bandwidth
By using an external lead-lag network, the follower circuit slew rate
and small-signal bandwidth can be increased. This may be useful in
situations where a closed-loop gain less than 3 to 5 is indicated. A
number of examples are shown in subsequent figures. The principle
benefit of using the network approach is that the full slew rate and
bandwidth of the device is retained, while impulse-related
parameters such as damping and phase margin are controlled by
choosing the appropriate circuit constants. For example, consider
the following configuration:
+2
–2V
V
IN
= 2 Sin
w
t
1K
1K
22pF
NE
5534
SL00854
Figure 5.
R
f
5
22pF
Rj

2
2V
C
C
0
8
R1
NE
5534
0
6
–V
O
C1
–V
i
3
+
D
t
1
D
t
2
SL00855
Figure 6.
1
GAIN
90
1K

R
LAG
NETWORK
NE5534
45
C
+
SL00856
0
Figure 7.
0
0.1
1.0 10 50
MHz
SL00857
Figure 8.
1984 Oct
5
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