that1512 THAT Corporation, that1512 Datasheet - Page 5

• Manufacturer Part Number: that1512
• Description: Low Noise, High Performance Audio Preamplifier Ic
• Manufacturer: THAT Corporation

Document 600031 Rev. 04
static discharge (ESD) or electrical over stress (EOS)
will damage the ICs.
base-emitter junctions of the input transistors pre-
vent excessive reverse biasing of these junctions
(which would degrade the noise performance of the
input devices).
odes, the 1510/1512 input pins are connected only to
the bases of their respective input devices.
proper operation, the bases must be provided a
source of dc bias that will maintain the inputs within
the IC’s input common-mode range. Two different
schemes for this are shown in Figures 2 and 3. Fig-
ure 2 is simple, but its output will need to be
ac-coupled to the next stage, particularly if R
able to allow gain adjustment. Figure 3 shows the
addition of an integrator to servo the output offset. In
this circuit, the output offset will depend on that of
the external opamp U2, which may be small enough
to avoid ac-coupling the output.
are small to minimize pickup of unwanted noise and
interference. 1kW is often used, which yields a differ-
ential input impedance of 2kW, often considered to
be ideal for many microphones.
3. In revisions 0 and 1 of this data sheet, we recommended using Schottky diodes (1N5819 types) to protect the 1510/1512 inputs against overloads.
Other than the connection to the protection di-
Note that the values of R1 and R2 in these figures
Subsequently, we discovered that the leakage of these diodes could cause problems with DC at the 1510/1512 output. Upon further investigation, we
believe that conventional rectifier diodes like 1N4004 provide adequate protection and do not introduce unacceptable leakage. Additionally, 1N4004
diodes are much cheaper and more readily available than the Schottky types.
-In
+In
THAT Corporation; 45 Sumner Street; Milford, Massachusetts 01757-1656; USA
C1
470p
C2
470p
Tel: [phone]; Fax: [phone]; Web: www.thatcorp.com
Other diodes across the
47p
C3
R1
1k
Figure 3. 1510 / 1512 Circuit with Output Offset Servo
R2
1k
Copyright © 2007, THAT Corporation
RG
G
is vari-
+In
-In
100n
RG2
RG1
For
C9
-15
+15
V-
V+
100n
Ref
C6
Phantom Power
microphones. THAT recommends the circuit of Fig-
ure 4 when phantom power is included
are used to limit the current that flows through the
bridge circuit of D1 through D4 when C4 and C5 are
discharged after being charged to 48V from the phan-
tom voltage supply. R3 and R4 should be kept very
small as shown in order to introduce minimal addi-
tional noise. C4 and C5 should be kept large to mini-
mize high-pass filtering of the signal, and to avoid
amplification of low-frequency current noise in the
1510/1512 input stage.
many pro audio products include, a zener diode ar-
rangement connected to the bridge rectifier instead of
the connection to V+ and V- as shown in Figure 4.
While this arrangement does not keep the inputs in-
side the common mode range, it has the advantage of
working even when the power is off. For further in-
sights into this subject, see the Audio Engineering
Society preprint “The 48 Volt Phantom Menace,” by
Gary K. Hebert and Frank W. Thomas, presented at
the 110th AES Convention.
approach, R3 and R4 must be made larger (e.g., 51W)
Out
Phantom power is required for many condensor
Other manufacturers have recommended, and
When using the more conventional zener diode
THAT 1510/1512
U1
LF351
U2
100n
C8
510k
R3
Out
3
. R3 and R4
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