THAT1512S08-U Datasheet, PDF (5/8 Pages) List of Unclassifed Manufacturers – Low-Noise, High Performance Audio Preamplifier IC

THAT 1510/1512 Low-Noise
High Performance Audio Preamplifier
Page 5 of 8
Document 600031 Rev 08
+15
C6
-In
-In ¹⁰⁰ⁿ
C1
470p
R1
RG1 _V+
1k
Out
RG
Out
C2
+In
470p
Ref
RG2 ^V-
+In
U1
THAT
1510/1512
C3
47p
R2
1k
C9
100n
-15
Figure 3. Basic 1510 / 1512 Circuit
These diodes reduce the likelihood that accidental
electrostatic discharge (ESD) or electrical over stress
(EOS) will damage the ICs. Other diodes across the
base-emitter junctions of the input transistors
prevent excessive reverse biasing of these junctions
(which would degrade the noise performance of the
input devices).
resistors) to allow gain adjustment, RG should be
ac-coupled as shown in Figure 4. By adding CG in
series with RG, dc gain is fixed (at unity for the 1510,
and ½ for the 1512). This constrains the output dc
offset to just over +/-5 mV, and prevents it from
varying with gain. With this low offset, ac coupling of
the output is usually unnecessary.
Other than the protection diodes, the 1510/1512
input pins are connected only to the bases of their
respective input devices. For 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. Figure 3 shows the simplest approach;
dc bias is supplied via R1 and R2. At 1 kΩ each, they
will minimize pickup of unwanted noise and interfer-
ence, as well as generate relatively little noise due to
input current noise in the 1510/1512. However, at
high gains, their inherent voltage noise, plus the
1510/1512's input current noise drawn across these
resistors, adds significantly to the noise at the
1510/1512's output.
Because RG is dc coupled in the circuit of
Figure 3, the dc level at the output of the 1510/1512
will vary with gain. In most applications, the output
should be ac-coupled to the next stage. For applica-
tions where RG is variable (via a pot or switched
CG must be large enough not to interfere with
low-frequency response at the smallest values of RG.
For 60 dB gain, RG=10 Ω (1510) or RG=5 Ω (1512).
For a -3 dB point of approximately 5 Hz,
CG=3,300 μF (1510), or CG=6,800 μF (1512). For
other maximum gains or minimum frequencies, scale
CG accordingly.
Phantom Power
Phantom power is required for many condenser
microphones. THAT recommends the circuit of
Figure 5 when phantom power is included⁴. R3, R4,
and D1 - D6 are used to limit the current that flows
through the 1510/1512 inputs when the circuit
inputs (-In and +In) are shorted to ground while
phantom power is turned on. This causes C4 and/or
C5 to discharge through other circuit components,
often generating transient currents of several amps.
R3 and R4 should be at least 10 Ω to limit destructive
4. In revisions 0 and 1 of this data sheet, we recommended using Schottky diodes (1N5819 types) at D 1 ~ D4 to protect the 1510/1512 inputs against overloads. Subse -
quently, we discovered that the leakage of these diodes could cause problems with DC fluctuations (hence noise) at the 1510/1512 output. Upon further investigation, we
concluded that conventional rectifier diodes like the 1N4004 (the glass-passivated GP version) provide adequate protection and d o not introduce unacceptable leakage.
Additionally, 1N4004 diodes are much cheaper and more readily available than the Schottky types.
Since publishing revision 4, we determined that the internal reverse-bias diodes between the pins +In/RG2 and -In/RG1 may be damaged by phantom power faults under
certain conditions. Small-signal diodes (D5 and D6) avoid this problem by appearing in parallel with the internal diodes, diverting excess current around the 1510/1512.
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