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).

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;

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.

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-

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.

For a -3 dB point of approximately 5 Hz,

other maximum gains or minimum frequencies, scale

Phantom Power

Phantom power is required for many condenser

microphones. THAT recommends the circuit of

through the 1510/1512 inputs when the circuit

inputs (-In and +In) are shorted to ground while

often generating transient currents of several amps.

THAT 1510/1512 Low-Noise

Page 5 of 8

Document 600031 Rev 08

High Performance Audio Preamplifier

THAT Corporation; 45 Sumner Street; Milford, MA 01757-1656; USA

Tel: +1 508 478 9200; Fax: +1 508 478 0990; Web: www.thatcorp.com

Copyright © 2013, THAT Corporation

RG

+In

Out

-In

RG2

RG1

U1

THAT

1510/1512

-15

+15

-In

+In

R1

1k

R2

1k

C1

470p

C2

470p

C3

47p

Out

C6

100n

C9

100n

V+

V-

Ref

Figure 3. Basic 1510 / 1512 Circuit

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.