Handbook for Sound Engineers

Tubes, Discrete Solid State Devices, and Integrated Circuits 351

Solid State Music, or SSM, which later became Solid
State Microtechnology, developed the first active micro-
phone preamp IC for professional audio around 1982.^30
SSM specialized in producing niche-market semicon-
ductors aimed at the professional audio business. The
SSM2011 was almost completely self-contained,
requiring only a handful of external resistors and capac-
itors to provide a complete preamp system. One unique
feature of the SSM2011 was an on-chip LED overload
and signal presence indicator.
SSM later produced the SSM2015 and the SSM2016
designed by Derek Bowers.^31 The SSM2016, and the
SSM2011 and 2015 that preceded it, did not use a fully
balanced topology like Wurcer’s AD524 and the
Harrison PC1041. The SSM parts used an internal
op-amp to convert the differential stage output to
single-ended. This allowed external feedback resistors
to be used, eliminating the performance penalty of
on-chip diffused resistors. The SSM2016 was highly
successful but required external precision resistors and
up to three external trims. SSM was later acquired by
Precision Monolithics and eventually by Analog
Devices (ADI). The SSM2016 was extremely
successful and, after its discontinuance in the
mid-1990s, became highly sought after.
Analog Devices introduced the SSM2017 self
contained preamp, also designed by Bowers, as a
replacement for the SSM2016. The SSM2017 used
internal laser-trimmed thin-film resistors that permitted
the fully balanced topology of the AD524 and discrete
preamps to be realized as an IC. Analog Devices manu-
factured the SSM2017 until about 2000 when it was
discontinued. A year or two later, ADI released the
2019 which is available today.
The Burr Brown division of Texas Instruments
offered the INA163, which had similar performance to

the SSM2017, but was not pin compatible with it. After

the 2017 was discontinued, TI introduced its INA217 in

the SSM2017 pinout. Today, TI produces a number of

INA-family instrumentation amplifiers suitable for

microphone preamps including the INA103, INA163,

INA166, INA217, and the first digitally gain-controlled

preamp: the PGA2500.

In 2005, THAT Corporation introduced a series of

microphone preamplifiers in pinouts to match the

familiar SSM2019/INA217 as well as the INA163. The

THAT1510 and the performance-enhanced THAT1512

use dielectric isolation to provide higher bandwidth than

the junction-isolated INA and SSM series products.

(Dielectric isolation is explained in the section on audio

VCAs.)

While all offer relatively high performance, the three

different families of parts have different strengths and

weaknesses. Differences exist in gain bandwidth, noise

floor, distortion, gain structure, and supply consump-

tion. The optimum part for any given application will

depend on the exact requirements of the designer. A

designer considering any one of these parts should

compare their specs carefully before finalizing a new

design.

12.3.5.4 Integrated Circuit Mic Preamplifier Application

Circuits

The THAT1510 series block diagram is shown in Fig.

12-57. Its topology is similar to those of the TI and ADI

parts. A typical application circuit is shown in Fig.

12-58. The balanced mic-level signal is applied to the

input pins, In+ and In. A single resistor (RG),

connected between pins RG 1 and RG 2 , sets the gain in

conjunction with the internal resistors RA and RB. The

input stage consists of two independent low-noise

amplifiers in a balanced differential amplifier configura-

tion with both ac and dc feedback returned to the emit-

ters of the differential pair. This topology is essentially

identical to the AD524 current feedback amplifier as

described by Wurcer et al.

The output stage is a single op-amp differential

amplifier that converts the balanced output of the gain

stage into single-ended form. The THAT1500 series

offers a choice of gains in this stage: 0 dB for the 1510,

and 6 dB for the 1512. Gain is controlled by the

input-side resistor values: 5 k: for the 1510 and 10 k:

for the 1512.

The gain equations for the THAT1510 are identical

to that of the SSM2017/2019 and the INA217. The

INA163 and THAT 1512 have unique gain equations.

Figure 12-55. AD524 block diagram. Courtesy Analog

Devices, Inc.

–In

C 3 C 4

+In

Reference

Sense

A3

4.44 k 7

404 7

40 7

G = 100

G = 1000

Q 1 , Q 3 Q 2 , Q 4

+VS

I 1

50μA

I 2

50μA

A1 A2

R 52

20 k 7

R 55

20k^7

VO

I 4

50μA

–VS

I 3

50μA

VB

R 53

20 k 7

R 54

20 k 7

RG 1 RG 2

R 55

20k 7 R 56

20 k 7