For digital-camera audio recording,
Maxim announced the MAX9814
microphone amplifier with automatic
gain control (AGC) and low-noise
microphone bias. Integrated AGC lets
designers optimize the signal level prior
to digital signal processing. The device
also integrates a low-noise preamplifier, variable gain amplifier (VGA), output
amplifier, and an internal low-noise electret-
microphone bias-voltage generator.
Back with the audiophiles
National's demonstration centered
around two products. The first was a
pair of audio op-amp families with typical
THD+N of 0.00003% (guaranteed
maximum is 0.00009%). Other performance
specs include a 2.7-nV/√Hz
input-noise density, a 60-Hz 1/f noise
corner, 20-V/μs slew rate, and a 55-MHz
gain-bandwidth product.
There are two package variants of
the 44-V LME49860 dual op amp and
single, quad, and dual versions of the
34-V LME4978x0. The nominal ±22-V
LME49860 is unity-gain stable down
to ±2.5 V. Over this supply range, the
amplifier maintains common-mode
rejection ratio (CMRR) and power-supply
rejection ratio (PSRR) better than
120 dB and a typical input bias current
of 10 nA.
On the input, the LME49860 can
swing to within 1 V of either powersupply
rail when driving 2-kΩ loads or
to within 1.5 V when driving 600-Ω
loads. The LME49710, LME49720,
and LME49740 amplifiers have lower
operating voltages and similar specs.
The other new product, the
LME49810, is a monolithic 200-V
audio power amplifier driver with an
integrated Baker clamp. Like the op
amps, each LME49810 can replace a
couple of dozen hand-selected and
matched discretes in a high-end audiophile
system. The LME49810's function
is to drive high-power discrete output
bipolars with up to 50 mA, for
systems delivering up to 3 kW. When
implemented in a complete power
amplifier design, typical THD+N is
0.0007%. Other specs include a 50-
V/μs slew rate and a 110-dB PSRR.
That Baker clamp deals with input
signal peaks. It's implemented by means
of an array of diodes connected between
the base and collector of a bipolar transistor.
It also prevents the collector-emitter
junction from saturating, making
clipping less noticeable by removing the
high-frequency spike that occurs when
the transistor recovers from saturation.
In National's sound room, all of the
electronics except for the CD player are
custom. The op amps are used in the
DAC signal-path (four in each stereo
channel), as well as in the power-supply
regulators. The audio power amplifier
drivers are, obviously, in the power
amps. How much would a commercial
implementation cost?
Brasfield estimates that the current
National prototypes could be sold for
approximately $300 each, bringing the
cost for the electronic portion of the
signal chain to a few thousand dollars.
That's exclusive of the speakers. Unfortunately,
Brasfield said that Wilson
Audio Specialties has informed him
that those $26,000-a-pair Watt Puppies
have been obsoleted and their replacements
will cost a whole lot more. Talk
about "golden ears."