Threshold 400 a brochure

Page 1

Threshold Corporation has quickly commanded a
reputation for design concepts and empirical per~
forrnance that set new boundaries for the classifi-
cation state-oi-the-art. The model 400A class A
power amplifier is the cornerstone for this repu-
tation and embodies Thresholds direct solutions for
those basic electronic anomalies to which the human
ear is most sensitive.

The Threshold model 400A achieves virtually perfect
program signal processing insofar as aural per~
ception is concerned through the use of an ingen-
iously simple circuit path and the operation of all gain
devices in the class A mode at all times and under
all signal conditions short of actual amplifier clipping.
Class A amplification has long been recognized as
the ideal in amplifier design since it yields the
smoothest transfer functions. widest bandwidths.
and significantly reduces the amount of feedback
required. However. until now. its realization in
solid~state technology has been unable to achieve
the magnitude of power required in todays finest
equipment.

The Threshold 400A is a completely new. patented
class A design that utilizes a unique dynamic biasing
circuit. This circuit senses the internal bias needs
continuously and instantaneously adjusts the idle
current to the levels required to maintain constant
class A operation of all output transistors. Instead of

data
sheet

400A

the fixed. maximum level biasing employed in con-
ventional class A designs, the Threshold active bias
configuration responds to the instantly varying needs
oi the amplifiers output stages. This allows the
Threshold 400A to idle at one fourth the power oi an
equivalently rated conventional class A design. yet
maintain class A operation. with its acknowledged
superiority. over an enormous range of output

power conditions.

Thresholds advanced concepts have made possible
the unchallenged excellence of class A operation at
power. reliability. size and cost levels competitive
with conventional audio amplifiers. Class A operation
of the Threshold 400A means distortion products
resulting from transistor turn-on. turn-off delays are
eliminated. Transient intermodulation effects are
sharply reduced. Residual distortion is restricted to
low-order harmonic and simple modulation com-
ponents. Ultra-high slewing for both voltage and
current is achieved with absolute stability.

Technical descriptions. however. only hint at the
impressions which result from personal listening to
a superior component recreating the finest program
material. We invtte you to compare any Threshold
amplifier with any other amplifier at any price or any
power rating under these meaningful conditions.
We believe you will agree the Threshold 400A fully
justifies our claim to designs that constitute the
leading edge of the art.

class A
stereo
power.
amplifier

Page 2

Threshold model 400A
class A power amplifier

description

Two channel audio power ampliller employing patented dynamic bias
Circuits that maintain the amplitier in class A operation to beyond 500
watt tranSient output levels per channel.

rated power

100 watts per channel. both channels driven into 8 ohms. 20 through
20000 Hz with uninterrupted FTC preconditioning '

harmonic & intermodulation distortion

No greater than 1% total harmonic or intermodulation distonion at
rated power. decreasrng monotonically with lower power. Distortion
virtually immeasurable at small srgnal levels Harmonic distonion
components are dominated by second and third harmonics. lnter~
modulation Sidebands are primarily lust and second order Distortion
components 01 higher orders are negligible below 40.000 H1
tranSIent intermodulation distortion

Transrent intermodulation distortion srdebands are at least 75 00
below a 10 watt output srgnal con5isting oi a 1 5 kHz square wave
linearly mixed with a 420 dB 80 kHz Sine wave The Sidebands are
symmetric about the central trequency decreasrng to appronmately
>90 dB by the seventh order

rise time

Leading and trailing edge less than t Microsecond

slew capabilities

MaXimum voltage slewing rate each channel 50 volts per
microsecond

Maxrmiim current slewing rate each channel. 25 amps per
microsecond

loop propagation time

Propagation delay appearing at the bases of the input dillerential
tran5isters 20 nanoseconds

current output capability

Manmum instantaneous ouput current capability in excess at 20
amps per channel Maximum continuous output current capability
5 amps per channel

voltage output capability

Maxrmum voltage swing :50 volts per channel

trequency bandwidth

+0 74 dB 1.5 Hz through 500.000 Hz at small Signal levels. :0 dB
20 Hz through 20000 Hz at 200 watts per channel

input impedance

23.000 ohms

gain tactor

23 dB

damping tactor

Constant 100 lrorn dc through 20.000 Hz measured at the output
terminals

hum and noise

Below 2 millivolts at the outputs

power consumption

Amplitier power draw at no Signal: approxrmately 200 watts
power requirements

120 volts. 50 - 60 N2 source

protection circuits

Current limiters with analog controlled reaction times. thermal
monitoring output tuses. resetable crrcuit breaker

displays

Indrvrdual and Simultaneous peak vs average output level readings
tor each channel

warranty

Limited three year warranty covering pans. labor. and shipping at
detective moldutes to and train the tactory through an Authorized
Threshold Dealer

dimensrons

Faceplate 19 inches wide by G's/is inches high. rack mount notched
Chasm: 175/ inches wide including heat sinks by 6% inches high
by 11 inches deep. Handle extenswn beyond laceptate 1 inch
Height 01 supporting teet: 1 inch.

shipping weight

51.5 pounds

'measured at a line source at 120 volts

Because Threshold is constantly researching new techonology and
materials. the option is reserved to incorporate deSign retinements
and modifications into exrsting product lines wrthout notice or
obligation.

The accuracy which can be achieved by operating an amplitier in the
class A mode is clearly illustrated in the spectrum anal 515 above. The
display shows the performance of the Threshold 40 A output stage
into a 2 microlarad load without feedback correction, Note that even
without feedback correction distortion components are limited to
second and third order harmonics only The Signal is a10kHz sine
wave at 1 watt output. The display is calibrated to 10d8 per divrSion.

The bandwidth capabilities of the Threshold 400A are revealed in the
two oscilliscope traces above The upper oSCilliscope trace shows the
output of the 400A at hall power reproducmg a 50 kHz square wave
into a resrstive load The trace is calibrated to 10 volts per diwsion
The lower oscrlliscope trace shows the output 01 the 400A at halt
power reproducing a 200 kHz sine wave into a resistive load. The
trace is calibrated to 15 volts per dwision '

Threshold Corporation

1832 tribute road sutee sacramento calrtornia 95815