Directed Electronics Incorporated (DEI) hails its
model 2101 power amplifier as a single-channel (mono)
power amplifier with functions enhancing its usefulness
as a dedicated subwoofer amplifier, and is
conservatively rated for 100 watts measured into a 4-ohm
load and 160 watts into a 2-ohm load at 14.4 volts DC. I
measured 123 watts into a 4-ohm load and 199 watts into
2-ohm load at the standard test voltage of 12.5 volts
DC.
This amp is made to be heard and not seen. Except for
the colorful DEI insignia, it is plain black and
compact. Two sets of terminals for power and speaker
connections share one long side of the amplifier with a
plug-in, 30-ampere fuse; four RCA jacks and all the
controls are on the opposite side. The three rotary
controls are 1/2-inch in diameter, slotted, and inset
for easy adjustability, but not easily moved
inadvertently later on. The two (left and right) RCA
input jacks are connected directly to a second pair of
output jacks making connecting to additional amplifiers
more convenient (outputs are unaffected by the settings
of the 2101). The left and right inputs are internally
summed to drive the amplifier's output.
The
gain control adjusts to allow signal levels as low as 250
millivolts, effectively letting use of almost any source unit with
this amplifier (including factory line-level outputs). A small
three-position switch selects the amplifier's operating frequency
range via an internal active crossover.
In the center position (OFF), the amplifier operates over the
full frequency range of 20 to 20,000 Hz. In the left position (HPF),
it operates above an adjustable cutoff frequency (set with a rotary
control between 30 and 300 Hz; with the filter having a
12-dB-per-octave slope in either mode); in the right hand position
(LPF), it operates below that cutoff frequency. As a subwoofer
amplifier, it would be operated in the LPF (low-pass-filter with
gain increases by about 7-dB) mode where two additional functions
are applicable.
One function is a variable, narrow-band bass boost centered at 40
Hz with a measured maximum boost of 22 dB—much too high to be
practical. At the maximum setting, running the amplifier at an
overall level greater than over 3/4-watt without having it clip at
40 Hz is impossible because the 2101 was designed to do this as a
warning to be careful with that control setting.
The second subwoofer function is embodied in a switch labeled
S/V. The S position (sealed subwoofer enclosure) controls the
excursion of the woofer's cone to very low frequencies; in that
position, the amplifier's frequency response (below the filter
cutoff frequency) is flat, down to less than 10 Hz. The V position
(vented enclosure) allows an excessive woofer cone excursion below
the system's resonant frequency; in that position, a very sharp,
24-dB/octave cutoff filter at 30 Hz is switched to protect the
subwoofer.
Except for a mild pop during turn on and turn off, the DEI 2101
performed flawlessly. The combination of the DEI 2101's high power,
40-Hz adjustable bass boost, switchable vented-enclosure high-pass
filter, and $290 list price make it an excellent subwoofer
amplifier.
Read about the Test Results:
All tests performed at 50 Hz with a 4-ohm load and
supply
voltage of 12.5 volts unless otherwise noted.
Output power at 1-percent THD (dBW/Watts):20.5/123
At 14.4 volts supply22.1/164
With 2-ohm load23.0/199
Frequency response (full-range) +/- dB from
20 to 20,000 Hz relative to 1,000 Hz.+0/-0.8
Distortion (THD + N) at rated power (percent)0.04%
Signal to noise ratio: A-wtd, full range (dB)91
Input signal voltage required for rated output
from a single input at max/min. gain (volts)0.23/>10
Input impedance (ohm)29 k
Damping factor>100
Idle current (amps)0.8
Turn-on delay + soft start (seconds)6 + 3
Low or high-pass filter frequency range (Hz)30 to 300
Filter cutoff slope (dB/octave)12
Bass boost center frequency/max gain 40Hz/22dB
Vented enclosure highpass filter frequency (Hz)30
Filter cutoff slope (dB/octave)24
