The GB300D features my unique fully symmetrical
discrete power amplifier topology that achieves absolute Hi
End performance at low cost. The design features very high
PSRR for reduced sensitivity to power supply quality and the
output stage Class AB commutation artefacts superimposed on
the supply impedance, which causes the harshness and loss of
spatial and timbral detail in lesser designs. The 8 x 150W
common source complementary MOSFET output stage swings to
within 2V of the supplies, maximizing power output for greater
power efficiency than conventional designs, achieving 300W
into 8ohms on unregulated +/-75V supplies! The unique topology
elimates the Vas stage which compromises conventional designs,
instead employing positive feedback to achieve highly linear
and very high first stage gain. The input stage is a
complementary bipolar cascode differential stage driving a
complementary 300MHz Class A buffer into the output MOSFETs
with only feedback lead compensation for excellent stability
with all loads. The amplifier is particularly suited to
driving electrostatic loudspeakers, with typically < 0.001%
THD at 100 ohms, and less than 0.025% mostly second harmonic
at average listening levels into 8 ohms, with third harmonic
taking over at higher power.
The amplifier may be
configured as a simple AC coupled design, or DC coupled to
eliminate signal path capacitors, with onboard DC nulling and
bias adjustment. The kit includes all matched components
(input diff'ls to 5% Hfe, MOSFETs to 10mV on Vgs), quality
metal film resistors, polystyrene, silvered mica and
polypropylene capacitors, 105 degreeC long-life electrolytics
and a fully ground planed and through hole plated PCB. All
components for AC or DC coupling are included. Full assembly
and support hardware instructions are provided, including a
variety of options, optimisation tweaks, as well as
modifications to introduce 0.25% second harmonic 'bloom' for a
'fuller' more tube-like sound if desired. The amplifier may
also be configured in pure Class A to 100Wrms at 8 ohms on
+/-43V
supplies. |
