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.

 

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 Power Output
300Wrms max into 4/8ohms
 Idle Power
30W on +/-65V supplies
 Freq. Response
20Hz - 20kHz 0.15dB @ 1W
 Sensitivity
1Vrms for 100Wrms/8ohms
 Input Impedance
27k // 330pF
 Slewing Rate
>18V/uS into 8ohms
 THD
<0.025% @ 100W/8ohms
 typ
<0.01% 2hD @ 10Wrms
 Damping Factor
>500 @ 50Hz for 8ohms
 Hum & Noise
< -100dBA w.r.t 1W
 Dimensions
180mm x 50mm x 30mm