PrimaLunas amps are essentially classic valve designs, but they bring distinctive aesthetics and a few modern design touches to the party. One such notable feature in this amp is Adaptive auto bias. Bias is a long-standing pain in the neck of valve amps: quite simply its the DC (standing) current in the valves under conditions of no audio signal and its critical.
Usually amps either have manually adjusted bias, which may even require test equipment to set, or auto-bias (also called self-bias), which does what it says but, in the traditional implementation, reduces maximum output power. Its really surprising how few firms have done what PrimaLuna does and made solid-state monitoring circuits which control bias. It makes the amp far more tolerant of imbalance between output valves.
Input switching and volume control use good-quality mechanical components and behind them a good deal of the amps circuitry is based on solid wiring and tag strips, with large resistors in most positions. Critical capacitors are brand-name plastic-film parts, while a couple of substantial electrolytic capacitors are joined by a smoothing choke in the power supply.
The valve complement, apart from the output KT88s, runs to two each of the ECC83 and ECC82. The cover over the transformers is so very resonant that wed be tempted to remove it!
ProLogue Two Integrated Specifications Output Power 40 watts x 2 Inputs 4 Pair RCA Outputs 4 & 8 Ohm Freq. Response (+/- 0.5dB) 20Hz-30kHz THD Less than 1% at full power S/N Ratio 89 dB Input Sensitivity 300mV Input Impedance 65k Ohm Power Consumption 300 watts Standard Tube Compliment 2 - 12AX7 2 - 12AU7 4 - KT88 Dimensions (WxHxD) 11" x 7.5" x 15.5"