Интегральные усилители — Qualiton A20i

The A20i is a stereo valve integrated amplifier from Audio Hungary, sold under the company's Qualiton name. It works in Class A push-pull, and in the Qualiton line it sits below the higher-power A35i integrated amplifier. The maker now lists the A20i as discontinued. It is a line-level design with three inputs and a single control.

Key specs that matter

Rated output is 2 x 20 W into a nominal 8 ohm load. The output transformers also accept 4 ohm speakers, with some deviation from the published figures. The valve complement is four 5881 output valves, two E88CC/6922 drivers and two Tungsram ECC83 preamplifier valves. There are three unbalanced RCA inputs and one pair of speaker terminals per channel. Gain is 34.8 dB, input sensitivity is 230 mV and input impedance is 10 kOhm. Frequency response reaches 25 Hz to 100 kHz at -3 dB measured at rated power. Total harmonic distortion stays below 0.3% at 1 kHz and full output, signal to noise ratio exceeds 90 dB, and residual output noise is below 1 mV. Power consumption is 150 W. The amplifier measures 270 x 180 x 300 mm and weighs 16 kg.

Engineering and use context

In a Class A push-pull stage each pair of 5881 valves conducts through the entire signal cycle, so neither valve switches off at the crossover point where the two halves of the waveform meet. The cost is lower efficiency, which shows in the 150 W drawn from the mains for its modest output and in the heat produced by the eight valves. The E88CC/6922 double triodes drive the output stage, while the ECC83 double triodes provide the voltage gain at the input. Output transformers couple the valves to the speakers and set the load the amplifier is designed for, which is why the published figures refer to the 8 ohm load. The chassis is made from 1.5 mm polished stainless steel with a black mirror-polished finish. A single front control combines volume and input selection, and LED indicators show the active input and operating status. With its high input sensitivity, the amplifier reaches full output from a low input voltage, so standard line sources drive it with a wide margin.

Pairing

The modest output suits efficient loudspeakers with a benign impedance in a room of about 20 m2. Speakers with a low sensitivity or an impedance that dips low will use up the available power quickly. There is no phono input, so a record player requires a separate phono preamplifier, and CD players, DACs and streamers with line outputs connect directly to the three RCA inputs.

Alternatives

The Qualiton A35i offers more output power in the same Audio Hungary line for less sensitive loudspeakers.