Усилители мощности стерео — Trafomatic Audio EOS+

The EOS+ is a stereo tube power amp made by Trafomatic Audio, built as a dual mono design. It works in push-pull with KT150 output tubes and comes in two boxes, an amplifier chassis and a separate power supply unit. The standard finish is black, and custom RAL colours can be ordered for an extra charge.

Key specs that matter

Output is 150 W per channel in class AB push-pull, a figure the maker considers enough for most loudspeakers, including models with lower than average sensitivity. The valve complement is four Tung-Sol KT150 output tubes, two ECC99 and two 5687 double triodes. Connection is via RCA or XLR sockets at an input impedance of 100 kohm. Loudspeaker terminals are provided for 4 and 8 ohm loads. Distortion is given as 0.03 % at 1 W and 1 kHz, rising to 3 % at the full 150 W. Bandwidth runs from 10 Hz to 100 kHz within 1 dB, with an 82 dB signal to noise figure. The amplifier chassis measures 450 x 350 x 230 mm and weighs 27 kg, while the power supply box measures 150 mm wide, 300 mm deep and 200 mm high and adds 11 kg.

Engineering and use context

The feedback loop is set at -6 dB and taken from the cathode, a scheme Trafomatic tuned so that the push-pull stage behaves in a way close to a single-ended amplifier. The separate power supply is built around an 800 VA toroidal transformer, and each channel has its own C-L-C filter, so the two sides do not share a smoothing stage. Output transformers use Double-C cores, and Solen capacitors are specified in the signal path. Power consumption is 500 VA, and the mains input can be switched between 230 V at 50 Hz and 115 V at 60 Hz, which lets the same unit be used on either supply standard.

Pairing

As a power amplifier the EOS+ has no volume control, so a preamplifier or a variable-output source must sit ahead of it, and that unit has to supply 1.2 V RMS to drive the amplifier to its full rated output. The balanced XLR input suits a fully balanced preamplifier such as the Trafomatic LARA, which has both XLR and RCA outputs, and single-ended preamplifiers plug into the RCA pair. Since the output transformers carry separate taps, the owner connects each loudspeaker to the tap that matches its nominal impedance, so low and higher impedance models can both be driven.

Alternatives

Trafomatic Audio also makes the EOS, a stereo valve power amplifier from the same product range.