Power amplifiers stereo — Aries Cerat Diana Forte

The Aries Cerat Diana Forte is a two-channel SET power amplifier from the Cyprus-based tube specialist, and it completes the Diana series alongside the Diana integrated and the Diana Mezzo preamplifier. The circuit takes the output and driver stages of the Diana integrated and scales the output section up to more than twice the power, and Aries Cerat places it among the most powerful single-ended triode stereo amplifiers built. It was launched in the US at around 27,500 dollars.

Key specs that matter

Output is 60W per channel in single-ended Class A, with about 70W peak. Each channel has two paralleled 813 output tubes driven by one 814 operated as a triode, for a total of four 813s and two 814s. Power bandwidth extends from 15Hz to 110kHz, combined gain is 26dB (x20) and the noise floor is quoted at 100dB. The chassis is 570mm wide, 590mm deep and 350mm high, and it weighs 110kg.

Engineering and use context

With two 813s in parallel per channel, the output stage stays single-ended, with no push-pull pair splitting the waveform, yet the current available to the output transformer is doubled. The output transformer has an oversized core and special winding methods so that bandwidth remains wide at full power, where single-ended transformers usually lose extension. A double-C-core, bifilar-wound interstage transformer loads the 814 driver, and every stage uses Aries Cerat's AC link coupling in place of coupling capacitors. The same AC link connects the Diana Forte to the Diana Mezzo preamplifier, so together they form a two-chassis version of the Diana integrated, and owners can buy the preamplifier first and add the power amplifier later. The output stage draws on two completely separate choke-filtered capacitor banks made from the company's film super-capacitors, which are specified with ESL and ESR about 100 times lower than electrolytic types. The driver stage has its own choke-filtered supply and a separate power transformer, which prevents crosstalk between the supplies. Two meters on the top plate allow every tube to be biased and monitored while music plays, and the amplifier can also work as a simple tube tester for matching replacements.

Pairing

Its output lets the Diana Forte drive a much wider range of loudspeakers than typical low-power SET amplifiers, though speakers of good sensitivity remain the natural match. Given its weight and heat output, it needs a sturdy, well-ventilated floor position.

Alternatives

The Aries Cerat Diana integrated combines a similar all-DHT circuit with a preamplifier section in one chassis, at 25W per channel.