Headphones amplifiers — Erzetich Audio Bacillus II +

The Bacillus II + is the fully balanced version of the compact Bacillus amplifier from Erzetich Audio, a Slovenian company building headphones and headphone electronics. The maker lists it at 1999 EUR, describes it as an amplifier made to be as flexible as possible, and covers it with a 5-year limited warranty. In the price list it sits between the 799 EUR Bacillus II and the 4000 EUR Deimos, and above the class A Perfidus at 999 EUR, making it the costliest class AB model the company offers. Production takes place in the EU, and each unit is burned in for 12 hours before it leaves the factory.

Key specs that matter

Through the balanced path the amplifier delivers 314 mW per channel, with a frequency response of 0.5 Hz to 900 kHz within 1 dB. The single-ended path is rated at 157 mW and 4 Hz to 450 kHz, again at 1 dB. Balanced connections are a 3-pin XLR pair at the input and a 4-pin XLR headphone socket, while RCA inputs and a 6.35 mm jack handle unbalanced gear. Erzetich quotes a headphone load range of 8 to 600 ohm. The unit draws 9 W and is supplied for 230 V at 50 Hz or 115 V at 60 Hz. The case measures 260 mm wide, 105 mm high and 240 mm deep and weighs 2990 g.

Engineering and use context

Topology is class AB dual-mono, each side built as its own balanced amplifier. Its power supply is described as triple reinforced, meaning one section feeds each channel and a third feeds the auxiliary electronics, and no rail is common to both sides. Volume is controlled by a quad Blue Velvet potentiometer from Alps, which is needed to track four signal legs in balanced mode. Silver-plated copper links the boards inside. The chassis is steel with wooden side panels, keeping the look of the smaller Bacillus II while growing in every dimension to hold the extra circuitry. Erzetich states the unit is completely serviceable. Having both connection families on one chassis means a listener can move from a single-ended to a balanced source or headphone later without replacing the amplifier.

Pairing

The balanced inputs suit a DAC or preamplifier with XLR outputs, and the RCA pair takes older single-ended sources. The maker names its own planar magnetic Charybdis headphone as a match, and the doubled balanced output favours such headphones fitted with a 4-pin XLR cable. Single-ended headphones can use the front jack at the lower rated power.

Alternatives

The Erzetich Perfidus is a class A headphone amplifier by Erzetich, placed lower in the price list.