T+A’s awesome HV electronics are mighty beasts, but like most might beasts in audio, they are not exactly ‘cheap’. You do get your money’s worth with the HV series amplifiers, but you still need a lot of money in the first place. In an ideal world, there would be an amplifier that uses a lot of what makes those HV amplifiers so good, at a more affordable level, and that’s precisely where the AMP 8 comes in.
The AMP 8 is part of T+A’s two-strong smaller form factor products, the other component being the DAC 8. It’s logical to think of the two as a pairing, with the DAC 8 as processor and digital preamp hub and the AMP 8 as ‘just’ the power amplifier. Which is why we broke them apart like this. The AMP 8 is pretty far removed from being ‘just’ a power amplifier, and its small case and top line 2× 80W into eight ohms, 110W into four ohms specification might easily make it an afterthought in any review of the pairing. In fact, what the AMP 8 does is provide the perfect ‘straight wire with gain’ style power amplifier for any sophisticated system builder who is not keen on spending tens of thousands on a stereo power amp.
The overall circuit design of the AMP 8 is very similar to the German company’s PA 3000 HV integrated amplifier, in that the input and voltage amplifier stages operate at much higher voltage potentials than usually found in domestic amplifiers. In the case of the AMP 8, the input stage is a cross-coupled J-FET cascode amplifier, while the voltage amplifier stage is a single-ended Class A FET cascode amplifier, of a design first thought up by Dr Malcolm Hawksford, Emeritus Professor of Engineering at the University of Essex. In a high-voltage amp design like this, the output stage is responsible for current amplification, and the AMP 8 sports high performance ‘ThermalTrak’ audio-specific transistors designed for bias point stability and freedom from inertia effects.
Another T+A innovation, the voltage and current amplifier stages are completely separated from one another, even to the point of not sharing the same power supply. This is more than just electronics overkill, it prevents any feedback from the loudspeakers affecting the more sensitive and sonically vital voltage amplifiers. This circuit design is known as an Isolated Current Amplifier (ICA) circuit and has been used by the brand for several years, and was first seen in its R-Series. This inherent isolation of individual stages makes for an amplifier with low circuit track inductance, and a design that doesn’t need high levels of global negative feedback to create a linear, wide bandwidth amplifier, and this is evidenced by the AMP 8 having a bandwidth of more than 200kHz.
The amplifier features an over-specified, low-field leakage toroidal transformer, claimed to generate up to 400W and this, coupled with a large local capacitive reservoir across the output stage acting as buffer, means this relatively small amplifier can deliver a surprisingly powerful sound to surprisingly difficult loudspeaker loads. Naturally, the T+A bristles with high-grade electronics components including non-magnetic Vishay resistors and high quality WIMA and ELNA audio-grade capacitors. There is also a down-firing case fan, which remains silent until needed under duress and even then runs slow and quiet enough for it not to be troublesome for listeners.