A Tale of Three Phono-Stages - The Conrad-Johnson TEA-2 – In All Its Guises (Hi-Fi+ 89)

When it comes to cars, the concept of a shared platform is both widely accepted and understood: you can buy a Volkswagen Golf with an 85hp/ 1200cc engine, a 105hp/1600cc Blue Motion turbo diesel injection engine or a 270hp/2000cc petrol injection. These cars are all built on the same body pan and all look pretty similar from the outside, but neither the general public nor the insurance companies think that they’re the same thing. Drive them and you quickly realize that despite the common DNA, these are three very different vehicles indeed – and that they exist to appeal to very different customers.

It’s a developmental culture that the hi-fi industry has been slow to adopt. Many companies have produced ‘breathed-on’ editions of their products, but generally speaking, these have simply superseded the donor unit, rather than augmenting it and spreading its appeal. Perhaps the one real exception to this rule has been Marantz, with their KI Signature special editions – although these tend to be tweaked versions of the original rather than wholly new products. Power amps have appeared in stereo and mono versions that share the same metalwork, but that’s about as far as it goes.

But here we have three outwardly identical units from conrad-johnson that straddle a price band from £2,695 to £5,995. And when I say identical, I do mean identical. You need to look at the small, stamped product identifier plate on the rear panel to tell them apart – unless you take the lid off, that is. Inside, you’ll find identical circuits and tube complements, but the components differ markedly; about as markedly as the engine in a 1.2 Golf and the motor you find under the hood of a GTI. These products take the concept of a shared platform pretty much as far as they can, with common casework, circuit boards and principal power-supply components.

“So what?” you might well ask. Well, when it comes to performance and what you have to pay to get it, those shared parts reduce build costs significantly, meaning purchasers get a lot more music for their money. But just as interesting, at least on an academic level, is the opportunity that the ‘Tea-2 three’ provide to compare and contrast the influence of and benefits to be had from component quality as opposed to circuit topology or the size of the power supply. The audible differences here – and they are extremely audible – are purely down to the quality of the components populating the PCBs. Given the amount of advertising ink (and review column inches) that have been expended on the subject of audiophile components, it’s too good a chance to miss, especially given the presence of this year’s fashionable must have parts – Teflon caps – in the SE model and top-price Tea-2MAX. But we’re getting ahead of ourselves here. Perhaps we should start by examining the basic product architecture – and what changes c-j have made to produce the more expensive versions.

The Tea-2 was first reviewed by AS back in Issue 70. It costs a pretty approachable £2,695, given that this is a fully active tube moving-coil phono stage, delivering 55dB of gain from a pair of cascaded 12AX7s for the input with another 12AX7 split between the two channels to provide a second gain stage. A mosfet output buffer provides a suitably low output impedance. The circuit is global feedback free and employs passive RIAA equalization. Two small banks of dip-switches placed inside the casework, adjacent to the single pair of input sockets, allow for user selectable load resistances in seven discrete values ranged between 130 Ohms and 47 kOhms – and that’s all the adjustment you get, although you can order a low-gain (LG) version of the TEA-2 that uses a 12AU7 in place of the second-stage 12AX7 to deliver 40dB of gain that’s more appropriate to medium and high output cartridges (moving-coils though, rather than full-fat moving magnets, with their even more robust signal levels). This isn’t just a case of swapping tubes, so although a high-gain unit can be switched to low-gain or vice versa, it requires a trip back to the factory and some component changes. In other words, don’t think you can do this at home…

The first thing to say about the TEA-2 is that by avoiding the use of input transformers to deliver low-noise gain, c-j has decided to challenge the performance envelope of their chosen active devices exactly where they are traditionally weakest. If that seems like an odd choice, the thing you need to bear in mind is the superior phase performance and linearity of active amplification over transformers. In a phono stage that means pushing tubes about as far as they can comfortably go – but no further; hence the modest 55dB gain. Not so long ago, low-noise and heaps of gain where top of the phono stage priority list, but nowadays things have got a lot more sensible. Cartridges with an output level below 0.4mV are few and far between, meaning that the TEA-2 will comfortably accommodate all but a select few cartridges currently on the market (and most of those come with a firm recommendation as regards a matching transformer). Interestingly, c-j’s own TEA-1 phono stage offers purchasers a choice of 54.5dB of all-tube gain, or 63dB if you opt for transformers, but it’s an option that’s been deemed unnecessary at the TEA-2’s price point(s) – and I can understand why. Running a range of different Lyra and Clearaudio cartridges I never suffered noise or gain problems, so I think it’s safe to say the c-j has called this one right.