conrad-johnson ET7-S2 line preamplifier

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Tubed preamplifiers
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Conrad Johnson ET7-S2
conrad-johnson ET7-S2 line preamplifier

Although we are one of the keenest magazines to get conrad-johnson products into print, sometimes it’s hard to keep up. We reviewed the original ET7 in February 2018 (Issue 156) and a year or so later, conrad-johnson improved the ET7 to ET7-S2 status, the product tested here. The changes are both physically and sonically significant, moving the ‘baby GAT’ ever closer to the performance of its bigger GAT Series 2 brother.

To recap (there is a pun in there, watch this space), that ‘ET’ prefix to the name means ‘Enhanced Triode’ because the circuit uses a single 6922 double triode tube, acting as a single-ended triode for each channel. This provides voltage gain and sends the signal to a similarly minimal high-current MOSFET buffer, which helps provide a very low output impedance. This makes the single-ended only ET7-S2 extremely flexible in terms of interconnect cable design and length. DC voltage is provided by a discrete voltage regulator that isolates the audio circuit from the power line by maintaining negligible impedance across the audio frequency band. In addition, infra-sonic noise is minimised by operating the tube heaters on a DC voltage supplied by a separate regulated power supply. All of which is a direct ‘trickle down’ from the design developments that took place in moving from the original GAT to the GAT Series 2.

The ET7-S2 retains the microprocessor-controlled relay system and network of metal-foil resistors as its gain control, allowing one hundred 0.7dB steps in volume and balance. The preamplifier has five single-ended line inputs, and two external processor loop input/outputs, the second of which puts the preamp into ‘Theater’ mode and automatically switches the ET7-S2 to unity gain. Unlike the entry-level ET6/6SE, there is no optional built-in phono stage, but there are two standalone phono stages in the range. Also, unlike the ET3, the ‘balance’ control on the remote control actually works, even if there is no replication of that balance control on the ET7-S2’s front panel. As ever with c-j, volume is displayed by a pair of two-digit yellow LEDs in the centre of the front panel, and these are flanked by yellow LEDs to denote source and function. Power up puts the ET7-S2 into soft-start heat-up mode, and the blinking mute switch is a reminder of that. The classic gold front is unique to c-j models, but it has a timeless, almost Art Deco style all its own. In fact, the front panel is completely identical to its predecessor, and even the ‘S2’ suffix is not included.

So, what’s changed? The power supply reservoir section is substantially improved, with the addition of five large c-j capacitors (hence the ‘recap’ pun) to the right side of the circuit board. In addition, the quality of the input and output connectors have been improved to bring them to GAT S2 standard. Visibly the product appears unchanged aside from the ‘S2’ part, and the much-improved build quality seen in recent models (including the ET7 it replaces) continues unabated. 

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