The Conrad-Johnson ET250S Power Amp

The ET in the product designation of this amplifier stands for Enhanced Triode, while the 250 is the rated output – Watts into 8 Ohms, naturally. But before the bearded triode brethren start getting all excited, the tubes in question are the 6922 twin-triodes used to provide the front-end of the hybrid circuit. That’s right – it uses a solid-state output stage, which is where all that power comes from, while truth be told, you are hard pressed to put your finger on those vacuum tubes’ contribution to the sonic picture as a whole.

The ET250S is a large, stereo amplifier built into c-j’s new “niche” casework, where the tubes peek from between semi-circular Perspex slats sitting in the forward facing alcove. Unlike the trio of pure tube designs that featured in Issue 52, the top-plate is barely perforated while the chassis sides comprise full depth heat sinks. In use the amp runs reasonably warm but not excessively so, making it a much better bet for enclosed installations than its valve brethren. Combine that with the high power output and you might start reaching a few conclusions regarding the ET250S’s target audience – but I couldn’t possibly comment. Facilities are as Spartan as ever, with a single pair of RCA/phono inputs and one pair of five-way binding posts per channel. The mains input is via a standard IEC socket, but watch out for the small dip-switch on the top right of the rear panel, which activates the remote trigger sensor. Knock it up by accident and you’ll be faced with a large and utterly unresponsive lump! In common with other c-j amps, the amplifier inverts absolute phase, meaning that you should reverse the polarity of your speaker leads in most cases, although not if using a c-j pre-amp. And therein lies a story, but I’ll get to that.

There’s no mistaking this amplifier’s power, headroom and transparency. Having spent three days sharing a room with it at the Denver Show, I can also vouch for its easy, relaxed sound quality, devoid of edge or hardness. In these two conflicting descriptions we find the core of a curate’s egg. In some respects the ET250S has all the classic qualities of a large solid-state amplifier. In others it’s more akin to a tube design. Does that make it the best of both worlds? Well, not exactly, and how well it sits with you will depend on your system and what you want from your music.

Stage width, depth and especially height are exceptionally well defined with the ET250S, but like many solid-state amps, it majors on sound sources and their locations rather than establishing boundaries and a coherent acoustic. So listening to the studio chatter and intro to ‘True Love Ways’ from the Buddy Holly Legend album, instruments are fixed and stable in space, the various control room speakers located perfectly for height and position. The relative heights of Holly’s vocal and the sax are also clearly defined, while the rhythm guitar and piano, which can easily blend together on this track were here quite distinct. Yet the rear wall of the studio, its side-walls and the floor were virtually absent, with some sense of the acoustic’s extent immediately behind instruments but no coherent overall space.

Results on the synthetic soundscape that typifies Jim White’s latest album (the superb Transnormal Skiperoo) are in many ways more obviously impressive. The stark contrasts created as guitars and samples pop out of discrete parcels opf space are extremely effective, especially given the crisp, clean presentation of the ET250S’s broad mid-band.

But it’s an album that also throws up a worrying discontinuity, the deep bass burbles that underpin proceedings seemingly soft, abstract and detached. It’s an impression further underlined with acoustic bass. The familiar, repetitive opening bars of Art Pepper’s ‘Las Cuevas De Mario’ may not have the tightest low frequencies ever recorded, but here they lack texture and shape, taking on a softened, almost blurred quality. The weight of the notes is in the right place, which means that rhythm, pace and the tempo of the music don’t suffer, but only if you work on your speaker placement. The c-j’s bottom-end certainly doesn’t lack depth or weight, but get the speaker positioning slightly wrong (which means you can’t simply rely on what worked with the amp that went before) and there’s more than enough of it to get you into real trouble.

However, even with the bass working at its best, the lack of leading edge precision and definition leaves a disconcerting contrast with the clarity and incisive dynamics of the mids. In truth, the bass issues are no worse than with many other amplifiers, but the rest of the range acts to draw attention to them. So those rounded bass notes with their softened edges stand against the sharp pace and purpose of Pepper’s fluid, surefooted lines and the beautifully timed cymbal work. But, much of that punch and clarity comes from an over-emphasis on the leading edge of notes – and a corresponding failure to fully develop their harmonic tail; wherein lies our curate’s egg. If purchasers assume that the ‘ET’ element in the c-j’s circuit will deliver warmth and colour to counter or temper the often monochromatic precision of solid-state, they couldn’t be more wrong. Likewise, the conrad-johnson name on thefront panel, for the ET250S sounds distinctly different to other, recent c-j designs. Indeed, as far as it’s fair to generalise, you could readily suggest that harmonic development, the colour and texture of notes has always been a strength in the company’s products, along with top-to-bottom coherence. Look no further than the all solid-state Premier 350 for evidence to support the contention.