The Audio Research LS17 Line-Stage and Ref 110 Power Amplifier

If any company has established a distinctive visual identity over the last thirty years or so it has to be Audio Research. Witness the fact that I still regularly use an SP 10 pre-amplifier dating from around 1986, yet sitting the LS17next to it I think that the casual observer would be hard pushed to determine which is current and which is the ‘vintage’ model. That continuity, disturbed only by a few labels and control functions, is as strong on the inside as it is on the surface.

My first experience of Audio Research products dates back to the D115 power amp and SP8 pre-amp somewhere in the early 80s, and they made quite an impression, partly because they were both stunningly good products, but also because they were my first contact with US high-end valve gear, designs that didn’t adhere to the established Mullard/GEC model. Somehow, despite reviewing various bits of Audio Research kit in the intervening years, nothing has quite elevated me to the dizzy plane of that first encounter. And initial impressions did little to suggest that the LS17 and Ref 110 were about to change this, but living with this Audio Research combination for a few weeks has caused me to considerably modify that opinion.

While clearly reticent to change the external aesthetics, when it comes to electronics the company have been continuously updating and refining their products with new topologies and components, and it has been interesting to observe this. Different models over the years have swung from the highly complicated, incorporating large numbers of semiconductors, to elegantly simple purist designs with barely a transistor in sight, typified on one hand by the D125 and on the other by one of the ‘Classic’ or VS series power amplifiers. Both the LS17 and the REF110 tend towards the latter school. Concepts that initially appear within flagship products are often passed down through the range, and this is an intrinsic part of the product development process. Thus we have the LS17 replacing the LS16, incorporating circuitry inherited from the flagship Ref 3 pre–amp, while the Ref 110 looks up to the mighty Ref 610 mono-blocs.

The 17 has a large, solid-state regulated power supply, and active circuitry based around a pair of Russian military 6H30 double triodes and an FET or two, to provide around 17dB of gain. There are five single-ended and two balanced inputs that are switched via discrete relays, two balanced and one SE output, together with both tape and processor loops. On the front panel, two rotary controls provide input selection and volume. Between these are two recessed panels the lower of which has small push button switches for power, mute, tape and processor selection, while the upper displays status and position of the 104 step volume control. The basic but functional remote handset controls volume, mute and input selection.

The REF 110 is, save for the power switch and a small green led on the front panel, a featureless box within which all the electronics are enclosed. Only balanced inputs are provided, which on the face of it might seem a little inflexible, but my understanding is that as this was conceived as a fully balanced design from the ground up, the addition of a single ended input would not have been a viable option. Loudspeaker outputs for 4, 8 and 16 Ohms are provided (as with previous ARC designs be aware that the 4 Ohm tap is at ground potential) and mains input is via a 20 Amp IEC socket, not the usual kettle type connection. The custom made binding posts are of high quality, but offer no easy way of connecting 4mm plugs (which is a pain from a reviewers point of view). Spades would be the connection of choice.

Internal layout represents a bit of a departure from previous Audio Research designs. A central channel runs from back to front on which the three transformers are mounted, mains at the front. On either side lies a quartet of 6550 valves that are force cooled by two fans situated on the back panel (three speeds are internally selectable depending on the ambient temperature). At its lowest speed there is still a small amount of noise, audible if you are sitting close, but bear in mind that cooler running valves will tend to last longer. A small LCD display on one of the circuit boards counts valve use in hours. Bias adjustment is a little more accessible (and slightly les hairy) than with previous ARC designs, with sockets now provided on the board for meter measurement, together with adjustment for each pair of valves via trim pots.

The 6550 power supply valve has been dispensed with in favour of solid-state regulation for the front end (there is no longer a need for a screen supply) where FET’s feed a pair of 6H30’s for gain and a cathode follower driver. The output stage continues an Audio research tradition by coupling the cathodes to the secondary of the output transformer, providing a degree of negative feedback and a tighter grip of the loudspeaker. The screens are now tapped in the more common ultralinear configuration; for many years ARC favoured running the valves in straight pentode mode, a factor that might have contributed to the trade mark ‘grunt’ at the bottom-end that I associate with many of their earlier amplifiers.