Having held a firm position in our product lineup for two-and-a-half years, the LS25 has proved highly popular for both its musicality and its many features and system flexibility. With recent engineering breakthroughs at Audio Research, however — especially stemming from the development of the VTM200 input stage technology — it became increasingly clear that the venerable LS25 was the perfect preamplifier candidate for these latest performance enhancements.

Because it already has so many useful control functions, the LS25MKII remains almost entirely unchanged in its exterior configuration — meaning original units can be updated at the factory to the MKII spec. Inside, however, you will find a new motherboard architecture that incorporates a JFET input stage similar to that used in the VTM200, followed by a cathode-follower / output driver stage using two 6H30 twin triodes.

The 6H30 is a new tube for Audio Research ideally suited to its function in the LS25MKII. It is a Russian military tube in current production and use, and is rated by its manufacturer to have an estimated service life of up to 10,000 hours. It has shown highly stable and consistent in its operating characteristics. While its pin configuration is similar to the 6922, it is not a direct replacement. It has higher current requirements for the heater filaments, so it requires a different power transformer than used in the original LS25, as well as power supply adjustments.

Finally, like the VTM200, the LS25MKII also incorporates a rear-panel 12V on/off trigger for even easier incorporation into audio-video installations, or simply for installations where the customer wants more convenient system control. This is the only external modification to the original. You will see this feature appear on future models from Audio Research as well.

The complete MKII changes are available to original LS25 owners as a factory update. New 6H30 tubes with damping rings are included. Contact the Audio Research Customer Service department to schedule any LS25 updates. Units sent in without prescheduling may encounter substantial delays in turnaround.

In performance, we believe the LS25MKII blows by the original in every respect. It is faster, more dynamic, more open-sounding and presents a more tightly focused soundstage. Bass response is cleaner, quicker, with more apparent impact, while high frequencies are much purer sounding than the original. You will love the coherence of the new MKII — vividly alive from top to bottom, with an immediacy that is stunning when driving really capable power amplifiers like the VTM200’s!

Once again, Audio Research brings new life and improved performance to an existing model, enhancing value for every owner.