Microstrip,
It is my understanding that the, Lp275 and Art Mono share the same ultra wide bandwidth Output transformers. The lower powered models, LP140 and Lp70 share a different output transformer which does not have the same bandwidth. The leap in performance from an LP140 to LP275 is considerable and the output transformers accounts for a part of this.
The major change from Premier 8 to Lp275 was in the input circuit and a refined board layout with of course the use of Teflon capacitors. The change from LP 275 to ART is mainly the input circuit and a few refinements in output stage that changed. For the whole the 8 – 275 – and ART mono’s all share the same basic output design….with the ART and 275 being the most similar overall.
As for modification to the Lp275 Amplifier ….. Progress slowly, evaluate each step on its own and allow at least 50 hours of play in-between changes ---It is all very personal at this point------pre ‘burn in’ of new components is recommended using a signal generator or other source ( a cheap receiver playing 24/7 with components wired in series to the speaker works well .
All signal series resistors –Vishay vsh1 ( yellow ) can be systematically exchanged for Vishay Z foil 2575/Charcroft. The grid resistors in the input stage are also worth looking at.
As good as the CJ Teflon capacitors are– I have used Dueland Cast to very good effect in the coupling capacitor position and prefer it . Thankfully the coupling cap sizes in the power amps are low value compared to the pre amplifiers and cost considerably less.
There is more scope for improvement with the older pre amplifiers – Premier 16 and ART than on the power Amplifiers.
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