If not a model1 amp, any medium wattage deep class A solid state, with a reasonable input impedance (+10kOhm). Some of the old electrocompaniets, old mark levs (the 25W? ones), are possible candidates TRY a few, the pre1 is easy to carry along to dealers! You want to check for midbass and upper bass frequencies (most spkrs can manage these), and upper treble detail & energy when reproducing transients (cymbals, etc). I do mean check for energy & presence in these frequencies... whether the overall sonic result is to your liking is another matter (that you settle on the spot!). Cheers
