Suggestion used tube amp between $1,500-2,000

I noticed that in your other recent thread you indicated that at an early stage of their breakin the new SF speakers have been sounding bright. Presumably that will improve as more hours are accumulated. But I want to caution that a tube amp, somewhat counter-intuitively, may not be helpful in that regard, and depending on the particular tube amp may actually increase the brightness.

The reason I say that is that the impedance of your speakers, as shown here, varies from less than 4 ohms in the mid-bass region to very high values, more than 20 ohms, in much of the brightness region (e.g., 2 to 5 kHz). The relatively high output impedance of most tube amps (compared to nearly all solid state amps) will interact with that kind of impedance variation in a manner that will give greater emphasis to the frequencies at which the speaker impedance is high. The degree of that effect will depend on the output impedance of the particular tube amp.

The RM-200 which bdp24 suggested has significantly lower output impedance than most tube amps (see Stereophile’s measurements), especially on its 4 ohm and 1 ohm taps, and so in that respect, at least, it would seem like a good choice. I’m not so sure about the other amps that have been suggested. However the 15.4K input impedance of the RM-200 is less than the 20K minimum load that is recommended for your ARC preamp.

I’ll mention also that nearly all solid state amps have output impedances that are near zero, and so with your speakers would not emphasize the brightness region as a result of the effect I described above. However many solid state amps will intrinsically tend toward brightness, compared to many tube amps, in part due to their tendency to incorporate greater amounts of feedback than many tube amps. So it may be matter of picking your poison.

I don’t have any particular suggestions to offer that are within the price range you indicated, but those are some thoughts I would consider. And before making any decisions about amplification it would probably make sense to wait until the breakin process of the speakers is further along.

Good luck. Regards,
-- Al

Regarding power requirements, I would add that in addition to room size, listening distance, and individual volume preferences, a very major variable is the dynamic range of the type of music that is listened to.  Dynamic range meaning the difference in volume between the loudest notes and the softest notes.

Many and probably most pop and rock recordings are compressed to dynamic ranges of less than 10 db, meaning that less than 10 times as much power is required to reproduce the loudest notes as is required to reproduce the softest notes.  While many recordings in other genres, such as classical symphonic music, can have dynamic ranges of 30, 40, or even 50 db. A 30 db dynamic range means that 1,000 times as much power is required for the loudest notes as for the softest notes. A 40 db dynamic range means that 10,000 times as much power is required for the loudest notes as for the softest notes.  And music having wide dynamic range will generally be played at levels such that brief dynamic peaks reach much higher volumes than the peaks of music that never gets much above its average level.

Which is one reason that like most recommendations for amplifier power that are provided by speaker manufacturers, SF's recommendation for the Venere 2.5 (40 to 250 watts) covers a very wide range.

Regards,
-- Al

Thanks bdp24. But note that the LS7 preamp only provides unbalanced RCA outputs. And using an adapter to put the unbalanced signals into the amp’s XLR inputs would most likely still result in the LS7 seeing a 15K load, as the 30K figure most likely reflects the sum of the impedances of the two legs of each of the balanced inputs.

Regards,
-- Al