Threshold S/500 versus Mark Levinson ML2

I don't have directly relevant listening experience, but I see several problems:

1)Not enough power, despite the fact that the ML2's would only be powering the mids and highs. I say that especially considering that a lot of your listening appears to be to wide dynamic range symphonic material. This review of the Eros MkIII indicates that Innersound recommends amplifier power of 80 to 300W, while the ML2 is only 25W. Also, note in Figure 2 that the external crossover provides a boost of several db in the mid-range, which would increase the amount of power the ML2 would have to supply by a factor of more than 2, relative to what it would have to supply if there were no boost in that region.

2)The age of the ML2's (30 or so years) is likely to be a sonic variable that is both significant and unpredictable.

3)Repairs are likely to be expensive, if necessary in the future, and some parts may be unobtainable.

4)I believe that a pair of ML2's in prime condition will set you back upwards of $6K, which seems like a lot of money to invest given the risks I've listed above.

Regards,
-- Al

Unsound, thank you most kindly.

George and Brian_Eno, not to belabor a three year old thread, but your comments, while probably applicable to many electrostatics (for example, the original Quad ESL, with which the ML-2 is a classic pairing), are not applicable to THIS electrostatic.

As indicated in the Stereophile review I linked to earlier, it has a built-in low frequency amplifier, and uses the external amplifier for higher frequencies, with the crossover point being at 360 Hz. As indicated in John Atkinson's measurements in that review, the magnitude of its impedance is EXTREMELY high from that frequency up to around 8 kHz, when it finally descends below 8 ohms. Its impedance through most of the mid-range region is greater than 50 ohms(!), reaching 137 ohms(!) at 490 Hz.

A voltage-limited solid state amplifier rated at 25 watts into 8 ohms, such as the ML-2, simply cannot provide much power into those kinds of impedances.

Consider all of that in the context of the manufacturer's recommended power rating of 80 to 300 watts for the amplifier used to drive the electrostatic panel. Consider also, as I mentioned in my post three years ago, "that a lot of [the OP's] listening appears to be to wide dynamic range symphonic material."

Simply put, the ML-2, whose forte is delivery of high current into low impedances, is not a suitable choice for use with this speaker, and that is especially true if material having wide dynamic range is to be listened to. Although it should be noted that current capability is nevertheless not an insignificant consideration, given the speaker's highly capacitive phase angles in the treble region.

Regards,
-- Al

George, the impedance of the Quads at frequencies below the upper treble is far lower than that of the Eros. See the curve here, and compare it with the one for the Eros III that is shown in the Stereophile review I linked to earlier.

At 490 Hz, for example, the Quad is about 12 ohms, while the Eros III is 137 ohms, with a phase angle that is only very slightly capacitive. At that frequency, given that the ML-2's power capability into high impedances is limited by voltage swing capability, it would therefore be able to deliver more than 11 times as much power to the Quads as it could deliver to the Eros III.

At other frequencies, the Quad never gets above about 33 ohms, while the impedance of the Eros III is far higher than that throughout most of the midrange.

Also, as I alluded to in my initial post above, Figure 2 of JA's measurements indicates that the Eros crossover provides a boost in the mid-range that appears to be on the order of 5 db, which would add significantly to the voltage swing requirements that are imposed on the amplifier.

I don't know how the sensitivities of the two speakers compare (JA measured 88 db/2.83V/1m B-weighted for the Eros, with its crossover set for unity gain). But it seems clear that the two speakers are very different animals, and I would expect that when the manufacturer of the Eros provided an amplifier power recommendation of 80 to 300 watts, that they put some thought into those numbers.

Regards,
-- Al