Is powerfull Amps only for low sensitivity speakes?

Kalali 1-20-2018
The OTLs are exceptions because they tend to have an un-tube like very low output impedance thus a higher than average damping factor.

Hi Kalali,

This is a rare instance in which I must correct an oversight in your usually sage commentary. OTL power amps do NOT have very low output impedance. A fundamental purpose of the output transformers that are incorporated into most tube amp designs is to transform the typically very high impedance of tube-based circuits to a much lower output impedance, which is accomplished by stepping down the signal voltage provided by those tubes while stepping up the current. OTLs typically compensate for the lack of the impedance conversion a transformer would provide by using a plurality of output tubes, and by choosing tubes suited to operation at relatively low voltages, but nevertheless the resulting output impedances and damping factors are usually in the same ballpark as those of many tube amps which have output transformers.

Atma-Sphere OTLs, for example, have damping factors ranging from a bit more than 1 to around 5 or so. An OTL that used to be made by Tenor had a higher damping factor, around 20, but even so the recommended load impedance for that amp was 8 ohms minimum.

Also, speaking of sage commentary, +1 to everything in the post by Charles which followed shortly after yours.

Best regards,
-- Al

Sounds good, Ozan! The Sonic Frontiers Line 3 is a fully balanced design, so it can certainly be assumed that it provides a balanced pair of signals on its XLR output connectors. And given the very high 300K input impedance of the GS150 there certainly won’t be an impedance compatibility issue.

Enjoy! Regards,
-- Al

I took a look at John Atkinson’s measurements of your speakers and at the description and specs of the GS150, and as far as I can tell from those documents the speakers and amp should be a fine pairing.

I assume that your preamp can provide balanced signals to the power amp, because like many ARC balanced power amp designs I’m pretty certain the GS150 will not work properly if provided with single-ended inputs via RCA-to-XLR adapters (or, for that matter, if the preamp provides single-ended signals via XLR connectors, although that would be unusual in a high quality design).

To address your initial question more generally, IMO using an amp that is more powerful than necessary can raise at least two concerns (although neither appears to be applicable in this case):

1)There tends to be a **loose** correlation between the power ratings and the gains of various amplifiers. If the overall combination of speaker sensitivity, amplifier gain, preamplifier gain, and source output level is too high, the volume control on the preamp may have to be used at very low settings, where various undesirable effects can occur.

2)Everything else being equal, more watts = more $. So with a higher powered amplifier a greater percentage of the dollars one chooses to spend may go toward power rather than quality, compared to spending the same number of dollars on a lower powered amplifier. Assuming at least that the topologies and class of operation (A, AB, or D) are similar between the amps that are being compared.

Good luck. Regards,
-- Al