In need high-efficency speakers

The difference between 6 watts and 40 watts is about 8 db.  Roughly speaking, for a rotary volume control an 8 db change typically corresponds to about 60 or 70 degrees of rotation (aside from settings near the bottom of the control's range, where volume changes occur more rapidly).

So I would expect that you should be able to get to at least the 2 o'clock position without driving the amp into clipping.  And in any event I would expect that you would hear obvious distortion well before any damage would occur to either the speakers or the amp.

Good luck.  Regards,
-- Al 

Mjcmt, given that you’ve purchased a pre-owned amplifier, I’m wondering if the reason the sound "hardens" when the volume control is turned up past the 12 o’clock position might simply be that some of the tubes might not be in good condition.

In any event, consistent with my earlier comments it seems to me that buying new speakers to compensate for the fact that turning the volume control up high enough to utilize the majority of the amp’s power capability is not possible without significant sonic degradation, while not first determining what the root cause of the problem is, would not be a good approach. And if the root cause of the problem ultimately cannot be determined, I would consider replacing the amp, not the speakers. As I indicated earlier, you are probably not using more than about 6 watts of its specified 40 watt capability.

Good luck. Regards,
-- Al

Btw Al, Mystere doesn’t have regular rotary pot volume but resister ladder control, if that matters.

Photos of the amp appear to show that the minimum position of the control is around 6:30 or 7 o’clock or so, and the max position is around 5 or 5:30 o’clock or so. And of course the control is rotated between those positions, as opposed, for example, to a control that is rotatable through multiple turns (with a separate indication of the volume setting being provided), or a control that consists of an up button and a down button. Given that, whether the control is a continuous pot or a stepped resistor ladder makes no difference with respect to what I said earlier.

Good luck. Regards,
-- Al

...there is a bit of hardening to the sound at 12:00.

Thanks for the additional info, Mjcmt.

Roughly speaking, a typical single-turn rotary volume control such as the one on your Mystere will provide around 22 db or so of attenuation at the 12 o’clock position. Your Yamaha Blu-Ray/CD/SACD player has a maximum output that is nominally spec’d at 2 volts. The approximately 8 db of gain provided by the amp at the 12 o’clock setting (30 db max gain - 22 db of attenuation by the volume control) will boost a 2 volt input to about a 5 volt output.

5 volts into what I suspect is the 4 ohm impedance of your speakers corresponds at most to 6.25 watts, and to less than that to the extent the speaker’s impedance is not purely resistive.

So as I see it you are not turning the volume control up high enough to utilize most of the power capability of the amp. However I have no thoughts as to why the sound is hardening at higher settings of the control.

Regards,
-- Al

P.S:  I see that you also have a FiiO D-3 DAC.  Its maximum output rating is 1.6 volts, which is only about 2 db less than that of the Yamaha.  So what I said in my previous post with respect to the Yamaha is essentially applicable to the FiiO D-3 as well.

Regards,
-- Al

P.S. to my previous post: Keep in mind also that the difference between the 120 watt capability of your previous solid state amp and the 40 watt capability of the Mystere is only 4.8 db. And the resulting maximum volumes provided by the two amps may have differed by even less than that, if the speakers were starting to undergo "thermal compression" as the 120 watt amp approached its maximum power capability, and also because tube amps tend to enter their clipping region less abruptly than solid state amps.

All of which adds to my suspicion that the issue might be a gain problem and not a power or speaker sensitivity problem.

Regards,
-- Al

A question for the OP: When you say that you can’t get enough volume with the combination of your 40 watt amp and 87 db speakers, is the symptom (a) if you turn the volume control up past a certain point you hear clipping distortion, indicating that the amp can't supply enough power, or (b) you simply run out of range on the volume control, and at its maximum setting the sound is undistorted but is not loud enough, which would signify a gain problem rather than a power problem?

One reason I ask is that the 30 db gain of your Mystere integrated amp is on the low side, for an integrated. Another reason I ask is that as Audiothesis stated earlier "40 watts will get you around 103 db at 1 meter and that isn’t anything to scoff at." (And that is from just one speaker, not two. Although it assumes that the specs on the amp and speaker are accurate. Also, at distances greater than 1 meter that volume will fall off at 6 db per doubling of distance, neglecting room effects).

All of which leaves me unsure as to whether the problem is not enough power capability for your 87 db speakers, or not enough gain, or perhaps both. If the problem is not enough gain, there are probably solutions that are considerably less expensive than purchasing new speakers.

Regards,
-- Al