Zyx Universe. O.24 mv vs .48 mv with low eff spkrs

You're using OTL's with 84db speakers? Why?

I never understood the point of low efficiency speakers. They put such demands on the amplification chain that sonics are bound to suffer. Show an amplifier an easy load and it'll dance or whisper or roar, as the music demands. Weigh it down with inefficiency and difficult impedance levels and, well, it just won't.

A pair of Krell monoblocks could drive those speakers easily... but you'll never hear what a UNIverse is capable of through a SS amp. Time to re-assess your priorities?

I agree with Doug Deacon. You are using the wrong amp with this speaker. Atmospheres really do not like loads below 6 ohms and with this low efficiency you really need at least 200 tube watts. I would not like the match of these two pieces as they have the same sonic character. The Salk speakers are very open but tend to be on the lighter side and this is the same signature of the atmaspheres. Oh boy what a poor synergy. Thats why you see atmaspheres with Sound Labs because Sound Labs are on the warm side of neutral and the atmaspheres are on the leaner side. I'm not judging you as you make like this kind of sound. I wish you the best.

Do you ever want to crank the volume beyond the highest setting you have available?

getting close to wanting to, it is usually just enough for my louder listening, but I have to use a hi watt amp (Van Alstine 600r)

As a point of information, the 84 db/2.83 volts/1 meter/4 ohm specs of the speaker correspond to only 81 db/1 watt/1 meter.

The Van Alstine amp, having a solid state output stage, will presumably be capable of delivering considerably more power into 4 ohms than the 300 watts it is rated at (presumably into 8 ohms). But I suspect that the power capability of the MA-1's will not be a whole lot greater than their 140 watt/8 ohm rating regardless of what transformation ratio you choose on the Zeros you appear to be using with them.

140 watts into 81 db/1W/1m speakers will just get you to maximum SPL's of around 95 to 98 db at a listening distance of around 10 feet, neglecting room reflections, and less than that at greater distances. That will be enough for most listeners for most recordings, but I suspect it will not be enough to cleanly handle the dynamic peaks on some of the symphonic recordings you mentioned that you listen to.

So using those speakers with the Atmasphere amps + Zeros may leave you with a power shortfall even if the gain issue were somehow resolved. While with the Van Alstine amp you have a gain marginality and probably also some degree of sonic compromise. Depending on the input impedance of the Van Alstine amp you MIGHT be able to resolve the gain marginality, without introducing significant additional sonic compromise, by putting a suitably chosen Jensen transformer having a 2:1 step-up ratio between the preamp and power amp. Doing that would give you close to 6 db of additional gain (equaling the volume increase that would result from going to the HO version of the cartridge), but would result in the preamp seeing a load impedance equal to the input impedance of the power amp divided by 4, which may or may not be acceptable. (There does not appear to be a spec on the input impedance of the amp).

However, given the extremely high quality of your turntable setup, your preamp, and of the Atmasphere amps you apparently still have, I would have to agree with the previous posters that what would make the most sense is to replace the speakers with ones that are both more efficient and higher impedance (and are also known to work well with OTLs), and selling the Van Alstine amp.

Regards,
-- Al

So they're actually just 81db efficient when stated with industry standard specs? Ouch.

Very good discussion here and with wise opinions.
Syntax, your heavy/light car analogy for high/low efficiency speakers is a excellent illustration. I've never understood the prevalence of inefficient difficult to drive speaker that require behemoth amplification. This results in poorer sound quality in my opinion. In this case the Salk-Atmasphere isn't a good pairing, one or the other has to go.High End audio moved away from high efficient-high impedance speakers a couple of generations ago. This was a wrong turn and not a good direction to follow.
Charles,