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

To summarize what I think Doug and Syntax are saying, don't do it. If your phono stage had sufficient gain for the 0.24 version of the UNI in the first place, then you will gain nothing by switching to the 0.48 version, and the latter is not as good sounding. If the phono gain was never sufficient, by criteria described by Syntax, then you may need to have it modified or replaced. If you really think you have a bad bearing in your tonearm, then first and foremost you need to have it fixed or replaced.

If you are married to those speakers, I agree with all the others; you need to select a different amplifier. As a long time Atma-sphere devotee, I would instead choose a speaker better suited to the amplifier. For me, I don't know which came first, because I have been listening to OTLs driving ESLs all my audio life, as a matter of preference. If you should choose to switch to Sound Lab ESLs, I have many useful ways in which to improve dramatically the match between an Atma amp and an SL speaker. In this case, the word "dramatically" is an under-statement, not an exaggeration. I am driving my Sound Lab 845PXs with my highly modified Atma OTL amplifiers, but the modified speaker can be driven to very loud levels by ANY 50W tube amplifier, after modification. In addition to a vast upgrade in efficiency, the modifications also increase the impedance across most of the audio band, not less than 20 ohms from 50Hz to 5kHz. A win-win. Just let me know if you want input on that subject.

Since the jumpers used in the Atma amplifiers to reduce gain do reduce gain by converting the voltage amplifier stage from a dual-differential cascode to a simpler dual-differential topology, it is entirely possible that the signal to noise ratio might well go UP rather than down with vs without the jumpers. Cascodes have a pretty darn good signal to noise ratio. But in either case, there would likely be no problem except possibly with ridiculously efficient speakers, i.e., >105db. (I chose a number out of thin air.)

On the subject of speaker efficiency: I think the benefits of efficiency, if you define that as 90 or 92db and up, are huge, provided the speaker is otherwise well designed and pleasing to its owner. I do not care for much less efficient speakers, if they come by their inefficiency by virtue of a multi-way complex crossover, regardless of how huge and powerful the driving amplifier may be. I don't find that huge power can overcome the sluggish behavior of such speakers. On the other hand, horns are not my cup of tea, either. They invariably sound great for the first 15 minutes, however. This is purely and only my own opinion.