Rhea vs Pass XP-15

I own the Pass XOno and have heard the Rhea in a different system. But I have never compared the two directly. So, like the OP, I'm interested in how they sound different. I wish Mechans and others who have a preference for the Rhea would explain why they like it over the Pass. Dfhaleycko does provide a helpful opinion with a clear description.

Dhcod, I too feel the instruments being played, and that is with my Xono in my system. I find the XOno to be very transparent and silent. It adds very little to the signal from what I can tell and it has plenty of gain for a cartridge with .3mv output. The XP-15 is supposed to be even better, though I have not heard it.

With respect to the Rhea, there is an impedance compatibility issue that needs to be considered.

You mentioned in your other recent thread having a Bryston BP26 preamp, which has input impedances of 15K balanced and 50K unbalanced.

According to JA's measurements of the Rhea in Stereophile:

The [Rhea's] output impedance was a low 110 ohms at 1kHz from the balanced jacks, this rising inconsequentially to 156 ohms at 20kHz but, more significantly, to 3846 ohms at 20Hz. This rise at low frequencies is due to the limited size of the coupling capacitors and implies that the Rhea must be used with a line stage having an input impedance of at least 30k ohms if the bass is not to sound lightweight. The output impedance from the unbalanced RCA jacks was a high 2k ohms across most of the audioband, but as this rose a relatively small amount at 20Hz, to 3.05k ohms, the preamp's tonal balance will be less affected by the line stage having a lowish input impedance.

So using a balanced connection between the Rhea and the BP26 would stand a good chance of perceptibly degrading deep bass response, at least slightly.

On the other hand, while using an unbalanced connection between the two components would avoid that problem, you would be sacrificing the potential advantages of a balanced interface with respect to noise rejection and reduced susceptibility to ground loop issues. And you would be using an unbalanced connection at the output of a component whose internal signal path is differential aside from its input stage, which does not seem ideal.

Regards,
-- Al

Thanks Almarg, I think the XP-15 has an output impedance of 300 OHMS the 25 is 150 and as you said the Rhea only 110. Thinking with the combo of a low output cart and a solid state pre, the Pass may be the best choice.

Initially I was all Rhea, but thinking technically rather than emotionally (mmmm tubes) now I leaning towards the Pass. These two new Pass units are also using some,pretty damn nice output devices. Think they are what are making the 15 sound so much better than the older xono.

Almarg's remarks make good sense. I note that the "Signature" version of the Rhea uses coupling caps that are twice the value of those in the non-Signature version. (4uF vs 2uF, respectively.) The larger caps would go some distance to ameliorate the problem noted by the Stereophile tester. That is a worthwhile upgrade and could be done rather cheaply if one knows how to solder and owns a non-Sig Rhea. The output impedance at 20Hz would be halved.

Dhcod,

Yes very well put and clear! I totally agree that the Rhea puts the flesh on the bone sort of speak!