Pass x250.8 vs Boulder 850 vs Spectral DMA250

08-15-14: Maz65
@I was asking for suggestion because coupling tube preamp and solid state amp could be very critical but I feel to follow this way, because I hear the potential of this solution.
Maz65 (System | Threads | Answers | This Thread)

Yes Maz65 a tube pre to a solid state power amp/s needs to be thought about, as it's just like impedance matching a passive pre to a solid state

A tube pre's are generally much higher in output impedance than a solid state pre's, therefore they need amp/s that have higher input impedances, 47kohm or higher would be a good start, there is no problem with tube amps because they are usually 100kohm input.

But your Sonus Faber Elipsa Red to get the very best out of them demand an amp like I outlined above, one that gives current all the way down to 1ohm, and that means solid state BJT (bi-polar) output stage that can almost keep doubling it's wattage down to at least 2ohms if not 1ohm.

I can think of even better ones, but out of the three amps you gave us to recommend, only the Spectral has close to goods I've mentioned above.

And it is tube preamp and passive preamp friendly as it has 100kohm input impedance.

Cheers George

Thanks George, about input impedance I also see Pass x250.8 has input impedance 50k unbalanced and 100k balanced.
Bouder 850 have 50k balanced and 25k unbalanced, so it seems not working at its best with a tube preamp.
Very intresting.
Now I'm writing do McIntosh asking them the C2500 output impedance: I was not able to find this info elsewhere.

Maz65 look in your manual of the C-2500 under specs, it's 220ohm so no problem either.

As you still mention the Pass and the Boulder these are both Mosfet output amps, while they both are very good amps, for your speakers they are not going to drive them to their absolute potential. Because of the nasty phase/load they have in the bass, only a bi-ploar (BJT) output amp will do that.
And the only one that can that you mentioned is the Spectral.
But there are even better than this if you care to know, just say so and I'll do searching for you and post them up.

Cheers George

George, any contribution in that sense will be greatly appreciated by me. So please give your suggestions. I'm in the situation where I'm "free" to test almost everything.
Max

@George, yes the C2500 output impedance is 250 ohm (I just received the email from macintoshlabs).