Pass x250.8 vs Boulder 850 vs Spectral DMA250

Hi Max65.

I would say the best amp of the three you mentioned for the Sonus Faber Elipsa Red is the Spectral DMA250 being BJT (bi-polar)output it can almost double it's wattage for each halving of load impedance all the way down to 2ohms, and that means it can do current better than the other two which are Mosfet and cannot do the doubling act like the Spectral can.

Your Sonus Faber Elipsa Red are magnificent speakers but are a pig of a load in the bass region and demand an amp that do current, even though they are 91db efficient.

Quote from Stereophile:
"Though this is slightly lower than the specified 91dB, the shortfall is not important. While it will therefore require less of a voltage swing to play loud, the speaker is still a demanding load for the partnering amplifier, with an impedance magnitude that drops to 2.5 ohms throughout the upper bass (fig.1). There is also a punishing combination of 4 ohms magnitude and –50 ° electrical phase angle at 70Hz that will suck gobs of current from the amplifier."

And that -50% phase angle could mean a load down to even 1ohm at 70hz.

Cheers George

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

You welcome Maz, it's all about the current delivery (even at low volume level) with speakers like yours and many others that have nasty load areas.
(Good current delivery is Doubling watts or close to it.)
EG: 50w-8ohms 100w-4ohms, 200w-2ohms, 400w-1ohm.

This is why at normal listening levels the very old Mark Levinson ML2 monoblocks, even though they were only 25w into 8ohms (yes 25w!!), sounded more powerfull than 400w amps driving the same speakers that had hard loads, like yours and many other expensive ones that are around.

Cheers George

I don't know the vintage of these and there are many many others to look at, so this is a bit of a guide only for you to do your own home work with.

Here are just some that look to have bi-polar output transistors as they seem to come close to doubling wattage for every halving of load impedance from 8ohm 4ohm 2ohm.
I dug these out of Stereophile's test results they seem to do the current needed for the heavy load in the bass your speakers have, but as for the sound it's up to you to decide

Parrasound JC1 monoblocks

Ayre MX-R monoblock

Simaudio Moon Evolution W-8

Mark Levinson No.431

Mark Levinson No.436 monoblock

Classé CAM 350 monoblock

Classé Omega power amplifier

Most of the older big Krells, the ones with masses of heatsink are bi-polar (BJT) So is Dan Agostino's new Momentum and others are out there.

With your speakers stay away from Mosfet output and look at bi-polar (BJT) if you want the very best out of an amp that can drive that nasty bass load your speakers have.

Cheers George

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