Thoughts of Pass XA30.5, 60.5

Samhvcc,

You are right on in the comparison of the 30.5 & the 60.5.
I own a 30.5 & I continually consider buying another.
My Avalon Avatars & my Apogee Stages are biwirable/biampable. Both speakers would obviously sound better with more power.
There are a consistent number of 30.5s for sale here simply because the owners want more power. They're happy with the 30.5 sound, they just want more grunt.
From a purist standpoint, the 30.5 should sound better, because you are dedicating a discrete channel to the hi/lo section of each speaker. As long as each 30.5 is biased the same, you can use one amp on each speaker (vertically biamp). This allows short speaker cale runs - you can place each amp very close to each speaker, like a monobloc.
If you're not sure each amp is biased the same, you can just use one for the tweeter section of each speaker, and one for the low frequency (horizontal biamp).
I've done all this before, on my Magnepan 3.3Rs.
I used Adcom 555IIs and Parasound HCA1200IIs. I had my dealer bias the Parasounds, they did sound better/stronger than the Adcoms because by definition the vertical biamped setup allows more power to each low frequency section,
simply because the tweeter section draws less power & leaves more of the power supply for the low frequency section.
All these details become moot on a speaker like the Wilson, with only one set of speaker inputs. This speaker type requires that you use one stereo amp or two monoblocs..

One thing to be careful of is the load impedance that would be seen by the preamp. The XA30.5 has an input impedance of 30K balanced and 20K unbalanced. If the preamp were driving two XA30.5 inputs, and if the preamp has two pairs of outputs that are not individually buffered (as is often the case), it would see only 15K balanced or 10K unbalanced, the same as if a y-adapter were used with a single pair of outputs. Many preamps, especially tube preamps, cannot properly drive that low an impedance.

If the preamp provides two pairs of outputs that are individually buffered (as opposed to simply being wired together inside the rear panel), that would not be a concern (although the 30K/20K is still low enough to be a problem for some preamps).

Regards,
-- Al

You also need a very, very good Xover such as the Pass XVR1 which costs $4,000.

You are talking an additional $9,500!!!

Don c55,

All the speakers I mentioned do not need an active crossover.
It is an optional luxury.

Another option would be to look for a non XA series Pass amp for less money than a second XA 30.5, maybe a 150.5 or 250.5 for the lower frequencies and run a XA 30.5 on the top. As much as a crossover may be of benefit, I would try every technique possible to do this with the existing speakers' crossover. Additional active crossover will likely reduce the system's 3D performance, another pair of ICs and a power cord will be required. That's a lot of money.

Ultimately, I think the XA 60.5 would be better performance than all the extra connectivity to biamp.

Thanks all for your input!
I'm not sure about the impedance issue raised by Almarg.
What would the sound become if the impedance drops to 15K balanced or 10K unbalanced? I've no ideas in the technical issues actually.

If your preamp is solid state with an output imp. of 100 or so Ohms then you should be just fine with the 2 amps.

What would the sound become if the impedance drops to 15K balanced or 10K unbalanced?

The rule of thumb for proper matching of preamp output impedance and power amp input impedance is that the power amp input impedance (or the combined impedance of two amp inputs, if they are driven by the same preamp output stage) should be at least ten times the output impedance of the preamp, at the frequency within the audible frequency range for which that output impedance is highest.

That requirement will be met by most (but not all) solid state preamps under most circumstances. However, many tube preamps have output impedances of a few hundred ohms at mid and high frequencies (which is also ok under most circumstances), but which rise substantially at deep bass frequencies, often reaching a few thousand ohms at 20Hz. That rise occurs because of the coupling capacitors that most tube preamps (and some solid state preamps) have between their output stage circuits and their output jacks. That rise in output impedance at low frequencies will roll off the deep bass significantly when connected to a load impedance as low as 10K or 15K.

If the 10x rule is not satisfied, frequency response irregularities can also occur in other parts of the spectrum, to the extent that the impedances vary as a function of frequency. Under extreme circumstances, distortion can also worsen significantly.

If the preamp has been reviewed by Stereophile, John Atkinson's measurements which are usually included with the review will indicate the preamp's worst case output impedance, and whether or not this may be an issue.

Regards,
-- Al

Jafox's suggestion seems to make a lot of sense XA highs/mids X bass.

Why not ask Mr. Pass for his opinion? That's what I'd do.

Some folks trust users more than sellers, though NP does have a reputation of being a straight shooter.

I'd contact Pass directly as some have suggested. I'd also request that you post the response in this thread. It's an interesting question.

Nelson Pass is one of the most honest designers there is. He will give you an honest opinion. Anyone who questions his integrity is a fool.

Agree with Liguy.

I've asked Nelson dozens of questions over the years and the responses have always been independent of his business interests.

IMO

Dealer disclaimer

I'm sorry, I must have missed it, did someone question NP's integrity? Yes, please post NP's response; it is an interesting question.

I'm having the old Pass X250 and thinking to upgrade to the XA30.5 to run my Mini Utopia (db 91.5). I read great reviews on the XA30.5 but will I lose a lot for the low frequencies? Or a little more cost to go with the X250.5 ?

Any opinion?

Thanks.

Per the Pass Labs website statesthe XA30.5 has enough power for most people on speakers with 87dB sensitivity and above.

I drive my Magnepan 3.6s (86 dB sensitivity) with the XA30.5 and get great bass down close to 30Hz in my average sized room.

I do not listen to peaks above 90dB, except rarely, and the meter shows A/B only 2% of the time at most. I cannot detect an audible degredation in the instants that the amp changes to A/B. At 4 Ohms the XA30.5 can go to 195 watts A/B, giving adequate headroom.

If you are a loudness maniac you may not be satisfied.