Upgrade from Pass Labs XA30.8 to X250.8. Worth it?

Your calculation of the 18K is correct, and I feel pretty certain that your diagnosis of the bass issue is correct. The 18K load impedance divided by the 4.7K output impedance at 20 Hz is a ratio of 3.8, well under the rule of thumb guideline of a minimum of 10. And the wide variation from 410 ohms to 4.7K makes that situation particularly bad. (If the output impedance were 4.7K throughout the audio band the consequences would be mainly a slight gain reduction and increased sensitivity to cable effects, and perhaps a small degradation in the distortion performance of the preamp. While the large difference between the output impedance in the bass region and at higher frequencies, in conjunction with the heavy load impedance, will cause both frequency response issues and frequency-dependent phase shifts in the bass region).

To add to bdp24’s suggestions, a few years ago another member here, who uses Audio Research Reference series electronics, very successfully resolved a similar issue by having a tube-based buffer stage, providing suitably high input impedance and low output impedance, custom made for him by Tom Tutay of Transition Audio Design in Florida. It would be inserted between the preamp and the sub. I believe the cost was considerably less than $1K, although in his case balanced interfaces weren’t necessary. I don’t think Tom has a website, but a Google search should provide you with his contact information.

Good luck. Regards,

-- Al

A slightly old thread but thought I'd comment.  I have an XA30.8 (which itself was an update from an XA30.5) and had upgraded my speakers to Tekton Double Impact in my living room/primary setup.  The tonality was great, but I wanted to get more of that super-sharp imaging feeling/a bit more accurate reproduction, so after a few questions to Mark at Reno HiFi he strongly suggested trying the X250.8.

I did and have been quite happy with the results.  Mark may have found the perfect setup for me in the X250.8 + Tekton DI.  I haven't really noticed any degradation in tonality (but I never get anywhere close to the end of the class A envelope of the X250.8 even in my large living room at reasonable listening levels), but I *have* noticed the increase in imaging clarity, bass reproduction, and sense of crisp/dynamic control across the whole range.

I still have the XA30.8 in my secondary setup with some Amphion Argon 2's and the sense of lush tonality is great when I'm in the mood for it.

So I think it depends on what you're after.  The XA30.8 is already a bit of a move away from the "lush class A" sound in the XA30.5 I'd had before, but I enjoy accuracy of reproduction.  The X250.8 seems to be where they tried to give it yet more control and sharper reproduction while keeping at least some of the XA.8 magic.  Maybe that describes the differences between the X and XA series in previous generations as well, but at the .8 series it seems to have found a point where I'm pretty happy with the X and XA lines, with the X250.8 being my personal favorite so far.

In this price range Luxman m700u could have the edge in term of power and industrial design and I hope someone can compare them. I know WC compare the brands but different models.

@ebolyn

Even though this thread is a little old, your observations are still incredibly relevant. When I first started this thread, the question came down to new speakers, or a new amp. I made the decision to get new speakers, which was the right decision at the time. The Double Impacts have had a remarkable impact on my system. 

But it here I am again, looking at the upgrade to the X250.8! In a way, your timing couldn’t be better! 

I recently upgraded to the x250.8 from the xa30.8. While the xa30.8 sounded very good overall with a very lush midrange, beautiful highs and great imaging, I found it somewhat lacking in bass. The x250.8 is very close in the midrange (a tad less bloom) but has much better bass and slightly better imaging. I would call them equal in the treble range - excellent. Both amps extract an amazing amount of detail and have that live music feeling. Except for the bass I would have been very happy with the xa30.8. However, after directly comparing the two, I prefer the x250.8.

@jp_60173 Great input. What speakers are you using?

Sonus Faber Guarneri Tradition. Very slightly on the warm side and a great match with Pass amps. The x250.8 has a little less midrange lushness than the xa30.8, but to me with my speakers, this makes them sound more true to life. With lean sounding speakers the xa30.8 might be a better match. But then you may have that issue with bass. 

CH Acoustic X20 power cords, can someone provide me a link to their site?  My search revealed nothing.  Thank you in advance.

Hello,

I'm the exclusive retailer for CH Acoustic new products, including the Zafiro cables currently available on Audiogon and @amorsound.com.  In addition, I also have access to the CH Acoustic legacy products.

Please feel free to contact me if I can be of assistance.

Amor Sound

Hello,  Reading this just now and following along on the sub issue.
I have no experience with Tekton or BAT, but I do with REL.  Changing my setup from other subs with RCA inputs to dual REL (I have the Carbon Limiteds) and hooking them up with the high level inputs made all the difference.  Now the subs are just 'part of the music', and blend seamlessly.  They IMPROVED the imaging and soundstage, and pressurize the room beautifully.  They do not jump out at you, but sure are missed when turned off to compare.  the hook up is a bit daunting, and hum can occur in some situations, but there are clear videos from REL to work around this.  Highly recommend REL's musical subs.  I actually use the LongBow wireless from REL; I use the high level speaker outputs on my amps and then wirelessly to the subs...works great.  Ken