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


I am getting ready to make some upgrades to the system. I currently running a DAC into a BAT51SE, then a Pass Labs XA30.8, then finally into Decware DM947 speakers (don't worry if you've never heard of them; not the last word in speakers, but have been doing a solid job for about 5 years now.)

I am contemplating moving up the Pass Labs amplifier line, and the X250.8 looks attractive. I would like to hear more bass authority and definition, but I don't really want to sacrifice the mids and highs of the 30.8. 

I would love to hear some of your impressions of the X250.8, especially if you are able to make some direct comparisons to the XA30.8. I've spoken with both Mark at Reno Hifi, and Kent English of Pass Labs; both are wonderful and informative people. What I am interested in now is the opinions and experiences of end users of either of these amps. 

Thanks! 
willrich47

I thought I would follow up to give some closure to anyone reading this down the line. I always like to hear how people’s decisions turned out. Hopefully you do too. 

 

I purchased the Tekton Double Impacts, largely due to the advice I got from members here. While I am not ruling out an amplifier upgrade at some point in the future, I think the Double Impacts have had a more significant impact on my system, than an amp upgrade would have. 

 

The Tekton Double Impacts: 

 

The DI’s need some time to break-in. When I actually got my pair, I was surprised to hear they sounded “OK.” And by “OK,” I mean thoroughly OK, middle of the road, mediocre, and most of all: disappointing. But, it didn’t take long for the midrange to start opening up. The mid and upper range only took about 3-4 days to open up and sound wonderful. The bass, was a little different. 

 

I’ve been using an SVS SB16 subwoofer for a little over a year. When I started using the Tekton’s, it seemed apparent to me that the sound was improved with the SVS. A little over 30 days after getting my Tektons set-up, the bass seemed to change. All of a sudden, there was too much bass. I turned my sub down. A couple of days later, it seemed like too much again. This time I turned the subwoofer off. I eventually achieved the best integration with the SVS by crossing over at around 35-40 Hz. My RTA app on my phone says I had a relatively flat response down to 20 Hz. 

 

I remembered an email conversation I had with Victor Khomenko a while back. The VK-51se has two sets of balanced outputs on the back. I had asked VK if they could both be used at the same time. He said they could, but I had to be aware of the combined impedance of all the amplifiers attached to the VK-51se. 

 

My Pass Labs XA30.8 is relatively easy for my preamp to drive. The balanced input impedance is 100K Ohm. The SVS SB-16 on the other hand, is not as friendly; its balanced input impedance is 22K Ohm. I believe the combined impedance is found through the calculation (100 X 22)/(100 + 22) = 18K Ohm (I would appreciate if someone with some actual EE knowhow would fact-check me here).

 

As an experiment, I removed my SVS SB16 subwoofer from the system entirely. In my system, the DI’s start rolling off at about 40 Hz, so I lost some bass extension from the removal of the SVS. But what I gained was more drive and authority from the DI’s, and more color and clarity through the entire range. 

 

I don’t believe that I noticed this with my old speakers because they simply lacked the clarity of the DI’s, and did not have the same bass extension. With the old-speakers, the SVS simply improved the overall quality of the system. With the DI’s, there is a clear trade-off. Bass extension for overall sound quality (especially bass quality).

 

I have had my SVS completely unhooked from the system for about 2 weeks now. After about 1 week, I added it back to the system and found I disliked how simply hooking it up to the preamp affected the system. I quickly removed it from the system again. This has been an unanticipated side effect of adding the DI’s to the system, and has all but de-railed my plans for a second SVS-SB16 subwoofer. 

 

If anyone has some clever tricks for getting around this problem, I am all ears! 


@bobheinatz I think you were right ;-)


Just for clarity, the SVS SB-16 subwoofer is still the single best sub I've heard. I simply think the impedance drop is having a negative impact on the sound of the overall system. If I could use it without changing the load on the preamp so much, I think I would have some stunning results. 
Will, one thing you could try is a sub that provides high-level hookup from a power amp, rather than line-level from a pre. Two that do are REL and Rythmik. I don't know about REL, but Rythmik provides for both high (on binding posts) and low (on RCA jacks) inputs on their A370 and H600 plate amps, the non-XLR versions. On the XLR versions, low (line-level) only.
Haha, well, I just confirmed what I heard in this review of the BAT 51se: 

"The balanced output impedance was twice that specified, at 410 ohms over most of the audioband. This is low, though it did rise to a high 4.7k ohms at 20Hz, due to the size of the output coupling capacitors. (There is only so much room within the chassis for these high-performance but physically large components.) This will not be an issue with components having high input impedances, such as BAT's own power amplifiers, but it does mean prematurely rolled-off low frequencies with low load impedances (fig.1), such as those offered by some solid-state amplifiers."

Read more at https://www.stereophile.com/content/balanced-audio-technology-vk-51se-line-preamplifier-measurements

Now the question is, how do I fix it without replacing a preamp?
@bdp24 I was thinking along the same lines. I was hoping to do it without replacing the SVS. I've been searching for a high-level to RCA input converter, but haven't found a suitable solution yet. 

But you might be right. Maybe REL is where it's at. I am a little surprised that SVS doesn't offer this type of input solution, especially on their top-of-the-line unit. I have to think that more preamps would have this issue than just mine. Could be wrong though.