From Pass X250,5 to 350,5 : what to expect?

The XA.5 series DO double down in power. The XA series do not. There was a mild re-design to allow the doubling of power. It is sonically insignificant, but if you want or need more power on tap the doubling down is a bonus.

Let's let Taboooe do the calcs for your power requirements. As for the amp size, I never recommended the X350.5 over the X250.5 or anything else, I just chimed in and said it sounded better to my ears for the reasons I listed. I believe the XA60.5 or XA100.5 would do just as well and offer things the regular series do not such as righer midrange, more liquid highs. At the end of the day, do you want pure class A or hybrid A-A/B?

Tboooe, since I am replacing both amplifier and speakers, info on my existing equipment won't do any good. I am going to go with Wilson Watt Puppy 8, thus rated sensitivity is 92 db, and impedance is 4 ohms. Distance between the tweeters and my ears would be 7 feet. Rock music is typically played at 70 db. Classical music goes anywhere from 55 to 85 db, but then it does not have as high a demand on the power hungry woofer.

spatine, assuming the sensitivity you provided is at 8ohm, here is what I calculated based on your numbers (these are only best estimates):

at an average volume of 70 db assuming a peak of +15db, you will need 0.03W at 4ohm and 1.0W at 85db

at 81 db average you will need 0.5W at 4 ohm and 16W at 96db.

If you speakers dip down to 2ohms. then double the power.

As you can see, you really do not need a lot of power. For you to use around 250W of power at 4ohm, you will need to be listening at 108db!

In opinion, most people do not need high power amps. However, as it has pointed out, sometimes higher power amps have better circuits or designs which produces higher quality power at lower output.

Note that these calculations were obtained from a spreadsheet I developed which has some assumptions, approximations, and estimations. For example, I assume it takes double the power to increase the volume by 3db. I also assume that the volume decreases by 5db for every doubling of distance from 1m.

Tboooe, I think all your assumptions are right and your conclusion regarding the need for power is right - we generally need a lot less than we think. I would only argue that given the same basic design approach, the lower power version of that design will sound better at a given volume level if the amp has enough power to reach that volume level with a given speaker. In the case of the 250.5 versus 350.5 comparison, the more powerful amp may sound better in this case if it is a no negative feedback design and the lower power amp isn't.

Thank you for the calculation, but it's pretty obvious that theory does not match reality.

As to the whole thread it does not seem that there is agreement either. The punch line actually reads 350W is preferred over 250W, yet 200W is as good as it's going to get (assuming the doubling of power for a 4-ohm). To be exact, even 120W is plenty. This does not, I think, help the originator of this thread or myself. The whole discussion is strictly about Pass Labs. So to make sense out of the power vs performance question, design differences between these amplifiers of the same designer must be pretty drastic. It's too bad that Pass Lab does not have enough dealers for a convenient audition. By default, I begin to lean more and more toward Ayre MXR by the week.