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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
kosst_amojan
2,095 posts
 
Auxinput,
I'm not sure you understand class A, especially in push-pull. The demand on the power supply in a class A push-pull amp hardly changes at all until you're laying out double the rated power. An amp like the XA25 is biased to 25 watts, but it has a class A envelope of 50 watts. As the amp swings voltage, one half turns on more and the other half turns off an equivalent amount. Most class A amps will deliver current way beyond what will melt the outputs. Mine certainly will. Every Pass amp I'm familiar with will. Push-pull class A amps are really nice because they just transition to AB and keep swinging voltage when pushed outside their envelope, and most are designed with power supplies that will do that. That's why the XA25 measures so well way beyond power rating. 
auxinput
1,538 posts
 

kosst, honestly, I really don't trust anything you say anymore.  Now if almarg came in and corrected me, I would believe him.

I do know that Class A amps have a much larger constant A/C draw.  In Class AB an amp might have an idle current of 63 watts, but if biased to something like 30 Watts Class A, the constant "idle" A/C draw may go up to something like 160-170 watts.

kosst_amojan
2,095 posts
 
Auxinput,

Where do you think all that constant power draw goes? It goes straight into the heatsinks. Use some thinking here. If a 30 watts amp is dissipating 120 watts in pure heat just sitting there, do you really think that's anywhere near the full extent of the power supply's capacity? Unlike a class AB amp, that thing needs to deliver close to 5.6 amp constantly assuming 32V rails, which is what you'd want. A 600VA transformer (typical for a 30 watts class A amp) is going to put 12.5 amp per rail. You're pushing that amp WAY out of class A before you peter out the power supply. You can get away with torpidly built transformers in class AB amps that run higher voltages with lower current ratings because they hardly get warm under idle. That's the major reason class AB exists. The most expensive part in the entire amp doesn't need to be as expensive. 

All of that said, a well designed class AB amp with a decent regulated supply can certainly hold it's own against a similar class A amp with a massive unregulated power supply. 

I know people like to think those boards with the transistors on them are the real special, expensive parts, but nothing costs more than the transformer and the chassis. That's why class A is so expensive. 
browndt
83 posts
 
You should consider the X350.8. It is in a whole new league compared to the X250.8. It has all of the tonal qualities of a class A amp but with
detail and pure strength when needed. It is probably their best amp for the money.
willrich47 OP
25 posts
 
@browndt that amp is also intriguing. There’s one listed on Audiogon right now. Do you have personal experience with those two amps X350.8 and X250.8? 

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