XPA_2 vs XPA2 ?

[klinemj]

Dec 10, 2018 7:42:32 GMT -5 gentlejax said:

well lots of posts mow...

I have not heard a bad word about the W4S St-500 and it wasnt mentioned if the other owners were stereo or monoblock owners. but there is always that difference between systems and ears.

I guess I have no choice now but to test the W4S ST-500 vs the adcom GFA-555MKII later this week when I get them. I bought the 555 before I found the W4S. friend is all about class D got me thinking to try one out besides all the crown XLS stuff which I have had.

in the end same old story ..dont know till you try it.

For me, the only reasons to try class D are:
1) curiosity..."how good are they now?"
2) Wanting/needing low power consumption
3) wanting/needing low weight.

I got into my Hypex because of #1 and was wowed. But, I like #2 and #3...fyi, mine are so light, I hang them on the wall behind my speakers with ordinary picture hangers (I have custom built cases that look cool hanging on the wall. And, I could...so I did!

Mark

[gentlejax]

Back in my car audio days I liked the old school stuff and some of the old school amps were works of art like the old phoenix gold amps but when class D amps came out it was hard to ignore the amount of power and small footprint. I finally stopped all that years ago.

But i was always bothered by the amount of wasted power in a/b designs. so inefficient. ive just been waiting for it to evolve. I have tried the crown amps and again good for subs but I mever really used them for mains cause I had great old a/b power hungry amps.

I realized after slimming down my system and removing parts like voltage increasers and eq that I wasnt actually getting all 400 watts out of my pro amp. at more than 3/4 volume I wasnt getting full power out of the amp due to the amp being a pro amp.

I was also told I was missing out using my pro amp so I got curious and now I have been l00king at more modern home options.

I really like the idea of more power ending up in the music than in heat . I know heat kills electronics so if I can find a amp that runs cool and sounds good thats a plus.

I now have chance to try both types. adcom has been meticulously rebuilt. the other a much more expensive amp but used so I can afford it. both cost me about the same.

[brutiarti]

Dec 9, 2018 22:33:35 GMT -5 teaman said:

Dec 9, 2018 22:16:07 GMT -5 brutiarti said:

For 2ch definitely Bryston is a big contender. I found emotiva very good but the long term reliability is a question mark for me, I had several products that went back to TN for service

I have been very lucky, with all of the Emotiva gear I have owned only a broken platter in an ERC-2 has needed repair. I don't think any other Emotiva gear is in my future plans though, not a fan of the direction they are taking. Plus their prices are much more in line with the majority of their competitors now.

I'm really glad for you. I have an XDA, UPA, Airmotiv 5 and big ego with no issues. My main system was the one with issues.

[leonski]

First? I don't think Pass likes the Mk11 version of his 555 as much as the original.

You should find the 'D' amp, depending on what exact flavor of B&O Module W4S uses, at least 'better'. And much better than the Crown XLS 'stuff'.

As for the W4S? 6 Moons reports a propietary input buffer raising input impedance and select OTHER parts upgraded. Some resistors (now DALE) and Capacitors are 'upgraded'.
These upgrades, IMO, are of limited value. The amp is still fundamentally unchanged. I doubt is is THAT much better. You decide.

As for mono or stereo? In the case of these amps, NO connection exists between 'sides' after the power enters the case. Each module has its OWN power supply and both are balanced,
which I think means NO speaker ground in common.

ALL 'D' amps share certain......technical limits, many of which do not apply to people simply using them as intended....to listen to music.

I'm not going to go into detail, but the problems with 'D', for ME exceeded the benefits.

Just to keep it real, my speakers are very low sensitivity Magnepan which are otherwise NOT a bad or difficult load.

[donh50]

Class G uses two or more rail voltages and switches between (among) them.
Class H uses a tracking supply.
I have read conflicting reviews about the Gen 3 amps being class G or H.

SMPS makes it much easier to track the input without wasting a ton of power in the supply itself.

For class D circuits, biasing varies widely IME, but is still much lower than a typical AB circuit since the outputs need only switch (no linear region requirements that class A or AB have). You do not want both output devices on at the same time in an ideal class-D design so the quiescent energy is more from the driver, control and low-level (input) circuits than the output stage. That said, a lot of amplifiers (inside AVRs or not) have dropped biasing significantly from what I used to see in "the old days". Still, what I have seen puts class D at a hefty advantage over a few watts of output. The improvements I have seen in class D are generally much higher switching speeds and better feedback design (taking advantage of the higher switching speeds and of feedforward correction) so their output impedance does not rise nearly as much as earlier designs. They are also much more stable and reliable these days.

Regarding sound quality and such, I think the Gen3's are too new for long-term reliability, but I have not heard or read of any issues. What I do remember is the relatively large HF distortion components in the unit Stereophile tested. Emotiva claims that is fixed but Stereophile did not redo the measurements to confirm. I do not know if anybody else has; does Emotiva still provide full AP test reports for the amps? I have not looked... I would think if it was still a problem it would be discussed so suspect it was either a defective unit or an early design flaw subsequently fixed.

Switch-mode power supplies (SMPS) gained a bad rep for reliability from early designs. Current designs seem much more robust, at least based on my experience with lower-voltage high-current designs and anecdotal evidence from various audio fora. These days I do not think I would let class D sway me one way or the other, just one more factor on a list. I tend to look at SNR, output impedance, power level (enough for the task?) as roughly equal, glance at THD, and then think about things like the amp and power supply configuration (though lighter, cooler designs are appealing to my back and HVAC system).

The old Adcoms were could amps if a little hot and Wyred4 Sound has a good reputation. Be interesting to see what you think. Be sure to keep notes and go back and forth when you try them out. Any time you get a new toy it tends to focus your attention more sharply on the sound. Many times I have heard "new things" with a new piece of gear only to go back to the old and find it was there all along... A bunch of DBTs years ago was pretty humbling to myself and my fellow "golden-eared" buddies. That said we could distinguish among certain amps at certain levels with certain music and driving certain speakers. It was just harder and much less prevalent than we thought.

Bryston has been on my "short list" for ages. Used but never actually owned them. I had planned to pick up a couple about ten years ago when I re-entered this hobby but sticker-shock drove me to Emotiva. I have several Gen1 amps that are still doing fine so can't really justify the change. I'd also look at ATI (class D and the other lines) as well as Benchmark and a few others. The current astronomical pricing for what we used to call the "esoteric" high end is stunning to me.

FWIWFM - Don

[leonski]

Thanks for straightening out G and H. Now it shsould be clear to everyone that they are NOT amplifier classes.

G and H are probably not the best choice for an 'A' amp but where demand varies, they can gain some leverage.

Minimum biassing, to the 'edge' of A/B is one way to save energy. Even though it would seem to be at the expense of SQ.

And I'll repeat that 'D' amps have some very real disadvantages to this day. Minumim heat sinking, for example, limits REAL long term power output.
You'll find in the notes for the ASP modules from B&O that maximum time is either 30 seconds or 60 seconds at full tilt. And FTC power is a fraction of the 'rated' power.
Being rid of the high frequency PS 'hash' requres an ouput zobel. This is another limit on power output AND causes phase shift and impedance interactions. This is what I blame for
my problems with 'D' amps on my panels.

If I were to try going down the 'D' amp rabbit hole again, I'd use nCore400 as start material. Build a dedicated biamp with an internal MiniDSP so each speaker had 2 ampss with dedicated frequency range WITH each amp having its
own sub output. Maybe build an INTERNAL splitter into each amp, so they'd only require a single balanced cable EACH. I think the MiniDSP would work in that fashion.

The very high efficiency numbers you see quoted are usually at full power and in the case of B&O, rated 'plug to speaker'. This is a sane way to rate