New Pass Labs Website

Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.
@Mr. Pass
@Mr. Harrington

Nice to see that service manual of X2 is coming soon !
Date of publication already fixed ?

Some links dosn't work :
Products -> XA Series -> "Like Peanut Butter and Chocolate"
Products -> X Series -> "Super Symmetric Amplification"

Otherwise, dirty yellow. Why not. Looks good to me.

Regards
 
Confused with XA100 Specs

I am confused. But maybe it is just my stupidity.

According to the specs on the website, the XA100 delivers a maximum OUTPUT voltage of +/- 25 V, a maximum output current of +/- 12A, but only consumes 300W.

So even if there are no losses in transfomers, rectifiers, CRCRC's (or maybe CLCLC's), ..... we would still need rail voltages of +/- 25+? V, and bias current of at least 12A (total) in order to achieve those ouput values. And then we should then certainly get much more power than 100W at 8 ohms at Class A.

Or would the commercial XA's have 100% efficiency ??
Someone care to enlighten me ?


Patrick
 
Being a bridged amp, the bias would only need to be about 3A for 100W into 8 ohms. This would lead to a Pd for the amp of about 150W at idle, so I suspect that the amp is biased--more or less--for a 4 ohm load (about 6A). Given heat losses elsewhere in the circuit, I'd guess that it's actually slightly less than that. Hence the amp probably peaks out--wattage-wise--somewhere just north of 4 ohms.
The "maximum" numbers in the literature are going to be peak, not RMS...something that has caused more than one person to get confused over the years. Just be glad that there aren't also average (or any of the other spec schemes developed over the years) numbers to further muddy the waters.
It's not that any of the numbers are inaccurate. You just have to know when to shift gears. Since I tend to think in terms of RMS, I find myself having to squint sometimes when reading spec sheets.

Grey
 
Still confused

> Being a bridged amp, the bias would only need to be about 3A for 100W into 8 ohms. This would lead to a Pd for the amp of about 150W at idle, so I suspect that the amp is biased--more or less--for a 4 ohm load (about 6A).


Let's see if I understand you correctly :

6A bias means 3A for each side of the bridge, and at +/- 25V rail, the amplifier consumes 6 x (25+25) = 300W. With the Aleph current source, maximum current going from one side of the bridge to the other (i.e. through the speaker) would be, with the current souce supplying 50% of that current, 6A.

I doubt you could get rail to rail voltages at the output, so let's say 4 V less than rail, maximum output voltage would then be +/- 21V, at maximum output current 6A -- not quite the +/-25V 12 A quoted. And I do understand that these figures refer to peak and not rms.

Unless of course that the XA100 is operating with 75% current delivered by the current source.

Or am I missing something ??

P.S. It was mentioned on the website that reducing speaker impedance would NOT increase power, so I understand that as the XA100 being set for maximum power at 8 ohm. Which makes it even more confusing.


Patrick
 
Nothing like a good bottle of wine to cloud the mind. Lemme see if I can straighten this out. I'll just throw out some random factoids and maybe you can put them together in a way that makes sense to you.
A bridged class A amp is biased for the current you intend to use. For an 8 ohm load and 100W, that's roughly 3A. For 4 ohms we double it, of course, so that'll be 6A. Now, the thing to remember is that a bridged amp acts like a see-saw. Each half sees only half of the load. That means that if you're running an 8 ohm load, each side of the amp will see a 4 ohm load, which means that the doubling of the current that you'd expect from push-pull operation (speaking broadly--yes, I know the Aleph CCS is single-ended) gets used up by the "4 ohm" load.
In a 'normal' Aleph, the output stage is biased for all the voltage and half of the current that you expect to use. In a bridged Aleph (e.g. Aleph-X), you're swinging all the current and half the voltage. The other half of the voltage comes from the other half of the amp--the other end of the see-saw, if you will.
Imagine the fulcrum of the see-saw as being "ground" and the two halves of the amp swinging up and down relative to that point. It's not grounded in reality, naturally, it's sort of a virtual ground. Yes, in principle you could tap the voice coil at the midpoint and the amp would continue to behave exactly the same. In fact, it would reduce distortion by reducing even harmonics. Odd harmonics would remain, unfortunately, and the tone of the amp would change as a result. By all means, try it if you have a two identical drivers or a dual voice coil woofer hanging around. Wire the voice coils in series, connect the amp to each end, and ground the center tap. I traded e-mail about this with Nelson for a bit, but decided not to pursue it. Feel free to give it a whack, though.
As a practical matter, Nelson seems to shoot for max power at about 5 ohms, plus or minus a bit. The Aleph 3 was an exception in that it would actually double into 4 ohms. It would not surprise me if the XA100 was biased in the same manner. I haven't done a lot of math on this, mind you. It's all just rule of thumb stuff and having watched Nelson do his thing for a while. He has his own rules of thumb and it's our job to guess what they are. I've got a half-dozen hypothetical rules that I think Nelson works by and they usually seem to pan out. The exceptions are usually things where he consciously tries to do something off the wall to keep everyone else on their toes, e.g. the F1.
It keeps the game more interesting for him, you see...

Grey
(and here comes Grey toddling along behind, moving as quickly as he can)
 
Grey
I notice your post become more and more enjoyable again.
It’s nice to read a well written story now and then… ;)
The idea of the dual voice coil seems very tempting.
It would take a bit of rewiring but what would be the effect in a dual woofer speaker system, e.g. B&W 800 matrix, supposing only both woofers would be wired like proposed? Or both mid’s?
Oh well, this is OT, if it's worth it I'll start another thread.

/Hugo
 
> As misleading as it is, i'd say that the amp is capable of sourcing 6amps max @ 1 terminal while simultaneously sinking 6amps max at the other terminal.

I'd tend to agree with that, implying that Bias is 3A per side and thus peak power is at 8 ohm at +/- 24V. But that is far from 12A maximum output current quoted, and I doubt you could come under 350W power consumption, given a few volt loss in Tx and Rectifiers, perhaps also CRCRC or regulators, and a minimum or 4V from rail voltage either side for the Mosfet's to work properly.

Maybe Nelson would care to clarify ??


Patrick
 
Hugo,
If you follow though, you'll need to bypass the passive crossover and go active. Bear in mind that some passives have frequency eq hidden within, so plan accordingly. Otherwise, it should work fine.
Be sure to bias according to the load while you're at it.
Want more ideas? I've got 'em. I just dole them out sparingly so I don't confuse myself. I've got a one-track mind, and I find it difficult to deal with forty different things at once. Right now I find myself back on the tubed X preamp...and a little fine tuning on the Xenover...and a large Aleph-X (expecting the UPS man any minute now with a case load of big caps from Steve @ ApexJr)...and a mystery project...and trying to wrap up a problem with one of my old S-500s...and...
And I find my mind drifting from one project to the other, unfortunately.
Need sleep.
Patrick,
I dunno. It doesn't seem so confusing to me. I'm sure there are a few oddities in the published numbers, but that doesn't matter as much as people think it does. If you start with the rated power into a given load and work backwards, you can come pretty close. The Aleph-X is a fairly known quantity by now. If you want one with a certain amount of power, you can pretty much throw numbers into the formulas, turn the crank, and out pop the answers.

Grey
 
Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.