UCD180 questions

[classd4sure]

heh heh, glad your a fan of the idea.

Isn't it more of a class D buffered class A? Ah, nope, it's class D.

... your ' key's broken.

[matjans]

i know. so far, i've had my keyboard replaced twice and now the ' button fell off, my processor blew up (stopped working) once, my bluetooth card went awol twice (as in that it fell out of its socket), my soundcard has a dc offset of about 1,8-2.2 volt (on both channels), i can hear my network card (peep-peeeeep-pep-peep etc), if i use the touchpad something's crackling in the soundcard. AND it's not even a year old !!

Strange thing is, where i work there's about 40 other dell machines (both laptops & normal desktops) and no probs with them whatsoever.
stupid thing. Guess i'm just unlucky.

[phase_accurate]

I don't want to spoil the fun here but has anyone looked at

http://www.psaudio.com/articles/sdat.asp

An excerpt:

"The SDAT™ circuitry is revolutionary for several reasons, among them the elimination of the load variant problem. SDAT’s™ will sound pretty much the same regardless of the type of speaker you have. With the Hybrid Class A’s SDAT™ technology, you can rely on the fact that your speaker will perform the way it was intended to sound."

I wasn't able to figure out what this has to do with class A (they are talking about their class-D amp !).


Regards

Charles

[Jaka Racman]

Hi,

my guess it is a variant of switch mode assisted linear amplifier. This is a well known solution, but so far i have not seen any commercial implementation. For anyone interested, here is one link explaining the principle.

Best regards,

Jaka Racman

[classd4sure]

haha..... wow that IS bad luck!!! Hope you were joking! If it's a DELL I'm sure if you call them and throw a fit they'll replace the whole unit just to keep you smiling, (and make you go away) I've known a few people to have done that, when all they needed was a format.


Hi Charles,

I checked out that site and I dont' think you could figure it out because they gave you nothing to work with.

There's absolutely no info on what makes it work, why it works, how it works... nothing! Kind of thing to ignore and stay away from.

Wonder if someone could dig up the patent info on it, if it's so revolutionary.... there should indeed be a patent.

We know they arent' the ones to have solved the feedback and dynamic load issue, as they almost seem to claim.

They don't even say if they take the feedback before or after the filter, or both.

Wonder if there's a UCD module inside there with the op amps tweaked into class A lol.

Maybe it's one of those hybrids where they input a class A type signal directly into the filter and use the error to modulate the power stage.

Didn't even see any specs on it.

Blah! Nothing more than sales hype.

Regards,
Chris

[matjans]

sorry for the off topic post but here i go.

i wasn;t joking about that laptop. I've tried to get the whole thing replaced but they wouldn't do it. nasty.,

i still don't get the class a part in the psaudio piece.

[classd4sure]

Hi Jaka Racman,

Exactly what I was thinking, but either way they shouldn't be so afraid to not even say so. That makes me turn the other way in a hurry. Amps like that which I've read about all input the error into a hysteresis modulator. If that's indeed what it is, they seem to be staking claim to ideas they've had nothing to do with.

I can't recall exactly, but does that type of amp not have a class dedication of it's own?

Regards,
Chris

[Bruno Putzeys]

(on PS audio)
Apparently they were afraid simply to call their amp "class D". Class A refers to one of the buffer amps in the signal path, but the amp is class D as far as I know.

Has anyone heard it by any chance? Seen the inside?

---

(on biasing op amps)
I've seen quite a number of discussions on biasing op amps in class A. The ones I've seen were all wrong in their interpretation of what's happening and what they're trying to achieve.
Here's how it should go:
A current source is tied between output and the rail where the miller VAS is located. This rail can be recognised from the data sheet because it´s got 20dB worse PSRR than the other one.
By biasing the output transistor off, this current source will insure that this rail sees only a constant DC load, thus removing signal-related content from it.
From this you can see that it's not about class A, but about power supply effects. Some people think they can get round by using a resistor instead of a proper current source. Wrong, because the power supply will be affected same as if that resistor was just the load to ground. Only a proper current source will do, and if it's tied to the wrong rail - no cigar either.

(on laptop PCs) One day the mouse pointer started walking away. It transpired the purple "g-spot" (strain gauge pointing device) had gotten mechanically biased. There was no way of telling the software to ignore it (I don't use it anyway). I called up IT support and they told me the keyboard had to be replaced. So I opened up the thing and pulled the plug on the purple button (flex foil) and that's that.

Cheers,

Bruno

[classd4sure]

Hi,

Class A in the signal path, could be anywhere, input buffer, or the other type we had mentioned, with a small class A amp driving the load directly. They're calling it a hybrid so I'd think it's the later.

Oh, look what I found!

http://www.psaudio.com/products/hca.asp

Some info on it there, according to them, Bruno, Jan-Peter, you're old news

"This is the power amplifier that will set the standard for all "under $3000" power amplifiers on the market today. Revolutionary in its design, devleopment and performance, the Hybrid Class A " (sic)
HCA-2 Amplifier [Silver] $1,695.00
HCA-2 Amplifier [Black] $1,695.00


More to laugh at:
"Frequency resonse - 10 - 20 KHz (+/- 0.5 dB) "

They didn't even proof read their hype.. I wonder if the same level of attention to detail went into making the amp itself.

You'll notice they don't have a single graph in their manual or on their website for it.

I think the Sharp 1 Bit finally has a competitor. I agree they do seem afraid to call it class d... Thanks for the laugh guys.

Regards,
Chris

[Bruno Putzeys]

It's good that it doesn't set the standard for above $3000 amps. Then we'd be in a fix.