Is it mystery .... ? Questions to Nelson

[nar]

I am currently on an Aleph X project . Rails will be 24 V , bias 6-8 amperes.Don't know yet . I have to figure out the heatsink issue

I have been surprised reading the specs of the XA 200 .

Max output voltage +/- 60V , I can understand it . If rails are +/- 32 V , then it is OK .

Specified for the XA 200 : I quote :

" Maximum Output Current plus,minus 15 amps "

Here is the thing . The DC bias of the XA 200 is clearly 8 amperes , so thus it is bridged this is the max . output current .

So how the hell does come those 15 amps ?



How can the amp go such output current ? Is the AC current gain of the 2 CCS equal to 0,5 in the commercial version of the XA 200 ?

I have measured the input resistance of my XA prototype . I believe with a multimeter I don't get the real INPUT IMPEDANCE of the amp . In fact , I get same numbers as measuring my Aleph 2s. So I guess the input impedance of my prototype is same as the XA 200 specs . I used input coupling capacitors , with 100k parallel to GND before it , according to Grey's original schematic my resistors are

R 18 R 28 10k

R 19 R 29 10k

R 16 R 30 100k

I guess those values are the ones used in the XA 200 except R16 R 30 . Theorically to get the 26 dB gain figure those resistors would be 200k . Right ?

Do the XA sound better with less feedback ? Like a 26 dB gain figure is better for the sound than a 20 dB ?

In the case of a 24 V rails version with 6-8 amps bias , is it positive to go for a 26 dB gain instead of 20 ?

I think about a way to get those wonderful round control eyes on the XA 200 faceplate . I guess original ones would be too much expensive , but I think I can find voltmeters for that use . Round , with lights but interior reworked to have blue leds to illuminate ... the needle .... etc .

I would simply plug it parallel to one R of my CRCRC filter. If I can get some 0,5 ohms to do it , connecting the faceplate voltmeter parallel to this R and rescaling the V graduations inside ( just remove the paper , altering the numbers ) at a 6 amps bias on my 0,5 ohms , V would be 3V , and needle should be mid-way on a 6V range voltmeter.So graduations would be in A , not in V , this would do the trick for me .
I simply want a bias indication on the faceplate , while running , to be able to see the idle with a wonderful blue-lightened needle



I think I will go for the 8 A bias version if I have enough sinks

Last question : is the power supply for Zen V5 suitable to an Aleph X ?

Best regards

Anael

[AudioFreak]

Hi Anael,

I know that I'm not Nelson but I'll try to answer one of your questions..

The XA200 would appear to carry approx. 8 amps bias per side of the bridge and the current gain of each of the active CCS is set to 50% which means double the bias figure on peak output ie. around 15 amps or a little more. So each side of the circuit can source / sink approx. 15A on peaks.

Regards.

[nar]

hey !

8 amps "per side" or 8 amps for the whole amp ?

damn ... 16 amps total ....

I am

Is that possible ?

16 amps total bias ??

mistaken was I ?

Netlist , what do you think ?

[nar]

Hey !

According to the specs of the XA 200 ,

the amp draws 650 W .

According to the rail voltages ( = +/- 32 V , or 33 doesn't matter )

650 / 66 = 9,84 A .

So the bias is unlikely to be 16 amps . !!!

Must be around 8 A , plus voltage loss on thermistors of the CLCLC filter + bridge loss , gets to a bias of 8 amps or so .

I couldn't afford the 16 A , good news !!!

What about the other tips ?



Regards

Anael

[Netlist]

Originally posted by nar
Netlist , what do you think ?

What!!! You want me to think just before my holydays?
It's hard but I'll try.
If I come up with something I'll post it.

/Hugo

[Netlist]

Anael
Yesterday we received a nice formula from Henrik how to calculate in and output impedance: http://www.diyaudio.com/forums/showt...488#post208488

I guess AudioFreak gave you the correct answer about the current and voltage matters.
As for your last question: The Passdiy -site is currently down so I can't look at the PSU from ZEN V5.
What I remember from it is that it should be extremely quite and very powerful. If you cannot use it as-drawn it certainly will be easily scalable to fit AlephX.

/Hugo - Has to pack...France is calling...

[AudioFreak]

Hmm,

I made my earlier post when I was somewhat distracted ... I've done some more calculations and it looks like it is approx. 8 Amps total bias ie. 4 Amps per side. I Guess the Pass Labs website has an error.

[Nelson Pass]

Originally posted by AudioFreak
I Guess the Pass Labs website has an error.

It wouldn't be the first time. In general we quote the maximum
Class A output of the X amps as the same as the total bias,
however, they have been known to squeek some more out,
but not in Class A, as at least one of the current sources will
experience shutoff.

[AudioFreak]

How can the XA ever go past Class A as at least one active current source will always be active and it will not be able to source more than approx 8 Amps? Sure, in the Alephs it's a different story but I fail to see how that could work with the XA...

[Netlist]

Originally posted by AudioFreak
I've done some more calculations and it looks like it is approx. 8 Amps total bias ie. 4 Amps per side.

I'm so glad I said 'I guess'...

/Hugo