Addendum

Addendum

Posted by 13th Duke of Wymbourne (A) on March 11, 2019 at 19:21:59

In Reply to: Interesting! posted by John Elison on March 11, 2019 at 05:44:55:

John,
I was a little premature in my last reply. I thought the Pass XA200.8 a push-pull amplifier but it is not (though it sort of is)
The Pass Aleph series was marketed as single-ended class A except the designs had a neat twist to dynamically adjust the output stage bias current so the amplifier output current swing could be 2x the DC bias current (rather than 1x the DC bias current for a pure single-ended class A design). The subsequent Pass X series are balanced push-pull amplifiers but I forgot that the XA series is a combination of X and Aleph, so the XA200.8 does not have the push-pull output of the X series. Instead it will have an Aleph-like class A bias current that could provide a dynamic output current twice the bias. Arguably that extra range is equivalent to class AB but if we re-visit my previous calculations with twice the maximum output current:

200W into 8 ohms sets the voltage rails as +/- 60V
If the DC power is 760W then the bias current could be as much as 760/120 = 6.3A. If the Aleph-like output can supply double the DC bias that is 9Arms (2*6.3/SQRT(2)) which is more than enough to provide 200W/8ohms in class A and provide 324W/4ohms in class A. Stereophile's measurement shows that the XA200.8 can supply 400W/4ohms so there is still a deficit in my calculations but this second round is much closer to matching the product description.

Regards,
13DoW

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Follow Ups Full Thread

Topic - Class A power in A/B amp question - George6 18:23:50 03/09/19 (22)

you could also try to figure out if you like how the amp sounds driving your speakers - Chip647 15:03:58 03/13/19 (0)

Angels on a Pin question - bare 09:55:48 03/13/19 (0)

Ha Ha! - Duke vs John - who wins? - cawson@onetel.com 06:09:52 03/10/19 (11)

It is not a contest and we're both right - 13th Duke of Wymbourne 13:21:46 03/10/19 (9)

RE: It is not a contest and we're both right - John Elison 18:59:34 03/10/19 (6)

"However, the amplifier will still maintain 5.657-volts at its speaker terminals when the load changes from 8" - Caucasian Blackplate 08:46:01 03/11/19 (0)

RE: It is not a contest and we're both right - 13th Duke of Wymbourne 21:18:06 03/10/19 (4)

Interesting! - John Elison 05:44:55 03/11/19 (3)

Addendum - 13th Duke of Wymbourne 19:21:59 03/11/19 (2)

RE: Addendum - John Elison 12:52:46 03/12/19 (1)

A summary - 13th Duke of Wymbourne 18:47:37 03/12/19 (0)

RE: It is not a contest and we're both right - George6 17:40:08 03/10/19 (1)

RE: It is not a contest and we're both right - 13th Duke of Wymbourne 18:31:26 03/10/19 (0)

RE: 13DoW is correct. - BenM 10:50:29 03/10/19 (0)

RE: Class A power in A/B amp question - 13th Duke of Wymbourne 20:13:27 03/09/19 (1)

+1 nt - Caucasian Blackplate 10:10:12 03/10/19 (0)

RE: Class A power in A/B amp question - John Elison 18:54:45 03/09/19 (5)

RE: Class A power in A/B amp question - triamp 19:19:57 03/10/19 (1)

RE: Class A power in A/B amp question - John Elison 06:36:30 03/11/19 (0)

RE: Class A power in A/B amp question - 6bq5 12:07:49 03/10/19 (2)

RE: Class A power in A/B amp question - Hornlover 08:24:06 03/11/19 (0)

RE: Class A power in A/B amp question - John Elison 12:17:37 03/10/19 (0)

Follow Ups

Addendum - 13th Duke of Wymbourne 19:21:59 03/11/19 (2)

RE: Addendum - John Elison 12:52:46 03/12/19 (1)

A summary - 13th Duke of Wymbourne 18:47:37 03/12/19 (0)

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