Officially Class A - Page 3 - diyAudio
Go Back   Home > Forums > Amplifiers > Pass Labs

Pass Labs This forum is dedicated to Pass Labs discussion.

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 20th March 2002, 06:30 PM   #21
The one and only
 
Nelson Pass's Avatar
 
Join Date: Mar 2001
I have a nice rule of thumb evaluating claims of "pure
class A operation":

Take the continuous idle power draw from the wall and
divide it by the total rated continuous output per channel.
If it is a mono amplifier, divide the number by 2. If it is
a stereo amplifier, divide it by 4.

Now square the number and multiply it by the rated output
per channel. This gives the most generous estimate for
"pure" Class A operation, and twice this number is the
instantaneous point at which it leaves Class A.

Example:

A stereo amplifier draws 200 watts continuously
from the wall and is rated at 100 watts per channel:

200/100 = 2

2/4 = .5

.5 squared = .25

.25 times 100 watts = 25 watts. This is the rms Class A figure.

2 times 25 watts = 50 watts. The amp leaves Class A at
the instant of 50 watts, and probably operates AB to a 200
watt peak (the peak of a 100 watt rms sine wave).

All this assumes no weird circuits, and also assumes no
other losses. In real life, the numbers will be somewhat less.
  Reply With Quote
Old 20th March 2002, 09:29 PM   #22
diyAudio Member
 
Join Date: Feb 2002
Location: Charleston, SC
Thanks for the explanation Joe, that makes sense.
  Reply With Quote
Old 21st March 2002, 05:52 AM   #23
diyAudio Member
 
Lisandro_P's Avatar
 
Join Date: Oct 2000
Location: Argentina
Send a message via ICQ to Lisandro_P
Quote:
Originally posted by Nelson Pass
I have a nice rule of thumb evaluating claims of "pure
class A operation" (...)
Very good. I completely agree!
  Reply With Quote
Old 22nd March 2002, 01:49 AM   #24
diyAudio Member
 
Join Date: Mar 2002
My amp, the X 150, is rated at 150 watts per side into 8 ohms and 300 into 4 ohms. Its power consumption
is 200 watts idle, 600 watts max. Pass claims it runs Class A to 20 watts output then
switches to AB. Does the math work out, or is that not enough info? Doing Nelson's math as I
read it, I get Class A to 16.67 watts.


A friend, who owns the Llano Trinity 200 wrote this:


When I got into audio nobody told me there would be math involved, when I did the
math I got 112.5 wpc RMS and 225 wpc max class A into 8 ohms vs the claim of 200. If I
understand correctly, the power draw from the wall is the total and since the Llano draws 300wpc
at idle, the total would be 600watts. That is the first number in the equation. If that is wrong
then every step after that will be wrong.


Whereupon another aquaintance said this:


Don, your AC outlets carry 110 volts. No mater what you plug in it will always be 110. If you plug
something in with an impedance of say 100 ohms so much current will flow. If you plug in 50
ohms twice as much current will flow. Voltage remains the same. The amps power supply is
similar to your AC outlet. It supplies so much voltage in DC. Current flow now depends on load
impedance. As long as the power supply can provide the current flow it will provide what ever is
needed beyond Idle. Bias voltage remains the same regardless. How that translates into power
depends on the load.
Mike





  Reply With Quote
Old 22nd March 2002, 03:22 AM   #25
Warp Engineer
On Holiday
 
AudioFreak's Avatar
 
Join Date: Oct 2001
Location: Queensland, Australia
Quote:
Originally posted by muralman1
My amp, the X 150, is rated at 150 watts per side into 8 ohms and 300 into 4 ohms. Its power consumption
is 200 watts idle, 600 watts max. Pass claims it runs Class A to 20 watts output then
switches to AB. Does the math work out, or is that not enough info? Doing Nelson's math as I
read it, I get Class A to 16.67 watts.
Pass Labs rates the X150 @ 15W class A
  Reply With Quote
Old 22nd March 2002, 08:28 PM   #26
The one and only
 
Nelson Pass's Avatar
 
Join Date: Mar 2001
Looking at the Trinity, if that's 300 watts idle a channel,
then I would expect to be able to cook a steak on them.
  Reply With Quote
Old 22nd March 2002, 10:05 PM   #27
diyAudio Member
 
Join Date: Mar 2002
It gets warm with moderate volume play. Less so than with the X150. Something to do with very efficient Mosfets, or so its been said. Thank you for your reply. I'm still looking for the right front end to feed the X, something clean, detailed and musical.
  Reply With Quote
Old 25th March 2002, 08:34 PM   #28
The one and only
 
Nelson Pass's Avatar
 
Join Date: Mar 2001
Oh! Efficient Mosfets!
  Reply With Quote
Old 25th March 2002, 10:45 PM   #29
sonnya is offline sonnya  Denmark
diyAudio Member
 
sonnya's Avatar
 
Join Date: Oct 2001
Location: Denmark
I think they use a secret package with a looooow!! thermal resistance and a special coating on their heatsinks.

Back to reality : you can not get pass the thermal resistance who exists from the "die" through the package .. thermal compound .. and at last the heatsink...

High effiency MOSFET are only high effiency when shifted "on" where it is possible to use their low RDS... Like they do in Class D amps.

In a "linear" amp there is no miracle!!

Sonny
  Reply With Quote
Old 25th March 2002, 11:27 PM   #30
jduncan is offline jduncan  United States
diyAudio Member
 
Join Date: Nov 2001
Location: Boston, MA, USA
Send a message via AIM to jduncan
This is hilarious....I can't believe (well, given what some other manufacturers do, I guess I can believe.....) what this guy is saying. That's absolutely hilarious to use "high efficiency" mosfets as the reason a class A (not switching) amp doesn't dissipate very much power.

You've got to be kidding. As Sonnya just stated, this attribute of FET's only applies when they're fully on, not while they're switching.
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
I now officially hate M-Audio SY Everything Else 95 3rd August 2007 06:12 PM
How about a round-up of Class A kit power amps, or collectable vintage class A? Brisso57 Solid State 4 14th February 2007 11:30 AM


New To Site? Need Help?

All times are GMT. The time now is 02:08 AM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2