Officially Class A
 User Name Stay logged in? Password
 Home Forums Rules Articles diyAudio Store Blogs Gallery Wiki Register Donations FAQ Calendar Search Today's Posts Mark Forums Read Search

 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
 20th March 2002, 06:30 PM #21 Nelson Pass   The one and only     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.
 20th March 2002, 09:29 PM #22 Dustin Haug diyAudio Member   Join Date: Feb 2002 Location: Charleston, SC Thanks for the explanation Joe, that makes sense.
Lisandro_P
diyAudio Member

Join Date: Oct 2000
Location: Argentina
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!

 22nd March 2002, 01:49 AM #24 muralman1 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
AudioFreak
Warp Engineer
On Holiday

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

 22nd March 2002, 08:28 PM #26 Nelson Pass   The one and only     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.
 22nd March 2002, 10:05 PM #27 muralman1 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.
 25th March 2002, 08:34 PM #28 Nelson Pass   The one and only     Join Date: Mar 2001 Oh! Efficient Mosfets!
 25th March 2002, 10:45 PM #29 sonnya   diyAudio Member     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
 25th March 2002, 11:27 PM #30 jduncan   diyAudio Member   Join Date: Nov 2001 Location: Boston, MA, USA 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.

 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 Forum Rules
 Forum Jump User Control Panel Private Messages Subscriptions Who's Online Search Forums Forums Home Site     Site Announcements     Forum Problems Amplifiers     Solid State     Pass Labs     Tubes / Valves     Chip Amps     Class D     Power Supplies     Headphone Systems Source & Line     Analogue Source     Analog Line Level     Digital Source     Digital Line Level     PC Based Loudspeakers     Multi-Way     Full Range     Subwoofers     Planars & Exotics Live Sound     PA Systems     Instruments and Amps Design & Build     Parts     Equipment & Tools     Construction Tips     Software Tools General Interest     Car Audio     diyAudio.com Articles     Music     Everything Else Member Areas     Introductions     The Lounge     Clubs & Events     In Memoriam The Moving Image Commercial Sector     Swap Meet     Group Buys     The diyAudio Store     Vendor Forums         Vendor's Bazaar         Sonic Craft         Apex Jr         Audio Sector         Acoustic Fun         Chipamp         DIY HiFi Supply         Elekit         Elektor         Mains Cables R Us         Parts Connexion         Planet 10 hifi         Quanghao Audio Design         Siliconray Online Electronics Store         Tubelab     Manufacturers         AKSA         Audio Poutine         Musicaltech         Aussie Amplifiers         CSS         exaDevices         Feastrex         GedLee         Head 'n' HiFi - Walter         Heatsink USA         miniDSP         SITO Audio         Twin Audio         Twisted Pear         Wild Burro Audio

 Similar Threads Thread Thread Starter Forum Replies Last Post SY Everything Else 95 3rd August 2007 06:12 PM Brisso57 Solid State 4 14th February 2007 11:30 AM

 New To Site? Need Help?

All times are GMT. The time now is 02:34 PM.