NEW Aleph-X calculation sheet: AXE-1 - Page 3 - diyAudio
 NEW Aleph-X calculation sheet: AXE-1
 User Name Stay logged in? Password
 Home Forums Rules Articles diyAudio Store Gallery Wiki Blogs 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
 31st January 2004, 08:21 PM #21 diyAudio Member     Join Date: Sep 2002 Location: North of Boston total bias The question I was trying to get answered. Is does the total bias = the draw out of the transformer? __________________ MikeW
 1st February 2004, 09:53 AM #22 diyAudio Member     Join Date: Aug 2001 Location: Ingolstadt Germany yes __________________ een ooievaar is geen konijn want zijn oren zijn te klein!
 14th January 2005, 12:47 PM #23 Banned   Join Date: Aug 2002 Location: New York, NY wuffwaff I'm with MikeW on this one. I put in the following: Voltage=20V Bias=8A AC Gain=50% Mosfets=4 Peak Current=8A I don't understand why the dissipation per FET is 80W when the dissipation is 20V x 2A (ie:8A/4). Is your calculator assuming that the bias is only burdened by 2 of the four FET's in this the case above?
 14th January 2005, 01:03 PM #24 diyAudio Member     Join Date: Aug 2001 Location: Ingolstadt Germany Hi, the voltage is symmetrical so total voltage from plus to minus would be 40V. 40Vx8A=320 Watt is 80W/fet After rereading your question I can also give you the following answer: the current is not devided by 4 but by 2, so 4A is flowing in each half. It flows through the active current source into the output stage. This means 4A per fet with each fet only seing half the supply voltage: P=4x20=80 watt William __________________ een ooievaar is geen konijn want zijn oren zijn te klein!
 14th January 2005, 01:13 PM #25 Banned   Join Date: Aug 2002 Location: New York, NY wuffwaff Thanks for your reply. I have been trying to reconcile what PSUD2 outputs to your spreadsheet so if I am to understand you correctly, the FET will dissipate double the voltage rail times the amps going through the FET, correct? I had been told that the 50% AC gain reduces the dissipation back down to the bias times the rail. I just read your edit: By this new information, it would appear that each FET will now dissipate 160W since this new model indicates 40V times 4A. Something is wrong here. When you say that each FET only sees half the voltage, do you mean to say that is only sees +/-10V of the 20V rail or only the positive or negative side of the swing?
 14th January 2005, 02:02 PM #26 Warp Engineer On Holiday     Join Date: Oct 2001 Location: Queensland, Australia ok lets see.... Voltage=20V Bias=8A AC Gain=50% Mosfets=4 Peak Current=8A each side of the AX will have 4 amps running thru it and each of the 2 Fets / side will have 20V across it... 20x4 = 80Watts. __________________ - Dan
 14th January 2005, 02:50 PM #27 Banned   Join Date: Aug 2002 Location: New York, NY AudioFreak Thanks for sounding in but your reply doesn't address how the alledged 80W are produced. Isn't the voltage swing 40V as wuffwaff suggests? If the amps in that case are 4 per FET then why isn't the dissipation 160W? How does the AC current gain factor into the expected power dissipation or isn't it a factor at all? I should also point out that many of the members whom I have interviewed that have built the Aleph-X experience junction and heatsink temperatures that suggest the dissipation is usually a litte more than half of what the wuffwaff spreadsheet and you claim in your post and I haven't even started to address the disparities between the power numbers indicated in the wuffwaff spreadsheet graph with those presented by PSUD2. Your curt and definitive reply indicates that all this must be very elementary to you but perhaps you can address my questions more completely in the future?
 14th January 2005, 03:03 PM #28 diyAudio Member     Join Date: Sep 2003 Location: Upstate NY 40 v is the maximum potential swing, but we are talking about no signal conditions (worst case for class A amp heat dissipation) Since you have 4 amps per side, and we'll assume that your absolute DC offset is near 0, each transistor sees 20 volts. Since 4 amps flows through each transistor, you have 80 watts per transistor. Look at the junction temperature that produces with a real heatsink. Yikes!
 14th January 2005, 04:12 PM #29 Banned   Join Date: Aug 2002 Location: New York, NY BobEllis I am assuming that you built the Aleph-X and like many others, relied on the wuffwaff spreadsheet to model it. Did you measure the junction and heatsink temperatures? If so, how did they compare to the numbers produced by the spreadsheet?
Warp Engineer
On Holiday

Join Date: Oct 2001
Location: Queensland, Australia
Quote:
 Originally posted by yldouright AudioFreak Thanks for sounding in but your reply doesn't address how the alledged 80W are produced. Isn't the voltage swing 40V as wuffwaff suggests? If the amps in that case are 4 per FET then why isn't the dissipation 160W? How does the AC current gain factor into the expected power dissipation or isn't it a factor at all? I should also point out that many of the members whom I have interviewed that have built the Aleph-X experience junction and heatsink temperatures that suggest the dissipation is usually a litte more than half of what the wuffwaff spreadsheet and you claim in your post and I haven't even started to address the disparities between the power numbers indicated in the wuffwaff spreadsheet graph with those presented by PSUD2. Your curt and definitive reply indicates that all this must be very elementary to you but perhaps you can address my questions more completely in the future?
It is the bias current that determines dissipation, the AC current gain simply determines the ratio between bias current and peak current for each half of the circuit (each half essentially being a standard Aleph output stage). Since we are talking about dissipation at idle, the rails are evenly shared between the 2 FETs ie. 20V across each FET.
__________________
- Dan

 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 OffTrackbacks are Off Pingbacks are Off Refbacks are Off Forum Rules

 Similar Threads Thread Thread Starter Forum Replies Last Post unclejed613 Parts 3 13th May 2007 06:35 PM Phergus_25 Full Range 5 20th March 2007 11:14 PM quyda Pass Labs 2 29th January 2006 09:39 AM Smiffy Parts 11 13th December 2004 08:14 PM

 New To Site? Need Help?

All times are GMT. The time now is 09:05 AM.