F5 Turbo Builders Thread - Page 77 - 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 1st January 2013, 04:18 PM   #761
diyAudio Member
 
Join Date: Feb 2009
Lo_Tse. for 100W class A at 8ohm, you need around 45V rails and 2.5A bias.
with higher rail voltage and same bias, the amp will go into class A/B above 100W.
  Reply With Quote
Old 1st January 2013, 04:20 PM   #762
diyAudio Member
 
Join Date: Feb 2009
Quote:
Originally Posted by anilva View Post
I mentioned that it is 47V DC at no load earlier. Looks like I have to use a quite cooling fan mounted to the top cover to evacuate hot air from inside and also provide enough ventilation to the bottom cover to enable air flow.
mount some fans under the sinks that blows air up. it's not the heat inside the chassis that is critical. it's the sink temp.
  Reply With Quote
Old 1st January 2013, 05:22 PM   #763
anilva is offline anilva  India
diyAudio Member
 
Join Date: Mar 2004
Location: Bangalore
Backed off my bias to 225mV levels and now the amp is stable with it's bias and temperature. Also did some listening tests. The V3 is terrific. Absolutely quite and no noise or hum. Sounds wonderful with very tight hold on music and bass. Little more warmer than original F5.

For my setup at the moment, I am Ok with what it is delivering. I may add a fan little later to drive up the bias. For the moment, I will enjoy the amp.

Thanks for all the help.

Cheers.
__________________
DIY F5, F5T, F6, Aleph J, Fostex 206 based BLH, Altec Onken with 515B LF & 288H HF, Technics SP10 MKII & EMT938 turntables
  Reply With Quote
Old 1st January 2013, 05:51 PM   #764
diyAudio Member
 
buzzforb's Avatar
 
Join Date: Oct 2010
Location: Burlington, NC
Warmer was first noticeable difference compared to F5. Perhaps saying it has more body is more appropriate, dunno. Glad it turned out well.
__________________
...Shape the sound , Man!
  Reply With Quote
Old 1st January 2013, 05:53 PM   #765
diyAudio Member
 
Join Date: Feb 2009
you MAY want to try 1.5ohm source resistors for a total of 0.75ohm with that low bias pr device. then you can take advantage og the diodes. with 0.75ohm source resistance and 0.45A bias(drop of 225mV over 0.5ohm) pr device you get 337mV drop over source resistors.
or just use 2 output pairs. and 0.8-0.9A bias pr device.

Last edited by AudioSan; 1st January 2013 at 05:57 PM.
  Reply With Quote
Old 1st January 2013, 06:22 PM   #766
dazed2 is offline dazed2  Canada
diyAudio Member
 
Join Date: Jun 2010
Location: Toronto
Anilva, what is the depth of your case, and what is the height of your heatsinks?
They seem a little small for V3....
  Reply With Quote
Old 1st January 2013, 07:10 PM   #767
Lo_Tse is offline Lo_Tse  Canada
diyAudio Member
 
Join Date: Dec 2006
Quote:
Originally Posted by AudioSan View Post
Lo_Tse. for 100W class A at 8ohm, you need around 45V rails and 2.5A bias.
with higher rail voltage and same bias, the amp will go into class A/B above 100W.
Audiosan

Thanks! I get a little condused here. In the original F5, each device was biased at ~1.3 A and the rail voltage was set at 23V. NP mentioned that with these parameters, the dissipation per device was kept at ~30 watts, about 50% of its max rating.

Going to the V1, the rail voltage goes upto 32V, NP dropped the bias to ~ 1A, in order to operate within the 30 watts per devices target. If for the V3, with a rail voltage getting up to 45 V, the bias should decrease further, right (or am I missing something here)? Is the 2.5 A the current bias set for each output device?

I am not trying to be nitpicking here. I understand that one can change the rail voltage and/or bias around as see fit. I just would like get a better understanding of what are the "optimum" parameters for this V3 amp. This will be the starting point of any changes/experimentation.

I have sourced a bunch of big caps for the PSU but these are rated at 50V only (I assumes the rail voltage for the V3 is teh same as V2). With a rail voltage at 45V, it is getting a little too close for comfort.

Regards,
  Reply With Quote
Old 1st January 2013, 07:22 PM   #768
diyAudio Member
 
Join Date: Feb 2009
the 1A bias is pr device. but that is a litle maximum with 0.5ohm source resistance do to the diodes starts conducting around that level. maybe even before. and then you got a runaway problem.
the 2.5A bias is total for all output pairs.
for the v3 you must have minimum 45V rails to get to the 100W mark. with 32V rails you only get 50W at 8ohm. even with 10A bias.
  Reply With Quote
Old 1st January 2013, 09:15 PM   #769
Lo_Tse is offline Lo_Tse  Canada
diyAudio Member
 
Join Date: Dec 2006
Quote:
Originally Posted by AudioSan View Post
the 1A bias is pr device. but that is a litle maximum with 0.5ohm source resistance do to the diodes starts conducting around that level. maybe even before. and then you got a runaway problem.
the 2.5A bias is total for all output pairs.
for the v3 you must have minimum 45V rails to get to the 100W mark. with 32V rails you only get 50W at 8ohm. even with 10A bias.
Thanks again for the clarification.

Regards,
  Reply With Quote
Old 2nd January 2013, 02:21 AM   #770
diyAudio Member
 
Join Date: Nov 2004
Location: manila,PH
Suggest to reposition FET placement to heatsink center to maximize heat spread. Consider split output boards like one posted by Variac which will be available soon in diy store, this provide flexibility to maximize your already massive heatsink.
__________________
Pinoy ikaw ay pinoy... ipakita sa mundo... kung ano ang kaya mo...
  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
F5 Turbo Circuit Boards chchyong89 Pass Labs 2347 14th July 2014 02:19 PM
B1 builders thread Bas Horneman Pass Labs 696 14th July 2014 12:57 PM
F5 Turbo is posted Nelson Pass Pass Labs 635 6th April 2014 10:51 AM
F5 turbo problems Rob Dingen Pass Labs 17 11th January 2013 08:38 PM
F5 Turbo ............. if only !!!!!! a.wayne Pass Labs 23 21st January 2012 02:24 AM


New To Site? Need Help?

All times are GMT. The time now is 03:16 PM.


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