F5 Turbo Builders Thread - Page 59 - 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 3rd December 2012, 05:59 PM   #581
AndrewT is offline AndrewT  Scotland
diyAudio Member
 
Join Date: Jul 2004
Location: Scottish Borders
no.
using a 35Vac transformer you will likely get ~50Vdc to 51Vdc across the smoothing caps when mains voltage is nominally the same as the transformer rated voltage. Use 63V capacitors, not 50V.

The supply voltage will droop when you bias the amplifier.
Expect the droop to be about 2Vdc when passing 1A of bias and 3 to 4 volts when passing 2A of bias. For 100W into 8r0 the bias will need to be almost 2.6A and the likely supply droop will be around 4 to 5volts.
That will bring your rail voltage down into the range 46Vdc to 48Vdc.

This should be just about enough to ensure you get 40Vpk into your 8r0 dummy load.

Now your output stage is dissipating ~244W (94V * 2.6A) and will need big heatsinks.
__________________
regards Andrew T.
  Reply With Quote
Old 3rd December 2012, 06:47 PM   #582
a.wayne is offline a.wayne  United States
Sin Bin
 
Join Date: May 2008
Location: Front Row Center
He should use 30 volt transformer, this way he can still use 50v caps ....
  Reply With Quote
Old 3rd December 2012, 07:09 PM   #583
tinitus is offline tinitus  Europe
diyAudio Moderator R.I.P.
 
Join Date: Nov 2005
Quote:
Originally Posted by a.wayne View Post
He should use 30 volt transformer...
I guess that would still be enough for F5 amp

I still remember the times when 33V trafo was 'big', and close to the classAB 'safe limit' with any DIY amp
and now in classA...DIY certainly have changed
  Reply With Quote
Old 3rd December 2012, 07:31 PM   #584
diyAudio Member
 
buzzforb's Avatar
 
Join Date: Oct 2010
Location: Burlington, NC
Buy the spec'd 24V secondary trafo that Nelson recommends in the article. It will yield correct rail voltage(appx 32v) to take advantage of current avialable from output, set according to the article. Venture outside these lines and you must realize that you are on your own and need some level of understanding to finish the build. You must also consider that at greater voltages, dissipation becomes a major issue, even if you have big sinks, as the fets will be operating at a high level, despite what the sinks are able to do in getting rid of that heat. In my opinion, If you want higher voltage, you must begin to increse the amount of output pairs in order to bring down the individual temperature of the fets. Then the focus is again shifted to the sinks and their ability to dissipate heat.

The F5T V3 is a beast of an amp. There are speakers that need more, but i would venture to suggest biammping or buying some Pass Labs products.
__________________
...Shape the sound , Man!
  Reply With Quote
Old 3rd December 2012, 07:50 PM   #585
BigE is offline BigE  Canada
diyAudio Member
 
Join Date: Aug 2008
Location: Toronto
AndrewT,

I heard NP says to use 1.3 as the multiplier instead of 1.414 when calculating the expected rail voltage when for a class A amp. Then, 36 VAC secondaries make for 46.8 rails, with the bias droop built in. That agrees very closely with your observation. It will have no trouble making 100 watts.

The 1.3 multiplier makes 30 VAC become 39 volts, when accounting for droop, but that won't quite make 100 watts. Close enough maybe? Only dazed2 can say.
  Reply With Quote
Old 3rd December 2012, 07:53 PM   #586
diyAudio Member
 
Join Date: Feb 2009
with 39V rails, you end up at around 75W at 8ohms
1.3 ratio is almost spot on in classA amps.
  Reply With Quote
Old 3rd December 2012, 09:20 PM   #587
BigE is offline BigE  Canada
diyAudio Member
 
Join Date: Aug 2008
Location: Toronto
I am missing something here. Perhaps someone can help.

Suppose Prms = 100 watts into 8R0 -- pure resistive so that the current and voltage are in phase.

Then,

Prms = I^2 * R => I^2 = 100/8 = 12.5

so, I = 3.54 amps RMS

Then, Vrms = I*R => 3.54 * 8 = 28.28 volts RMS

(check P=IV =3.54*28.28 = 100 )

Let Vrms = Vsec -- the transformer secondary.

Now, Vrail = Vsec * 1.414 = 40 VDC (the peak voltage)

Using a factor of 1.3 instead of 1.414 for losses due to class A biasing, means to achieve a 40 VDC rail, you need a 40/1.3 VAC transformer => 30.75 VAC.

This suggests that 100 watts RMS is possible from a 30.75 VAC transformer.... but that's not right, is it?

Can someone please point out where I blew it?

Last edited by BigE; 3rd December 2012 at 09:31 PM.
  Reply With Quote
Old 3rd December 2012, 11:27 PM   #588
a.wayne is offline a.wayne  United States
Sin Bin
 
Join Date: May 2008
Location: Front Row Center
Quote:
Originally Posted by buzzforb View Post

The F5T V3 is a beast of an amp. T
And you know this how .....
  Reply With Quote
Old 4th December 2012, 12:18 AM   #589
diyAudio Member
 
buzzforb's Avatar
 
Join Date: Oct 2010
Location: Burlington, NC
Lets just say i had a single channel of the V3 working a month ago. Ran one speaker with V3 and the other with V2. Could hear a difference and I dont need but about 2W. The pretty versions always take longer., as you know.
__________________
...Shape the sound , Man!
  Reply With Quote
Old 4th December 2012, 09:47 AM   #590
AndrewT is offline AndrewT  Scotland
diyAudio Member
 
Join Date: Jul 2004
Location: Scottish Borders
Quote:
Originally Posted by BigE View Post
I am missing something here. ..........................
Can someone please point out where I blew it?
go and look at the F5 pdf.
It states a +-25Vdc supply and yet the maximum output is ~20Vpk
That difference (or loss) is due to current passing through the semiconductors and actual resistances, from supply to the terminals and then back to the supply.

The same applies to all amplifiers.
__________________
regards Andrew T.
  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 2363 27th September 2014 03:10 PM
B1 builders thread Bas Horneman Pass Labs 696 14th July 2014 01:57 PM
F5 Turbo is posted Nelson Pass Pass Labs 635 6th April 2014 11:51 AM
F5 turbo problems Rob Dingen Pass Labs 17 11th January 2013 09:38 PM
F5 Turbo ............. if only !!!!!! a.wayne Pass Labs 23 21st January 2012 03:24 AM


New To Site? Need Help?

All times are GMT. The time now is 06:18 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