F5 power amplifier - Page 668 - 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 17th January 2010, 04:25 PM   #6671
diyAudio Member
 
Join Date: Aug 2005
nope.... powersupply voltage is ok, 24 V positive and negative.

voltage over R3 and R4 is zero.. and over R11 and R12 no change in voltage by turning the potmeter (shows only 6 mV)

voltage meter is connected on both sides of R11 (and R12) parallel over R

this is the same on both channels.

thx for your reply!
  Reply With Quote
Old 17th January 2010, 04:28 PM   #6672
diyAudio Member
 
bobodioulasso's Avatar
 
Join Date: May 2008
Do not worry, the mosfets start turning on after several turns.
Not too many risks with a dim bulb.
You must have a voltmeter across R11 or R12 and another between output and ground. (Ofset)

Last edited by bobodioulasso; 17th January 2010 at 04:31 PM.
  Reply With Quote
Old 17th January 2010, 06:28 PM   #6673
diyAudio Member
 
Join Date: Aug 2005
We (my father and I) suspect that one or more resistors are in the wrong place.

Because turning p1 and p2 leads to nothing more then a measured value of around 8 ohms across r3 and r4.
Probably r3/r4 are of a much lower value then the 2.2k it should be, resulting in such low resistance...

We are in the procces of disasembling the amp and rechecking it. Kinda hard with the Dale resistors to see what is what sigh...
  Reply With Quote
Old 17th January 2010, 07:25 PM   #6674
generg is offline generg  Germany
diyAudio Member
 
generg's Avatar
 
Join Date: Jul 2009
Location: Near Frankfurt
p1 and p2 have really 5 kOhm? I had once 50 Ohm on a blue one. The inscription was 501 instead of 503. Good luck!
__________________
and the First Wtt is......a really First Class PSS Idea
  Reply With Quote
Old 17th January 2010, 09:37 PM   #6675
diyAudio Member
 
Join Date: Jan 2006
Location: Ireland
Post a few pics, that might help us diagnose your problem...
  Reply With Quote
Old 18th January 2010, 02:22 AM   #6676
gautamz is offline gautamz  India
diyAudio Member
 
Join Date: Jul 2009
Where I live (Bombay, India) I am unable to get the recommended input Jfets - 2sk170, 2sk370 or 2sj074. Currently I can only get the 2sj108...

Is there any other Jfet pair I could use for the inputs? What are the primary characteristics to look for when trying to source the input Jfets?

~Thanks a lot in advance.
  Reply With Quote
Old 18th January 2010, 10:36 AM   #6677
diyAudio Member
 
Join Date: Aug 2005
Quote:
Originally Posted by generg View Post
p1 and p2 have really 5 kOhm? I had once 50 Ohm on a blue one. The inscription was 501 instead of 503. Good luck!
Thanks for all the advise, the pots were 5k ones unfortunately. But on the bright side, we did find out that r 11 and r 12 were of a wrong value (4.7ohm instead of 0.47)

And we found out that alterating turns on the pots, gets the amp to play now!

So one side is luckily working

I guess I should have measured all my components before putting them in... Ah well.. Another valuable lessen learned
  Reply With Quote
Old 18th January 2010, 11:53 AM   #6678
tinitus is offline tinitus  Europe
diyAudio Moderator R.I.P.
 
Join Date: Nov 2005
Quote:
Originally Posted by rikkert1978 View Post

I guess I should have measured all my components before putting them in
Thats usually a good idea



Regarding power up with lightbulb
According to Andrew it could mean trouble if one lightbulb blows, due to classA load
It was adviced to adjust F5 into classAB only, with the lightbulb
Confirm that amp is ok
Remove the lightbulbs, and first then adjust it into pure classA
  Reply With Quote
Old 18th January 2010, 04:34 PM   #6679
diyAudio Member
 
luvdunhill's Avatar
 
Join Date: Jul 2006
Quote:
Originally Posted by mudihan View Post
For a gain in the range of 8-12x, what would be the rough range of values for R5&R6 (leaving out R7&R8) and R1&R2? Thanks!
Did you ever find suitable values? I've been playing with the gain as well, and wanted to see if anyone else has some values they've vetted.
  Reply With Quote
Old 18th January 2010, 10:47 PM   #6680
AndrewT is offline AndrewT  Scotland
diyAudio Member
 
Join Date: Jul 2004
Location: Scottish Borders
the lightbulb is there to prevent a disaster if there is a wiring fault.
Once the wiring has been proved and all modifcations completed the lightbulb should be removed and then the biasing can start.

If the light bulb is still in place when trying to bias an amp then as the bias adjuster is turned up, the bulb reduces the voltage fed to the transformer.
__________________
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
Rockford Fosgate Power 20001 bd amplifier power rating?? pachoorion Car Audio 8 8th May 2011 10:49 PM
Power transformers versus amplifier output power..what is your option? destroyer X Solid State 38 9th May 2009 05:23 PM
McIntosh Power Amplifier Power Guard johnnyrt Solid State 2 23rd August 2007 10:22 PM
Output power for a power amplifier Progg70 Solid State 33 10th September 2006 08:44 AM
Amplifier 3000 Wats Rms Power + Smps Higcht Power Bestiality MARAVILLASAUDIO Class D 1 5th November 2004 04:06 PM


New To Site? Need Help?

All times are GMT. The time now is 11:45 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