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 12th June 2009, 03:24 PM   #1
richD is offline richD  United States
diyAudio Member
 
Join Date: Jun 2009
Default F5 bias question

Does anyone have a ď How to Bias the F5 for DummiesĒ?
Iíve read Mr. Passís article and itís still not clear to me on how it is done.
Thanks
  Reply With Quote
Old 12th June 2009, 03:44 PM   #2
diyAudio Member
 
Join Date: Apr 2006
Location: Dallas, Texas
Default Re: F5 bias question

Quote:
Originally posted by richD
Does anyone have a ď How to Bias the F5 for DummiesĒ?
Iíve read Mr. Passís article and itís still not clear to me on how it is done.
Thanks

Maybe the scope of this issue could be narrowed if you could tell us
more specificly, what problem you're having (what is going well, and
what isn't). In general, you might find the Zen 5 paper helpful, as the
Zen 5 amplifier's bias is set by the same method.
  Reply With Quote
Old 12th June 2009, 03:59 PM   #3
juluska is offline juluska  Ukraine
diyAudio Member
 
Join Date: May 2008
don't worry, it's easy:
1.- Turn off your amplifier
2.- put the pots to 0 ohms position (measured between legs 1-2 and leg 3)
3.- turn all the pots about 5-7 complete turns
4.- then turn on the amplifier (with no speaker connected) and begin adjusting one channel, with one multimeter in the speakers output and other multimeter in R11 or R22.
5.- Now all you have to do is to turn P1 and P2 in half turns alternately until achieve a value near 0V DC at the output and .59V volts across R11 or R12
  Reply With Quote
Old 12th June 2009, 06:27 PM   #4
richD is offline richD  United States
diyAudio Member
 
Join Date: Jun 2009
Thanks juluska, I think I can handle it now!
  Reply With Quote
Old 12th June 2009, 06:38 PM   #5
juluska is offline juluska  Ukraine
diyAudio Member
 
Join Date: May 2008
Quote:
Originally posted by richD
Thanks juluska, I think I can handle it now!

take care with heat, it runs really hot but you can touch the heatsinks for 4-5 seconds.
  Reply With Quote
Old 12th June 2009, 10:37 PM   #6
richD is offline richD  United States
diyAudio Member
 
Join Date: Jun 2009
Thanks again. I have not build it yet. I just want to make sure I understand everything before hand.
  Reply With Quote
Old 20th August 2009, 08:13 PM   #7
diyAudio Member
 
vdi_nenna's Avatar
 
Join Date: Oct 2000
Location: PA, USA
Blog Entries: 1
Send a message via Yahoo to vdi_nenna
Hi juluska,

What you're saying is you can monitor R11 or 12 for .59v?
One doesn't have to monitor both at the same time? Let's say I monitor only R11. R12 will end up at .59v also?

Quote:
3.- turn all the pots about 5-7 complete turns
Also, in the above are you saying that there should be some resistance above zero before turning on the amp? What happens if I start the amp at zero on the pots?

I ask because I've had problems with my F5 build.

Thanks,

Vince
__________________
I build, therefore I am.
  Reply With Quote
Old 20th August 2009, 11:02 PM   #8
cviller is offline cviller  Denmark
diyAudio Member
 
cviller's Avatar
 
Join Date: Dec 2005
Location: Copenhagen
Blog Entries: 2
Quote:
Originally Posted by vdi_nenna View Post
Hi juluska,

1. What you're saying is you can monitor R11 or 12 for .59v?
One doesn't have to monitor both at the same time? Let's say I monitor only R11. R12 will end up at .59v also?

2. Also, in the above are you saying that there should be some resistance above zero before turning on the amp? What happens if I start the amp at zero on the pots?

3. I ask because I've had problems with my F5 build.
1. Exactly - you might not end up with precisely the same voltage on both R11 and R12, but that is not as important as DC offset.

2. That suggestion just saves you a few turns while the amp is ON. Do it the way you feel most comfortable.

3. Is it working now?
  Reply With Quote
Old 21st August 2009, 04:29 PM   #9
diyAudio Member
 
vdi_nenna's Avatar
 
Join Date: Oct 2000
Location: PA, USA
Blog Entries: 1
Send a message via Yahoo to vdi_nenna
Hey thanks. Not trying to hijack this thread...but here goes.

Not fixed yet, just got the replacement parts yesterday. I planning on removing the active components, marking them e.i., value and channel, then test them outside the circuit to see what went wrong. It's bugging the $#!+ out of me! Will also recheck all resistor placement and values. Something has to turn up. It's too simple a circuit and nothing burned up! I'm betting on a semi gone bad somewhere, but keeping all possibilities open.

thanks,

Vince
__________________
I build, therefore I am.
  Reply With Quote
Old 3rd March 2013, 11:46 PM   #10
rade95 is offline rade95  United States
diyAudio Member
 
Join Date: Apr 2010
Location: Boulder, Colorado
Hi guys, like the other diy-er, I also have a problem adjusting F5 BIAS on one of the channels. Only turning P1 makes voltage rise on R11 and R12 while turning P2 makes no difference. I power on with 2 turns on P1 and P2, then turning P1 by 1 or 2 turns suddenly makes voltage rise on R11 and R12 but if I then turn P2 by 2 turns, voltage stays the same. If I have say 0.35V on R11 I get about 0.53V on R12. P ch MOSFET IRFP9240 gets hot really fast and R11 starts getting hot also R12 but not quite as hot. Could it be that P ch JFET is not conduction or N ch MOSFET maybe bad? Any advise would be appreciated. I took R15/R16 and TH1/2 out of the PCB.
__________________
UGS pre, stock F5, PassLabs X2.5, Aleph P
  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
CCS bias question alexmoose Tubes / Valves 4 22nd July 2006 05:21 PM
Bias pot question Original Burnedfingers Tubes / Valves 1 1st January 2006 02:49 PM
A question of bias... DrG Tubes / Valves 30 28th August 2003 09:30 AM
a75 bias question SteveG Pass Labs 3 16th January 2002 11:06 PM


New To Site? Need Help?

All times are GMT. The time now is 05:35 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