How to build the F5 - Page 112 - 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 November 2013, 04:30 PM   #1111
diyAudio Member
 
KatieandDad's Avatar
 
Join Date: Nov 2011
Location: UK
Well the F5 is cooking nicely, the heatsinks are more than adequate and they are barely warm after nearly an hour.

Bias is hovering around the 0.6V mark and the output offset is about 1-3mV.
Attached Images
File Type: jpg DSIR9632.JPG (222.3 KB, 351 views)

Last edited by KatieandDad; 3rd November 2013 at 04:36 PM.
  Reply With Quote
Old 3rd November 2013, 05:28 PM   #1112
diyAudio Member
 
KatieandDad's Avatar
 
Join Date: Nov 2011
Location: UK
After three hours of cooking offset has stabilised at 0.5mV and bias at 0.6V. Can't better that.
  Reply With Quote
Old 4th November 2013, 02:51 PM   #1113
diyAudio Member
 
KatieandDad's Avatar
 
Join Date: Nov 2011
Location: UK
Well I've finally finished the project.

Now when I turn on the amp from cold I get an offset of about 30mV, after a few minutes of warming up that comes down to about 6mV, then it fluctuates between +6mV and -6mV but only on one channel ?? The other channel is stable.

Any ideas..
  Reply With Quote
Old 4th November 2013, 02:58 PM   #1114
diyAudio Member
 
KatieandDad's Avatar
 
Join Date: Nov 2011
Location: UK
I've just tweaked the bias to bring the offset back down to close to zero and it seems to have now stabilised ??

Is it normal to have a bigger offset when first turned ON.
  Reply With Quote
Old 4th November 2013, 03:01 PM   #1115
6L6 is online now 6L6  United States
diyAudio Member
 
6L6's Avatar
 
Join Date: Oct 2010
Location: Denver, Colorado
Just to clarify, you say it's fluctuating between +/- 6mV? 0.006V?

That's so low as to not matter, and anyway, apply a signal and it will fluctuate much more than that.

Essentially you are down in the noise that can only be fixed by lead dressing and the like. I'm sure Andrew will suggest twisting your leads and such.

Your build looks fantastic, I would button it up and listen to it for a week and then re-check the bias and be done.

Congratulations!!
  Reply With Quote
Old 4th November 2013, 03:05 PM   #1116
6L6 is online now 6L6  United States
diyAudio Member
 
6L6's Avatar
 
Join Date: Oct 2010
Location: Denver, Colorado
Quote:
Originally Posted by KatieandDad View Post
Is it normal to have a bigger offset when first turned ON.
Yes, very much so.

The little thermistors near the power Mosfets are part of a temperature compensation circuit for the bias, and they try to keep the bias stable as things heat up, but they can only do so much. That's why Nelson suggests making the final adjustments to the bias once it's been on at least 1/2 hour.
  Reply With Quote
Old 4th November 2013, 04:31 PM   #1117
diyAudio Member
 
KatieandDad's Avatar
 
Join Date: Nov 2011
Location: UK
Default All dressed up and ready to go.

The final product. Unfortunately I can't connect it up as I haven't got long enough interconnects yet.
Attached Images
File Type: jpg DSIR9636.JPG (196.8 KB, 299 views)
File Type: jpg DSIR9637.JPG (190.9 KB, 290 views)
  Reply With Quote
Old 22nd November 2013, 06:37 PM   #1118
diyAudio Member
 
Join Date: Feb 2011
Location: Exton, Pa
Default argh!

Hey guys,

Any thoughts on why the full bias voltage would show up at the outputs (DC offset)? ...done tons of reading. just haven't come across this particular f5 snafoo.

Mosfets are toast, aren' they?

6l6, thanks for these excellent build guides!
  Reply With Quote
Old 22nd November 2013, 08:17 PM   #1119
6L6 is online now 6L6  United States
diyAudio Member
 
6L6's Avatar
 
Join Date: Oct 2010
Location: Denver, Colorado
You have a short somewhere - or a Fet in the wrong position. Or both.

Please take well-lit, in-focus photos and we will take a look.
  Reply With Quote
Old 26th November 2013, 04:43 PM   #1120
diyAudio Member
 
Join Date: Feb 2011
Location: Exton, Pa
Default Board Images

Here are a couple shots of my board, as well lit as I can manage in my dungeon.

I believe my Fets are correctly positioned and I don't see any shorts.

I have found that Offset rises faster than Bias until .3-.35Volts (Bias). After that point DC offset levels off around .4volts and I can continue to increase bias.

Your help is very much appreciated.

Happy Turkey Day to those of you in the states.
Attached Images
File Type: jpg F5 Left.jpg (32.4 KB, 154 views)
File Type: jpg F5 Middle Board.jpg (27.0 KB, 122 views)
File Type: jpg F5 RIght Side.jpg (34.5 KB, 80 views)
File Type: jpg F5 Back.jpg (29.4 KB, 80 views)
  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
Another F5 build--beautiful music, different drummer CanAm Man Pass Labs 144 7th March 2013 09:41 PM
Transistors and Resistors for F5 Amp Build NYCOne Swap Meet 0 20th December 2010 04:29 AM
Next suggested build after F5 anilva Pass Labs 36 3rd December 2010 04:11 AM
F5 Build Instructions 1108 Pass Labs 4 12th May 2009 10:58 PM
Planning an F5 build - some beginner questions njepitt Pass Labs 144 15th March 2009 11:55 PM


New To Site? Need Help?

All times are GMT. The time now is 02:10 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