F5X -- the EUVL Approach - The Build Thread - Page 14 - 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 30th May 2012, 07:18 AM   #131
diyAudio Member
 
Join Date: Feb 2010
Location: Dallas Fort Worth area, Texas
Default Adjust final offset in floating X mode:

As mentioned in the last section, it is helpful to observe output offset as you do the final bias adjustments. Not doing so could lead to a good bias balance on all four corners with several volts of offset. Assuming you have made it to this point with a good bias balance and reasonable offset, tweaking pots at opposite corners should get you the final adjustment.

This final adjustment area is a bit more finesse and art that procedure and instructions can communicate so I invite builders to post questions or experiences that contribute positively to others biasing their F5X successfully.
  Reply With Quote
Old 30th May 2012, 07:18 AM   #132
diyAudio Member
 
Join Date: Feb 2010
Location: Dallas Fort Worth area, Texas
Default Test in floating X mode:

If you are like me you will want to test in floating X mode before attaching speakers. Remember that the amplifier is now a floating bridge. The output is from the + to – output pads and not to ground. You can drive the input from a single ended source if you ground the – input but I suggest that you drive the amplifier with a fully balance input to start.

Last edited by fitzfish; 30th May 2012 at 07:42 AM.
  Reply With Quote
Old 30th May 2012, 07:19 AM   #133
diyAudio Member
 
Join Date: Feb 2010
Location: Dallas Fort Worth area, Texas
Well there it is. You should be able to get your amplifier into working condition. Patrick and others will further document the wiring and other case specific details either here or in the case thread. Once the regulator option is flushed out the details will be posted as well.

I still have measurements to make and will be testing output devices that are not close matches from P to N to see how these compare to more closely matched devices. Until then...

Cheers,
Dave
  Reply With Quote
Old 30th May 2012, 07:31 AM   #134
EUVL is offline EUVL  Europe
diyAudio Member
 
Join Date: Oct 2003
QED. Excellent description, Dave.




Patrick
__________________
xen-audio.com

Last edited by EUVL; 30th May 2012 at 07:33 AM.
  Reply With Quote
Old 30th May 2012, 08:11 AM   #135
diyAudio Member
 
Join Date: Feb 2010
Location: Dallas Fort Worth area, Texas
Thanks Patrick.

Yes, done!

Dave
  Reply With Quote
Old 30th May 2012, 08:26 AM   #136
EUVL is offline EUVL  Europe
diyAudio Member
 
Join Date: Oct 2003
I have another volunteer to compare the cascode vs standard.
So that one still to come, but will take a while.
In the meantime, there is enough to keep all those subscribers busy for some time.

Due to requests by PM, I have put up a list for a potential batch 2.

Potential EUVL F5X Case 2nd Batch, Autumn 2012


Patrick
__________________
xen-audio.com
  Reply With Quote
Old 29th July 2012, 05:35 PM   #137
NicMac is offline NicMac  Italy
diyAudio Member
 
NicMac's Avatar
 
Join Date: Feb 2009
Quote:
Originally Posted by fitzfish View Post
Finding quads in the same range that he uses may be challenging unless you have a large number of parts to select from. In the table below Patrick lists calculated values for the degeneration resistors at various Idss combinations. This is a good place to start with selection based on the datasheets curves for the J74 and K70. Because every transistor is slightly different these numbers will not be exact. Select your parts to configure the front end bias at 5mA or higher (the yellow line and below in chart). A lower value here will dictate changing the drain resistor combination on the amplifier board. You can pre-select your parts with a Rdegen of zero ohms to see what you have, then change the 5 ohm resistor in the matching fixture to the calculated value from the chart. My quads ended up with the best match using 6.8/7.8mA Idss selected parts with 4R degeneration for the J74s.
Thank you for this careful explanation Dave.
I think to have understood that if one is in the lucky situation of having sufficient FETs to pick from, one can "simply" do SK170/SJ74 Idss matching with 5R degeneration for the SJ74. Is this correct?
Cheers,
Nic
  Reply With Quote
Old 29th July 2012, 07:05 PM   #138
EUVL is offline EUVL  Europe
diyAudio Member
 
Join Date: Oct 2003
Yes. But remember the 3 point match.


Patrick
__________________
xen-audio.com
  Reply With Quote
Old 29th July 2012, 07:33 PM   #139
NicMac is offline NicMac  Italy
diyAudio Member
 
NicMac's Avatar
 
Join Date: Feb 2009
Quote:
Originally Posted by EUVL View Post
Yes. But remember the 3 point match.
3 point Idss match? I admit I am a bit confused
I can find your test circuit in post#16, but as far as I understand the degeneration resistor is varied here (and not held at a constant 5R).
I guess I will have to study some basic FET function to understand this.......
Thanks,
Nic
  Reply With Quote
Old 29th July 2012, 08:13 PM   #140
EUVL is offline EUVL  Europe
diyAudio Member
 
Join Date: Oct 2003
Did I say 3 point Idss match ?

3 point match means matching with 3 different degeneration resistors values.
For 2SK170, they are e.g. 0R, 5R, 10R.
For 2SJ74, they are 5R, 10R, 15R.

So the extra 5R degeneration resistor for the 2SJ74 has been taken care of.
As Dave has already explained, one point match is IMHO not sufficiently accurate.

Of course curve tracer match is even better.


Patrick
__________________
xen-audio.com
  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
F5X -- the EUVL Approach EUVL Pass Labs 863 19th September 2014 11:31 AM
Potential EUVL F5X designed case user distribution check pchw Group Buys 1004 27th February 2013 04:32 PM
GB 2SK3497/2SJ618 for EUVL F5X or other projects pchw Group Buys 266 8th April 2012 07:05 PM
[B]PRP resistor group buy for the EUVL F5X build[/B] NicMac Group Buys 70 4th February 2012 05:20 PM
New Saburo Build thread Wha' DIYa know? Full Range 94 17th October 2010 05:49 PM


New To Site? Need Help?

All times are GMT. The time now is 09:02 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