F5X from diyAudio Boards P-F5c-2V20e - Page 3 - 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 20th October 2011, 06:43 AM   #21
JBL4435 is offline JBL4435  Germany
diyAudio Member
 
Join Date: Oct 2006
Quote:
Originally Posted by EUVL View Post
It is a voltage clip.

The circuit has a gain of 6. So output is at 13.8V with 16V rails.
As expected not enough headroom left for the MOSFETs.

Since you are using 2 output pairs, you can increase rail voltage and reduce bias current per FET while keeping dissipation per FET below 32W.

I would try 20V 1.6A per FET as a start.


Patrick
Thanks Patrick
I thought about that but I use 22V Rails and 1.3A per FET.

Can you explain how you get the 6dB gain? With 6dB I get 4.4V out with 2.2V in. Wasn't it 15dB?

Last edited by JBL4435; 20th October 2011 at 06:55 AM.
  Reply With Quote
Old 20th October 2011, 06:44 AM   #22
JBL4435 is offline JBL4435  Germany
diyAudio Member
 
Join Date: Oct 2006
Quote:
Originally Posted by NYCOne View Post
This is how I built one:

Building a World-Class Cascoded Balanced XF5 on a Budget

I used 1K and 100K as NP did in the original and have no problems.
Thanks for the help but this was solved a few posts before. 1k and 33.2k
  Reply With Quote
Old 20th October 2011, 07:12 AM   #23
EUVL is offline EUVL  Europe
diyAudio Member
 
Join Date: Oct 2003
Gain of 6, not 6dB (gain of 2).

The closed loop gain of a feedback amp is given by (Rfeedback + Rshunt) / Rfeedback.

In this case, Rfeedback = 50R, Rshunt = 10R.
So gain = (50+10)/10 = 6.


Patrick
  Reply With Quote
Old 20th October 2011, 07:33 AM   #24
JBL4435 is offline JBL4435  Germany
diyAudio Member
 
Join Date: Oct 2006
Quote:
Originally Posted by EUVL View Post
Gain of 6, not 6dB (gain of 2).

The closed loop gain of a feedback amp is given by (Rfeedback + Rshunt) / Rfeedback.

In this case, Rfeedback = 50R, Rshunt = 10R.
So gain = (50+10)/10 = 6.


Patrick
I've got this wrong. Thank you for clearification.

Any idea why I get this clipping? With +/- 22V Rail I should be safe.
  Reply With Quote
Old 20th October 2011, 07:35 AM   #25
EUVL is offline EUVL  Europe
diyAudio Member
 
Join Date: Oct 2003
Your output voltage should not come closer than say 4V to the rail voltage if you want to avoid clipping.
The MOSFETs do not have sufficient Vds to operate properly.


Patrick
  Reply With Quote
Old 20th October 2011, 07:59 AM   #26
JBL4435 is offline JBL4435  Germany
diyAudio Member
 
Join Date: Oct 2006
Quote:
Originally Posted by EUVL View Post
Your output voltage should not come closer than say 4V to the rail voltage if you want to avoid clipping.
The MOSFETs do not have sufficient Vds to operate properly.


Patrick
I understand that, but I'm missing a few Volts

Output with 2,3V in and gain of 6 (15,5dB) is 13,8V. With 22V Volt rail....

My PS is ultra stable. 800VA Transformer 2x18V, CLC with 2x99.000 uF, 2x 2,2mH/0,12Ohm.
  Reply With Quote
Old 20th October 2011, 08:16 AM   #27
EUVL is offline EUVL  Europe
diyAudio Member
 
Join Date: Oct 2003
You need to show an output waveform for the clipping for us to understand your problem.


Patrick
  Reply With Quote
Old 20th October 2011, 08:30 AM   #28
JBL4435 is offline JBL4435  Germany
diyAudio Member
 
Join Date: Oct 2006
Quote:
Originally Posted by EUVL View Post
You need to show an output waveform for the clipping for us to understand your problem.
Patrick
OK, I'll make several pics.
  Reply With Quote
Old 20th October 2011, 07:33 PM   #29
JBL4435 is offline JBL4435  Germany
diyAudio Member
 
Join Date: Oct 2006
Default Measurements and Waveform 1kHz 8Ohm

Amp info:
Vrail +/- 21.8V
Ibias 0.6V across 0.47 Ohm 1.3A 2 parallel output Fets Total Bias 2.6A
I out of PS measured 5.4A

NOT X-ed yet.

1. 8 Ohm 2.5Vin 0.5%THD right before clipping
2. 8 Ohm 2.6Vin 1.5%THD start of clipping
3. 8 Ohm 2.8Vin 4.5%THD clipping
Attached Images
File Type: jpg 8Ohm_2,5Vin_0,5THD.JPG (52.3 KB, 343 views)
File Type: jpg 8Ohm_2,6Vin_1,5THD.JPG (54.7 KB, 334 views)
File Type: jpg 8Ohm_2,8Vin_4,5THD.JPG (53.6 KB, 334 views)
  Reply With Quote
Old 20th October 2011, 07:36 PM   #30
JBL4435 is offline JBL4435  Germany
diyAudio Member
 
Join Date: Oct 2006
Default Measurements and Waveform 1kHz 4Ohm

1. 4 Ohm 2.3Vin 0.6%THD right before clipping
2. 4 Ohm 2.5Vin 3.5%THD start of clipping
3. 4 Ohm 2.8Vin 7.5%THD clipping
Attached Images
File Type: jpg 4Ohm_2,3Vin_0,6THD.JPG (50.6 KB, 245 views)
File Type: jpg 4Ohm_2,5Vin_3,0THD.JPG (48.2 KB, 236 views)
File Type: jpg 4Ohm_2,8Vin_7,5THD.JPG (51.3 KB, 20 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
F5X -- the EUVL Approach EUVL Pass Labs 863 19th September 2014 11:31 AM
Potential Other Group Buys related to EUVLs F5X heinz1 Group Buys 456 2nd March 2014 02:16 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
Unique or odd uses for the diyAudio CCS boards Geek Tubes / Valves 1 12th December 2006 03:45 PM


New To Site? Need Help?

All times are GMT. The time now is 02:08 AM.


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