F5 Help Needed - 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 August 2009, 12:51 PM   #1
diyAudio Member
 
vdi_nenna's Avatar
 
Join Date: Oct 2000
Location: PA, USA
Blog Entries: 1
Send a message via Yahoo to vdi_nenna
Default F5 Help Needed

Hi All,

Still having issues with my F5 build. Replaced all active components and 4.7 ohm thermistors. Checked all resistor values; all are ok. Check for output shorts to case and none found. No input shorts either.
BTW- I checked the semies out of circuit and they all seemed to check out ok. (Must be a resistor value is incorrect?)

I can't seen to get the bias right on this second build. One channel goes up to about .314v across R12 and the other channel gets to about .51v until I run out of turns on the pots. Could R3 and 4 be the wrong values? I check them and they are correct as far as markings go. Used Bourns pots this time and they are very accurate. They do not have markings for ohm value.
Voltage across R3 & 4 are close to 4.2v as indicated in the schematic, but not perfect. I assume P1 and 2 influence this voltage? Also no DC at output.

Thanks for your input,

Vince
__________________
I build, therefore I am.
  Reply With Quote
Old 30th August 2009, 03:45 PM   #2
tms0425 is offline tms0425  United States
diyAudio Member
 
Join Date: Oct 2006
Location: Ft. Wayne, IN
Quote:
Originally Posted by vdi_nenna View Post
Hi All,

Still having issues with my F5 build. Replaced all active components and 4.7 ohm thermistors. Checked all resistor values; all are ok. Check for output shorts to case and none found. No input shorts either.
BTW- I checked the semies out of circuit and they all seemed to check out ok. (Must be a resistor value is incorrect?)

I can't seen to get the bias right on this second build. One channel goes up to about .314v across R12 and the other channel gets to about .51v until I run out of turns on the pots. Could R3 and 4 be the wrong values? I check them and they are correct as far as markings go. Used Bourns pots this time and they are very accurate. They do not have markings for ohm value.
Voltage across R3 & 4 are close to 4.2v as indicated in the schematic, but not perfect. I assume P1 and 2 influence this voltage? Also no DC at output.

Thanks for your input,

Vince
I'm assuming you meant 4.7K not 4.7 ohm thermistors?
  Reply With Quote
Old 30th August 2009, 04:23 PM   #3
diyAudio Member
 
vdi_nenna's Avatar
 
Join Date: Oct 2000
Location: PA, USA
Blog Entries: 1
Send a message via Yahoo to vdi_nenna
Yes, I went back to the order and checked. It is 4.7k Ohm.

Also something of note- when I would blow air over the circuit boards, the R12 voltage would rise several hundred millivolts, then drop back down to their current voltage. If I put my hand on the heat sink the voltage would drop slightly.
__________________
I build, therefore I am.
  Reply With Quote
Old 30th August 2009, 08:58 PM   #4
Tea-Bag is offline Tea-Bag  United States
not politcally affiliated
diyAudio Member
 
Tea-Bag's Avatar
 
Join Date: Feb 2006
Location: Kennebunk
Blog Entries: 7
Quote:
Originally Posted by vdi_nenna View Post
Yes, I went back to the order and checked. It is 4.7k Ohm.

Also something of note- when I would blow air over the circuit boards, the R12 voltage would rise several hundred millivolts, then drop back down to their current voltage. If I put my hand on the heat sink the voltage would drop slightly.
Cooling the Jfets and Fets with air seems normal in my book.

I only measure voltage across one of the source resistors, and leave the other DVM across the terminals and measure DC offset. As one pot goes up in turns, the DC offset should move and the source voltage. The idea being that if the source voltage is reasonable, and the DC offset reasonably low, your good. There should always be a value here.
  Reply With Quote
Old 30th August 2009, 09:00 PM   #5
diyAudio Member
 
Join Date: Jan 2006
Location: Ireland
2 things to do:

check your grounding and take some pics and post them here. That will help hugely.


Yes, if R11 and R12 are different values (eg one is .47 and other is 0.33) then you will get different voltages across them. If they got a good burn at any stage they may well have drifted.

What boards are you using?


Fran
  Reply With Quote
Old 30th August 2009, 11:25 PM   #6
diyAudio Member
 
vdi_nenna's Avatar
 
Join Date: Oct 2000
Location: PA, USA
Blog Entries: 1
Send a message via Yahoo to vdi_nenna
I have no DC reading/movement at the outputs.

Using cviller boards. i have 2 coming from Peter Daniel soon.

I'll try to post pics but my camera is bad for close-ups.
__________________
I build, therefore I am.
  Reply With Quote
Old 31st August 2009, 12:29 AM   #7
The one and only
 
Nelson Pass's Avatar
 
Join Date: Mar 2001
I think it's either low Idss on the JFETs or high Vgs on the
Mosfets. I run into the latter often enough. Increase the
value of the resistor in parallel with the pot. I usually go from
1.2K to as high as 2.2K

  Reply With Quote
Old 31st August 2009, 12:36 AM   #8
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 Nelson,

I used Jfets from the B1...I remember using Jfets for this amp with a low Idss...let me see...this time I used .29 and .18 on th 2sk170s. I did not measure the 2sj74 jfets.

You think this would explain the lack of DC at the outs?

Thanks!

Vince
__________________
I build, therefore I am.

Last edited by vdi_nenna; 31st August 2009 at 12:48 AM.
  Reply With Quote
Old 31st August 2009, 12:39 AM   #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
Some pics...not good. BTW- I used IRFP9140 P-ch (100v 21a) and IRFP140 N-ch (100v 33a)

Used 2.2k for R3 and 4 from Fig 6. Should I go higher than 2.2k?

http://i145.photobucket.com/albums/r...s/DSCF0100.jpg

http://i145.photobucket.com/albums/r...s/DSCF0101.jpg

http://i145.photobucket.com/albums/r...s/DSCF0102.jpg

http://i145.photobucket.com/albums/r...s/DSCF0103.jpg

http://i145.photobucket.com/albums/r...s/DSCF0108.jpg

http://i145.photobucket.com/albums/r...s/DSCF0109.jpg

http://i145.photobucket.com/albums/r...s/DSCF0110.jpg

http://i145.photobucket.com/albums/r...s/DSCF0112.jpg

As you can see, I added board connectors this time for quick removal!!
__________________
I build, therefore I am.

Last edited by vdi_nenna; 31st August 2009 at 12:53 AM.
  Reply With Quote
Old 31st August 2009, 05:16 PM   #10
diyAudio Member
 
vdi_nenna's Avatar
 
Join Date: Oct 2000
Location: PA, USA
Blog Entries: 1
Send a message via Yahoo to vdi_nenna
Can I go up to 3.3k on the R3 & R4 resistors?

Thx.
__________________
I build, therefore I am.
  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
Help needed ! Inter M R300 schematics needed ! alexclaire Solid State 30 9th September 2009 06:14 AM
HELP needed cobology Car Audio 21 2nd March 2009 12:11 PM
Help needed please. sicknote Multi-Way 4 18th January 2008 08:27 AM
LT1964-adj Help Needed or Part Needed lgreen Parts 2 29th June 2007 02:50 PM


New To Site? Need Help?

All times are GMT. The time now is 07:20 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