new f5 bias problem - 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 1st May 2011, 12:13 AM   #21
diyAudio Member
 
Bksabath's Avatar
 
Join Date: Dec 2007
Board from top looks preaty neat

So supose no bubus on botom.

You may have caused same dammage already so beter cek the mosfet best
way by triing the VGS matching.

Same for the J fets

Burn look preaty bad on the 47? gate resistor so quite a bit of current/voltagge gone troug.

Did you use the light bulb?

PS I had a Jfet gone bad and with litle meter it mesured ok toke a couple of hours of major head bashing to finaly decide to put in a fresh one.

Once done problem solved.
  Reply With Quote
Old 1st May 2011, 03:24 AM   #22
diyAudio Member
 
Join Date: Sep 2006
Location: Santa Rosa Beach, FL
[QUOTE=crazycody1993;2557133]Actually no, I didn't test my supply voltages. QUOTE]

'Just always a good idea to test, as you go, wherever you can. Testing the power supply, before you hook up the amps is "insurance". In case the power supply has problems, you can catch them before you hook up the amp PCBs and damage them.

Having said that, unclear is the power supply is the source of your problems. Are you having identical problems with both Jim's Audio boards (burning the same resistors)?

I've looked at your pics, and compared them to my Jim's boards, and you seem to have the caps, semiconductors and trimpots installed OK (as long as they were set to minimal resistance at the start). Difficult for me to confirm your resistor values, from your pics.

I'll get into the schematic, and see if I can get some ideas.

In the meanwhile, here are some pics of my Jim's boards. I had no problems on start-up and in continued use. The first two pics are the left channel PCB, while the third pic is the right channel PCB. I've included the fourth pic, just because when the PCBs are illuminated by the blue LEDs inside the case and viewed through the bronze plexiglass top panel, they just look so darned sexy(!).

Don't be frustrated--the final F5 is well, well worth any agnst you may now be going through.....!

Ken
Attached Images
File Type: jpg 121.JPG (78.2 KB, 249 views)
File Type: jpg 122.JPG (72.0 KB, 208 views)
File Type: jpg 123.JPG (65.7 KB, 205 views)
File Type: jpg 124.JPG (44.1 KB, 204 views)
  Reply With Quote
Old 1st May 2011, 06:02 AM   #23
diyAudio Member
 
Join Date: Feb 2011
Location: Oregon
i dont know how to test any MOSFETs??

i didnt end up using the light bulb, i have a feeling i would be able to catch something if i did end up using the light bulb.

and i've double checked everything that i installed, and it all looks okay, from where i sit. but clearly something is wrong, otherwise i would be enjoying my F5 instead of trying to figure out whats wrong!

across R3 and R4 i dont have quite zero, roughly 1.3? but i dont imagine that makes a whole lot of difference. i ran into an interesting reading though, but i'm gonna replace that 47, and see if i found a fluke, or if the 47 has something to do with what i discovered.
  Reply With Quote
Old 2nd May 2011, 12:38 AM   #24
diyAudio Member
 
Bksabath's Avatar
 
Join Date: Dec 2007
Gate resistor is there to suply (depending on which flawor mosfet) a couple of volts to the gate.

Current there shuld be realy low just what the J fets can cope with.
From the dammage done to it same preaty large current went troug there.

Sorry cant help you more I am still preaty green but IMO Itsmee on post 3 got it.

Maybe there are beter ways but have a look at Fig 1 on practical Mosfet testing for audio article Simplified Test Setup that may hel with testing
  Reply With Quote
Old 2nd May 2011, 04:15 AM   #25
diyAudio Member
 
Join Date: Feb 2011
Location: Oregon
So i looked at my PS, unloaded, my voltages are 35.4V and -35.3V.

And i let it run for several hours, and continued to check it, and kept getting the same readings, no excessive heating, or any discoloring of the resistors in the circuit. seemingly functioning fine.

While waiting on what to do with the first channel, i tried getting the other one running, and ran into more issues. My offset is roughly -27V, and adjusting the pots is making no difference. While trying to get either to move, the voltage across R11 was .5mV, but R12 was 434mV. I just dont understand the damage?? and while trying to move my offset, R5, R6, R7, and R8 began to brown, with the scent of hot electronics.

I checked to make sure that the resistances across R4 and R3 move as well, R3 moves from almost 0 all the way up to about 2k while R4 only moves from 0 to 60.

i hope this information helps everyone. and just to clarify, this is on the second channel! not the first, that burnt the 47

Last edited by crazycody1993; 2nd May 2011 at 04:33 AM.
  Reply With Quote
Old 2nd May 2011, 11:19 AM   #26
Zen Mod is offline Zen Mod  Serbia
diyAudio Member
 
Zen Mod's Avatar
 
Join Date: Jan 2003
Location: ancient Batsch , behind Iron Curtain
your PSU voltage is in range where begins differentiation between boyz and men

so - either use other xformer ( with lower voltage ) or build cascoded F5
__________________
my Papa is smarter than your Nelson !
clean thread; Cook Book;PSM LS Cook Book;Baby DiyA ;Mighty ZM's Bloggg;Papatreasure;Papa...© by Mighty ZM
  Reply With Quote
Old 2nd May 2011, 03:06 PM   #27
diyAudio Member
 
Join Date: Feb 2011
Location: Oregon
Is that causing my problems??
  Reply With Quote
Old 2nd May 2011, 04:30 PM   #28
Zen Mod is offline Zen Mod  Serbia
diyAudio Member
 
Zen Mod's Avatar
 
Join Date: Jan 2003
Location: ancient Batsch , behind Iron Curtain
if not now - it will later , for sure
__________________
my Papa is smarter than your Nelson !
clean thread; Cook Book;PSM LS Cook Book;Baby DiyA ;Mighty ZM's Bloggg;Papatreasure;Papa...© by Mighty ZM
  Reply With Quote
Old 2nd May 2011, 04:42 PM   #29
diyAudio Member
 
Join Date: Sep 2006
Location: Santa Rosa Beach, FL
CrazyC...... If your intent is to build a "bone stock" F5, best to stick to the published Pass schematic (and Pass narrative) values. That would be rail voltages of +24 and -24 volts, with about 6 amp continuous rating, and 10 amp peak surge.

That means, in the standard CRC configuration, transfo secondary voltages of 18 VAC (dual secondaries), with about 400 VA transfo rating.

Can't say if your current power supply caused your current (no pun intended) problem, but best to go for +/- 24 VDC rails, if you are building the stock F5.
  Reply With Quote
Old 2nd May 2011, 04:45 PM   #30
diyAudio Member
 
komigenie's Avatar
 
Join Date: Jan 2006
Location: Spring Lake, NC
hmm, whats the value of this Capacitors on this red board ? 220/35 or something diferent .. i see ther 47/50 ...

what should be best value and what kind of cap ?
  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
Initial setting of F5 bias--help, please! CanAm Man Pass Labs 30 23rd June 2014 02:12 PM
F5 bias question richD Pass Labs 12 4th March 2013 01:57 PM
F5 Bias Problem maartentje Pass Labs 150 3rd August 2012 12:10 PM
F5 DC High, Bias Low vdi_nenna Pass Labs 8 9th April 2011 01:22 PM
Bias problem- 1 Socket shows extremely low bias! otokomae Tubes / Valves 12 31st December 2008 11:01 PM


New To Site? Need Help?

All times are GMT. The time now is 05:38 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