aleph 5 oscillating??? - 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 2nd February 2005, 02:39 PM   #1
diyAudio Member
 
Join Date: May 2002
Location: oz
Default aleph 5 oscillating???

Hi all

After much stuffing around i have seperated A5 power supply for the pcb's and output mosfets after upgrading heasinks to much larger size.

However i now have other problems which I didn't have before!!

1. I now have approx 1V offset at speak terminals as opposed to approx 50mV previously.

2. I now have hum at ouput (even with now input wiring to pcb.)

3. Votages on pcb appear ok.

4 . voltage across 1 source resistor on one mosfet starts off ok then rises rapidly and the other mosfets current essontially drops to zero....ish.

Is this one mosfet oscillating.????

I replaced it with another (matched ) and again voltage started off ok and then started to rise, is the mosfet dud , (it has 33ohm across gate to source...

the ouptut mosfet are only a couple of inches from the pcbboard.


any suggestions.????

thanks in advance

cheers
__________________
george a
  Reply With Quote
Old 2nd February 2005, 02:53 PM   #2
diyAudio Member
 
Join Date: Dec 2002
Location: Illinois, USA
The negative rail of the front end has to be the same as the negative rail on the output stage.

Jeremy
  Reply With Quote
Old 2nd February 2005, 03:01 PM   #3
diyAudio Member
 
Join Date: May 2002
Location: oz
Hi Jeremy
They are the same as they are fed from same point
I am using Mark Finnis PCb + mosfet pcb's


BTW I removed 1 ohm source resistor and turned on to check other mosfet and the resistor R22 221ohm which goes from Q2 (Ztx450) to junction between source of mosfet and 1ohm resistor ended up smoking itself
__________________
george a
  Reply With Quote
Old 2nd February 2005, 07:29 PM   #4
diyAudio Member
 
Join Date: May 2002
Location: oz
Anybody ...please??
__________________
george a
  Reply With Quote
Old 2nd February 2005, 11:53 PM   #5
diyAudio Member
 
Join Date: May 2002
Location: oz
please..??


BTW I don't have an oscilloscope to have a look at what's happening
__________________
george a
  Reply With Quote
Old 3rd February 2005, 06:08 AM   #6
diyAudio Member
 
Join Date: May 2002
Location: oz
anybody....please??
__________________
george a
  Reply With Quote
Old 3rd February 2005, 07:52 AM   #7
Electrons are yellow and more is better!
diyAudio Member
 
peranders's Avatar
 
Join Date: Apr 2002
Location: Göteborg, Sweden
Blog Entries: 4
The experts sleep sometimes
__________________
/Per-Anders (my first name) or P-A as my friends call me
Tube Buffered Gainclone in work |Thread || Diamond buffer |Thread for the group buy | Wiki
  Reply With Quote
Old 3rd February 2005, 08:46 AM   #8
diyAudio Member
 
Join Date: May 2002
Location: oz
Yes Peranders , the experts do sleep sometimes.

the problem is idiots like ME stay up all night worrying about what we've done wrong.

Sweet dreams , good night - sleep tight

regards from down under
__________________
george a
  Reply With Quote
Old 3rd February 2005, 11:13 AM   #9
diyAudio Member
 
macka's Avatar
 
Join Date: Dec 2001
Location: Australia
Sounds like a wiring fault,

Post a few pictures so we can understand

Macka
  Reply With Quote
Old 3rd February 2005, 12:48 PM   #10
diyAudio Member
 
Join Date: May 2002
Location: oz
sort of a wiring fault macka

looks like a dodgy 1 ohm resistor in the location that's blown 2 mosfets so far.
I replaced the mosfet with a sacrificial non matching one and put in a 1.5 ohm resistor just to see what happens....

result :
the non matched mosfet is pulling about twice the current of the others...
no hum (well almost all gone -acceptable level)
offset 6.7mV

heatsink is warming up...



I will get to shops tommorow to purchase new 1 ohm resistor...


there is much to be learnt in putting these things together!!!

Ta
__________________
george a
  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
PSU oscillating apolon34 Power Supplies 3 24th June 2005 02:20 PM
Aleph-X oscillating. What to do? AudioAngel Pass Labs 15 26th March 2005 07:17 AM
Oscillating DoZ rchua77 Solid State 1 30th January 2004 10:07 AM
Is your Aleph oscillating? kenny_(00)_ Pass Labs 5 2nd September 2003 04:46 PM


New To Site? Need Help?

All times are GMT. The time now is 07:06 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