Go Back   Home > Forums > >
Home Forums Rules Articles diyAudio Store Blogs Gallery Wiki Register Donations FAQ Calendar Search Today's Posts Mark Forums Read

Pass Labs This forum is dedicated to Pass Labs discussion.

ALEPH 5 Oscilating 600KHz
ALEPH 5 Oscilating 600KHz
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 22nd March 2020, 01:43 PM   #11
Alex79 is offline Alex79
diyAudio Member
 
Join Date: Jan 2018
Quote:
Originally Posted by Extreme_Boky View Post
Yes, exactly right. However, you will also change the AC gain by playing with a 1-ohm resistor. Nelson has explained how to empirically set the AC gain, so you can set the quiescent current properly, for symmetrical clipping, AND set the AC gain at 50% which seems like a desired amount of gain.

So I end up to have 1 Ohm resistor (0.5A current) together with 2.2K resistor instead of 1K. I was not going mainly for symetrical clipping, but measure for best THD regrding almost max power output. With 2.2K I get best THD and also clipping symetry get much better even it is still somehow assymetric. So thank you for help with biasing.



So main issue stay to be 600KHz oscilation when connected to speakers. Still trying to eperiment with it, however without success yet
  Reply With Quote
Old 22nd March 2020, 04:41 PM   #12
Nelson Pass is offline Nelson Pass  United States
The one and only
 
Nelson Pass's Avatar
 
Join Date: Mar 2001
ALEPH 5 Oscilating 600KHz
Several suggestions:

With lab supply, consider some capacitance from rails to ground

Doesn't oscillate without a source? what if you short the input to ground?

Oscillates with load? How about with about .1 uF + 5 ohms to ground?
  Reply With Quote
Old 22nd March 2020, 05:54 PM   #13
Alex79 is offline Alex79
diyAudio Member
 
Join Date: Jan 2018
Quote:
Originally Posted by Nelson Pass View Post
Several suggestions:

With lab supply, consider some capacitance from rails to ground

Doesn't oscillate without a source? what if you short the input to ground?

Oscillates with load? How about with about .1 uF + 5 ohms to ground?

Hello Nelson, thank you for great design.

It is strange, never see such behaviour with amp before. But first time building Mosfet amp. It doesnt oscillate if I use just dummy 8ohm load.

When I attach speakers, it starts oscillating 300-600KHz 10-20V pk-pk. It is oscillating even when no source or inputs shorted to ground. If no load or full load, the value doesnt change.

I tried to see what happening on rails. POSITIVE to GND nothing. GND to NEGATIVE - 4Vpk-pk 300-600KHz noise.

If I try different lab supply, same behaviour.

Something strange going on negative rail.
  Reply With Quote
Old 22nd March 2020, 05:57 PM   #14
rayma is offline rayma  United States
diyAudio Member
 
Join Date: Apr 2011
Try using the same speaker wires, but with the dummy load.
  Reply With Quote
Old 22nd March 2020, 08:22 PM   #15
Alex79 is offline Alex79
diyAudio Member
 
Join Date: Jan 2018
So after more experimenting, What really make difference is the 680pF capacitor. I have to increase it to 4nF or more and now oscillation is gone!


Thank you all for help.
  Reply With Quote
Old 22nd March 2020, 08:49 PM   #16
Nelson Pass is offline Nelson Pass  United States
The one and only
 
Nelson Pass's Avatar
 
Join Date: Mar 2001
ALEPH 5 Oscilating 600KHz
That capacitance figure is still higher than you want.

What about dummy load and RC network at output?
  Reply With Quote
Old 23rd March 2020, 11:36 PM   #17
Mark Tillotson is offline Mark Tillotson
diyAudio Member
 
Join Date: May 2018
Location: Cambridge UK
My immediate thoughts looking at the circuit diagram are where's the rail decoupling
and the Zobel network?
  Reply With Quote
Old 24th March 2020, 03:59 PM   #18
Nelson Pass is offline Nelson Pass  United States
The one and only
 
Nelson Pass's Avatar
 
Join Date: Mar 2001
ALEPH 5 Oscilating 600KHz
The production Alephs did not require either, but DIY versions will often
have different parts, layout, and/or errors. This case may be one of those,
and the decoupling and zobel won't hurt, and might help indicate where
the problem is.
  Reply With Quote
Old 24th March 2020, 04:33 PM   #19
Mark Tillotson is offline Mark Tillotson
diyAudio Member
 
Join Date: May 2018
Location: Cambridge UK
I note this is a likely known issue since the Aleph 3: Aleph 3 oscillations


I'd never recommend avoiding rail decoupling, its first and strongest defence against unwanted positive feedback paths. I note the Aleph P uses decoupling on at least one rail.


Skimping on this because it happens to work in a particular configuration is, erm, questionable, to say the least.
  Reply With Quote
Old 24th March 2020, 05:21 PM   #20
Zen Mod is offline Zen Mod  Serbia
Official Court Jester
diyAudio Member
 
Zen Mod's Avatar
 
Join Date: Jan 2003
Location: ancient Batsch , behind Iron Curtain
ALEPH 5 Oscilating 600KHz
originals were never oscillating

DIY iterations - sometimes ...... it all depends of physical layout and execution
__________________
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

Reply


ALEPH 5 Oscilating 600KHzHide 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

Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
shelf oscilating psu east electronics Power Supplies 9 22nd November 2012 12:57 AM
How to create self oscilating SMPS luka Power Supplies 10 7th January 2007 06:41 PM
Aleph P oscilating or something else!!! bbakota2000 Pass Labs 4 30th August 2004 04:17 PM
Looking for self oscilating class D lumanauw Class D 14 2nd March 2004 03:14 PM
oscilating in capacitive load borisov57 Solid State 3 24th January 2003 12:29 PM


New To Site? Need Help?

All times are GMT. The time now is 08:19 AM.


Search Engine Optimisation provided by DragonByte SEO (Pro) - vBulletin Mods & Addons Copyright © 2020 DragonByte Technologies Ltd.
Resources saved on this page: MySQL 14.29%
vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2020 DragonByte Technologies Ltd.
Copyright ©1999-2020 diyAudio
Wiki