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 21st March 2020, 09:50 PM   #1
Alex79 is offline Alex79
diyAudio Member
 
Join Date: Jan 2018
Default ALEPH 5 Oscilating 600KHz

Hello, I have build my first Aleph 5. Schematic bellow. I have matched IRF9610. Rail voltage +-34V



I have start with just one pair of IRF244 before adding others. When I connect dummy load 8Ohm, everything seems OK. 13v peak to peak before clipping- that is power output I would expect.

When clipping started around 14.5V, it clipping only postive side of sinewave, negative is ok even in much higher output. Somehow assymetric clipping... If I have added more output mosfets, clipping was symetric. With just one pair, always such assymetric - however same behaviour on both channels. Is it something I should deal with?

If I connect 6Ohm speaker instead of dummy load, there is quite big oscillation - 600Khz. Suprisingly, if I lower rail voltage to +-10V, everything going nice. No Oscilation and THD even lower then with +-34V, maximum output voltage cca 14V pk-pk. However, when rail voltage go over +-15, imediatelly there is big 600Khz oscilation.

As it is my first Mosfet amplifier, Im little bit lost how to prevent the oscilation. Im thinking to try increase gate serial resistor from 221 to 1K. Thinking to add some capacitors between Gate and source...however not really sure where to focus first.

Really appreciate any help from more experienced guys here, what should I try. Thank you in advance.
Attached Images
File Type: gif aleph-5.gif (13.6 KB, 337 views)
  Reply With Quote
Old 21st March 2020, 10:03 PM   #2
6L6 is offline 6L6  United States
diyAudio Moderator
 
6L6's Avatar
 
Join Date: Oct 2010
Location: Denver, Colorado
ALEPH 5 Oscilating 600KHz
Please post some well-lit, in-focus photos of your amp so we can start looking at what you have.
  Reply With Quote
Old 21st March 2020, 10:08 PM   #3
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
two 1nF caps will probably cure whatever you have there

see enclosed
Attached Files
File Type: pdf Aleph30 by Algar_emi.pdf (29.9 KB, 98 views)
__________________
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 21st March 2020, 10:35 PM   #4
Alex79 is offline Alex79
diyAudio Member
 
Join Date: Jan 2018
Quote:
Originally Posted by Zen Mod View Post
two 1nF caps will probably cure whatever you have there

see enclosed

Thank you for quick answer. As I see in the schematic, there are two 1nF caps.
C105 - In my circuit is 680pF. Quite close to 1nF, so Im not expecting there should be any change if I replace it.
C102 - I have added 1nF there. Unfortunatelly, it did not stop the oscilation.
  Reply With Quote
Old 21st March 2020, 11:13 PM   #5
Alex79 is offline Alex79
diyAudio Member
 
Join Date: Jan 2018
Quote:
Originally Posted by 6L6 View Post
Please post some well-lit, in-focus photos of your amp so we can start looking at what you have.
PCB is from HIFISTOR Aleph 5 60W A class Amplifier D.I.Y. - HiFiStor

Some components I used from kit, some resistors I replaced with more precise and matched IRF9610. I tried to swap IRFP244 multiple times. Somehow, the amplifier is more stable with 2- pairs of transistors and has even clipping than with one pair. However, due to smaller heatsink and enough power to drive my speaker just with 10W, I would like to make it run on one pair only.

What is not visible, I added 1nF from bottom C102.
Attached Images
File Type: jpg IMG_20200322_000253.jpg (427.2 KB, 310 views)
File Type: jpg IMG_20200322_000244.jpg (372.0 KB, 304 views)
File Type: jpg IMG_20200322_000248.jpg (426.8 KB, 298 views)
  Reply With Quote
Old 21st March 2020, 11:23 PM   #6
Alex79 is offline Alex79
diyAudio Member
 
Join Date: Jan 2018
Quote:
Originally Posted by Alex79 View Post
Thank you for quick answer. As I see in the schematic, there are two 1nF caps.
C105 - In my circuit is 680pF. Quite close to 1nF, so Im not expecting there should be any change if I replace it.
C102 - I have added 1nF there. Unfortunatelly, it did not stop the oscilation.
Also to mention, right now Im just using as rail power Lab power supply Fluke +-60V / 5A. Im not expecting any issue from here.

If the amplifier has no input, it stays ok. when I connect any source to input, even just wires without any signal (generator turned off) it start oscillating.
  Reply With Quote
Old 21st March 2020, 11:57 PM   #7
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
if you have your lab supply current limited anywhere near amp Iq , that setup is critical per se

build it with regular PSU and try it again
__________________
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 22nd March 2020, 02:38 AM   #8
Extreme_Boky is offline Extreme_Boky
diyAudio Member
 
Join Date: Dec 2003
Hi Alex 97,

The quiescent current would depend on the number of devices used in the output; the correct number of output devices would set the correct quiescent current, and hence -> you'd achieve the symmetrical clipping. Therefore, use 3 output devices, i.e. 3 x 1 ohm wire-wound resistors in parallel. This 0.33ohm value, together with that 1k resistor picking up the voltage drop across 1-ohm resistor & biasing the base of MPSA18, will set the correct operating point of the output stage.

Last edited by Extreme_Boky; 22nd March 2020 at 02:41 AM.
  Reply With Quote
Old 22nd March 2020, 09:31 AM   #9
Alex79 is offline Alex79
diyAudio Member
 
Join Date: Jan 2018
Quote:
Originally Posted by Extreme_Boky View Post
Hi Alex 97,

The quiescent current would depend on the number of devices used in the output; the correct number of output devices would set the correct quiescent current, and hence -> you'd achieve the symmetrical clipping. Therefore, use 3 output devices, i.e. 3 x 1 ohm wire-wound resistors in parallel. This 0.33ohm value, together with that 1k resistor picking up the voltage drop across 1-ohm resistor & biasing the base of MPSA18, will set the correct operating point of the output stage.

Thank you for answer. As Im still learning the pass aleph topolopogy, I was not sure how to properly bias it. So thx for pointing it out.



With 1ohm resistor, the amp is taking 0.5 Amp per transistor pair. With 3 pairs, 1.5 Amp. If I keep only one pair of transistor and lower value of the resistor to , 0.33 ohm the amp should draw more current, cca 2 Amps. That would drive transistors too hot. So I think, I should keep 1 ohm, but play more with the value of 1K resistor. Is it right idea? I will try some potenciometr there and see if I can find balance.
  Reply With Quote
Old 22nd March 2020, 10:58 AM   #10
Extreme_Boky is offline Extreme_Boky
diyAudio Member
 
Join Date: Dec 2003
Quote:
Originally Posted by Alex79 View Post
Thank you for answer. As Im still learning the pass aleph topolopogy, I was not sure how to properly bias it. So thx for pointing it out.



With 1ohm resistor, the amp is taking 0.5 Amp per transistor pair. With 3 pairs, 1.5 Amp. If I keep only one pair of transistor and lower value of the resistor to , 0.33 ohm the amp should draw more current, cca 2 Amps. That would drive transistors too hot. So I think, I should keep 1 ohm, but play more with the value of 1K resistor. Is it right idea? I will try some potenciometr there and see if I can find balance.
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.
  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 11:24 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