Go Back   Home > Forums > >

Solid State Talk all about solid state amplification.

Hifisonix kx-Amplifier
Hifisonix kx-Amplifier
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
Old 30th November 2020, 09:29 AM   #451
Rallyfinnen is offline Rallyfinnen  Sweden
diyAudio Member
 
Join Date: Jan 2017
Quote:
Originally Posted by Bonsai View Post
Tony/Rallyfinnen can you clip the scope probe earth to the scope probe tip and hold the loop near your scope screen. Please make sure the scope is at Max sensitivity (2mV to 10 mV per division).

What are you seeing?
I see only a straight line, not even noise.
  Reply With Quote
Old 30th November 2020, 09:42 AM   #452
Rallyfinnen is offline Rallyfinnen  Sweden
diyAudio Member
 
Join Date: Jan 2017
Default Measurements

After adding a cap over R9, my hum went down a lot since IMHO any voltage over this resistor will be amplified by the amp. Hum reduction was even enough to make me try bypassing the ripple eater, and looking at the FFT, now I can hardly see any change in PSU noise on the output with or without it. This is of course running single channel (dual mono) setup.
I had some question marks before about distortion, and now I added 10x more damping to the input on the sound card just to rule out an overloaded input, but the result is the same. Increased amplitude gives a lot of harmonics, and it is independent of current (load), and gets worse with higher frequencies.
This is full Iq mode, no ripple eater.
Attached Images
File Type: jpg KX 5Vrms 1k 7ohm.jpg (90.3 KB, 226 views)
File Type: jpg KX 5Vrms 10k 7ohm.jpg (89.7 KB, 225 views)
File Type: jpg KX 5Vrms 7ohm 40hz.jpg (85.9 KB, 217 views)
File Type: jpg KX 10Vrms 7ohm 40Hz.jpg (88.7 KB, 216 views)
File Type: jpg KX 10Vrms 7ohm 1k.jpg (94.8 KB, 218 views)
File Type: jpg KX 10Vrms 7ohm 10k.jpg (90.9 KB, 14 views)
File Type: jpg KX 10Vrms no load 10k.jpg (91.1 KB, 16 views)

Last edited by Rallyfinnen; 30th November 2020 at 09:48 AM.
  Reply With Quote
Old 30th November 2020, 10:02 AM   #453
Rallyfinnen is offline Rallyfinnen  Sweden
diyAudio Member
 
Join Date: Jan 2017
Here is one more where I removed the cap. Even more strange is that I had the HF oscillation again with the cap removed.
Attached Images
File Type: jpg KX 10Vrms 7ohm w_wo cap over R9.jpg (106.6 KB, 40 views)
  Reply With Quote
Old 30th November 2020, 10:18 AM   #454
Bonsai is online now Bonsai  Europe
diyAudio Member
 
Bonsai's Avatar
 
Join Date: Jul 2003
Location: Europe
Hifisonix kx-Amplifier
If your amp is prone to instability, that must be sorted first before doing anything else.

I will finish my tests later today and put the changes up. On.y after that can you address any other issues in your build.

R9 is a hum breaking resistor Rallyfinnen- it’s there to reduce cross channel ground loop currents. If you are getting hum with it in situ, please check for other noise sources but only after the above issue is fixed.

Last edited by Bonsai; 30th November 2020 at 10:21 AM.
  Reply With Quote
Old 30th November 2020, 03:03 PM   #455
Rallyfinnen is offline Rallyfinnen  Sweden
diyAudio Member
 
Join Date: Jan 2017
I did some probing around on my amp.

Strongest amplitude is on the emitter of Q10&11.
Then following it to the output bases:, all the bases of the outputs seem to have lower amplitude of oscillation. I guess this could mean that the drivers are driving the current into the bases of the outputs?

Putting my finger on the base of Q11 makes oscillation stop completely. Putting my finger on the base of Q10 only decreases the amplitude slightly.
I some stage of warming up, I could only see oscillation on the bases of the negative side outputs, and nothing on the positive side.

Could this have something to do with C2 on the positive side making it more stable, and no such cap on the negative side?

Maybe somebody could try the same to see if it's only my amp behaving like this?


BTW I tried to add some small caps parallel to C6 & C7, and that did absolutely nothing. (I only had two to test with)
  Reply With Quote
Old 1st December 2020, 11:09 PM   #456
rocksteady40 is offline rocksteady40  United States
diyAudio Member
 
Join Date: Apr 2010
Location: Near Boston
Sorry it took me so long to try the finger dampening test. On both my channels touching the drive transistors reduced the oscillation levels but did not eliminate it.
  Reply With Quote
Old 2nd December 2020, 05:39 AM   #457
polsol is offline polsol  South Africa
diyAudio Member
 
Join Date: Aug 2004
Location: Cape Town
Difficult to get one's finger on some PCB points. I find that touching the bases of Q10/Q11 with a small insulated screwdriver tip decreases the amplitude, or completely collapses the oscillation. Actually just touching the PCB itself (finger) close to the Q11 base diminishes the oscillation.

What I've found is that the oscillation is intermittent whilst the PCB/Heatsink is cold on startup but increases in amplitude as the heatsink temperature increases and the oscillation then becomes more 'permanent' as equilibrium is reached.
When still cold, touching various tranny contacts - and resistors - results in diminishing the oscillations.
When hot, many of the same components have no or little effect on the oscillation when touched.

My PCB is around 5 mm off the heat sink - and is currently lying 'flat' on my workbench, rather than horizontal - and will form a 'heat trap' between itself and the PCB. Even running in AAB mode the heatsink gets pretty damn hot. Not sure if this temperature is 'normal'. But because of the oscillation I don't run the amp for more than about 5 to 10 minutes to prevent possible damage to the components.
__________________
Tony M
  Reply With Quote
Old 2nd December 2020, 06:35 AM   #458
Rallyfinnen is offline Rallyfinnen  Sweden
diyAudio Member
 
Join Date: Jan 2017
Ok, so for polsol it seems to behave like mine, but for rocksteady40 touching Q10/11 does not stop the oscillation.
I will try to do some more experimenting today. Measure some more, and maybe try to add some RC in the sensitive areas to see what happens.
  Reply With Quote
Old 2nd December 2020, 08:59 AM   #459
Rallyfinnen is offline Rallyfinnen  Sweden
diyAudio Member
 
Join Date: Jan 2017
So here is a quick hack..
I took a RC based on what I had lying around: 150p & 1k5, and probed around a little bit. Adding it across R4 made oscillation silent on my board, and just for good measure I added the same over R5 too. It does not seem to affect the loop gain as far as I can see in my sim.
Maybe it has some other downside?

I hope Bonsai can examine this more in detail. I have now soldered them in and will see if it stays stable. So far so good..
If it works with no ill effects, it would be an easy and quick fix.
Attached Images
File Type: jpg stability mod proposal.jpg (176.4 KB, 66 views)
  Reply With Quote
Old 2nd December 2020, 11:05 AM   #460
Rallyfinnen is offline Rallyfinnen  Sweden
diyAudio Member
 
Join Date: Jan 2017
Update:
I wanted to check if it was stable without zobel on the output (I would prefer if it was). At the same time I also removed the bypass caps for C1 & C6. Now I have oscillation at abt 16MHz 400mVp-p.

With the zobel + bypass caps, it was stable without any load resistor connected (and with load resistor).

Will experiment a little bit more.
  Reply With Quote

Reply


Hifisonix kx-AmplifierHide this!Advertise here!
Thread Tools

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
Boss NXD3500 car amplifier hooked to an Onkyo 7.2ch home amplifier Evolver Class D 1 13th March 2020 11:48 AM
Hypex SMPS400 + 2x UCD180 wiring (DC error, Auto Amplifier Enable, Amplifier Standby) maxw Class D 48 26th May 2017 07:47 PM
hifisonix small signal class a? mlackey Headphone Systems 1 1st January 2016 03:16 AM
Motional feedback amplifier based on Philips 40 wats amplifier 1970s sanbadgujar Solid State 14 13th October 2013 02:35 PM
JLH Chiarra or Hifisonix Class A buffer? MondyT Headphone Systems 2 30th January 2013 05:14 PM


New To Site? Need Help?

All times are GMT. The time now is 08:22 PM.


Search Engine Optimisation provided by DragonByte SEO (Pro) - vBulletin Mods & Addons Copyright © 2021 DragonByte Technologies Ltd.
Resources saved on this page: MySQL 14.29%
vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2021 DragonByte Technologies Ltd.
Copyright ©1999-2021 diyAudio
Wiki