Oscillograms/Testing, and why layout matters. - diyAudio
Go Back   Home > Forums > Amplifiers > Solid State

Solid State Talk all about solid state amplification.

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 14th July 2008, 04:59 PM   #1
Mooly is offline Mooly  United Kingdom
diyAudio Moderator
 
Mooly's Avatar
 
Join Date: Sep 2007
Default Oscillograms/Testing, and why layout matters.

I was going to add some of these shots to another thread after a D.I.Y. member contacted me regarding their latest build, and he commented that all the amps he had constructed ( including my design on this Forum ) sounded totally different ( by the sound of it very very different ). Having seen the layout and pictures I couldn't help thinking that layout was as much to do with it as anything.
As it may help others I've decided to put it in it's own thread.
First shot then is the amp--- and how not to do it --- but as this is similar to many "veroboard type " constructions I think it valid.
The design is based on my own MOSFET amp but this is different, I've been playing around with some HEXFET's and this is the result so far.
Attached Images
File Type: jpg imag0057.jpg (78.4 KB, 589 views)
  Reply With Quote
Old 14th July 2008, 05:01 PM   #2
Mooly is offline Mooly  United Kingdom
diyAudio Moderator
 
Mooly's Avatar
 
Join Date: Sep 2007
Here is the output (Top trace) and input (Bottom Trace) at 20 Khz with no load.
Attached Images
File Type: jpg input and output no load.jpg (47.7 KB, 538 views)
  Reply With Quote
Old 14th July 2008, 05:02 PM   #3
Mooly is offline Mooly  United Kingdom
diyAudio Moderator
 
Mooly's Avatar
 
Join Date: Sep 2007
And the same, correctly grounded and supplying a load of 2.7 Ohms. This is a very severe test even though the amplitude is low at 4 volts peak to peak.
Attached Images
File Type: jpg 2.7 ohm load correct return.jpg (47.1 KB, 698 views)
  Reply With Quote
Old 14th July 2008, 05:05 PM   #4
Mooly is offline Mooly  United Kingdom
diyAudio Moderator
 
Mooly's Avatar
 
Join Date: Sep 2007
This time with the output returned to the wrong point so that the input ground is "contaminated" by the output current.
This is the only thing to have been changed -- compare the traces to the one above. Note the amplitude of the output now !
Attached Images
File Type: jpg 2.7 ohm incorrect return .jpg (48.6 KB, 613 views)
  Reply With Quote
Old 14th July 2008, 05:07 PM   #5
Mooly is offline Mooly  United Kingdom
diyAudio Moderator
 
Mooly's Avatar
 
Join Date: Sep 2007
A 0.1 Mfd cap directly across the output, but correctly returned.
Attached Images
File Type: jpg 0.1 mfd correct return.jpg (37.2 KB, 506 views)
  Reply With Quote
Old 14th July 2008, 05:08 PM   #6
Mooly is offline Mooly  United Kingdom
diyAudio Moderator
 
Mooly's Avatar
 
Join Date: Sep 2007
And incorrectly returned.
Attached Images
File Type: jpg 0.1 mfd incorrect return.jpg (50.4 KB, 376 views)
  Reply With Quote
Old 14th July 2008, 05:11 PM   #7
Mooly is offline Mooly  United Kingdom
diyAudio Moderator
 
Mooly's Avatar
 
Join Date: Sep 2007
A more severe test. The little PSU I am using cannot supply much current for sustained testing, but this is a good trick. Here is 12 volts Peak/Peak across the 2.7 Ohm load but with a lower duty cycle. The load was correctly terminated.
Attached Images
File Type: jpg 10 khz into 2r7 ohm.jpg (44.1 KB, 367 views)
  Reply With Quote
Old 14th July 2008, 05:13 PM   #8
Mooly is offline Mooly  United Kingdom
diyAudio Moderator
 
Mooly's Avatar
 
Join Date: Sep 2007
Last one, a shot showing a detail of using an incorrect ground. This was as above but with a 0.1 Mfd again as the load.
Attached Images
File Type: jpg detail of into 0.1 mfd with incorrect grounding..jpg (47.5 KB, 356 views)
  Reply With Quote
Old 14th July 2008, 05:16 PM   #9
AndrewT is offline AndrewT  Scotland
diyAudio Member
 
Join Date: Jul 2004
Location: Scottish Borders
why does the input signal change with the loading?
__________________
regards Andrew T.
  Reply With Quote
Old 14th July 2008, 05:19 PM   #10
Mooly is offline Mooly  United Kingdom
diyAudio Moderator
 
Mooly's Avatar
 
Join Date: Sep 2007
This was all a bit of fun on my part, I wanted to play with some HEXFET's, but it seemed a good opportunity to put this down so to speak. On a side note the amp design I use (single ended input) is very very stable and an amp with a differential input pair would give far more extreme results than this, with this type of layout . Try as I might it was hard to provoke this lash up into oscillation. If you look at the first shot you will see there is NO decoupling on the plugboard at all, and still it's stable.
  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
Water cooling, practical matters. kiwi_abroad Solid State 31 22nd September 2008 11:03 PM
What really matters? Quality loudspeaker design. Rounder Multi-Way 15 6th November 2007 09:17 AM
Pass and IP matters Magura Pass Labs 12 31st March 2004 11:07 PM
Minimum volume matters Raka Multi-Way 27 24th December 2002 11:03 AM
What REALLY Matters? Javaman Subwoofers 3 13th March 2002 12:43 AM


New To Site? Need Help?

All times are GMT. The time now is 09:45 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