LM317 experiments and measurements - Page 10 - diyAudio
Go Back   Home > Forums > Amplifiers > Power Supplies

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 26th December 2011, 08:38 AM   #91
just another
diyAudio Moderator
 
wintermute's Avatar
 
Join Date: Aug 2003
Location: Sydney
Blog Entries: 22
Well not too long turned out to be nearly six months But it's finally been built and I did some measurements tonight. I'm very happy with the results.

First a couple of pics of the implementation. I eneded up going with 4700, 3r3 4700 3r3, 1000uF before the reg.

The load for all the below results was only the on board load resistors which provide approx 40mA continuous load.

The first spectrum is taken with 1X gain on the preamp. The second is taken with the pre-amps inputs shorted, as you can see the anomylies above 40Khz are not from the PS.

The third spectrum is taken with 10X gain on the preamp, and the fourth is taken with 10X gain as well, but the right channel is post reg, and the left channel is pre reg taken at the base of the 1000uF smoothing cap. it is interesting to see how much lower the ripple is just by moving the probe down the track away from the capacitors leg. I did this to make sure that the measurements were indeed working

I was trying to get measurements using my new instrumentation amp, but I think I must have a problem with it, as I was not getting consistent results. In the end I went back to my original preamp. I set up outside with a long lead back to the computer, and my laptop running off batteries used to remote control the main computer. This seems to have worked wonders reducing the 50 Hz that has plagued the earlier measurements.

Tony.
Attached Images
File Type: jpg DSC_0116.jpg (142.3 KB, 453 views)
File Type: jpg DSC_0117.jpg (201.6 KB, 446 views)
File Type: jpg DSC_0110.jpg (151.4 KB, 433 views)
File Type: png yarps_spectrum.png (20.9 KB, 424 views)
File Type: png yarps_spectrum_10X.png (13.7 KB, 417 views)
File Type: png yarps_spectrum_10X_pre_post_reg.png (14.0 KB, 153 views)
__________________
Any intelligence I may appear to have is purely artificial!
Some of my photos
  Reply With Quote
Old 26th December 2011, 10:09 AM   #92
just another
diyAudio Moderator
 
wintermute's Avatar
 
Join Date: Aug 2003
Location: Sydney
Blog Entries: 22
It seems I may have spoken too soon. I thought I'd get out the scope and try and get a baseline for what the actual magnitude of the pre-reg ripple was, but when I hooked it up I saw some disturbing stuff on it. after clicking through the timebase, at 5uS / div I found I had an interesting waveform. an it is quite large, at around 60mV peak to peak! and the fundamental frequency appears to be around 833Khz....

I'm not sure if it is an oscilation or something else (perhaps AM radio?). the waveform shows up before the reg as well.

anyway below is a pic. If it were AM radio though, I'd expect the waveform to be changing, but it was rock solid as shown.

Tony.
Attached Images
File Type: jpg DSC_0120.jpg (946.1 KB, 146 views)
__________________
Any intelligence I may appear to have is purely artificial!
Some of my photos
  Reply With Quote
Old 26th December 2011, 10:16 AM   #93
AndrewT is offline AndrewT  Scotland
diyAudio Member
 
Join Date: Jul 2004
Location: Scottish Borders
Make sure everything in the house that could be triggering this oscillation is turned off.
CFL lamps are bad. Soldering stations are bad. HF radio transmitters are bad.

If that does not turn it off, could the repetition frequency tie in with twice the mains frequency? Diodes going into reverse bias at turn off?
__________________
regards Andrew T.
  Reply With Quote
Old 26th December 2011, 10:46 AM   #94
just another
diyAudio Moderator
 
wintermute's Avatar
 
Join Date: Aug 2003
Location: Sydney
Blog Entries: 22
Thanks Andrew, I did as you said, turned off the TV, all the lights, the printer, my amp and two computers. I went back out onto the balcony with the torch (I was measuring out there to try and get away from the interference) and low and behold the steady rather large waveform was gone!

There is still something there, but it definitely looks like AM radio, as the waveform is continually varying in amplitude, and is only about 10mV peak to peak now (the waveform looks like what you would expect to see when displaying someone's voice, except the time base is 5uS/div. My LM3886 will happily demodulate AM if I insert the rca jack only half way so I know it is around!!

I'm testing open on the bench at the moment so there is NO shielding at all, hopefully it will be fine when it goes into a proper case.

I'm curious now as to what was causing the interference. It wasn't the CFL's on the balcony or in the lounge room, as I turned them back on and it didn't come back.

I turned almost everything back on and can't reproduce the issue. The only things I didn't turn back on were the HT pc, and the other computer.

So apart from the obvious RF pick-up I think that its good

edit: it's definitely 833Khz, I set the scope to 1uS/ div and I get 12 peaks of the waveform across the 10 divisions. Still only 10mV p2p though, and it is harder to spot the amplitude modulation at that setting...

Tony.
__________________
Any intelligence I may appear to have is purely artificial!
Some of my photos

Last edited by wintermute; 26th December 2011 at 10:49 AM. Reason: minor fixes.
  Reply With Quote
Old 26th December 2011, 11:39 AM   #95
AndrewT is offline AndrewT  Scotland
diyAudio Member
 
Join Date: Jul 2004
Location: Scottish Borders
Mobile phone/s and wifi and wireless networks, the door bell or the burglar alarm?

The 833kHz could be the resonant frequency within a part of the amplifier.
The trigger could be a sharp single pulse.
Can you estimate the repetition rate?

That pulse could come in via the mains or be air fed.

If it's mains fed then chassis as shield/cage will not help.
__________________
regards Andrew T.
  Reply With Quote
Old 26th December 2011, 11:51 AM   #96
just another
diyAudio Moderator
 
wintermute's Avatar
 
Join Date: Aug 2003
Location: Sydney
Blog Entries: 22
It looks like it is airborne. Apparently I am a much better antenna than the PS!! If I disconnect from the PS (and disconnect it from the mains) and simply press the scope probe into my finger I can get the same waveform at 0.4V p2p (it was 0.01V p2p on the PS). If I drop the timebase back to 10mS / division and do the same I get a 0.5V p2p 50 Hz waveform on the scope!! (a fuzzy one as the other RF is there as well).

That's rather alarming I think... How can my Body be 1/2 V different in potential to the air around it (the scope earth probe was hanging in the air).

The really weird thing though is I don't get the waveform when the probe is connected to the PS but the PS is disconnected from the mains.

Tony.
__________________
Any intelligence I may appear to have is purely artificial!
Some of my photos
  Reply With Quote
Old 26th December 2011, 11:54 AM   #97
AndrewT is offline AndrewT  Scotland
diyAudio Member
 
Join Date: Jul 2004
Location: Scottish Borders
That's the same problem as I have described regularly for beginners.

"I find that the quietest amplifier is the one strung out on a board with no chassis.
I have never built an amp that is quieter inside the chassis nor when it is connected to PE (The third wire in the mains cable)."
__________________
regards Andrew T.
  Reply With Quote
Old 26th December 2011, 12:11 PM   #98
just another
diyAudio Moderator
 
wintermute's Avatar
 
Join Date: Aug 2003
Location: Sydney
Blog Entries: 22
Yes the RF protection on input (something I do need on my LM3886 amp, but haven't gotten around to adding). In this case the input is ~18V AC (without much load) and the output is supposed to be +/- 10V DC without any extra rubbish. If it doesn't go away after being put in a case I might need to add some small ceramics on the output, though that may not even help as even with both the earth and the probe tip touching the 0V on the board (the probe tip on the actual earth alligator clip) I still got the same waveform... If I took it off the board and shorted then I got a flat line.

Tony.
__________________
Any intelligence I may appear to have is purely artificial!
Some of my photos
  Reply With Quote
Old 26th December 2011, 12:16 PM   #99
AndrewT is offline AndrewT  Scotland
diyAudio Member
 
Join Date: Jul 2004
Location: Scottish Borders
Do you have passive RF filtering fitted to your amplifier?

I always recommend passive filtering on the input of every piece of audio equipment
__________________
regards Andrew T.
  Reply With Quote
Old 26th December 2011, 10:13 PM   #100
just another
diyAudio Moderator
 
wintermute's Avatar
 
Join Date: Aug 2003
Location: Sydney
Blog Entries: 22
Hi Andrew, no I don't (see the post above )

But *this* is a regulated power supply, that will be used for my active crossover. The iec socket has some caps on it (The transformer is currently in a stripped PC powersupply box) I don't think I can add any RF filtering to the PS, except maybe some say 220pf caps across the first filter caps and maybe at the output? I've not seen it done before...

Tony.
__________________
Any intelligence I may appear to have is purely artificial!
Some of my photos
  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
Screen drive and other P-P experiments tubelab.com Tubes / Valves 23 6th July 2010 06:08 PM
Initial Experiments for Fun stuphi Multi-Way 17 4th June 2009 05:19 PM
My first horn experiments till Multi-Way 110 31st May 2004 02:55 PM
x-over experiments, diff. orders etc. SimontY Multi-Way 25 19th February 2004 11:19 PM


New To Site? Need Help?

All times are GMT. The time now is 07:21 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