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

Headphone Systems Everything to do with Headphones

Cheap as Chips OPA1688 Low-THD Muscle Amp
Cheap as Chips OPA1688 Low-THD Muscle Amp
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 23rd July 2018, 03:27 AM   #121
Shaq888 is offline Shaq888  Ukraine
diyAudio Member
 
Shaq888's Avatar
 
Join Date: Feb 2009
Quote:
Originally Posted by anatech View Post

Just try not to be negative.

-Chris
I am and I was quite positive. I made, what I concider useful, posts with measurements in this topic before. Apparently xk971 is struggles to understand those. This ended up in a second round of our conversation and some deleted posts. That's where I had enough. Again, I'm quite positive, just I have my reasons to write what I wrote.

I'm sorry, but being nice should go both was. It obviously didn't.

Last edited by Shaq888; 23rd July 2018 at 03:33 AM.
  Reply With Quote
Old 23rd July 2018, 06:13 AM   #122
00940 is offline 00940  Belgium
diyAudio Member
 
00940's Avatar
 
Join Date: Sep 2003
Location: Liège
@shaq888: thx for the measurements. What did you use as floating supply? The one suggested by Self?

For those interested, Douglas Self has the whole series on opamp distortion from the small signal book available freely as articles on eetimes: https://www.eetimes.com/document.asp?doc_id=1278866 (for the relevant section).
__________________
All that is excessive is insignificant. Talleyrand
  Reply With Quote
Old 23rd July 2018, 06:56 AM   #123
Shaq888 is offline Shaq888  Ukraine
diyAudio Member
 
Shaq888's Avatar
 
Join Date: Feb 2009
No Problems.
Not exactly like Self's circuit. I prefer not to connect anything else to the input if possible. Anything injected into this point can't be compensated anywhere further along the line. Although it is not necessary a problem in every given design.
I just added a divider from the output with the same ratio as the feedback divider to create a voltage approx equal to the input common mode signal. Than I have a buffer made from 4 transistors. I think transistors can be replaced with one opamp if needed.
  Reply With Quote
Old 23rd July 2018, 01:25 PM   #124
anatech is offline anatech  Canada
diyAudio Moderator
 
anatech's Avatar
 
Join Date: Jun 2004
Location: Georgetown, On
Cheap as Chips OPA1688 Low-THD Muscle Amp
Hi Shaq888,
Your recent posts are helpful and more than civil. I'm not participating in this thread, which is why I can moderate it. Therefore I do not have the full history and can only go on what I see. You will notice that I didn't give an infraction or any points either as I felt a comment would do what was needed.

Don't let negative people drag you into a "fight" online. Just stick to facts and ignore the noise. You'll feel better if you do. Thank you for helping other members.

-Chris
__________________
"Just because you can, doesn't mean you should" © my Wife
  Reply With Quote
Old 23rd July 2018, 03:58 PM   #125
00940 is offline 00940  Belgium
diyAudio Member
 
00940's Avatar
 
Join Date: Sep 2003
Location: Liège
I thought I might as well post these here. Two more references for bootstrapping an opamp to reduce distortion.

http://www.analog.com/media/en/techn...22599AN232.pdf
http://www.proaudiodesignforum.com/i...er_11_2008.pdf
__________________
All that is excessive is insignificant. Talleyrand
  Reply With Quote
Old 23rd July 2018, 04:20 PM   #126
tomchr is offline tomchr  Canada
diyAudio Member
 
tomchr's Avatar
 
Join Date: Feb 2009
Location: Calgary
Quote:
Originally Posted by jcx View Post
cutting all loops at once is the best for stability analysis
In a composite amplifier, you need to simulate all loops. Both any inner loops and the outer/global loop. All loops need to be stable. Finding a good point to break the loop for the stability analysis can be tricky, especially if you have multiple loops.

Tom
__________________
Modulus-686: 240W/8Ω @ <0.00025% THD. Modulus-86: 40W/8Ω @ 0.000054% THD. DG300B & Other Tube Circuits.
Neurochrome : : Audio - www.neurochrome.com - Engineering : : Done : : Right
  Reply With Quote
Old 23rd July 2018, 04:32 PM   #127
xrk971 is offline xrk971  United States
Got Foam?
diyAudio Member
 
xrk971's Avatar
 
Join Date: Oct 2012
Location: Metro DC area
Cheap as Chips OPA1688 Low-THD Muscle Amp
Quote:
Originally Posted by 00940 View Post
I thought I might as well post these here. Two more references for bootstrapping an opamp to reduce distortion.

http://www.analog.com/media/en/techn...22599AN232.pdf
http://www.proaudiodesignforum.com/i...er_11_2008.pdf
Thanks for the links, <|00940|> - very helpful to get actual schematics. I use Danyuk’s cross feed circuit - a smart guy who is also an excellent communicator.

From second link above:
Cheap as Chips OPA1688 Low-THD Muscle Amp-6737237f-1fec-4589-ae03-7aa603e20a7c-jpeg
Attached Images
File Type: jpeg 6737237F-1FEC-4589-AE03-7AA603E20A7C.jpeg (320.6 KB, 213 views)
__________________
XRKaudio https://www.etsy.com/shop/XRKAudio

Last edited by xrk971; 23rd July 2018 at 04:48 PM.
  Reply With Quote
Old 23rd July 2018, 11:05 PM   #128
Shaq888 is offline Shaq888  Ukraine
diyAudio Member
 
Shaq888's Avatar
 
Join Date: Feb 2009
Connecting another opamp with non-bootstrapped supply to the feedback divider pretty much defeats the purpose. The only reasons why it works OK is that the divider has quite low impedance. It would be better to add separate divider as I described earlier. This would also allow conveniently control its frequency response for maintaining stability.

Last edited by Shaq888; 23rd July 2018 at 11:09 PM.
  Reply With Quote
Old 23rd July 2018, 11:08 PM   #129
xrk971 is offline xrk971  United States
Got Foam?
diyAudio Member
 
xrk971's Avatar
 
Join Date: Oct 2012
Location: Metro DC area
Cheap as Chips OPA1688 Low-THD Muscle Amp
Quote:
It would be better to make separate divider as I described earlier.
A schematic is worth a thousand words.
__________________
XRKaudio https://www.etsy.com/shop/XRKAudio
  Reply With Quote
Old 23rd July 2018, 11:40 PM   #130
Shaq888 is offline Shaq888  Ukraine
diyAudio Member
 
Shaq888's Avatar
 
Join Date: Feb 2009
Just add a second divider connected to the output of the amplifier that is identical to the feedback divider and use it to feed a signal to the bootstrap driver.
  Reply With Quote

Reply


Cheap as Chips OPA1688 Low-THD Muscle AmpHide 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
New Audio Op Amp - OPA1688 johnc124 Vendor's Bazaar 56 2nd November 2017 09:38 PM
P-P with some muscle bigjppop Tubes / Valves 43 18th October 2009 08:22 PM
Cheap DAC chips harryeng Swap Meet 1 16th September 2007 08:13 PM
cheap lm3886TF chips? jeffshort2000 Chip Amps 3 8th January 2007 08:38 PM
Help Cheap as chips speaker project DAVOhorn Full Range 2 5th November 2005 03:35 PM


New To Site? Need Help?

All times are GMT. The time now is 02:03 AM.


Search Engine Optimisation provided by DragonByte SEO (Pro) - vBulletin Mods & Addons Copyright © 2018 DragonByte Technologies Ltd.
Resources saved on this page: MySQL 14.29%
vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2018 DragonByte Technologies Ltd.
Copyright ©1999-2018 diyAudio
Wiki