Go Back   Home > Forums > >

Class D Switching Power Amplifiers and Power D/A conversion

Unity gain output stage Class D driver
Unity gain output stage Class D driver
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 20th July 2021, 05:02 PM   #1
rhythmsandy is offline rhythmsandy
diyAudio Member
 
Join Date: Aug 2012
Default Unity gain output stage Class D driver

Im thinking of using a Class D unity gain buffer ( which is meant purely for current gain basis ) and not using too much of feedback. Is there any way that I can do that in SI8244?
  Reply With Quote
Old 21st July 2021, 05:44 AM   #2
newvirus2008 is offline newvirus2008  India
diyAudio Member
 
Join Date: Jun 2008
Dear rhythmsandy,

To be honest, having minimal gain and not using much feedback sounds counter-intuitive to me. If I were you, I would use a lot of feedback, especially considering that it's a class-D amplifier that has several mechanisms contributing to pulse-width error. Besides, without much feedback, even power supply fluctuations would get through to the output, almost unopposed.

I would suggest adding enough feedback (with enough compensation) to get the best out of what you have. If you fear poor stability margins and instability, you may try self-oscillating designs such as UcD or the hysteresis control.

All the best.
  Reply With Quote
Old 21st July 2021, 07:28 AM   #3
analog_sa is offline analog_sa  Europe
diyAudio Member
 
analog_sa's Avatar
 
Join Date: Aug 2002
Location: Cascais
Unity gain output stage Class D driver
What if he just hates nfb sound?

Ah, yes, class D may then be the wrong amp for him
  Reply With Quote
Old 21st July 2021, 07:46 AM   #4
steveu is offline steveu  United States
diyAudio Member
 
Join Date: May 2005
Location: Colorado Springs
You can parallel more FETs to an existing class-D amplifier and use a bigger or multiple output filters.

But if you want to buffer an analog amplifier, you just have to attenuate it to compensate for the class-D amp gain because the PWM modulation is done at low signal levels and not at the output level. Some class-D amplifiers may be unity gain stable and some may not but it is unlikely the input common mode range is anywhere close to rail-rail. So it's pointless to drive a class-D amp with an analog amp. Just use the class-D amp.
  Reply With Quote
Old 21st July 2021, 06:00 PM   #5
rhythmsandy is offline rhythmsandy
diyAudio Member
 
Join Date: Aug 2012
ok then how devialet is using voltage gain in the front end calling AHD?
  Reply With Quote
Old 21st July 2021, 06:01 PM   #6
rhythmsandy is offline rhythmsandy
diyAudio Member
 
Join Date: Aug 2012
Quote:
Originally Posted by analog_sa View Post
What if he just hates nfb sound?

Ah, yes, class D may then be the wrong amp for him
Just thinking why not reduce the feedback in the class D.
  Reply With Quote
Old 22nd July 2021, 05:46 AM   #7
newvirus2008 is offline newvirus2008  India
diyAudio Member
 
Join Date: Jun 2008
If you do, you would lose error control / linearisation. Usually, smaller gains use larger amounts of feedback.

Last edited by newvirus2008; 22nd July 2021 at 05:56 AM.
  Reply With Quote
Old 22nd July 2021, 06:08 AM   #8
ubergeeknz is offline ubergeeknz  New Zealand
diyAudio Member
 
Join Date: Aug 2018
That's not what ADH does.

Based on the marketing video, ADH seems to be an adaptation of "Current Dumping" or "Feed Forward" amplification (a very old concept, but only used successfully in HiFi since about the mid 70's) but using Class D instead of a Class C / B / AB "Dumping" stage.
  Reply With Quote
Old 22nd July 2021, 06:10 AM   #9
ubergeeknz is offline ubergeeknz  New Zealand
diyAudio Member
 
Join Date: Aug 2018
Also the waveforms shown in the ADH video are nonsense. This is not what Class D amplifier output looks like at all. It actually looks like a square wave, the amplitude is the total Rail-to-Rail voltage, with a varying duty cycle. After it is filtered, it just looks like a regular sinusoidal audio waveform. The basic operation of a Class D amplifier is the same as a switch mode power supply, only that the output is varied dependent on the input, rather than set to a fixed voltage.

Last edited by ubergeeknz; 22nd July 2021 at 06:15 AM.
  Reply With Quote
Old 22nd July 2021, 10:39 AM   #10
steveu is offline steveu  United States
diyAudio Member
 
Join Date: May 2005
Location: Colorado Springs
It is difficult to say exactly what Devialet are doing but I suspect it is similar to the Yamaha hybrid amplifier where the power supply rails are switch-mode controlled so that the analog output devices operate with a maximum of about 4 Volts drop and therefore very little heat is wasted. In any case, the class-D outputs are not tacked on the output of an analog amplifier, but perhaps the other way around so that the analog amplifier dictates the final result.
  Reply With Quote

Reply


Unity gain output stage Class D driverHide 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
Transformer based voltage gain + unity gain stage? soundcheck Solid State 2 10th August 2010 03:44 PM
heretical unity gain OUTPUT stage... andrew_whitham Tubes / Valves 4 9th December 2006 04:36 AM
Heretical Unity Gain line stage PLUS a little gain ? yagas Tubes / Valves 7 24th January 2006 02:30 PM
Line stage preamp, based on SY's "Heretical Unity gain line stage" Danko Tubes / Valves 23 18th July 2005 05:07 AM
unity gain push pull output stage ergo Solid State 11 6th January 2003 11:32 AM


New To Site? Need Help?

All times are GMT. The time now is 08:34 AM.


Search Engine Optimisation provided by DragonByte SEO (Pro) - vBulletin Mods & Addons Copyright © 2021 DragonByte Technologies Ltd.
Resources saved on this page: MySQL 15.00%
vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2021 DragonByte Technologies Ltd.
Copyright ©1999-2021 diyAudio
Wiki