What causes BJT based amplifier distortion?
 User Name Stay logged in? Password
 Home Forums Rules Articles diyAudio Store Blogs Gallery Wiki Register Donations FAQ Calendar Mark Forums Read

 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
 6th February 2021, 07:10 PM #21 Cortez   diyAudio Member     Join Date: Dec 2002 Location: Hungary Maybe a better question would be: what does not cause distortion in a BJT based amplifier? As the device itself is far from ideal (almost everything depends from something other), unfortunately we are forced to adapt... And the only chance is to embed the devices to a "protected/relaxed" (electrical+thermal) environment where their imperfections does not have such a role. Also at first we have to forget about the GNFB as a holy grail as it does not solve all of these problems. My algorythm would be something like this:collect all known BJT errors/imperfections together in a list prioritize (but I'm afraid that step in itself could lead to a religion war ) collect all known solutions for each problem + a collective brainstorming could be interesting try to integrate as much as possible based on the prioritized list in one system or have multiple paralell versions crosschecked with eachother simplify (occam) goto 6; Last edited by Cortez; 6th February 2021 at 07:17 PM.
 6th February 2021, 07:43 PM #22 jstott   diyAudio Member   Join Date: Feb 2016 Location: Connecticut Douglas Self did that kind of analysis more than 20 years ago. Buy his book or read the article on the web. Short version: power output stages suffer from crossover-related distortion, but are usually low-distortion otherwise. Most of the distortion occur in the voltage gain stage(s). -JS
PRR
diyAudio Member

Join Date: Jun 2003
Location: Maine USA
Quote:
 Originally Posted by edbarx The first step to understand a philosophical statement is to search for and understand what assumptions/axioms it is based on. .....
Do you think distortion must be ZERO or else why bother?

 7th February 2021, 02:23 AM #24 RussellKinder   diyAudio Member   Join Date: Mar 2015 Location: Austin, TX Current SOTA of solid state amplifiers is pushing the magnitude of all harmonics below the noise floor of a very low noise amplifier. Most designers doing this have applied Doug Self's techniques of linearizing each stage of the amplifier, plus a few tricks of their own, while maintaining a very large open-loop gain. This means inaudible. Really. I contend that the proponents of zero global NFB have no idea what they are talking about. They think if a little feedback is bad, then more is worse. Incorrect. Feedback compensation is a noise/distortion shaping method, that translates nonlinearity and noise to higher frequencies. A small amount of feedback only manages to move the problems to a higher location in the audible band. A large amount of feedback moves the problems out of band, especially if a high loop gain can be maintained to at least 20kHz. __________________ Best Regards, Russell RK-Autobias-200W Amplifier
edbarx
diyAudio Member

Join Date: May 2018
Location: Maltese Archipelago
Here are some quotes from Douglas Self's book.

Quote:
 Originally Posted by D. Self You will also see, in Chapter 1, that in the last few years I have found no reason to alter my views on the pernicious irrationality of subjectivism. In that period I have repeatedly been involved in double-blind listening tests using experienced subjects and proper statistical analysis, which confirmed every time that if you cannot measure it you cannot hear it.
Quote:
 The principles of negative feedback as applied to power amplifiers are explained in detail, as there is still widespread confusion as to exactly how it works.
Quote:
 You may have two units placed side by side, one giving 2% THD and the other 0.0005% at full power, and both claiming to provide the ultimate audio experience. The ratio between the two figures is a staggering 4000:1, and this is clearly a remarkable state of affairs. One might be forgiven for concluding that distortion was not a very important parameter. What is even more surprising to those who have not followed the evolution of audio over the last two decades is that the more distortive amplifier will almost certainly be the more expensive.
These quotes show that Douglas Self is not himself an audio subjectivist and considers subjectivism as irrational. They also show, he regards negative feedback as a great way of realising highly performant, and at the same time, cheaply produced amplifiers.

Sincerily, I am perplexed reading posts in these fora very strongly defending subjectivist views with some even going to the extreme of entirely denying objective measurement.

May I ask, is Negative Global Feedback INHERENTLY BAD, or is it only, a delusion? The application of negative feedback in control systems is good as it is a simple way of achieving stability. However, when audio is concerned we have to deal with the perception of hearing, and perceptions are purely subjective as they cannot be shared directly with third parties.

I have seen the amplifier using no global feedback by, if I rememeber well, Valerie. My impression is that it still using feedback from the output, but instead of feeding it into the inverting input, it uses an intermediate opamp to compare the signal differentially with the actual signal at the non-inverting input. It then feeds the opamp output to feed the VAS.

Please, don't tell me it is all opinions, especially, making the claim that if it is my opinion that GNFB is bad, nothing can be done. I do not hold mere opinions highly, I make an effort to be open to facts. This is why I am asking. Douglas Self is a researching amplifier engineer who definitely knows his area of expertise.
__________________
Any fool can make things bigger, more complex, and more violent. It takes a touch of a genius, and a lot of courage, to move in the opposite direction. [Albert Einstein]

Last edited by edbarx; 7th February 2021 at 08:25 AM.

 7th February 2021, 09:22 AM #26 indra1   diyAudio Member   Join Date: Nov 2010 Location: Bogor D. Self only measure output voltages because 0.0005% acoustic distortion at full power is hard to believe. Normal humans can not perceive audio directly from output voltage of amplifiers but hear the acoustic output, so relevant distortion measurement should be obtained from the acoustic output. THD of amplifier output voltage can only show part of the picture but generates a lot of unnecessary confusion from incomplete interpretation on significance of the measured quantity.
 7th February 2021, 09:40 AM #27 JMFahey   diyAudio Member     Join Date: Mar 2009 Location: Buenos Aires - Argentina Amplifiers are designed by and for humans, so if accurate reproduction is desired, itīs enough to make distortion undetectable by humans, period. Which does not mean Mathematical zero by any means. __________________ Design/make/service musical stuff in Buenos Aires, Argentina, since 1969.
 7th February 2021, 10:27 AM #28 edbarx   diyAudio Member     Join Date: May 2018 Location: Maltese Archipelago I am not of the opinion zero distortion is a necessity, but I am curious to understand, why complicated workarounds succeed to reduce distortion to impressive values. __________________ Any fool can make things bigger, more complex, and more violent. It takes a touch of a genius, and a lot of courage, to move in the opposite direction. [Albert Einstein]
Charles Darwin
diyAudio Member

Join Date: Nov 2009
Location: Birmingham, UK
Quote:
 Originally Posted by N101N They don`t.
This one looks half decent independently measured:

MC2 Audio MC650 Amplifier Test Results :: ABELtronics

RussellKinder
diyAudio Member

Join Date: Mar 2015
Location: Austin, TX
Quote:
 Originally Posted by indra1 D. Normal humans can not perceive audio directly from output voltage of amplifiers but hear the acoustic output, so relevant distortion measurement should be obtained from the acoustic output.
It's true. Amplifiers at this point are contributing almost nothing to the total distortion. I have some former co-workers at Purifi Audio in Denmark that have done a great job in reducing loudspeaker distortion. Someone here on diyaudio interviewed Lars Risbo on YouTube. He did a great job of explaining how they have lowered loudspeaker distortion.
__________________
Best Regards, Russell
RK-Autobias-200W Amplifier

 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 Rules
 Forum Jump User Control Panel Private Messages Subscriptions Who's Online Search Forums Forums Home Site     Site Announcements     Forum Problems Amplifiers     Solid State     Pass Labs     Tubes / Valves     Chip Amps     Class D     Power Supplies     Headphone Systems Source & Line     Analogue Source     Analog Line Level     Digital Source     Digital Line Level     PC Based Loudspeakers     Multi-Way     Full Range     Subwoofers     Planars & Exotics Live Sound     PA Systems     Instruments and Amps Design & Build     Parts     Equipment & Tools     Construction Tips     Software Tools General Interest     Room Acoustics & Mods     Music     diyAudio.com Articles     Car Audio     Everything Else Member Areas     Introductions     The Lounge     Clubs & Events     In Memoriam The Moving Image Commercial Sector     Swap Meet     Group Buys     The diyAudio Store     Vendor Forums         Vendor's Bazaar         Sonic Craft         Apex Jr         Audio Sector         Acoustic Fun         Chipamp         DIY HiFi Supply         Elekit         Elektor         Mains Cables R Us         Parts Connexion         Planet 10 hifi         Quanghao Audio Design         Siliconray Online Electronics Store         Tubelab     Manufacturers         AKSA         Audio Poutine         Musicaltech         Holton Precision Audio         CSS         exaDevices         Feastrex         GedLee         Head 'n' HiFi - Walter         Heatsink USA         miniDSP         SITO Audio         Twin Audio         Twisted Pear         Wild Burro Audio

 Similar Threads Thread Thread Starter Forum Replies Last Post shredhead Analog Line Level 13 7th June 2015 02:00 PM zigzagflux Class D 20 13th November 2014 12:10 PM blubberboy Solid State 4 11th August 2013 02:49 PM shzmm Solid State 4 9th February 2010 01:58 AM matthias Parts 1 5th June 2004 04:47 AM

 New To Site? Need Help?

All times are GMT. The time now is 01:08 AM.

 Home - Contact Us - Advertise - Rules - diyAudio Store - Sponsors - Privacy Statement - Terms of Service - Top - Opt-out policy

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