TL431 as an audio amplifier. - Page 1
Forum section: electronics / general

author: schmitt trigger
author_rank: Super Contributor
timestamp: April 01, 2019, 05:13:30 pm
content: You have read correctly: TL431.At first, I thought it was an April Fool's joke.But apparently there are a significant amount of these circuits in the web.For instance:http://vu2ppp.com/_simple_audio_amplifier_using_tl431One day, I might breadboard one, just out of curiosity.

author: Raj
author_rank: Frequent Contributor
timestamp: April 01, 2019, 05:20:33 pm
content: Amature radio folks...Perfecting the art of using components in surprising ways since 1920s

author: Kleinstein
author_rank: Super Contributor
timestamp: April 01, 2019, 05:38:58 pm
content: I have not heard of the TL431 used for this before, but I have seen the LM317 used for this.

author: schmitt trigger
author_rank: Super Contributor
timestamp: April 01, 2019, 05:43:56 pm
content: Thoughtfully, they concede that it is not an audiophile grade amplifier.

author: amyk
author_rank: Super Contributor
timestamp: April 02, 2019, 03:16:46 am
content: Quote from: Raj on April 01, 2019, 05:20:33 pmAny nonlinear component can detect radio signals. Any active component can have gain.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: April 02, 2019, 04:07:15 am
content: Why not? It's not an "adjustable zener", whatever that means; it's a proper op-amp.Albeit a somewhat quirky one: whopping (yet suspiciously stable) 2.50V input offset voltage, too few pins (+in is tied with VEE), self powered through the output -- which is an open-collector output, too?It's rated for 36V and 100mA so quite capable of real power, limited by package dissipation more than anything. The OC output limits operation to class A, of course.Another way to think of it: an ideal BJT, if a slow one (fT ~ low MHz). Precision Vbe, hFE > 25k (practically infinite). Acts more like a precision Darlington actually, as "Vce(sat)" isn't very low (about 1.9V). Effectively, internal Baker clamped. (Don't know offhand what saturation recovery and rise/fall time are like, aside from multiple ~us.)Tim

author: floobydust
author_rank: Super Contributor
timestamp: April 02, 2019, 06:27:31 am
content: This 0-15V 5A power supply uses four TL431's instead of any op-amps:https://www.eevblog.com/forum/beginners/cheap-chinese-adjustable-lab-power-supply-kit-on-ebay-(-3ag1-xiaolin-)/msg1412511/#msg1412511

author: johnwa
author_rank: Frequent Contributor
timestamp: April 02, 2019, 06:39:04 am
content: Quote from: schmitt trigger on April 01, 2019, 05:13:30 pmYeah, I saw Charles Wenzel's"one transistor" radio, meant to give it a go. I guess you could use a ZN414 or equivalent, and make a "two transistor" radio that should go pretty well.

author: aidan.walton
author_rank: Newbie
timestamp: December 19, 2020, 07:45:22 pm
content: In fact I have used a 431 exactly in this mode within a conversion I did to an older guitar amplifier. The problem I faced and the reason for using the 431 I think is quite interesting. I will share......The original power output stage of the amplifier was a class AB 'cooker' I was converting the unit to run on batteries, so I replaced the class AB with a class D output stage for improved efficiency. However the pre-amplifier stages all ran off a split rail supply of +-15V. Unfortunalty the class D IC required a single rail supply and to obtain the power out of the IC it required the full 30V of the supply and I had to span the class D IC across the entire split rail. This had the unfortunate consequence that the input stage to the power amp was now signal referenced to the -15V rail. The pre-amps where signal referenced to the 0V midpoint. At switch on, capacitivly coupling the pre-amp to the power amp caused (or would have caused) enormous thumps and prolonged DC offsets on the output from the power amp as the 2 stages setteled into their respective reference levels. The power amp input impedance being quite high meant these setteling times would have been enormous. To get around this I used a TL431 and drove its reference input coupled from the pre-amp stage and its anode on the -15V rail and its cathode (pulled up to the positive rail through a suitable resistor) acting as the drive stage into the power amp. In this way as the power rails came up and diverged, the TL431 rapidly pulled the power amps input signal down to the correct reference level (well much closer to it) as the power amp had a quiescent input voltage of ~3V. So now I only needed to capacitively couple across of 1V or so difference. Goodbye problem.My experience is that when driven carefully the TL431 is a very reasonable amplifier and a prefectly good op-amp.

author: David Hess
author_rank: Super Contributor
timestamp: December 19, 2020, 11:27:18 pm
content: Quote from: T3sl4co1l on April 02, 2019, 04:07:15 amSee? There is nothing unusual about configuring an operational amplifier with the output as an input and each power lead as an output. Right? RIGHT?

author: SiliconWizard
author_rank: Super Contributor
timestamp: December 20, 2020, 02:01:04 am
content: Well, you can even make linear amps out of CMOS gates. Not extremely linear either, but that's fun too.

author: Refrigerator
author_rank: Super Contributor
timestamp: December 21, 2020, 07:42:51 pm
content: I tend to think of TL432 as a perfect MOSFET.

author: StillTrying
author_rank: Super Contributor
timestamp: December 21, 2020, 08:24:10 pm
content: Here's a 555 radio.http://electronics-diy.com/am-radio-lm555.php

author: daqq
author_rank: Super Contributor
timestamp: December 21, 2020, 10:41:21 pm
content: Cool!...so... is this component abuse? Do we call PETA or something?

author: magic
author_rank: Super Contributor
timestamp: December 21, 2020, 11:51:18 pm
content: Quote from: schmitt trigger on April 01, 2019, 05:43:56 pmClass A, predominantly 2nd harmonic distortion if any, what's not to like?

author: exe
author_rank: Unknown
timestamp: December 22, 2020, 01:17:49 pm
content: I was surprised by such circuits too until I realized it has ~1MHz bandwidth, more than enough for audio or a power supply. TI's datasheet draws the part a zener, hence, probably confusion. Other datasheets draw it as an opamp with reference and output transistor, which should accepting such circuit. E.g., look here:https://www.onsemi.com/pub/Collateral/TL431-D.PDF.I'm not sure how practical such circuits because there are plenty opamps that are cheap and designed for audio (e.g., tl071 or ne5532). Nonetheless, I don't mind listening such amplifier, I don't think I'll hear a difference.Quote from: daqq on December 21, 2020, 10:41:21 pmNot according to me. Who's PETA?

author: AVGresponding
author_rank: Super Contributor
timestamp: December 22, 2020, 01:43:40 pm
content: Quote from: exe on December 22, 2020, 01:17:49 pmPETA is a charitable organisation, People for the Ethical Treatment of Animals.Following this reasoning we should have PETE, People for the Ethical Treatment of Electronic.

author: schmitt trigger
author_rank: Super Contributor
timestamp: December 22, 2020, 03:43:13 pm
content: I am sure most of us in this forum would be guilty.Who here hasn’t overstressed a component until the magic smoke comes out?Sometimes on purpose

author: tszaboo
author_rank: Super Contributor
timestamp: December 22, 2020, 05:05:32 pm
content: Wow, with all these circuits posted here, I wonder if anyone can build an audio amplifier with the NE5532.

author: Refrigerator
author_rank: Super Contributor
timestamp: December 23, 2020, 09:55:40 pm
content: Quote from: schmitt trigger on December 22, 2020, 03:43:13 pmOne time when i couldn't be bothered to fetch a BJT i used TL432's instead because they were on hand.

author: David Hess
author_rank: Super Contributor
timestamp: December 24, 2020, 12:12:26 am
content: Quote from: NANDBlog on December 22, 2020, 05:05:32 pmIt has been done several times:https://eecaldas.wordpress.com/2017/10/02/ne5532-power-audio-amplifier/

author: tszaboo
author_rank: Super Contributor
timestamp: December 24, 2020, 11:57:59 am
content: Quote from: David Hess on December 24, 2020, 12:12:26 amI guess the irony didn't really came through."Using an audio amplifier to amplify audio? Unheard of!"

author: exe
author_rank: Unknown
timestamp: December 24, 2020, 12:14:34 pm
content: Quote from: NANDBlog on December 24, 2020, 11:57:59 amI think it did.

author: magic
author_rank: Super Contributor
timestamp: December 24, 2020, 01:03:43 pm
content: Quote from: David Hess on December 24, 2020, 12:12:26 amThese puppies are RC4558, thoughAliBay is the final mythbust to all audiphoolery

author: harerod
author_rank: Frequent Contributor
timestamp: December 25, 2020, 05:25:10 pm
content: Quote from: daqq on December 21, 2020, 10:41:21 pmAny LTspice users here? The appropriate organization would be the SPCS.

author: schmitt trigger
author_rank: Super Contributor
timestamp: December 25, 2020, 05:32:19 pm
content: I believe an important bylaw is missing;- You will thoroughly read AND understand the semiconductor’s data sheet, prior to applying power for the first time you use said semiconductor.

author: harerod
author_rank: Frequent Contributor
timestamp: December 26, 2020, 02:44:12 pm
content: Thanks for pointing that omission out! This GIF has been on my website for ages and I would have bet that this bylaw was included. Now, where do I get a more complete set?