Electronics > Beginners

TL071 distortion - bad amplifier design?

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spec:

--- Quote from: AngraMelo on December 13, 2018, 04:56:19 pm ---As a musician that has been for 20 years listening to a very specific recording, one can get extremely familiar with the particulars of how it sounds and be able to perceive very small nuances. How scientifically small? I dont know. It was initially a song that I really liked nowadays I use it just to test speakers and amps. But I sometimes can hear the difference from the same model of amp/speaker if they are in the same room and position.
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This is the crux of the matter- what the system sounds like. That is the final arbiter.


--- Quote from: AngraMelo on December 13, 2018, 04:56:19 pm ---Look, most engineers would laugh (as they have done to me) at you if you say that if you wanted to buy a guitar amp, and had all the money in the world, a tube one would be brought home.
They know it has more THD than solid state but the sound at the end is what matters. I get that it must be frustrating to listen to the enormous amount of bullshit that surrounds this subject but is the example you gave on the link measurable? Correct me if Im wrong but if you wanted to see if a pot at the beginning of the chain affected the frequency response wouldn't that be easy to measure?

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Hmm, sounds like you have been talking to the wrong engineers, it that is what they actually were. :)
Any engineer worth his salt would evaluate the customer's requirement and try to understand it. Besides which, it is well known that guitar amplifiers and guitar speakers color the sound, some amplifiers in one way and another in another way. For example Fender amps produce a clean sonorous sound, while Marshal amps give a thicker bluesy sound. So guitar amplifiers are not like high end audio amplifiers which, in the main, aim to reproduce sound without any distortion. If you play a solid electric guitar through a normal audio amplifier the sound is thin, truncated, and lifeless.

There is an enormous mountain of BS about sound reproduction. but it is on both sides. On one side there is the "audiofool" brigade who like the pun in the accolade and use it on every occasion. Very often the closest they come to quality sound reproduction is a sound bar on their TV. Then there is the other end of the spectrum, the true audiofools, who talk about such things as rewiring the mains supply to their house with extra thick wire directly connected to their consumer unit, or fitting gold plated mains sockets to their house.

You mention about measuring the quality of an audio amplifier and ask if it can be measured. The straight answer is no. To illustrate this, some amplifiers, especially valve, sound fantastic, but show high levels of distortion, when measured. On the other hand, other amplifiers, nearly always transistor, have distortion figures that are so low that they literally cannot be measured, but only sound mediocre. In general, though, an amplifier with a measurably low distortion will sound better.

There is a coming together of the musician and engineer though. Through painstaking testing it has been found that certain techniques and components sound better than others and Douglas Self's book, describes these techniques and throughout his book Self develops, what he calls a 'blameless'' amplifier, which embodies these techniques. This book is for engineers though and not intended for musicians or the general public.

Just a word about my own experience in this field. I have been designing, building, and auditioning audio preamps, power amps, and speakers for years and, being technical, I dismissed the audiofoolery of the day. For example, I said categorically that turntables made no difference- they just went round, that amplifiers had so low distortion that they were like a piece of wire with gain and made no difference, that speaker cable made no difference. All of these were demonstrated to be wrong. I cringe remembering the time I told a guitarist that the wood of a Strat guitar made no difference. So you have to be very careful to separate armchair theory with actual listening.

And finally, any audio engineer who does not take note of the views of the listener, especially a musician, is a genuine audiofool.

AngraMelo:
Spec,
I had BATTLES with the father of a long time ex girlfriend. He was a badass engineer that was mainly into cameras, digital image and security system. The guy was a local pop star and traveled the country with big security corporations developing new ways to see a dude in the dark dressed in black 200m away from climbimg your backyard wall and charging the least possible for it so they could compete with China.
The day I told him that most good guitar amps take tubes, he FLIPPED and had a crazy argument with me.
I told him this. If you find a way to charge the price of a solid state amp and deliver a tube sound and make a good profit, I'll sell everything I own and invest every penny in your company. I said thad we would retire in 10 years if he accomplished that. I told him that I would even pay for a prototype! No need to say that it never got out of paper and we quickly started avoiding that subject. I still remembers his face when I said That, the whole.family was there and silence was all one could hear.
But for you to have a laugh... after years playing tube amps, having intense pain from carrying that huge thing around and spending way more than reasonable, the last 5 years or so of my career was playing a small solid state. It is literally called Jazz Amp. A single 12' speaker with a kickass sound that was carried back and forth on the subway. Nowadays it is a major decoration piece in my living room.


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Mechatrommer:

--- Quote from: AngraMelo on December 15, 2018, 06:14:39 am ---The day I told him that most good guitar amps take tubes, he FLIPPED and had a crazy argument with me... I still remembers his face when I said That, the whole.family was there and silence was all one could hear.

--- End quote ---
maybe he had no problem with tube or solid state. his issue i guess that you play guitar >:D


--- Quote from: AngraMelo on December 15, 2018, 06:14:39 am ---But for you to have a laugh... after years playing tube amps, having intense pain from carrying that huge thing around and spending way more than reasonable, the last 5 years or so of my career was playing a small solid state. It is literally called Jazz Amp. A single 12' speaker with a kickass sound that was carried back and forth on the subway. Nowadays it is a major decoration piece in my living room.

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so have you give a thought what you have gained throughout all those years? other than temporal joyness. your ex-g's dad gave his life to give peace to the community... cheers. ;)

Zero999:
Sigh.

Why does nearly every thread involving audio turn in to an argument about audiophoolery?

Who are the right and wrong engineers to ask? Just because the person you asked about something, violently disagreed with you, it doesn't mean their view is invalid. The advantages of forums such as this, over asking a friend, relative colleague etc. is, one can ask a lot of engineers and gather a consensus on a matter, not just take one person's word for it. Also remember this is a technical discussion and no one should feel offended, if they're contradicted.

There's a lot of the usual nonsense here about using passives and capacitors to avoid noise and distortion and speaker cables. There's nothing special about polypropylene, over polyester capacitors. I bet no one will be able to tell the difference, if subject to a blind test. Metal film resistors are less noisy, than carbon film, but it's wrong to say the latter shall be used everywhere in the audio amplifier, where there are plenty of parts of the circuit where it won't make any difference, i.e. the resistors used to bias the zeners diodes. It's amusing when a circuit mandates high end capacitors and metal film resistors, then uses carbon potentiometers, especially with a DC bias.:-DD In this case, the circuit has non-polarised capacitor, (220µF) carrying an AC signal, with no DC bias, which will distort the signal more than any polyester capacitor. :palm: Polarised capacitors act as poor diodes, (the electrolytic capacitor is derived from the electrolytic rectifier) and need a DC bias to avoid rectifying, thus distorting the signal. As far as resistors are concerned: I'd be more concerned about the type of resistor used for the 0R22 on the output stage, which could cause problems with oscillation if it's very inductive i,.e. wire wound, on a ferrous former.

It is simply untrue that amplifiers can't be measured and characterised. This is a common audiophool myth. In reality, everything which can be heard and more, can be accurately measured and characterised. Measuring equipment is well over an order of magnitude better than the human ear at picking up distortion. The problem is it's important to measure the right thing and plenty of the traditional tests used to characterise amplifiers don't. For example, pure sinewaves, which in no way resemble music or speech, are often used to obtain THD figures. The video linked to by Mark Hennessy demonstrates this perfectly and is well worth watching.

As far as the thermionic vs solid state is debate is concerned. It's true that both amplifier topologies have different characteristics, yet paradoxically can be made to sound exactly the same: please read on, I'm not trolling, its true! It's possible to make a thermionic and a solid state amplifier with imperceptible amounts of distortion, when played below the clipping threshold, at which point they'll both be audibly transparent i.e. sound the same. The difference is a thermionic amplifier will have a nicer sounding distortion, than a solid state model, when over-driven and this effect is often desirable in a guitar amplifier, where the distortion is part of the sound and hi-fidelity is not a requirement.

Over 40 years ago a double blind test was done on three amplifier designs: one thermionic and two solid state, with golden eared audiophiles and they couldn't tell the difference. Of course both of the amplifiers were designed for minimal distortion and weren't driven into clipping, but the test was for hi-fi, not a guitar amplifier.
http://www.keith-snook.info/wireless-world-magazine/Wireless-World-1978/Valves%20versus%20Transistors%20DCD.pdf

As far as hi-fi is concerned, it's fairly easy to make an amplifier an imperceptible level of distortion. In reality speakers and room acoustics are the dominant factor, not the amplifier. It's possible that a high end hi-fi system will sound the same as a TV, if they're both connected to the same speakers and played at a low enough level to avoid clipping.

This goes back to the requirements of the original poster. Is this amplifier going to be used for hi-fi, where the distortion should be minimal or a guitar, where a certain type of distortion is required? With the appropriate modifications, there's no reason why this circuit can't give a reasonable faithful reproduction of the source, but if you want a guitar amplifier, with nice distortion, then look elsewhere.

AngraMelo:

--- Quote from: Mechatrommer on December 15, 2018, 07:36:27 am ---
--- Quote from: AngraMelo on December 15, 2018, 06:14:39 am ---The day I told him that most good guitar amps take tubes, he FLIPPED and had a crazy argument with me... I still remembers his face when I said That, the whole.family was there and silence was all one could hear.

--- End quote ---
maybe he had no problem with tube or solid state. his issue i guess that you play guitar >:D


--- Quote from: AngraMelo on December 15, 2018, 06:14:39 am ---But for you to have a laugh... after years playing tube amps, having intense pain from carrying that huge thing around and spending way more than reasonable, the last 5 years or so of my career was playing a small solid state. It is literally called Jazz Amp. A single 12' speaker with a kickass sound that was carried back and forth on the subway. Nowadays it is a major decoration piece in my living room.

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so have you give a thought what you have gained throughout all those years? other than temporal joyness. your ex-g's dad gave his life to give peace to the community... cheers. ;)

--- End quote ---

The point of the story is not to show that he was a bad person, bad engineer or anything like that. As described, he was a great professional and to this day I use stuff he produces in my house and it does help to keep my family safer, for that Im eternally greatful. The main point is that low level distortion is ONE way of pursuing greatness while designing an amplifier. If money was not a problem, there is a large portion of the music business that still would not buy your amp even if it had infinit gain, infinit power and 0% distortion. For years we had people to help us with our gear and we could afford such heavy amps. The budget got thinner and tube amps were no longer an option, by buying the solid state I had to make a compromise. It does not have the sound I want but it saves me from ending up in the hospital after a small tour.
The example illustrated my point of having a very good engineer that was not concerned about what I was talking about, or trying to understand where I was coming from instead, I was made fun of for no reason. I didnt know the first thing about electronics at that time (Im still a beginner but it is completely different) and what led me to tell him about tube amps was a comment he made that tubes were no longer in use.

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