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| TL071 distortion - bad amplifier design? |
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| AngraMelo:
--- Quote from: Hero999 on December 15, 2018, 02:51:08 pm ---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. [url]http://www.keith-snook.info/wireless-world-magazine/Wireless-World-1978/Valves%20versus%20Transistors%20DCD.pdf[/url] 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. --- End quote --- The engineer´s point was clear, he thought that tubes in a amp made no sense. Even after I told him that the distortion they add is why they are still used. I dont know if he view was invalid or not. I simply stated a fact: if guitar players like some distortion in their sound, they will most likely look for an amp with tubes if they can afford it. The forum is a great place to learn! No wonder I cant keep myself from reading the posts! I have nothing but gratitude for you guys! If the whole point of using a tube amp is so you can have the characteristic sound of their distortion, how can you say that it is possible to make a solid state sound just like a tube amp? They are made with low wattage on purpose so they will start to distort even at moderate volume. What we are looking for is exactly that light distortion it adds to the sound. If you say your solid state amp sounds just like a tube amp except when distortion starts to happen, isnt that the same as saying that your car does exact the same thing as an airplane except flying? |
| Zero999:
--- Quote from: AngraMelo on December 15, 2018, 04:40:38 pm ---The engineer´s point was clear, he thought that tubes in a amp made no sense. Even after I told him that the distortion they add is why they are still used. I dont know if he view was invalid or not. I simply stated a fact: if guitar players like some distortion in their sound, they will most likely look for an amp with tubes if they can afford it. The forum is a great place to learn! No wonder I cant keep myself from reading the posts! I have nothing but gratitude for you guys! If the whole point of using a tube amp is so you can have the characteristic sound of their distortion, how can you say that it is possible to make a solid state sound just like a tube amp? They are made with low wattage on purpose so they will start to distort even at moderate volume. What we are looking for is exactly that light distortion it adds to the sound. If you say your solid state amp sounds just like a tube amp except when distortion starts to happen, isnt that the same as saying that your car does exact the same thing as an airplane except flying? --- End quote --- Yes, I do understand that the whole point of a tube amplifier is the distortion. Perhaps the person who you spoke to doesn't get this or believes the extra cost doesn't justifies it. In any case he's entitled to his point of view. To answer your question. You're talking about a guitar amplifier, which will be driven into distortion, where as the paper I linked to is about hi-fi, which has totally different requirements to a guitar amplifier. A high amplifier should never be driven into distortion. The results of the experiment are that for hi-fi, both solid state and thermionic amplifiers give equally good sound quality, so there's no point in selecting one over the other, based on how they sound. The solid state designs are just cheaper and more reliable but people may like the way thermionic tubes look and the idea of having something old. For a guitar amplifier, a tube amp is a totally different beast to a solid state amp and there are good reasons to choose it, for the way it sounds. |
| AngraMelo:
--- Quote from: Hero999 on December 15, 2018, 06:49:36 pm --- --- Quote from: AngraMelo on December 15, 2018, 04:40:38 pm ---The engineer´s point was clear, he thought that tubes in a amp made no sense. Even after I told him that the distortion they add is why they are still used. I dont know if he view was invalid or not. I simply stated a fact: if guitar players like some distortion in their sound, they will most likely look for an amp with tubes if they can afford it. The forum is a great place to learn! No wonder I cant keep myself from reading the posts! I have nothing but gratitude for you guys! If the whole point of using a tube amp is so you can have the characteristic sound of their distortion, how can you say that it is possible to make a solid state sound just like a tube amp? They are made with low wattage on purpose so they will start to distort even at moderate volume. What we are looking for is exactly that light distortion it adds to the sound. If you say your solid state amp sounds just like a tube amp except when distortion starts to happen, isnt that the same as saying that your car does exact the same thing as an airplane except flying? --- End quote --- Yes, I do understand that the whole point of a tube amplifier is the distortion. Perhaps the person who you spoke to doesn't get this or believes the extra cost doesn't justifies it. In any case he's entitled to his point of view. To answer your question. You're talking about a guitar amplifier, which will be driven into distortion, where as the paper I linked to is about hi-fi, which has totally different requirements to a guitar amplifier. A high amplifier should never be driven into distortion. The results of the experiment are that for hi-fi, both solid state and thermionic amplifiers give equally good sound quality, so there's no point in selecting one over the other, based on how they sound. The solid state designs are just cheaper and more reliable but people may like the way thermionic tubes look and the idea of having something old. For a guitar amplifier, a tube amp is a totally different beast to a solid state amp and there are good reasons to choose it, for the way it sounds. --- End quote --- The article is great! Really appreciated it. I agree with that guitar amps and hi-fi are totally different things. I expressed myself badly on the last comment |
| Mechatrommer:
--- Quote from: AngraMelo on December 15, 2018, 04:33:44 pm ---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. --- End quote --- so i guess you dont need this thread. your heavily distorted amp originally should give you the better (or whitier) sound you required, no? ;D i agree with earlier commenter that good engineer should listen to their clients. so maybe another thread on how to purposely introduce distortion out of solid state to get tube's quality sound? ;) |
| spec:
--- Quote from: Mechatrommer on December 16, 2018, 04:22:59 am --- --- Quote from: AngraMelo on December 15, 2018, 04:33:44 pm ---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. --- End quote --- so i guess you dont need this thread. your heavily distorted amp originally should give you the better (or whitier) sound you required, no? ;D i agree with earlier commenter that good engineer should listen to their clients. so maybe another thread on how to purposely introduce distortion out of solid state to get tube's quality sound? ;) --- End quote --- Not sure if you are leg pulling or not, but making transistor amps sound like valve amps and also producing distortion, has been standard practice for years in the music industry. :) Incidentally, just in case, there is a vast range of guitar and bass speakers that have a tailored frequency response and generate a lot of distortion, of all kinds, to add character to the sound. https://www.jensentone.com/ |
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