| Electronics > Projects, Designs, and Technical Stuff |
| Guitar amplifier - Current-drive & Soft-clipping, combining both |
| << < (4/5) > >> |
| SiliconWizard:
Yeah. Emulating a tube power amp stage with just a tiny tube preamp stage just doesn't work. Not even saying about emulating it with no tube at all. There are many effects, not just on clipping (as some naive approaches assume), but also on frequency response, which are not even fixed, but dynamic. Whether one particular person doesn't like the sound of tube amps doesn't matter here. It's just a matter of taste indeed. It just so happens that many, probably most guiitar players do. Of course tube amps distort the sound all over the place in several, and intricated ways. That's extremely tough to emulate. The point is not whether this technically makes sense. We're not listening to music with audio analyzers. (Which is incidentally why "HiFi" is still such a hot, and often controversial topic.) I have never really come across pure solid-state approaches that came close. Digital emulations - some now are pretty good, but still. Not quite there either, and the "good" ones are pretty complex. Not sure the constant current output stage would approach this much better. I'd guess this could rather be some kind of output stage that would adapt smoothly between a voltage source and current source, effectively adapting its output impedance dynamically. |
| TinkeringSteve:
--- Quote from: magic on September 22, 2019, 12:26:20 pm ---There is indeed some errors in your article. I have to nitpick: neither current, nor force, nor power going into the speaker should be kept constant with frequency for accurate reproduction. It's a common myth, it's wrong. And possibly neither voltage, to the horror of all the damping factor fanboys. --- End quote --- Interestingly, this dude wrote an entire book about current-driving speakers for, different than in my guitar tinkering, lower distortion: https://www.current-drive.info/ I have not read the book or much of the text, but frmo what I remember having glanced over, only certain speaker types, which lend themselves to it (i.e. those seem to exist or could be made), are apparently recommended. |
| SiliconWizard:
I remember an old project in Elektor (early nineties), "the current amp". It was designed to directly drive ribbon speakers, which have extremely low impedance, and are more commonly driven through transformers (which obviously are costly and introduce a significant amount of distortion.) |
| magic:
--- Quote from: TinkeringSteve on September 22, 2019, 04:13:45 pm ---Interestingly, this dude wrote an entire book about current-driving speakers for, different than in my guitar tinkering, lower distortion: https://www.current-drive.info/ I have not read the book or much of the text, but frmo what I remember having glanced over, only certain speaker types, which lend themselves to it (i.e. those seem to exist or could be made), are apparently recommended. --- End quote --- There is a surprising lack of any decent information on the workings of speakers and microphones on the Internet. I also haven't read any trustworthy books on the topic because I don't even know where to look for them, probably not in the local book store or library. So I am actually quite clueless. But I can say that much: Firstly, I wouldn't necessarily trust somebody who starts with saying that everything done in the 100 years history of audio is wrong. Chances are that the author just doesn't fully understand what is being done in audio. Secondly, there is a common misconception among current drive fanboys that current is what determines the speaker's movement. Case in point: --- Quote ---According to laws of physics, electric current is that which in a speaker driver effects diaphragm acceleration, which in turn produces sound pressure. Yet all power amplifiers strive, often tooth and nail, to control the voltage at the loudspeaker terminals, which only indirectly affects the current flowing in the voice coil. --- End quote --- By the well known Lorentz law of magnetic force, force exerted on the cone by the flow of current is proportional to the magnitude of current. Fair enough, school level physics. It is also a well known fact in the world of electric DC motors. Acceleration is force divided by mass, another known fact. But what those people invariably miss is that this isn't the only force acting on the cone. At low frequencies, force exerted by the suspension becomes relevant too. At the frequency of (mechanical) resonance, it is indeed the only force required to keep accelerating and decelerating the cone's mass back and forth, like a pendulum. In theory at least, because in practice the cone is damped by frictional losses. Current drive is blind to that and pushes the same amount of force, increasing the swing until frictional losses rise sufficiently to absorb the excess force. That being said, voltage drive has its own problems due to non-mechanical and non-linear impedances which occur in the voice coil, such as inductance or thermally induced resistance drift (supposedly a real thing in some circumstances). If you can build a transducer which doesn't suffer from resonance at its operating frequencies, current drive may indeed reduce distortion and power to you. But that's an "if". |
| radioactive:
I haven't really played around with the electronics for guitar much, but I will say that Line6 has got the tube amp, effects, and speaker cabs down to an art in DSP for at least 11 years now. At least when it comes to direct line-in recording from their devices. Maybe not as good through an external amplifier/cabinet. |
| Navigation |
| Message Index |
| Next page |
| Previous page |