41–50 of 52 posts
I studied vacuum tubes back when I was in school. What a fascinating thing, the physics of it. It was a cool tech for its time but there is no way they could match the speed of the transistors that followed, it is just physically impossible, but still, it is nostalgically cool.
Weren't there specialized tubes that could operate in the gigahertz range - nuvistors, for example.
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Eh. As far as instrument amps go, it's not about perfect fidelity. It's about color and distortion. You'd never say "perfectly white lights are the best for your living room." No one actually wants a perfect white light, people want some more yellow in there because it looks better. The goal isn't equal spectrum coverage or whatever. People like the non-linearity of tubes and that's ok.
The thing is, much like "perfectly white lights" you can mimic the non-linear behavior of tubes with transistor circuitry. On the extreme end you can integrate a DSP into the line to add a "vacuum tube" filter onto the sound in pre-amp. Thinking you can't do that is like thinking all LED bulbs must be 5000k and only incandescent can give that warm glow (Which, funnily that color was chosen to mimic gas lights before…
Earlier quoted context omitted.
Eh. As far as instrument amps go, it's not about perfect fidelity. It's about color and distortion. You'd never say "perfectly white lights are the best for your living room." No one actually wants a perfect white light, people want some more yellow in there because it looks better. The goal isn't equal spectrum coverage or whatever. People like the non-linearity of tubes and that's ok.
The thing is, much like "perfectly white lights" you can mimic the non-linear behavior of tubes with transistor circuitry. On the extreme end you can integrate a DSP into the line to add a "vacuum tube" filter onto the sound in pre-amp. Thinking you can't do that is like thinking all LED bulbs must be 5000k and only incandescent can give that warm glow (Which, funnily that color was chosen to mimic gas lights before…
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Kind of astonishing that they managed to retain the institutional / folk knowledge to be able to create a new vacuum tube product, never mind the machinery and inputs to manufacture them.
In the 90s China bought the whole Mullard factory and shipped it over from England. If you buy cheap Chinese valves, you're buying Mullard ones which seem to be made to a higher standard than they ever managed in the 80s. Any two random EL34s out of the box will be a closer match than the crazy expensive "super matched pairs" that we used to buy.
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I disagree. There is nothing in the digitally sampled and modelled world comparable to plugging your guitar into a hot over-driven tube amp and showing the feedback who's the boss. Pure analog transistors don't give that luscious even harmonic distortion and usually just clip like a meth-addled dog stylist in a poodle-grooming station.
As a guitarist with over 30 years of playing, and owner of many tube and non-tube amps, I disagree. Even experienced guitarist cannot reliably distinguish between transistor and tube circuits in a blind test. Having said that, if only the knowledge of playing a tube amp gives someone a better experience, even if its not empirically distinguishable, thats a perfectly valid reason to prefer it.
One very common trick that has appeared in transistor guitar amps from the 1970's and onward is current feedback. The return terminal of the speaker doesn't go straight to ground, but feeds a tiny current-sensing resistor, like 0.1 ohms. Signal from the current-sensing resistor is combined into the negative feedback. This gives the amp a nonzero output impedance against the speaker, which changes the frequency response: more power is driven at the frequencies where the speaker impedes more, like its resonant frequency (about 70 to 100 Hz for a 12" guitar speaker) and high frequencies (due to voice coil inductance: rises from about 2 kHz up or something like that).
This doesn't reproduce everything that happens with tubes, but it goes a long way.
I built a circuit like that into an off-the-shelf amplifier, with a switch. I tell you, whenever I switch that off, it's not long before it goes back on again. Without the current feedback, it's sounds blatty/tubby and lifeless. It's not just the frequency response, because even if we dial in a similar EQ curve before the amp to eliminate the difference, it's not "it".
The TubeWorks people have an interesting design in the MosValve 500 amp. Rather than using current feedback, that amp places the MOSFET output stage outside of the negative feedback loop. Negative feedback is drawn from the VAS (voltage amplification stage) before the output stage. That means that the speakers will see the impedance of the MOSFETs. Plus the supposedly "tube like" overdrive characteristics of the power devices will come into play when that thing is cranked. Because they are outside of the NFB loop, it will just be soft onset clipping. Here is the important thing: unusually, the VAS and the output stage are on separate power rails, and those of the VAS are a significantly higher voltage (+/- 93V versus +/- 71V). So it is hard to make the VAS clip; it requires a much higher signal than what it takes to make the output stage go into progressive clipping. When an output stage is included the feedback loop, like in almost every amplifier out there, the amp is perfectly linear up to the limit, and then clips really hard.
The schematic: https://img.photobucket.com/albums/v202/xr3drumx13/MV500Sche...
Tube amplifiers "do their thing" without extra gimmicks like this, though.
I think this is an odd article. It mixes together a variety of technologies that have little in common (gas discharge tubes, CRTs). It doesn't really say anything about the operation of vacuum tubes, their advantages, or disadvantages. And doesn't even really support its own thesis. The reign of vacuum tubes lasted for less than the reign of the transistor and is in no way unusual in the world of electronics. There a…
For my daily band life my amp of choice is a Roland JC-120 for guitar (transistor amp) and a Eich T-500 (class D) for Bass.
Can't wait for class D to catch up to tubes, I really don't dig having to carry 30kg amps around.
I think this is an odd article. It mixes together a variety of technologies that have little in common (gas discharge tubes, CRTs). It doesn't really say anything about the operation of vacuum tubes, their advantages, or disadvantages. And doesn't even really support its own thesis. The reign of vacuum tubes lasted for less than the reign of the transistor and is in no way unusual in the world of electronics. There a…
There's really not benefits to vacuum tubes pretty much anywhere. The only place I can think of where they are superior (which may not be true anymore) is high power transmission in, for example, radio and radar towers. In all other applications transistors will be superior. Especially because any problem from a transistor can be fixed by adding more transistors until the problem is gone or imperceptible. The audioph…
But if all you want is the sound of an overdriven tube amplifier, getting yourself an overdriven tube amplifier is still the least complex option technically, in terms of parts count, repairability, etc. It is a primitive technology, but it is also well known and works. It also has no menus, minimal settings and doesn't need firmware updates or registered accounts.
Personally I use both Class D and transistor based audio amplifiers for my musician life, since those are much lighter to carry for the same power and work for the type of sound I want.
If we talk Hifi unless they also want to overdrive the sound (they usually don't), tube amps are useless. The distortion figures of good transistor amps are much better, class D is making massive leaps in the recent years and has reached indistinguishable quality levels for a while now. These people should focus on room acoustics.
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The thing is, much like "perfectly white lights" you can mimic the non-linear behavior of tubes with transistor circuitry. On the extreme end you can integrate a DSP into the line to add a "vacuum tube" filter onto the sound in pre-amp. Thinking you can't do that is like thinking all LED bulbs must be 5000k and only incandescent can give that warm glow (Which, funnily that color was chosen to mimic gas lights before…
No one said you can't do it. There's just no reason to do it. Tube amps are basically a standard and it's what the amp repair guys know how to work on and it's easiest to work on.
- Tube amps need regular tube swaps. For a small guitar Combo a set of tubes (3× preamp + 2× power amp) can cost between 100 to 150 Euros. If you're a poor musician that is a factor
- Tube amps use heavy power and output transformers. If you ever had to carry an Ampeg SVT (36 kg for 300W) you will cherish the idea of a 0.25 kg 500W class D amp. If you're a touring musician that is a factor
- Tube amps are limited in terms of sound. While this could be seen both as a feature and a bug, if you want to recall the perfect settings for each song as a touring musician, tube amps are not the right choice unless you have a horde of roadies and technicians
This is why amp sims have become more popular in the recent years with people who play music for a living.
That being said, if you're in a simple band and you want the sound of a tube amp, a tube amp gives it to you pretty reliably without making you drown in options or giving you the feeling your gear is outdated every other year, since it is outdated since decades anyways. A tube amp also needs no firmware updates and requires no subscription and has less parts that can break.
Earlier quoted context omitted.
Eh. As far as instrument amps go, it's not about perfect fidelity. It's about color and distortion. You'd never say "perfectly white lights are the best for your living room." No one actually wants a perfect white light, people want some more yellow in there because it looks better. The goal isn't equal spectrum coverage or whatever. People like the non-linearity of tubes and that's ok.
The thing is, much like "perfectly white lights" you can mimic the non-linear behavior of tubes with transistor circuitry. On the extreme end you can integrate a DSP into the line to add a "vacuum tube" filter onto the sound in pre-amp. Thinking you can't do that is like thinking all LED bulbs must be 5000k and only incandescent can give that warm glow (Which, funnily that color was chosen to mimic gas lights before…
Earlier quoted context omitted.
The thing is, much like "perfectly white lights" you can mimic the non-linear behavior of tubes with transistor circuitry. On the extreme end you can integrate a DSP into the line to add a "vacuum tube" filter onto the sound in pre-amp. Thinking you can't do that is like thinking all LED bulbs must be 5000k and only incandescent can give that warm glow (Which, funnily that color was chosen to mimic gas lights before…
No one said you can't do it. There's just no reason to do it. Tube amps are basically a standard and it's what the amp repair guys know how to work on and it's easiest to work on.
