Stop copying the Valve Caster circuit, it doesn't always work!

[teemuk]

You can put your question in another light: what is the Fender blackface sound... ?

Sorry but I don't think this is a really good analogy. You see, one could actually analyze the moderately small number of Fender's "blackface" amplifiers and find certain archetypal characteristics common to all of them.

I don't think such approach could be equally applied to each and every possible method to build an audio circuit around a triode tube, let alone to thousands and thousands of amplifiers that have triode tubes inside them in various amounts, orders and configurations. At that point it would become rather evident that it is difficult to find common archetypal characteristics of such a broad category as "triode tone".

Those blackface amps have triodes, so does the OD channel of a Dual Rectifier, Butler's starved plate voltage tube driver effects, Fender Roc Pro amps with triodes wired as clipping diodes, or perhaps an Audio Research high end hi-fi amplifier. Care to elaborate what is the audible characteristic that makes one go "Oh, that's 'triode tone. I can hear it clearly, no question about it."

[Steben]

You can put your question in another light: what is the Fender blackface sound... ?

Sorry but I don't think this is a really good analogy. You see, one could actually analyze the moderately small number of Fender's "blackface" amplifiers and find certain archetypal characteristics common to all of them.

I don't think such approach could be equally applied to each and every possible method to build an audio circuit around a triode tube, let alone to thousands and thousands of amplifiers that have triode tubes inside them in various amounts, orders and configurations. At that point it would become rather evident that it is difficult to find common archetypal characteristics of such a broad category as "triode tone".

Those blackface amps have triodes, so does the OD channel of a Dual Rectifier, Butler's starved plate voltage tube driver effects, Fender Roc Pro amps with triodes wired as clipping diodes, or perhaps an Audio Research high end hi-fi amplifier. Care to elaborate what is the audible characteristic that makes one go "Oh, that's 'triode tone. I can hear it clearly, no question about it."

Yes. Exactly. I never had the intention to point to any magic.
As I said: "if" there is such a thing as triode sound, IMHO it is the smaller amount of harmonics compared to first gen solid state stages. That's why class A triode power amps are a thing in the HiFi world.
Does that mean you hear it instantly? No. Absolutely not. What I mean is the idea might be you are not hearing the solid state... It is the lack of .. you know unclean.
It is a very specific look at things. Once you start adding feedback and keen design, the specifics are obsolete and you can mimick the lower harmonic spectrum with transistors. Or just have opamps.
What most people refer to when talking tube sound is things like great responsive overdrive in power amps and "great warm cleans". The first has nothing to do with triodes while the last one IMHO simply refers to great amp EQ design and headroom. In comes my idea: triodes are cleaner than early days transistor amps rather than having magic harmonics.
We know how triodes clip, it can be damn harsh. I never cared for metal oriented tube preamps. There are no laws against them but they just don't move me.

My point is actually that preamp triodes are double faced: once you have high supply voltages, they are rather easy components in class A amplification design and certainly more controlable than a jFET. If you want to go low voltage though, they are to be missed the least since their clipping is known and the harmonics they add in clean high voltage circuits is as said quite small.
There are these Musicman amps renowned for clean tones that combine solid state preamps and tube power amps... I do feel given the high supply voltage they could have had preamp tubes, but the amps simply sound great. Just because there is no such thing as a huge preamp triode thing that is missing. And all that filament current is gone.

The one most influential tube in a classic tube amp just might be the rectifier tube, not even the power tube. And that one is easily replaced with an added resistor.
And the most overrated one might be the triode in SS hybrid preamp channels.

Just as when people start talking solid state amps down it is almost always about "shitty overdrive". Honestly, I can't remember anyone giving a ss amp credits for a great natural warm overdrive sound while talking bad about the "sterile tranny clean" channel.

[amptramp]

You can put your question in another light: what is the Fender blackface sound... ?

Sorry but I don't think this is a really good analogy. You see, one could actually analyze the moderately small number of Fender's "blackface" amplifiers and find certain archetypal characteristics common to all of them.

I don't think such approach could be equally applied to each and every possible method to build an audio circuit around a triode tube, let alone to thousands and thousands of amplifiers that have triode tubes inside them in various amounts, orders and configurations. At that point it would become rather evident that it is difficult to find common archetypal characteristics of such a broad category as "triode tone".

Those blackface amps have triodes, so does the OD channel of a Dual Rectifier, Butler's starved plate voltage tube driver effects, Fender Roc Pro amps with triodes wired as clipping diodes, or perhaps an Audio Research high end hi-fi amplifier. Care to elaborate what is the audible characteristic that makes one go "Oh, that's 'triode tone. I can hear it clearly, no question about it."

Yes. Exactly. I never had the intention to point to any magic.
As I said: "if" there is such a thing as triode sound, IMHO it is the smaller amount of harmonics compared to first gen solid state stages. That's why class A triode power amps are a thing in the HiFi world.
Does that mean you hear it instantly? No. Absolutely not. What I mean is the idea might be you are not hearing the solid state... It is the lack of .. you know unclean.

We had one person in the London Vintage Radio Club (London Ontario, not England) bring in a Class A Single-Ended Triode amplifier for demonstration purposes at one meeting.  When you heard music played through it, it was obviously different from what you heard through a low-distortion amplifier but the harmonics you could hear on the single-ended triode amplifier were quite pleasant.  The harmonic distortion was in the 4% to 5% range and no feedback was used.  This is triode sound at its most extreme without requiring clipping to produce extra harmonics.

[Steben]

You can put your question in another light: what is the Fender blackface sound... ?

Sorry but I don't think this is a really good analogy. You see, one could actually analyze the moderately small number of Fender's "blackface" amplifiers and find certain archetypal characteristics common to all of them.

I don't think such approach could be equally applied to each and every possible method to build an audio circuit around a triode tube, let alone to thousands and thousands of amplifiers that have triode tubes inside them in various amounts, orders and configurations. At that point it would become rather evident that it is difficult to find common archetypal characteristics of such a broad category as "triode tone".

Those blackface amps have triodes, so does the OD channel of a Dual Rectifier, Butler's starved plate voltage tube driver effects, Fender Roc Pro amps with triodes wired as clipping diodes, or perhaps an Audio Research high end hi-fi amplifier. Care to elaborate what is the audible characteristic that makes one go "Oh, that's 'triode tone. I can hear it clearly, no question about it."

Yes. Exactly. I never had the intention to point to any magic.
As I said: "if" there is such a thing as triode sound, IMHO it is the smaller amount of harmonics compared to first gen solid state stages. That's why class A triode power amps are a thing in the HiFi world.
Does that mean you hear it instantly? No. Absolutely not. What I mean is the idea might be you are not hearing the solid state... It is the lack of .. you know unclean.

We had one person in the London Vintage Radio Club (London Ontario, not England) bring in a Class A Single-Ended Triode amplifier for demonstration purposes at one meeting.  When you heard music played through it, it was obviously different from what you heard through a low-distortion amplifier but the harmonics you could hear on the single-ended triode amplifier were quite pleasant.  The harmonic distortion was in the 4% to 5% range and no feedback was used.  This is triode sound at its most extreme without requiring clipping to produce extra harmonics.

Thing is, that 4 to 5 % would be even much higher for a non feedback pentode or BJT with the same scaled output and gain setting. In other words: the triode would sound acceptable, the others much less... That's how it needs to be looked at imho "historically".

The input stage of a classic amp usually has a very very large headroom compared to the signal. We're talking inputs of 0.2 to 0.5 volts average which lead to 50V max output way under the clipping limits. This brings it pretty much in the most linear region of the transfer curve.

[amptramp]

You can put your question in another light: what is the Fender blackface sound... ?

Sorry but I don't think this is a really good analogy. You see, one could actually analyze the moderately small number of Fender's "blackface" amplifiers and find certain archetypal characteristics common to all of them.

I don't think such approach could be equally applied to each and every possible method to build an audio circuit around a triode tube, let alone to thousands and thousands of amplifiers that have triode tubes inside them in various amounts, orders and configurations. At that point it would become rather evident that it is difficult to find common archetypal characteristics of such a broad category as "triode tone".

Those blackface amps have triodes, so does the OD channel of a Dual Rectifier, Butler's starved plate voltage tube driver effects, Fender Roc Pro amps with triodes wired as clipping diodes, or perhaps an Audio Research high end hi-fi amplifier. Care to elaborate what is the audible characteristic that makes one go "Oh, that's 'triode tone. I can hear it clearly, no question about it."

Yes. Exactly. I never had the intention to point to any magic.
As I said: "if" there is such a thing as triode sound, IMHO it is the smaller amount of harmonics compared to first gen solid state stages. That's why class A triode power amps are a thing in the HiFi world.
Does that mean you hear it instantly? No. Absolutely not. What I mean is the idea might be you are not hearing the solid state... It is the lack of .. you know unclean.

We had one person in the London Vintage Radio Club (London Ontario, not England) bring in a Class A Single-Ended Triode amplifier for demonstration purposes at one meeting.  When you heard music played through it, it was obviously different from what you heard through a low-distortion amplifier but the harmonics you could hear on the single-ended triode amplifier were quite pleasant.  The harmonic distortion was in the 4% to 5% range and no feedback was used.  This is triode sound at its most extreme without requiring clipping to produce extra harmonics.

Thing is, that 4 to 5 % would be even much higher for a non feedback pentode or BJT with the same scaled output and gain setting. In other words: the triode would sound acceptable, the others much less... That's how it needs to be looked at imho "historically".

The input stage of a classic amp usually has a very very large headroom compared to the signal. We're talking inputs of 0.2 to 0.5 volts average which lead to 50V max output way under the clipping limits. This brings it pretty much in the most linear region of the transfer curve.

It's not that much higher for a pentode.  A lot of radios were made with a triode first amplifier and a pentode or beam power tube for the output with no feedback and the total distortion was still in the 5% range.  The typical radio had a 120 volt B+ and the triode plate voltage was about 82 volts.  The beam power tube output was fed from 120 VDC through the output transformer.  But the harmonic structure was different.  The sound was a lot more harsh with the beam power tube.  Check out the distortion curves here:

http://diyaudioprojects.com/mirror/members.aol.com/sbench101/

I have one radio at home that I haven't got operating yet that has an all-triode audio amplifier with 6AC5GT outputs that have a µ of 125.  The tube looks like a tetrode with control and screen grids connected internally.  This will be a good one to get going.

[Gattoconglistivali]

https://www.its.caltech.edu/~musiclab/feedback-paper-acrobat.pdf

found it!

Check the comparison of harmonic spectrum bewteen triodes, jfets and bjts.... And how feedback through source or emitter resistors reduces the harmonics and how jFET (square law) and BJT (log)comes closer to a CLEANER triode (1,5 law).
Now think about what I ment with using class A transistors stages with some feedback reducing their gains (in relation to lower supply voltage) and reducing higher harmonic content (flattening the square or log function).

Bottom line: many old school tube preamps have a decent design by nature for guitar use. Yet solid state in preamps can sound great by understanding the component and typology. It needs careful biasing and feedback to shape the response and "tame the gain".

Thank you for sharing  this document, it's very interesting

This research analysts distortion behaviors of same type of amplifier made from different components, NOT analyzing general performance of these components.

In the very beginning it had been claimed "the amplifier is modeled in general non-linear "(p5) means in the following research, all amplifiers are all distortion causing -so that they cause significant amounts of "intermodulation distortion, the subject of the research.

The line in p21 stating " triode is fundamentally more linear than either the bjt or the fet" is about the distortion characteristics of the amplifiers, not components themselves

Thank you again for sharing the source(though a bit off topic), this is something I always wanted to look into.

[Steben]

The line in p21 stating " triode is fundamentally more linear than either the bjt or the fet" is about the distortion characteristics of the amplifiers, not components themselves

Thank you again for sharing the source(though a bit off topic), this is something I always wanted to look into.

Well.... summarised a high feedback stage with jFET or BJT by source or emitter resistor with rather low gain will be quite linear compared to a triode stage. But it will still have a lot of gain relative to the supply voltage compared to a typical triode stage.
A classic "just make it work" high gain triode stage on the other hand has less harmonics than a high gain jFET or BJT stage. A classic tube preamp will sound rather "clean" with less IM components compared to a high gain jFET or BJT preamp. Do not underestimate IM distortion.

While the triode can be improved as well if wanted by less gain and more cathode feedback, the improvement in jFETs and especially BJT is much higher.
At least my conclusion is a lower supply voltage unit (like most SS amps) benefit so much from some local feedback and even gain reduction, tube preamps become "less necessary" to be polite. Tube power amps are different still, given the complex dynamics.

Now look at the AC30. With its pentode input stage. It's put there for more input gain clearly. Now think of the vast distance between supply voltage (and working region) and input signal. The gap between end of the headroom and the amplified signal is still wide. And the fact other stages are .... triodes.
Will the AC30 stop sounding like an AC30 with a triode input or will it stop sounding like an AC30 with a power amp IC ...

[teemuk]

Now that's an interesting question... will a DSP and triode hybrid -based Vox Valvetronix amp with AC30-like characteristics amplified with a generic IC sound more like a Vox AC30 than a Mullard SE hifi amp with a genuine EL84 output and EF86 pentode preamp? I would bet on the Valvetronix amp.

[Steben]

Now that's an interesting question... will a DSP and triode hybrid -based Vox Valvetronix amp with AC30-like characteristics amplified with a generic IC sound more like a Vox AC30 than a Mullard SE hifi amp with a genuine EL84 output and EF86 pentode preamp? I would bet on the Valvetronix amp.

Yes. Definitely. EQ for starters and hmmmm SE will never sound like a cathode bias push pull

[Gattoconglistivali]

Yeah, but what's that "triode sound" anyway. If you look back at the history of distortion effects the first ones were solid-state and built to mimic the archetypal sound of broken equipment, and yes, possibly also overdriven tube amps mixing consoles, mic preamps et cetera.


But none of this "triode sound" was yet even important: a half-assed circuit like the FZ-1 or Fuzzrite could produce the most important: Distortion. The effect - nevertheless what it was or what nuances it had - was simply marketed with less glorifying terms such as "fuzz", "buzz" or even "mud". No one was marketing "tube sound". (Well, some effects were marketed of being able to produce "mud" of tube amps).

It took several years before someone even invented they can use tubes for producing distortion (aside from cranking amps to inconvenient volume levels). It took several years more to invent the idea that "tube distortion" is the only good sounding distortion. It took a few more years to invent the idea that "soft clipping" or "asymmetric clipping" are not actually realistic tube distortion emulations. It took even a few years longer to invent the idea that this "distortion" should actually sound like a complete amplifier system distorting, etc.

So, I kinda think that most of these ideas how distortion should sound like ideally are more or less just gimmicks. "Triode sound"... do we even have a generic consensus what that is? I don't think so. It's just a vague marketing phrase like "transparent overdrive".

Very interesting question, I haven't find any research clarify that yet.
Some says even order harmonic, asymmetric clipping, soft clipping ... And there are scientific data proved them all otherwise .

But for me, my standard is quite simple : least gears needed.

I tried run a pedal straight into a interface, hook a whatever cab sim. A tube screamer, a rat, an amp modeling from multi-effect , all sound terrible. But a 12au7 preamp built without any thinking makes platable sound (not great of course)

And I found myself favoring "hard clipped signal further clip with tubes" sounds, whether
the hard clipping in the first place from tubes or semiconductor diodes doesn't seems matter.