Where does the tone come from in a guitar amplifier ?

[Steben]

Overall this has major thruths in it.
Yet ..... Saying a cathode bias non feedback amp sounds the same as a fixed bias feedback amp is not true.
Feedback is not mentioned, I know. But is exactly why I mention it.
It depends on what you compare. Power chords full blown? What moderate players / enthusiasts really prefer to look for is dynamics. All other things can be done with metal zones and EQ.
Reminds me of fuzz face vids without volume roll off parts.... It's completely off track past the essence.

I suggest comparing a fuzz face, a rangemaster + amp, feedback and non-feedback amps. And all with dynamic ranges.

[Rob Strand]

He beautifully illustrated exactly what RG Keen, Teemu K, other gurus here, Fractal Mimic paper, Yamaha patents, Rockman patents, Peavey patents and others have been saying for a very long time.

You can throw the Tech21 Sansamp concept in there.  It's pretty much EQ and EQ placement.

[Vivek]

Yes !

Teemu K had a section on the SansAmp in his book

It's just EQ and Rail saturation

[dschwartz]

When i designed the simplifier, i took a similar approach.
Simulated the vox ac30TB, Plexi, and bassman, the three have similar preamp structure, but different voicing and tonestack.
The power amp stage was only based on the frequency response for usual feedback values for each type, and the cabs well, analog cabsims with different F points.
It always surprise me how users find it to be the "most natural" sounding AIAB, since i didnt bother too much on getting tube dynamics (except for getting the gain staging right).

Now I'm working on a prototype with tube dynamic simulation (triode bias excursion, asymmetric clipping, power amp crossover distortion, global negative FB, etc etc) and so far the interstage filtering and final EQ has proven to be the most impactful of all tweaks..

Nevertheless , about the video, there's something i find a little suspicious..the vox power amp with no negative feedback has a lot of impact on the frequency response (a big peak on the speaker low end resonance, and a high boost) and we was using a solid state power amp with flat response ( i suppose)..fender and marshall have some NFB that flattens the output response (not 100%, but much flatter than a vox) and that didn't seemed to show on his test.

[Steben]

Most of the specifics about tube amps is about dynamics.  It is hard to capture on recordings. Especially when not "played for." Does not change any 90% is eq statement. But a recording only can give what a recording can give.

[Vivek]

When i designed the simplifier, i took a similar approach.
Simulated the vox ac30TB, Plexi, and bassman, the three have similar preamp structure, but different voicing and tonestack.

Now I'm working on a prototype with tube dynamic simulation (triode bias excursion, asymmetric clipping, power amp crossover distortion, global negative FB, etc etc) and so far the interstage filtering and final EQ has proven to be the most impactful of all tweaks..

Thank you for your inputs, Daniel !

I was interested in studying effect of dynamics of the tube (Sag, bias changes)

One of my friends. Dr Buffa, wrote some tools to emulate some dynamics of transfer curve based on signal envelope.

https://www.youtube.com/watch?v=zBhn7odezUQ
https://output.jsbin.com/zotaver
https://mainline.i3s.unice.fr/AmpSim5/index.html

Given that most hardware pedals till now did not bother to implement any dynamic behaviours, do you feel that the difference can be heard and felt ?

[StephenGiles]

https://www.youtube.com/watch?v=nV9bnaqqfq8

Sorry but I'm not at all convinced by all this technical qtoomy - the tone is in the fingers and nothing else, proved by the master Jeff Beck, who as the presenter of the video sais is one of one!!!

[dschwartz]

When i designed the simplifier, i took a similar approach.
Simulated the vox ac30TB, Plexi, and bassman, the three have similar preamp structure, but different voicing and tonestack.

Now I'm working on a prototype with tube dynamic simulation (triode bias excursion, asymmetric clipping, power amp crossover distortion, global negative FB, etc etc) and so far the interstage filtering and final EQ has proven to be the most impactful of all tweaks..

Thank you for your inputs, Daniel !

I was interested in studying effect of dynamics of the tube (Sag, bias changes)

One of my friends. Dr Buffa, wrote some tools to emulate some dynamics of transfer curve based on signal envelope.

https://www.youtube.com/watch?v=zBhn7odezUQ
https://output.jsbin.com/zotaver
https://mainline.i3s.unice.fr/AmpSim5/index.html

Given that most hardware pedals till now did not bother to implement any dynamic behaviours, do you feel that the difference can be heard and felt ?

I still havent finished the power amp part.
As far as the preamp prototype, i used a pair of CMOS stages inside the ckt with dynamic bias excursion and tested pure cmos clipping, asymmetric led/cmos, symmetric LED, with and without bias excursion, different excursion intensities and times, etc
My goal is to get a gain range from clean to high gain, varying the voicing as turning the gain up, mantaining a consistent nice tone.
So far i found that for high gain, a delicate balance between symettric and assymetric stages with hard clipping are needed (assymetric with enhance the pinch harmonics, but will mush the tone a bit due to intermodulation). The effect of symmetry is audible, and the bias shift can be felt on the attack, and it adds sustain (i feel, at least)
The other (really hard) goal is to achieve a nice fizzless decay on mid-gain tones..so far i see that gain staging is critical for this, but it is really hard to remove it 100% while retaining an aggressive "bite" at high gain.
So...i think ill go back to opamps for these ideas..cmos sound good, but too much hiss and some impredictability are a no go for serious production.

[Rob Strand]

It's all too obvious:

[PRR]

Don't you just buy a bottle of tone?

(For added fun: the business next to that one is the 'Enter in rear book store'.

[Fancy Lime]

When i designed the simplifier, i took a similar approach.
Simulated the vox ac30TB, Plexi, and bassman, the three have similar preamp structure, but different voicing and tonestack.

Now I'm working on a prototype with tube dynamic simulation (triode bias excursion, asymmetric clipping, power amp crossover distortion, global negative FB, etc etc) and so far the interstage filtering and final EQ has proven to be the most impactful of all tweaks..

Thank you for your inputs, Daniel !

I was interested in studying effect of dynamics of the tube (Sag, bias changes)

One of my friends. Dr Buffa, wrote some tools to emulate some dynamics of transfer curve based on signal envelope.

https://www.youtube.com/watch?v=zBhn7odezUQ
https://output.jsbin.com/zotaver
https://mainline.i3s.unice.fr/AmpSim5/index.html

Given that most hardware pedals till now did not bother to implement any dynamic behaviours, do you feel that the difference can be heard and felt ?

I still havent finished the power amp part.
As far as the preamp prototype, i used a pair of CMOS stages inside the ckt with dynamic bias excursion and tested pure cmos clipping, asymmetric led/cmos, symmetric LED, with and without bias excursion, different excursion intensities and times, etc
My goal is to get a gain range from clean to high gain, varying the voicing as turning the gain up, mantaining a consistent nice tone.
So far i found that for high gain, a delicate balance between symettric and assymetric stages with hard clipping are needed (assymetric with enhance the pinch harmonics, but will mush the tone a bit due to intermodulation). The effect of symmetry is audible, and the bias shift can be felt on the attack, and it adds sustain (i feel, at least)
The other (really hard) goal is to achieve a nice fizzless decay on mid-gain tones..so far i see that gain staging is critical for this, but it is really hard to remove it 100% while retaining an aggressive "bite" at high gain.
So...i think ill go back to opamps for these ideas..cmos sound good, but too much hiss and some impredictability are a no go for serious production.

What works really well for "fizzless decay", in my experience, is diode clipping to ground or in NFB loop. The key is, to design the currents such that you can really "ride the knee". That makes is so that the harmonic orders increase smoothly as you transistion into more clipping. The Blues Breaker topology is ideal for this (with the series resistor of the diodes removed) because it asks less current of the diodes at lower gain settings and more at higher settings. That helps preserve a more aggressive crunch at high gain settings while reaping the maximum benefit of fizz suppression at low settings. It also helps to use diodes with a pronounced knee. 1N4148 are actually not too bad here. Low voltage Zeners (2V7 or lower) have a very soft knee in Zener mode and are my favorites for fizzlessness for that reason. I don't like them at higher gain so much, though. Sound a bit "spongy" to me comparred to Si or LEDs, likely also as a result ot the soft knee. Tradeoffs... Or switchable diodes.

[Steben]

When i designed the simplifier, i took a similar approach.
Simulated the vox ac30TB, Plexi, and bassman, the three have similar preamp structure, but different voicing and tonestack.

Now I'm working on a prototype with tube dynamic simulation (triode bias excursion, asymmetric clipping, power amp crossover distortion, global negative FB, etc etc) and so far the interstage filtering and final EQ has proven to be the most impactful of all tweaks..

Thank you for your inputs, Daniel !

I was interested in studying effect of dynamics of the tube (Sag, bias changes)

One of my friends. Dr Buffa, wrote some tools to emulate some dynamics of transfer curve based on signal envelope.

https://www.youtube.com/watch?v=zBhn7odezUQ
https://output.jsbin.com/zotaver
https://mainline.i3s.unice.fr/AmpSim5/index.html

Given that most hardware pedals till now did not bother to implement any dynamic behaviours, do you feel that the difference can be heard and felt ?

I still havent finished the power amp part.
As far as the preamp prototype, i used a pair of CMOS stages inside the ckt with dynamic bias excursion and tested pure cmos clipping, asymmetric led/cmos, symmetric LED, with and without bias excursion, different excursion intensities and times, etc
My goal is to get a gain range from clean to high gain, varying the voicing as turning the gain up, mantaining a consistent nice tone.
So far i found that for high gain, a delicate balance between symettric and assymetric stages with hard clipping are needed (assymetric with enhance the pinch harmonics, but will mush the tone a bit due to intermodulation). The effect of symmetry is audible, and the bias shift can be felt on the attack, and it adds sustain (i feel, at least)
The other (really hard) goal is to achieve a nice fizzless decay on mid-gain tones..so far i see that gain staging is critical for this, but it is really hard to remove it 100% while retaining an aggressive "bite" at high gain.
So...i think ill go back to opamps for these ideas..cmos sound good, but too much hiss and some impredictability are a no go for serious production.

Tube amps can have fizz as well. 

I have to say the modded bluesbreaker (check Mark's ideas and mine) is perhaps of all two stage circuits the one that has imho the least "clean up" fizz.
The boost section (switches between classic BB lug to modern lug with higher high pass freq) still has too much high freqs going into the all the clipping parts (not in the clip below). Need to figure out the balance.

[zbt]

My ... Brain ... Wash ... By ... Tone Control ? 

no wonder bigmuff has many version, ha ha ha

Feel like Purist and Audiophile has something in common
whatever they argue and fight about distortion
in the end they like tubes, and they are cute like teletubbies

What about the sustain? may be this New Techie guy can explain
(I thought this guy for real and serious) 



The Sustain, please set volume to 0 not 11  , Enjoy

Peace Everybody

[Steben]

Tube amps can have fizz as well. 

I have to say the modded bluesbreaker (check Mark's ideas and mine) is perhaps of all two stage circuits the one that has imho the least "clean up" fizz.
The boost section (switches between classic BB lug to modern lug with higher high pass freq) still has too much high freqs going into the all the clipping parts (not in the clip below). Need to figure out the balance.

Look here for the schematic and sketchy curves
https://www.diystompboxes.com/smfforum/index.php?topic=129708.msg1254562#msg1254562

[Steben]

What works really well for "fizzless decay", in my experience, is diode clipping to ground or in NFB loop. The key is, to design the currents such that you can really "ride the knee". That makes is so that the harmonic orders increase smoothly as you transistion into more clipping. The Blues Breaker topology is ideal for this (with the series resistor of the diodes removed) because it asks less current of the diodes at lower gain settings and more at higher settings. That helps preserve a more aggressive crunch at high gain settings while reaping the maximum benefit of fizz suppression at low settings. It also helps to use diodes with a pronounced knee. 1N4148 are actually not too bad here. Low voltage Zeners (2V7 or lower) have a very soft knee in Zener mode and are my favorites for fizzlessness for that reason. I don't like them at higher gain so much, though. Sound a bit "spongy" to me comparred to Si or LEDs, likely also as a result ot the soft knee. Tradeoffs... Or switchable diodes.

You are correct.

Think of Germanium diodes in a non-feedback loop. Usually they are not liked. The circuit simply become too soft.

In a classic tube amp not only clipping comes in, but a lot of other stuff like multistage distortion, transformers, sag.... Even crossover distortion when circuits get out of bias at higher output and start adding a kind of fizz (X over is nothing but fizz) at higher clipping levels. X over distortion at low levels - I mean constant distortion - sound like a buzzy fizzy bug. But when it comes into play when distortion levels are already high one notices a kind of mushy character that goes away at clean. It's part of what some call "tube sounds". It is something impossible to create with simple diode clippers. Again, a (solid state device as hell) fuzz face has such dynamic character on its own but different.

Thing is, the ideal amp like distortion is determined by what a person thinks of when saying "amp like". Which amp?
Tweed Deluxe, Deluxe Reverb, a VOX AC30 or a 1959 Plexi are completely different distortion profiles.

And we have to add: the plexi is the easiest to define and emulate. It has negative feedback and a solid state rectifier. They designed it to have reliability, headroom and a stable performance. This means almost no sag and a very sharp transfer curve. Any device capable of having sharp clipping without periferic trash (like latch-up in some opamps) is a go with correct filtering. The marshall-in-a-box sound is everywhere. In a pretentious mode I'ld say: because the amp has the least of tube quircks ....
Just think of it: one the most popular and rumoured "tube" amps is the one that omitted typical elements of saggy and slow-onset-harmonics tube circuitry... Makes you wonder.