No Two Amps Sound the Same - Fact or Fallacy

ML SOUND LAB said:
Is a difference like this tweakable with the EQ knobs alone?
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Your question led me to another one:
Cliff talks about tone controls here but...being also pots...what about gain and master volume controls?

If they have the same tolerance then is another factor to consider
 
ETOLKIEN said:
Your question led me to another one:
Cliff talks about tone controls here but...being also pots...what about gain and master volume controls?

If they have the same tolerance then is another factor to consider
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Cliff stated that the master volume + presence + depth (IIRC) on the Axe does not correlate to the value on a real amp.
 
Neither the tone pots, a tolerance of 20% plus/minus (40% total) led to a grade of uncertainty that's worth to consider.
We're talking here about compare 2 real amps of the same brand and model, the modeling in the Axe is the next step.
Strictly speaking an amp block may correlate to a particular unit, but the conclusion is that we can't say is representative of all the units of this amp model.
In other words, if Cliff models amp #1 he can make a "Print" of this particular device and nail the pot spots...but when he picks amp #2 (same brand, model and year, simply other serial number) the game changes...but is nothing that a little tweaking can't adress...
My question was refering if the gain and master pots share this high tolerance.
 
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Ok Cliff, so one question remains for me: When you model an amp, do you implement values of theoretically, mathematically perfect pots or do you implement the tolerance of this actual amp you used for modelling?
 
axifist said:
Ok Cliff, so one question remains for me: When you model an amp, do you implement values of theoretically, mathematically perfect pots or do you implement the tolerance of this actual amp you used for modelling?
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Here is your answer:
http://forum.fractalaudio.com/threa...axe-fx-to-bogner-blue-chan.31706/#post-449541

I think Cliff tries to respect fully the real amp but if he find something weird he corrects it with good taste, you may consider the amp block as an improved version of the real thing.
In consecuence the behaviour of the pots in some amp models of the axe are more user-friendly that the real amp pots of this particular model.
 
Thanks for the link ETOLKIEN! But it's not exactly what I asked ;) What I meant was: If the amp uses for example a linear pot for e.g. the treble, but the built-in pot isn't exactly linear, does Cliff then implement a perfectly linear virtual pot or does he implement the tolerance the actual pot has. So in other words, does he "idealize" the amp when it comes to pots or not? My guess is that he idealizes it! And I also hope so! ;)
 
axifist said:
If the amp uses for example a linear pot for e.g. the treble, but the built-in pot isn't exactly linear, does Cliff then implement a perfectly linear virtual pot or does he implement the tolerance the actual pot has. So in other words, does he "idealize" the amp when it comes to pots or not? My guess is that he idealizes it! And I also hope so! ;)
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The "tolerance" here refers to the range that the pot can sweep over, and not the actual behavior of the sweep itself. To answer your question: presumably, yes: (1) it's simpler to code up, and (2) it wouldn't (to the best of my knowledge) affect the behavior in a nontrivial way (this is certainly the case when, as has already been mentioned, when it functions as a rheostat).
 
axifist said:
What I meant was: If the amp uses for example a linear pot for e.g. the treble, but the built-in pot isn't exactly linear, does Cliff then implement a perfectly linear virtual pot or does he implement the tolerance the actual pot has.
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I can't speak for Cliff, but my experience with him over the last 6 or so yrs has been that he has been true to the amp.. meaning (and this is just MY opinion, as I may be incorrect) that he would implement a non-linear pot if the amp he modeled had one.
Of course, one still needs to be familiar with the actual amp to be able to duplicate what it controls do - to get an exact A/B :)
 
I read the original post last night, but I don't think it accounted for differences in tubes which will make a big difference that can't always be "normalized" through tone controls.
 
I'd say idealizing it makes sense, because it averages the tolerances the actual pots have. Then again this makes it harder to compare the virtual model to the actual amp to see (or hear) how close his modelling comes to the original.
 
rickboot said:
Yes, but the "aging" parameter might actually be fun. Variable vintage.
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I have a Markbass head from when I played bass in a band for a while. Check out the description of the VLE control. ;-)

What do the VLE and VPF filters do?
The VLE and VPF are useful EQ filters that help you adapt your sound for different styles of music. The VLE (Vintage Loudspeaker Emulator) is a shelf EQ that cuts a wider and wider range of high frequencies as you turn it up. Markbass amps are very clear-sounding, and this filter has the effect of drawing you into the mix more, making your sound less present. It's kind of like an "old school" knob! The VPF (Variable Preshape Filter) boosts lows and highs, and cuts mids. Some call this kind of effect a scoop, a smiley-shape EQ, or an enhance knob. It's very effective for slap bass, pick playing, and driving eighth-note rock. These two filters can be combined for interesting effects. But remember that they are off when they are all the way counterclockwise--we suggest you start in that position and turn the filters up gradually, one at a time, to hear and understand what they do.
 
axifist said:
I'd say idealizing it makes sense, because it averages the tolerances the actual pots have. Then again this makes it harder to compare the virtual model to the actual amp to see (or hear) how close his modelling comes to the original.
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It's no harder to compare than two examples of the same model of tube amp. In each case, you have to bump the tone knobs a bit to get them to actually match.
 
...this reminded me why I always have to do the odd thing with my JCM900 with turning up the bass and taking down the mid/range to get that specific amp to sound good.
 
Rex said:
From the description, the VLE rolls off the highs, and the VLF is a three-band pre-EQ with limited control of the bands.
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You missed the point. "It's like an old school knob." Changes the sound from modern to vintage. How they do it is irrelevant to the point I was trying to make in response to this: "Yes, but the "aging" parameter might actually be fun. Variable vintage."

... ;-)
 
FractalAudio said:
Fact, but with caveats.

Secondly the resistance at the midpoint can vary widely. A Log10A pot should be 10% of the resistance at midpoint. But, again, this can be off 20%.

Let's take the case of a bass control which is typically wired as a rheostat. On one amp the pot might be 10% high and the midpoint 10% high. Therefore with the control at noon (assuming, say, a 1M pot) the resistance will be 121K. Another amp off the assembly line might be 10% low. Therefore the pot will be 81K. That's a 40K difference between the two amps and that's not even worst-case.

So when your friend says "well, no two amps sound the same" you can explain to him that they are probably more similar than not and a small twist of the tone controls will bring them into agreement.
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To Cliff and Community

Yes very much so.I had long ago the honour to choose out of 4 new Mark IV's heads-->All different a bit with frame numbers within 10 and played with same guitar and cab-->So fully understandable

BUT what would explain that especially Mark's ( had almost all of them and many other amps) change tone so often,audiable,even between 2-3 days non playing ( its not aging of tubes ( I think a joke in itself)as too short period between "tone changes"( even once we measured frequency's-->Changes)

Thanks for enlighting a 35 + years tube amp user

Roland
 
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axifist said:
Thanks for the link ETOLKIEN! But it's not exactly what I asked ;)
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Like S0C9 I can't speak for Cliff, but I am a tireless follower and learned how his method had evolved.
In the early days he worked with schematics and/or by ear, Das metal is a good example of that:
http://forum.fractalaudio.com/threads/das-metal-dizzy.68969/#post-847579
In the present time he needs the schematic and the real amp for make an accurate modelling.
The reason for that is the inconsistency between the schematic and the real amps due to non-ideal behavior of some components.
http://forum.fractalaudio.com/threads/another-v10-preview.62489/page-4#post-775692


In the case at hand of the pots...let's say we have the schematic of an amp, the treble pot is linear: 0 minimum, 5 noon, 10 maximum. Then we take 2 real specimens of that model. With +/- 20% of tolerance we can find a treble pot that behaves "cold" (-2 min, 3 noon, 8 max) and other that acts "hot" (2 min, 7 noon, 12 max).
Then you may find that a extreme setting in the cold amp can't be replicated in the hot amp: you run out of range!!
Plus...we've been talking about one single treble knob, think of all the pots and the inconsistently grows!
A good solution is to implement the "ideal" values because they are central and was the initial idea of the designer.
But...you may find cool to play with Robben Ford or Slash amps...some deviate from the schematic...other are modded post-factory.
I think Cliff aproach is simple: I give you this amp that you want so bad. This is not an schematic, is a real amp. But you can go beyond.
Good news with axe is that you are not constraint to the limits of a schematic, neither a real amp, in fact you can change the tonestack type, choose an active tonestack and widen your range, change tubes, MV location...this amp is not Ford's anymore, is YOURS, this makes you an amp customizer.

I see schematics as shake the dices, the real amp as throw them and the tools inside the axe lets you continue the game: catch the dices, shake and throw them again.
 
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