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No Two Amps Sound the Same - Fact or Fallacy


Fractal Audio Systems
Fact, but with caveats.

Internet wisdom states that no two amps of the same type sound the same. That is true, but the reasons are far more simple than many would have you believe. Tales abound of esoteric effects such as wire dress, transformer orientation, phase of the moon, etc. And while these do have some effect, it is arguably inconsequential relative to the single biggest source of deviation: tone control tolerance.

I've spent the last ten years modeling tube amps and the number one thing I see is that tone controls are very inconsistent devices. First of all the tolerance of the control is typically 20%. That's plus or minus 20% so 40% total. A 100K pot can be as low as 80K or as high as 120K. This is contrast to the tolerance of a typical passive component which is 5% or less (usually much less IME).

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.

Now you can make the amps sound the same by simply turning down the control on one and/or turning it up on the other.

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.


Fractal Fanatic
Cliff, do you find this all through comparable amps? Some pots are horrendously constructed, and it's amazing they last for decades. But I wondered if you also found transformers, chokes, resistors, capacitors, and such to also vary like that, and if you've found that they affect the overall tone as much as some insinuate. Last but not least, I have been on a recent discovery of how critical to final sound the speaker (or IR) is, and I'd assume there is some variation in the cheap old speakers common to some pretty famous amps. Yet, as you point out, with a little knob twisting a Super sounds like a Super, a Deluxe sounds like a Deluxe, and so on.

Interesting subject!


Power User
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.
Finally... Jimmy Page and The Edge can agree on something... ;)

Thanks for the education Cliff, intriguing indeed. Was this type of challenge with live amps what drove some of your inspiration to create a unique modeler that was more accurate and more consistent? I appreciate all your hard work because I flip a switch, and there it is: tone, consistently. :cool:


please don't bring experience and research into internet arguments. it makes it really difficult for anyone else to win at the internet ;) :)

underlying this excellent information is the explanation to why setting the knobs on your Axe-Fx the same as your real amp of the same model doesn't always produce the same sounds. many of us always suggest set parameters with your ears not your eyes, and this information supports that :)


Power User
Component tolerence variance was the first thing I thought of when somebody posted an AX8 to analog pedal comparison earlier today. People overlook this when comparing guitars too -- pots, pickups, caps all vary.


Yes! Turn the knobs! That's as tech as I like to get, but it works for me!

Someone should calculate the variance or tolerance of people's hearing! Everyone thinks their ears are the best! :eek:


OK got it - sounds reasonable when considering component tolerance variation....now the next question is : Do any two Axe FX units sound exactly the same?


Is a difference like this tweakable with the EQ knobs alone?
It theoretically should be.

Since most pots are "off" in one position and effectively out of the circuit when maxed, if they are wired like a simple rheostat.

So any in between value should be able to be matched; but not in the same knob position.

Let's get it all down to resistance values for the basic tone stack :) Screw 0-10, we want ohms!


Power User
Maybe Cliff can randomize the modeled components in each Axe-FX so no two will sound the same. Plus a real time timer parameter that ages the amp and speakers.
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