Tubes vs Solid State - the real difference


I ran across this on The Fender Forum submitted by Algernon and it certainly clarifies many of the misconceptions I have heard. I was halfway there in understanding the electronic side but this reprint from Electronic Engineering Times got my head straightened out, I think...... :rolleyes:

Either way it's a good informative read:


Hammer on......Blair

John Phillips

Very good stuff - pretty much all of that is true AFAIK. But it's not the whole truth - he didn't mention output transformers! I can't quite believe that. IMO (and in some practical research I did a long time ago) the OT is the single most important difference between tube and SS amps. Not the majority probably, but a very substantial minority.

Take a SS amp and run it through a transformer before the speaker and you can make it sound quite tube-like. The reason is simple (and he does touch on this in the bit about harmonics) - a transformer cannot accurately reproduce a square wave, since it can correctly respond to neither an infinitely steep transient (because of its inductance) or DC (because it requires a changing current to work); and a pure square wave consists of both. Feed one (or even a hard-clipped wave that is not purely square) through a transfomer and what comes out is softened and more triangular - and does contain more of a mix of odd and even harmonics than the original.

The OT also substantially lowers the damping factor, which exaggerates the back-response to the speaker (which he does mention partly). This also helps to explain the one bit where I think he's slightly wrong - an un-clipped tube amp still does not sound the same as an unclipped SS one, so it's not just down to the response to clipping.

I've said this before but I am by no means a 'tube purist' - I believe that if someone was to design a SS amp using the right circuit characteristics of tube amps, it would sound good (although not necessarily 'the same'). But it would cost as much as a tube amp too, so we're still waiting.

Tag will find the comment about players who use a wall of tube amps driven from a little solid-state overdrive pedal amusing... ;)


Silver Supporting Member
Yes, all that engineering gobbly-gook makes sense but let me ask all of you this question: When you A/B a good tube & a good ss amp at gigging volume, but pre distortion, do the amps "feel" different to you? I have played some very good sounding ss amps, but they typically "feel" too tight & sound somewhat sterile to me....or is this something that's pre-programmed into my tube brain?

I believe they have pretty much broken the tube tone barrier but I have yet to play a ss guitar amp that "felt" quite right to me. As unquiet stated though, could it be mainly due to the output transformer?


A Tribe of One
Staff member
Originally posted by unquiet
Very good stuff - pretty much all of that is true AFAIK. But it's not the whole truth - he didn't mention output transformers!
This article was mentioned in a post farther down that thread. I found it to be a bit more informative and it goes on quite a bit about OTs.


Uneven periodtime is a function of the input caractheristics of a typical triod and it's easily shown that the timeconstant of the cathodedecouppler comes into play regardiong classic sound - actually in the textbook of the Electronic Circuits for Beginners of 1976. Dutycycledistortion has been argued as the primary source to the distortion guitarist like. Observing the waveforms around a typically biased preampstage,this effect is clearly seen as the controlgrid takes on a rectifieraction. The relative strengh of the overtones can then be set by approprite selection of anodeload. Soundwise this means the lower the load the harsher distortion as shown by the works by Hiraga and zur Linde. At full overload a push pullstage, such as a poweramp will show an even pattern. Regardless of ampclass chosen the halves will never interfold giving rise to yet another distortion mechanism among the seven. In the case of the DC couppled cathodefollower a knee in different direction is created and forces a a little more symmetrical behavior. Preequalization to distortion
generator will force anomalies onto response.
For instance raised bass will produce overtones rivalling the upper frequencies, which is why most overdrivecircuits have some portion of bass cutoff
at a rate apppropriate to ensure a clear response
but still allow bottom.
Amplifierdesign very much comes down to, IMHO, the composition of trebleresponse and amount of distortion.

Now for the difference between solid state and tubes, it can be made minuscle in that were it only
uneven periodtime, that can be done, but one might also invetigate the logarythmic behavior versus the quandrantic behaviour of distortiondevelopment
as in transitors versus tubes. This really explains what kind of distortionproducts can be expected,
albeit that is not to say that a solid state device could not come scaringly close to what one might define as a typical tube sound.
As in any computation one can not isolate one function and still see whole picture, but must make all aspects equal for comparision. Therefore a tube amp of sorts may have a feel unrivaled but that distortion generation may be relied upon semiconductor devices at just right results given
if due care is taken in ensuring that faul sounds do not result from what being the norm.

I do profess to say that time can only tell that
would there be distortion making tubeamps obselete.

It has perhaps come to a point where a solid state device in conjunction with the soft distortion and in particurlar the compression of a tubeamp might be the answer to many a player, but there would be other players in want of less compression and very fast action for their expression.
The real difference has been at question since the advent of solidstate and miles of information on the subject has been written..

Something is hinted in the works of Hiraga as to
the difference in 10% distortion versus 10% distortion, in that the relative amplitude of the overtones is the vital quantaty, this in turn is set by dynamicload per individual stage, the composition of which amounts to something differently than the induvidual
If anyone with definate answers would come fourth
singing the gospel of god tone, but alas, it is all an approximation much in the way stipulated as to the contents of the Sun - there can only be models to describe what's reality.

Just a mere thought
I'll be the mad one

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