Are these ancient ideas still considered as truths ?

[Vivek]

This forum is a veritable gold mine of information nuggets !!

Most times, I try to be disciplined and search the forum before making a new post. Then I find almost all the ideas that I have were already discussed, dissected and dispatched 10 or 15 years ago.

In fact, it is an honor that many of those great pioneers who wrote the ancient wisdom are still active and with us on this forum, continuing to share their experiences and showing us the light.

But then I wonder if advancements in technology, changes in outlook, new components have changed the earlier accepted truths.

Question 1: Do these concepts still stand after 10 years of being posted on this forum ?

A) The best number of distortion stages in an multiple gain stage Amp simulator or Distortion pedal is 2.5

B) The filters before and after a distortion stage are more important than the method of creation of the distortion

C) The idea that an FET can fully emulate a Tube is a hoax. Just enjoy FETs for what they are, rather than hanker for them to sound like Tubes.

D) Each FET emulation that you build will sound different. When you adjust the bias for a particular FET, you also change the frequency response of that stage.


Question 2: Which other ancient 1-2 sentence nuggets have you found on this forum ?

[teemuk]

"Tubes introduce even order, solid-state odd order, distortion".

"Hard clipping equals bad tone, soft clipping good".

"Opamp clipping sounds horrible".

"Amp's or circuit's tone is solely explained by the response of tonestack".

"Class-D amps hard clip and always sound poor if overdriven".

"One can hear the difference of 1N4148 vs. 1N4009".

"Tube circuits operating at starved voltage a) don't sound good b) don't have real tube sound c) are featured just for fashion and actually do not operate at all".

"Tubes have specific tone and that applies to everything with tubes. When some device features a tube you immediately will know what it sounds like because: tube".

"Transistors, diodes, FETs, opamps, etc. have particular tone as well. You will immediately know what each will sound like so descriptions such as "diode clipping distortion" will immediately reveal to everyone, without any doubt, how such circuit will sound like".

"Greater circuit complexity means weaker tone, incrementally. Thus i.e. single common cathode gain stage as is sounds better than the complete SLO100 OD channel".

 

[Fancy Lime]

1A) If you add the error margin of personal taste, that sounds about right.

1B) True.

1C) There is no such thing as "Tube Sound" or if there is, no two people seem to agree on what it is. Therefore, it cannot really be emulated by FETs or anything else.

1D) If you use tightly specced of carefully selected FETs, you can get around that problem. Fun for DIY and über-Boutique stuff, not feasible for production line stuff. Questionable if that is ever really "useful".

Teemuk's examples are mostly of the humorous variety.

Andy

[Steben]

Well, there is at least "a" tube sound or my amp wouldn't give signal. 

[Steben]

A simple non feedback class A tube preamp without feedback at high efficiency (high gain) produces LESS distortion than a simple BJT stage at high gain.
Just a pertinent addition in the theme here. Tubes are not distortion monsters, triode stages are actually the most simple amplifiers that produce so little distortion if not pushed.
That's why the fetzer circuit for example needs gain taming feedback, because it is like any transistor too non-linear without it.
But it can be even done somewhat with BJT.

Just as pre and post EQ are crucial in any design, the circuit design itself is crucial instead of tube vs transistor.
Fuzz Faces are a very old example of softclipping transistor circuits without diodes.
Most standard phase inverter feedbacked pushpull amps clip harder on the onset than a Face.

[Fancy Lime]

Well, there is at least "a" tube sound or my amp wouldn't give signal. 

Steben, you know full well what I mean! 

[aron]

Did you save the links to where these things were said? I never knew #1A.
I think maybe 1B might be true for tone, but as I have said repeatedly, the FEEL (to me) is more important than the tone as long as the tone is not horrible.

[Steben]

Did you save the links to where these things were said? I never knew #1A.
I think maybe 1B might be true for tone, but as I have said repeatedly, the FEEL (to me) is more important than the tone as long as the tone is not horrible.

If one has 2 EQ pedals 1B falls into oblivion. What remains is the method of creating distortion.

[Vivek]

Akai G2D with 2 equalisers

[aron]

Is that one EQ for input into clipper and another for output after clipper?

Wow I guess it is.... does anyone have one?
I tried this myself. The concept works, but I still think the feel is just as important.

[ElectricDruid]

The (pedalbuilding) code is more what you'd call guidelines than actual rules...? 

[teemuk]

Considering point C) FET family devices actually do have some characteristics that are comparable to vacuum tubes.

For one, their characteristic curves are very much like characteristic curves of pentode tubes or beam tetrodes. On that note, also generic BJTs feature similar characteristic curves and overall in practice these curves also vary from device to device. Therefore there are differences between one tube and another just as between one FET and another, between FET and BJT, and between FET and tube. Usually portrayed curves are generalisations based on mathematical approximations. But overall we can say FET is not similar to triode in this regard.
..Except for the (obsoleted) VFET. 

Secondly, FET family devices have similar characteristic to vacuum tubes of having a very high, (theoretically infinite), input impedance and being voltage driven devices. The input draws no current and it is voltage change, not current change, that controls current flow between anode and cathode terminals, or respectively drain and source.

Just like from different tubes we find great variance between actual transconductance, bias voltage range and overall operating voltages. And, for instance, we can't really say that 12AX7 or EL34 or 12DV7 are similar devices to each other though common denominator is that they are all "tubes". Even 12AX7 and 12AU7 are very different from one another and operate dissimilarly in the same circuit although - and because of that - it is common to experiment with swapping in one to another.

Overall, I would say that certain FETs can do a great job replacing certain pentodes, in similar circuits and with certain operating limits. However, one will not get such great results when expecting that a FET can replace a 12AX7 in an identical common cathode amp circuit with high B+ neutered down to 9 volts. And yes, drain load trimmer resistor will provide different output impedance and operating point at each setting so forget consistent results between different units. However, we can expect some similarities in operation to occur solely due to similarity in circuit architecture (and this applies to BJTs as well).

[amptramp]

One area where semiconductors cannot match tubes is interelectrode capacitance.  In a tube, these values are small and do not change much with the operating point.  The input capacitance is small and goes up slightly from the off state because the cloud of electrons at the cathode is a little closer to the grid and therefore operating capacitance is higher than when the tube is off, but these capacitances are on the order of a few pF.  The relative permittivity is 1 because this is a vacuum capacitor.

A semiconductor has a much smaller separation between electrodes and a higher relative permittivity so the capacitances are larger but more importantly, they vary with the relative voltage as the carriers move closer or farther from the junction.  Some power MOSFET's have capacitances on the order of 2000 pF and this varies dramatically with voltage.  Bipolar transistors are similar.

Even if you could build a circuit to match the transfer function at all DC points between a tube and transistor stage, the dynamic characteristics would vary dramatically for AC signals and the capacitance change would add even-order harmonics.  Not so bad if that's what you want but certainly not identical to a tube.