Some people say that what REALLY matters for the tube amp's unique tone is the distortion that occurs in the power tubes. Is it true?

I think so.

Each tube has it's own sound when it clips and while some 12AX7s sound pretty good when they clip, they just can't hold a candle to a 6L6, or EL34, or EL84 when those clip.

If you look at an analysis of a TrainWreck amp (widely reputed for awesome distortion.... true gain monsters), the great tone is supposed to come from the power tubes clipping first, followed by the phase inverter, followed by the 3rd stage of the preamp.

I'm jaded, but from buying about 70 12A_7 tubes from different makers and testing them all out, I noticed that the larger the plate structure, the better the clipping tone.... at least to my ears.

Take care,
-Peter

Andy Marshall at THD told me once that the power tranny and tubes are the most important tone wise for overdrive/distortion.

Hi Bluesgeetar

Did you mean *output* tranny, or did Andy really say *power* tranny?

I must admit, I can understand how under-rated and over-rated power supplies will dramatically change how a power amp overdrives, and even more how it recovers from overdrive as notes sustain.  But I would have expected a more noticeable difference from solid-sate rectifier vs tube rectifier if he was talking about how power supplies affect tone.

rgds,
GM Arts

So, with all this in mind, why can't we build a fet emulation of a complete tube amplifier, preamp and power?

Peace!
Arn C.

Ah, I wasn't after fet emulation in particular. But runoffgroove probably will anyway.

I guess I have to build myself a little amp like Marshall 18watt and play with it for some time, listen to EL84's overdrive.

All my amps now have 6L6s, so you can imagine, what volumes I have to be at in order to hear them distort...  :twisted:

This brings up another awesome option....

How about blending the preamps?  :twisted:

Take care,
-Peter

AAAAAAAAAAAAAAAAAA!!!
Don't let the runoffgroove team hear you!!!
We will drain the Earth's supply of J-fets before we know it!!!

Constantin, also check out ax84.com if you haven't already.

Power Transformer's in general term's only supply the voltages needed to operate the amplifier,
But when you Crank my Old Plexi or my Tweed Bassman there is a certian Grind that the power transformer exhibit's when pushed over the hill, without this I don't think I would care as much for the Plexi, not all amp's do this so I think that's why a lot of people skip the P/T when talking in term's of tone.
JD

Personally, i reckon you can get desirable sounds with both. I wouldnt say ones better than the other, theyre just different. For instance, with my Ampeg J-12t, if i push the power valves, i get a crunchy distortion, but if i hammer the front end with a treble booster, i get smooth overdrive. Its all a matter of personal taste...

Hey GM arts!  No he said power tranny.  Kind of stumped me too.  He did go into it about how most people think otherwise but he insisted that the main tone for overdrive and all comes from the power section.

Just for a future reference for ya, he also said that the most favorite of all the combo amps to tinker with is the Peavey classic 20.  He was saying more great tone can be gotten in that Peavey with modding than any other combo he knows of (for vintage type tones).  He was saying he has modded a many for friends and clients.

I remember at that time I was calling him to ask him about Supros and Tweed fenders and modding my Fender twin reverb to have different tones switch box ss rectifier.  Super nice guy!  The man surely knows his stuff.

Quote from: Constantin Necrasov... Is it true?

No not really ... it's a balance of both ...

You can set the headroom characteristics of a tube-based guitar preamp by playing with the series resistance in the power supply feed - there's typically two stages of resistance in vintage-era designs ... I've got info on this on my MarshallAmps page  to make older Marshall amps cleaner in the preamp ... compare these two resistance values in the 2-channel reverb Fender amps that run on 6L6's and see which ones are low and which ones are high, in the cleaner amps (Twin) they're low, in dirtier ones (Showman) they're higher - and a lot higher in the classic Marshall designs (40k-Ohm typically) ... even though the signal cap feeding the phase driver is smaller in the Showman (500pF) and passes less signal to the output stage the overall sound is gnarlier ... more preamp distortion there ...

You can set the headroom characterstics of a tube output stage by playing with the feedback ratio (if present) ... not so much by adjusting the feedback resistor but by altering the resistor in the phase-driver leg that voltage-devides with the feedback resistor - I like to "half" it ... this does two things, it increases overall gain of the combined phase-driver and power tube stage output pair, but more so presents a proportionately greater signal level in front of the power tubes per volt of input signal ... basically the dynamics are more lively and harmonics richer ...

If you combine both steps in a Medium gain guitar amp like in a Tweed Bassman or BF topology you can get a considerable increase in sexy warmth because the preamp distorts later in relation to the power stage ... but it would be untrue to state that it's all pentode distortion at that point, the preamp and phase-driver will only distort less relatively speaking ... Triode clipping tends to sound cold and raspy whereas the interaction of the power tubes, transformer and speakers produce a warmer sound (provided the speakers are not underpowered and clipping like nuts) ... it would be untrue to state that you can remove all instances of triodicity in a tube amp, all you can do is tip the balance somewhat - which is immediately apparent ...

Part of the reason why you can't simulate this using other means is because of the very complex synergistic relationship that exists between power tubes, tranny and speakers ... there's a tendency to overlook this and only mention the power tubes, it's not that simple ... in fact the most overlooked aspect is the speakers themselves ... stick Greenbacks in an AC30 and it doens't sound like the famous VOX sound anymore, most of that sound comes from the Bulldogs, conversely stick a Bulldog in an 80's high-gain Princeton and it sounds very VOXish ... lots of people claim the AC30 sounds the way it does because the output stage is class-A push-pull, this is in large part untrue - it's still a class-AB stage but with a wider class-A range (when the power stage is clipping it is running in class-B by definition) - the clipping transition is more spread out and gradual then in the class-AB stage of a Fender or Marshall (it's harder to tell in the later because of the higher preamp distortion index) ... of course the circuit topology in an AC30 does add some signature tone, but the Tranny and Speakers specs tend to dominate the distortion picture in that amp ... another extreme example of TRANNY tone would be some of the Garnet tubes amp with their starved-core OT's - but that's a discussion for another time ...

Personally I think this FET emulation business is a bit of a dead end for players who don't play to an A/D converter ... I've noticed from soundclips and from building a few that these circuits tend to sound the same  - granted Doug's Meteor still sounds unique to me (it can be finnicky in front of a blaring amp - maybe the filter stage at the end of these circuits needs to be buffered for more uniform response) ... I suspect that a loss of character can happen when cascadeding too many FET stages, fewer seems better to me - not surprising, the same thing happens in tube distortion chains ...

btw, careful with those small Peavey Classsics - they have serious reliability problems over time ... I'd replace the power resistors with higher wattage ones and be careful with bending those leads between the folded boards, and especially tightening the boards in the end - there's a risk that if the nuts securing the board to the chassis sets the pcb the wrong way initially the boards will flex slightly from heat and cause those thin traces to break open ... what a pain $%$%!#@!$# ...

well, bye bye ... :wink:

Hey Eb7+9, That's a FANTASTIC post!

Take care,
-Peter

Very interesting.

So if the Jfet immulation is covering the pre-amp part, how should we go about simulating the power amp, speaker, etc. interactions contribution to the overall sound?

I think Doug used a Black Fire stage at the end of the Meteor didn't he?

Much ado about nothing, IMO...

People try to isolate "tube amp sound" down to a few characteristics: "It's preamp distortion", "It's power amp distortion", "It's the output transformer", "It's a saggy power supply", etc, etc....

It's actually a big soup of a lot of different factors all interacting with each other synergistically.  And it all depends on what kind of amp you are talking about, what kind of a sound you are interested in. FWIW, 5150's, Mesa Triple Rec's, SLO's and other "ultra gain" type amps are pretty much preamp distorters. In that particular case "the tone" (the distortion part of the tone, that is) is pretty much due to preamp distortion.

These FET circuits are fun but IMO the thing to work on next is some sort of "voicing" control. The biggest problem I see with pedals right now is how finicky and  dependent they are on what amp or amp setting they are used with. Come up with a control that allows your pedal to work with a multitude of differently voiced amps. When you have a pedal that sounds the same, or just as good with a silverface twin as it does with a marshall 1987 or 1959, then you'll really have something.

Doug

Quotesounds the same, or just as good with a silverface twin as it does with a marshall 1987 or 1959,

The issue of voicing is a little tricky.  The amp and speaker EQ varies,  different amps sound different even before you put a pedal into the picture.  Adding a pedal just adds another variable to the equation.

A big problem with a pedal is you want to set the amp for clean then when the pedal kicks in it sounds good for distortion.  I know you personally don't use this method but it is a common set-up.  The variation in how people set-up there amp clean introduces yet another variable.

Across the board the high end varies a lot and that's why the old tone control is so successful  balancing the sound on different set-ups.  The next useful control is the lows.  All we can hope for is that the controls cover enough of the map for common set-ups.

The speaker influence on the sound of a tube amp is a very complex equation, the easiest way I think has been found to produce this so far is:
 1. With a Tube amp driving a speaker
 2. With a digital tube emulation
 3. Analog devices
 In some order, in my book #1 is the best way.
 The speaker, as it moves/and is moved by the amp, influences the ohmage swing/amp load as the kinetic energy/brake force/suspension/cabinet etc. increasing and decreasing load on the amps output section in varying amouts regarding pitch/frequency...wide changes in load/transient peaks etc. as the speaker moves in then out.
 That kind of complex reactivity is a hard thing to mimic electronically, especially when you have to use an amp and speaker for the device to function, which of course has it's own ... stuff' going all in out and over it.
 Say...your'e running a tube emulator into a Clean as can be SS/speaker setup. If the emulation is perfectly representing the emulation of reactivitly between tube and speaker, then the altered signal that comes out will sound different, [IMO ALL amps 'sound' a certain way, I suppose a digital reproduction system could be very close or close enough as could a SS amp/speaker setup]
 Or...if you're running into a tube amp, your'e likely to get AloT of change in tone character...
 Tube Emulators seeem to have become widely accepted, with at least two diverse groups of beliefs...that's another matter, they can sound very good, super wide usable vairiability with initial purchase...not everybody needs an amp to do 'this', I've never heard  a T.E. amp that really did 'that' that I know of, I could have missed the nail entirely, this is just my view at this point...well it's been that way for a long time...maybe I just whatever...or set in my ways...
   What I need is what sounds good through a MkII 50w Plexi re-issue, great sounding amp, if a bit picky...definitely more picky than my cleaner type amps.
 I haven't done an FET amp sim yet, can't decide which one to try for with the MkII [stage amp]. I love the clip sounds of the English Channel and the Matchbox, and the Supreaux, and the Fender one etc. they all sound real good!!!
 Meanwhile the BSIAB sounds good with the transistors, [a J201 or two shy of being a BSIAB...Mpf 102 and 2N7000 sub] sounds PDG...it too is in the prelim stages
 Perhaps there's a device that is very speaker like, and has inertial/loading properties that could be attached to a small signal circuits output....imparting subtle transient loads like a speaker does to a tube amps output section...lol... :idea:  :?:

My 2¢ worth...

Bluesgeetar, Yes/No/Maybe, dunno.

If we're talking "pure" tube sound, then oh yeah, the power amp has a considerable contribution to make ...but... many of the most popular guitar "overdrive" sounds we like (and seek) are in fact NOT pure tube sounds at all.

Just to mention a few classics (and sorry if I left out anyones favorite) but take Jimi Hendrix for instance, though he played through Marshalls, he used solid state preamp devices (Wah, Fuzz Face, Univibe, Axis) before the tube Marshall for everything but the "clean" sound. Jimmy Page though he played through Marshalls also used solid state preamp devices a Vox Wah, Tonebender, and often an echoplex. SRV as we all know used the ever popular TS808 among other pedals, and David Gilmore ...well lets not even go there!.

Hendrix, Trower, E C, SRV, R. Bachman, S. Stevens, R Rhoads, S. Vai, Satch, the list goes on, and on, and on, and on. Most all of the best "tone" kings used some sort of solid state device(s) prior to the tube amp they played through (and yes of course used post processing too) with the possible exception of Richie Blackmore, but then the Deep Purple sound is more attiributable to Jon Lord's Keyboard/Leslie's skills than Blackmore's Marshall Majors.

Just food for thought (or debate, as it were) but it begs the question... is the "tube overdrive" sound actually created from tubes (only)? is it possible we are in denial about the "tube overdrive" sound?

QuoteThe speaker, as it moves/and is moved by the amp, influences the ohmage swing/amp load as the kinetic energy/brake force/suspension/cabinet etc

I've seen that quoted before, believe it or not that part of the speaker is fairly easy to emulate (at least at lower levels).  A slighlty harder part to emulate is the losses on the speaker's pole-piece.  The tube output impedance under overdrive seems to be the hardest thing to emulate.