True Class A Amplifiers

Joker said:
Based on the postings of Smilzo, this seems like a prime opportunity for a truly digital amp model, one that transcends the physical realm. I'm thinking of a 100W true Class A amplifier, not limited by huge and costly physical transformers, failing extra hot biased tubes and exorbitant electricity bills. From what I've read so far, anything Class A above 10W output power gets a bit tricky and very costly in the real world, but since the Axe FX is not constricted to the real world, we could maybe play the first "impossible", yet real sounding Class A amp.

I recognize that Cliff has probably done these "impossible" mods to create the idealized FAS Crunch, Lead etc. models. I wonder if the currently available, idealized FAS Class A amp model can be manipulated enough through the advanced settings to always remain in Class A mode, no matter how hard it's driven...
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We can already (in Fractal's) set bias so high that tube conduct always (class A) for push pull amps with lots of authenticty. For SE amps there could be some difference, I guess, because of interleaving/insulation of OT. I don't know how to make a PP OT sound like a SE OT.

So if you want PP class A to the max, rise bias up to the melting point! If you want a SE class A... I suggest try 5F1 amp, change power tubes/bias to taste. One of the best amp I have ever played is the Peters JP10, a SLO-100 like preamp into a 10 watt SE poweramp. Touch sensitive, lots of gain, vintage vibes with modern feel. Damn, how I wish @FractalAudio FAS take!!!!
 
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When I think class A amplification… This comes to mind always… I hand-carried this up to CES in the late 1970s to a hi-fi vendor suite. Ended up at my parents home for the next 45 years.
 
Ok, so everyone says "Class A is touch sensitive" and all, but this is I see in Wiki. Please help me understand this:

The Axe-Fx is immune to tube wear so there is no danger in running the bias hot if you like that sound. However the hotter the bias the less dynamic the response becomes. Also some people like a bit of crossover distortion. Legend has it that EVH liked his amps biased cold. Whether that was because of the added dynamics or the extra grit due to crossover distortion is unknown.
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So... actually "cold" AB is more dynamic - means touch responsive - or what?
Or do I misunderstand this and both terms are actually different?
 
Chromatizm said:
Ok, so everyone says "Class A is touch sensitive" and all, but this is I see in Wiki. Please help me understand this:


So... actually "cold" AB is more dynamic - means touch responsive - or what?
Or do I misunderstand this and both terms are actually different?
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I think different terminology. Dinamics should be about the range between lowest to highest volume level. Touch sensitive should be how the frequency shift with the pick strenght or guitar volume. The more you dig in, the more the amp "compress/distort...", the less "dynamic" you have. Class A (Vox, to name one...) is resistante cathode bias. The shift in bias as the signal increase give distortion, hence "touch sensitive". VH need more distortion, so he cold biases the amp, even reduce voltage to reach tubes voltage saturation and distort more... ;)
 
Jonathan Thomas said:
Laney Lionheart L50H with its 5x EL34 power tubes is probably the king of Pure Single ended Class A amplifiers, IMO. Let's get one in the Fractal library! :)
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I had the 20 watt version. Hated to had to let it go. Also a great looking amp.
 
Tonedeaf said:
I had the 20 watt version. Hated to had to let it go. Also a great looking amp.
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Me too. I've had pretty much every version except the 50 watt. Mainly due to what someone alluded to above...cost of tubes and upkeep alone!!! The 20w was my favourite and the 5w was a cool little thing to have around! I'd love any of them in the Fractal, tbh!
 
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