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Quantum 2.00 Tips Part 1

FractalAudio

Administrator
Fractal Audio Systems
Moderator
Power Supply:

The new power supply modeling is a significant improvement over previous versions. The power supply sag is now incredibly realistic and far superior to the "expander/compressor" techniques used in other products. Learning to adjust the pertinent parameters can make a good tone great.

Supply Sag is the most fundamental of the power supply controls. It controls the virtual resistance of the AC input. In a real tube amp the supply sags due to a combination of power transformer resistance and rectifier resistance. Increasing Supply Sag increases this resistance and vice-versa. The higher the resistance the more the supply sags and the more bouncy and spongey the amp will feel. I like to increase Supply Sag a bit and reduce gain. You can monitor the virtual supply on the hardware by selecting the Supply Sag parameter. The gain reduction meter will display the supply voltage in dB relative to idle.

Tube Bias controls the idle current of the virtual power tubes. The models, in general, are biased on the hot side because that's how most people like their amps. Reduce Tube Bias to simulate a colder bias. It is rumored that EVH liked his amps biased cold. When the bias is reduced the amp sags and bounces more and the bass will be a little tighter and the tone edgier.

B+ Time Constant controls the capacitance of the virtual power supply. The more capacitance the "slower" the supply and vice-versa. Most guitar players like a fast supply but too fast will cause excessive AC ripple and create ghost notes (although I think a little ghost note is cool). When the supply is fast it will sag rapidly accentuating the pick attack and compressing after. This parameter works in conjunction with Supply Sag parameter. The time constant remains constant so if you increase Supply Sag the virtual capacitance decreases.

Cathode Bias controls the virtual resistance for "cathode bias" amps, i.e. AC-30. In these amps the grid bias is held at ground (ignoring bias excursion) and a resistor is inserted between the cathode and ground which self-biases the power tubes. These amps are typically marketed as "Class A" but in reality they are not truly Class A but rather a hot Class AB. The cathode biasing keeps the tubes in the safe operating area (SOA). A Cathode Bias value of 50% represents full Class A operation. Both tubes will be on over the full input signal range. Values less than 50% are actually beyond Class A. Why would you want to go beyond full Class A? Bias shifts always push an amp towards Class B operation so if you bias beyond full Class A you will get pushed back into Class A operation when you actually play. Typical "Class A" amps, as stated earlier, aren't really Class A. The default Cathode Bias values reflect this and are usually around 70%. Decreasing Cathode Bias will give a rounder, softer tone. Increasing it will give a bouncier and edgier tone. You can adjust the time constant of the cathode bias network as well, if desired.
 
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Tsunamijuan

Inspired
Thanks cliff this is super helpful. I been enjoying messing with this.

Btw is there a chance we are gonna get a gain reduction meter in AXE-Edit, that corresponds with this? Similar to being able to view the Envelope and ADSR graphs.
 

Carl

Inspired
Yes thanks, great to have a concise explanation of what these controls do and how they interact.
Much appreciated!
 

edo

Power User
Does "tube bias" refer to preamp of power amp tube bias? If I remember correctly there are parameters for each
 

jjozwia

Power User
Thank you! Exactly what looking for, I've been pretty stale in my tones recently and finally have a little time to tinker. Know some of this has been mentioned in past and captured on wiki but had no idea what to search for so appreciate having a go to to help me along.

Cheers
 

Jimmytwotimes

Experienced
yes - this is great information ! Many times I wonder what certain "knobs" do and don't do, and how it effects the tone. Sometimes a specific combination of "knobs" is what makes the tone sing. I agree with a previous poster, it would be great to have a thread dedicated to tips like these. Maybe once a month go through a page in the amp ( or cab, or effect) block and give tips like this on each knob. This is very helpful to understand in layman terms what these controls do. Much appreciated Cliff.
 

jesussaddle

Power User
Helpful info! Thanks for reminding me about the gain reduction meter. I am blown away that you understand the electrical operations at the same time as the fx on sound.
 

Pinkycramps

Experienced
Uh... ... ... ... What?

No... really though. What if we had a breakdown like that for every control in the amp settings, and then a description of how one affects the others? For me THAT would me more game changing than anything. The Axe is so powerful that the real frontier is in learning how to harness that power.

Then... some working scenarios of how to take a tone from "this to that" by using the controls. Finally, tutorials on how to dial in various kinds of tones. I smell an opportunity for someone to open a real can of whoopass how to... That info on power supplies is just awesome.
 

electronpirate

Moderator
Moderator
What if we had a breakdown like that for every control in the amp settings, and then a description of how one affects the others? For me THAT would me more game changing than anything. The Axe is so powerful that the real frontier is in learning how to harness that power.

Then... some working scenarios of how to take a tone from "this to that" by using the controls. Finally, tutorials on how to dial in various kinds of tones. I smell an opportunity for someone to open a real can of whoopass how to...
I smell Chris doing this right now...it's like a mango Margarita under your nose...and just as cool.
 

Brownmatthall

Power User
Uh... ... ... ... What?

No... really though. What if we had a breakdown like that for every control in the amp settings, and then a description of how one affects the others? For me THAT would me more game changing than anything. The Axe is so powerful that the real frontier is in learning how to harness that power.

Then... some working scenarios of how to take a tone from "this to that" by using the controls. Finally, tutorials on how to dial in various kinds of tones. I smell an opportunity for someone to open a real can of whoopass how to... That info on power supplies is just awesome.
http://forum.fractalaudio.com/forums/tech-notes.77/
 

manu68

Inspired
Power Supply:



Cathode Bias controls the virtual resistance for "cathode bias" amps, i.e. AC-30. In these amps the grid bias is held at ground (ignoring bias excursion) and a resistor is inserted between the cathode and ground which self-biases the power tubes. .
Hi,
Why Bias excursion Default is set at 52% for AC30 TB model in Quantum 2.0
Should it not be set at 0% then ?

Cathode Bias is the Cathode squish parameter in Axe edit 3.5.0 ?

Thanks !!
(great information ;) )
 
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