Preamp Bias ... Yes!

VegaBaby

VegaBaby

Fractal Fanatic
not sure if many of you have explorered the recently added Preamp Bias parameter. some people complain that there are too many parameters in the Advanced menu to tweak, I'm always curious what new ones do and Preamp Bias is just fantastic !

you can entirely change the amp's drive character, make it "rounder" or more "broken" sounding to the point of a sputtery gated bias disaster. really like its versatility ! it's kind of what I was always looking for in the Power Tube Bias parameter, and as much as this goes in the right direction for modding, Preamp Bias does exactly what I like to hear. absolutely love it ! that's all.
 
So, you're saying it can take the preamp's drive characteristics anywhere between gritty to smooth and back?
 
Man I keep forgetting about that one. I will have to check it out. Sounds like a powerful knob. FUN
 
Am I missing this in Axe-Edit, or is it there? I see it on the front panel in the advanced section. Does it have another name in Axe-Edit?

I'm running 1.0.317
 
Mott said:
Am I missing this in Axe-Edit, or is it there? I see it on the front panel in the advanced section. Does it have another name in Axe-Edit?

I'm running 1.0.317
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no, not in there. you have to use the frontpanel for now.
 
guitarzpt said:
Is the famous 5150 bias mod done in the preamp or the poweramp tubes?
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Power amp.

The 5150s came from the factory with very cold power tube bias allowing for a healthy dose of crossover distortion in the final tone (it's also a big part of why the 5150 sounds like it does stock). Once the bias mod is done, you can adjust the bias to any level you wish hot or cold. This does however change the way the amp sounds and behaves. You can try taking the 5150 amp model (6160?) and tweak the power tube bias control to get a similar effect. Warmer bias tends to sound rounded, colder bias tends to sound crisper. Tweak and enjoy!
 
VegaBaby said:
not sure if many of you have explorered the recently added Preamp Bias parameter. some people complain that there are too many parameters in the Advanced menu to tweak, I'm always curious what new ones do and Preamp Bias is just fantastic !

you can entirely change the amp's drive character, make it "rounder" or more "broken" sounding to the point of a sputtery gated bias disaster. really like its versatility ! it's kind of what I was always looking for in the Power Tube Bias parameter, and as much as this goes in the right direction for modding, Preamp Bias does exactly what I like to hear. absolutely love it ! that's all.
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Yes! Essentially what Cliff has done is given us control over the last Triode stages Cathode resistor, allowing us to control the bias of that stage.

This parameter, called PREAMP BIAS, sets the bias point of the last triode (cathode follower not counted). Depending on the bias points of the previous stages increasing or decreasing this value can alter both the harmonic content and the attack characteristics. Typically, if the previous stage has a negative bias then increasing this value will be more noticeable and vice-versa. This value is set to a default value for the model whenever the type is changed but can be overridden by the user.
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Warmer bias largely equals fatter warmer sounds, colder bias equals more odd order harmonics and a grindier sound to the point of tube cut-off where you get that wicked crackling sound.
 
I had asked about the preamp bias in THIS thread, but I only found out about the acronym OT.
In all fairness, you have to understand the real workings of an amp to "get it". That is a bit of information Ive not yet conquered. Im sure it would be a lot easier to see and hear it, than to read about it.
Im not saying using your ears wont get you what you want, but if you have no idea how to translate the sound in your head to the real life amp mods and parts, then it will take significantly more time.
Im going to read and watch what ever I can. Tired of not understanding the inner workings of amps.
Just my 2 cents.
 
I was just "friggin'" with this today for a bit and I must say, very cool parameter. I'll have to spend some more time with it. I can see it being a definite asset.
 
EdgE said:
Huh,gotta check this out ,didn't even know it was there :D
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yeah... reading the release notes can sometimes help ;).

I seriously wonder how many users by now have found the newly added "null" clip type in the Drive block ? that one's not even mentioned in the release notes ;)
 
I've been allllll about that control. You can realllly shape the character of the amp to your specific application with it!
 
shasha said:
I would not be in the group of having discovered it. ;)
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I discovered this by accident the other day while I was messing around with a few pedals in the drive block. But as with some of the firmware updates, I found some little surprises from Cliff not mentioned in the release notes. ex. added tonestacks in the ad. param. pg.

... leaves me feeling like, your kid cleaning up after themselves without being told... just a very pleasant surprise! :D
 
Very interesting. This should be in the axe-edit page. Between this and lowering the trim level a little, a sweeter sound comes from raising the bias. In the case of my FAS6160 patch, I raised the bias to 200. 300 made the tone a little dull.
 
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