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I had a B+ time constant epiphany

Cobrango

Power User
So yesterday I had a B+ time constant epiphany. is there any models in the axe-fx that's using say a B+ time constant of say 100ms? Because 100ms seems to be a magic number for me. I can only describe it as the sounding more pleasant, and it's as if the sound comes after the pickstroke in a nice way. at lower values say 10ms or 20ms (normal values) the sound kind of "gets in the way" of the pick stroke when I'm practicing using a headset and turning the B+ time constant from 10ms or 20ms or whatever, up to 100ms for all my presets really makes everything *feel* a whole lot better.

It's hard to describe, you just have to feel it for yourself. I'll make a more detailed post about this with sound examples when I have more time, because it's also doing small dramatic awesome things to the tone, but for now I just want to spread B+ time constant awareness, hehe. It's seriously doing something dramatic with the feel of the amp, and now I'm hooked. B+ time constant at 100ms for all my presets forever. it makes sense to have all the presets and different amp models I use, feel the same way.

Of course I'm not sure there are things like sag and MV and a whole bunch of stuff that actually affects the B+ time constant even if set to 100ms because "everything is connected", but it just makes total sense to use 100ms for the B+ time constant on everything. I've searched like crazy on the internet and youtube for "B+ time constant" and the only thing worth mentioning is what's here:

http://wiki.fractalaudio.com/axefx2/index.php?title=AMP_block_parameters#B.2B_TIME_CONST

and, yes it's been posted 100 times on the forum it seems, but this video is the only one I can find where someone is talking about B+ time constant and what it's doing, but what this guy says in the video beneath, between 1:18 and 3:30 in this clip, describes exatcly what I mean and feel about the B+ time constant. he also says this "guitar players of all styles, agreed on the same amount of time" - what time in ms do you think he's talking about? I'd love to know. my love for B+ time constant of 100ms is real, that's for sure!


this has got to be one of the most dramatic things I've ever come across when it comes to the feel of an amp ever. What it does is hard to say, but the way it changes the feel and tone also is pretty insane. You just have to "fidaddle" and find out!

I'd love to hear some more input on this subject from Cliff or anyone who knows how to describe what's happening, the wiki just mention the ghost notes and that it feels stiffer when you go lower, but for me the magic lays in the higher values, 100ms :)

as for tone the value of 100ms feels and sounds better for legato because the amp does not "spit" as much and the attack feels as if there's less of a transient when hitting the note, and the note sounds more constant (pun intended) from start to finish. It keeps what you're hearing from the start to the end of the note in the low end for example. at lower values like 10ms or 20ms I feel the low end is more boomy and there's something going on in the treble and mids too. 100ms not only feels the best to me but also sounds the best.

It may be that it acts kind of like a compressor (in a none compressing way) with a slower attack, letting the note just kind of hang there with not so drastic moves. way awesome for legato! I'm insanely excited about this, even though I found out about the 100ms thing back in 2013 (check post #9 : http://forum.fractalaudio.com/threads/vox-ad120vt-tone-match-preparation.67463/#post-832260 ) but I kind of forgot about the whole B+ time constant and I guess with all the firmware updates and everything this even more noticable now.

What say you?
 

FractalAudio

Administrator
Fractal Audio Systems
Moderator
The higher the value the stiffer the power supply. This will result in less compression from the power amp. "Most" guitar players prefer a value around 10ms as it it accentuates the attack without excessive ghosting. It seems as though you prefer less attack so raising the value will accomplish that. Another option is to change the supply type to DC. This will eliminate any ghosting and give you a more "ideal" response. Most modelers use a DC power supply model but I've found that an AC supply model is key to achieving that last few percent of realism. The supply ripple is a big part of why old amps sound the way they do.

Most guitar players actually like a percussive attack so that's why about 10ms has become a de-facto standard.
 

Randalljax

Fractal Fanatic
The higher the value the stiffer the power supply. This will result in less compression from the power amp. "Most" guitar players prefer a value around 10ms as it it accentuates the attack without excessive ghosting. It seems as though you prefer less attack so raising the value will accomplish that. Another option is to change the supply type to DC. This will eliminate any ghosting and give you a more "ideal" response. Most modelers use a DC power supply model but I've found that an AC supply model is key to achieving that last few percent of realism. The supply ripple is a big part of why old amps sound the way they do.

Most guitar players actually like a percussive attack so that's why about 10ms has become a de-facto standard.

So Cliff would this be the same as power supply filtering ,to get the tighter looser response.

Also one other Question the Bogner 100b vs the 20th .

I Remember talking with an amp guru who said the 20th had a higher voltage applied to preamp vs the classic and older XTC that run pretty low 295 volts or something in the preamp to get that chewy ,low mid . is this accurate?

Is there a parameter in the Axe that affects the preamp voltage, can you actually turn it higher /lower

Finally if you were going after the 100b or Classic ,besides changing the power tubes to El34 ,increase SAG a bit what would be your other suggestions recommendations
 

Cobrango

Power User
regarding tone, copy x to y in the amp block, then set the B+ time constant to 1ms vs. 100ms, 10ms vs. 100ms, 30ms vs. 100ms and so on, then A/B the different states with a foot switch or something clicky, so that you don't have to stop playing and can hear the effect without a pause. just strike one note and compare how it rings out, listen to the boomy stuff going on in the lows at lower settings, at 100ms it's just there and sounds less transient in a booming way (hard to describe). I find the mids more focused and pronounced but after some more testing I also notice that less than 100ms would work more for rhythms and riffs where you want the notes to spit more. I think it works well for legato, leads or single notes because I've compared a lot of single notes and 100ms seems to make it more fluid and mellow/round. I guess one could say less attack also make it rounder because attack is kind of high end/treble in a way.

thank you for a great response Cliff!
 
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gammajoe

New Member
I also experimented with the B+ Parameter. On lower settings ( 10ms ) I liked the immediate attack, on higher settings (max. 25 ms) I liked the roomier response, the sound went more complex and organic. I never tried settings in the 100 ms values, so I can't comment on this, but I have to try for sure. I assume , that I'll get a sound which is too spongy for my style but I'll try.
 

nccarg

Inspired
I've been using it more lately but I haven't tried any extreme settings. I seem to like the B+ somewhere in the 20s for playing leads but I don't have a specific number that works for everything.
 

Cobrango

Power User
Are the results of tweaking this setting more noticeable on high gain amps than mid to low gain amps?
Hard to say, because it affects the sag and tone so it depends if you're using a saging clean tone or a transistor high gain amp etc.
In general I would say that it's easier to hear on high gain because if you bend two strings the intermodulation sounds different on different settings, also why I like 100ms.
 

Cobrango

Power User
I've been using it more lately but I haven't tried any extreme settings. I seem to like the B+ somewhere in the 20s for playing leads but I don't have a specific number that works for everything.
you could always use it as a way to make rhythm guitar sound more aggressive on low settings like 10ms and lead sound more fluid on 100ms, but for me I'd like to always have it on 100ms because it's a feel thing and the way you hear the note after you pick it, it's like the note gets a bit behind the pick stroke kind of. you know when you play the electric guitar unplugged you get a better feel of the instrument in a sensory way - you're not using the ears as much so you start noticing how the strings feels in the fingers because you're not just listening to what comes out of the amp (headset in my case). this is kind of why I like it at 100ms. I get a better feel for the instrument, it's as if I can feel the strings in my fingers and the pick letting go of the string, just a fraction before I hear the actual note. at low settings like 10ms I feel that the note I hear coming out of the speakers/headset gets in the way for the feeling of the strings against the fingers and the feel of the pick, it's as if my body is focusing more on the sound and as a result I get less of a feel from the instrument, because I can't focus on everything at once.

It may sound strange, but it's as there is some kind of delay, maybe it's the less pronounced attack of the note, that makes me have a better feel of the strings and the pick as I'm playing. I get more of that unplugged raw guitar feel as I play with the guitar into an amp with the settings at 100ms. The sound does not come in the way of the feelings of the pick leaving the string, it's like I get the physical feeling of the strings first, then I hear the sound after.

I'm not sure if it works that way or if it's even possible to hear that small of a difference because it's not really just a difference between a delay of 10ms or 100ms, but somehow that's exactly how it feels. it's all about the feeling of the instrument.

To me the amp *feels* more "behind", giving room for the feeling of the pick in your fingers and strings without the sound of the speakers/headset getting in the way. the best way I can describe the difference is if you imagine in example one (100ms) you're drinking a sip of hot chocolate, you have all the time you need and you can really get a feel of the smell, the taste, and how sweet it is, then when you're done you put the cup down and 15 seconds later you have to listen to a guitar string being plucked with a pick. you still have all the time you need, so you get to focus on details like sustain, eq, reverb, and if you like it or not. that's how 100ms feels to me.

in example two (10ms) you're also drinking a sip of hot chocolate, only this time exactly when the hot chocolate hits your lips there's a loud noise playing and a red light blinking at the same time making you believe the hot chocolate is way too hot and you don't really get a feel of how sweet it was or anything, all you could think of was the loud noise and red light blinking. actually the loud noise was the same pleasant sound from the guitar string as in example one, but because you were eager to sip the hot chocolate you percieved this as noise, and the whole experience got ruined because you were trying to sense all the things at once.

Of course this can be great for aggressive rhythm guitars but for fluid legato and single note stuff, I like the feel of 100ms way better. And that's what I do the most so for me I'd love to have the same feel for every amp, then I can adjust other parameters to make up for it.
 

muudrock

Experienced
This is a great "trick" and I have been setting the B+ to about 30 ms on several live patches for a while now.. Not so much on recording versions of those patches. Like Cobrango, I like what it does to the feel and the overall response and tone. I love how deep you can go in this box!
 

Stratoblaster

Fractal Fanatic
From this thread (would make for a good Tech Note):

http://forum.fractalaudio.com/threads/b-time-constant.46615/

It's both attack and release. B+ Time Constant is the time constant associated with the Supply Sag parameter. The power tubes draw current from the supply. The supply has a finite resistance. As the power tubes draw more current the supply voltage droops. The rate of change of the droop and recovery is dictated by the supply capacitance. The product of the resistance and capacitance is the time constant. It's typically around 10 ms. You can vary this using the B+ Time Constant parameter.

It is not a simply compression though. As the supply sags, the headroom is reduced but many other things happen. One thing that happens is that the screen voltage droops. The screen voltage is derived from the B+. However the screen has it's own dynamic response, which is often 2nd-order since there is often a filter choke. If you listen carefully to the models with a filter choke you can hear the screen voltage "bounce" when you hit a power chord. The damping of the screen filter is not exposed to the user. When the screen voltage droops, the power tube gain decreases. It effectively shifts the bias point.

There is quiescent draw from the supply as well. As you increase the bias (Power Tube Bias) the quiescent draw increases which decreases available headroom.

The Axe-Fx II does not model all this stuff with compressors, like other products do. It actually uses a differential equation for the supply and the current from the power tubes. It then solves the equation at each sample instant to find the supply voltage and screen voltage.
 

carlguit

Member
Just tried it… Really cool!! Especially good on patches where lots of FX are involved. i.e. delays. It seems like it's cleaner and the you don't get drown by the Fx. Though I do found that with ''extreme'' settings like the 100ms suggested above, it removes too much compression for my taste. It's all very subjective and I can see why some people like it better like that. I'm sure many fusion players will like those kind of settings. As said earlier, it's a bit hard to describe but if I had to use a cliché, i'd say it makes things more Hi-fi. After messing around for a few hours now and playing some backing tracks with it, i'd say that increasing it to 12-20 ms ( yes even only to 12 ) makes a noticeable difference and it makes a nice tone shaping tool to find the balance between compression and clarity.
 
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