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Papery buzz under some models?

Tommy Tempest

Experienced
I’ll have a look at my meters. I didn’t see that when I was creating it, but I’ll double check. Thanks for looking!
The paper buzz is usually clipping. I experienced that when I first tried to balance my preset. I kept turning up the level on my clean preset to get it equal to my others. Ended up doing the opposite and turned down all the other presets.
 

chucma

Power User
@greiswig, I have a Strat that when you play through certain presets/amps there is no buzz (sounds perfect), but then in my clean, treble boosted presets the buzz is very noticeable. However if I play my Tele through that same preset it is perfectly fine (and also fine with all my other guitars except my Strat).

The solution was to recheck/adjust the action on my Strat even though I thought it was perfectly fine before. Sometimes your ears cannot hear the very slight buzz that is coming from somewhere on the guitar, but the amps can.

Do you have access to another guitar to try the same preset? Just for the elimination of fret buzz?

The reason why I am suggesting this even though you have already said your guitar is fine, is because the sound you are getting is exactly like what I had.
 

phil92

Inspired
Alternatively just always play with a drummer; I’m pretty sure there’s not going to be any papery buzz to bother you anymore
 

Perdikament

Power User
Okay, here is a simplified version of it. I am still hearing the same buzz on Scene 1, but not on Scene 8.
Ok just played with this, thanks for updated patch btw, makes it so much easier. Scene 1 is still a tad hot but it’s not pegged like before. There are a lot of lows especially on the neck p/u. I hear exactly what you are talking about & have heard it myself many times. I believe it’s just the very beginning of the amp breaking up. It is annoying & enough to drive ya nuts. A few solutions I have found are: if you’re aim is a clean tone, lower the Input Trim all the way and make up the volume with the Level Control. Take a little of the Lows out pre the amp, either with a Filter Block or the Low Cut with the amp block. (Depends if ya want to stay Authentic or not, & touch those Bass & Mids on this amp?) but I think perhaps that’s where that bit of extra power is coming from that’s causing that little clip, in the low end.
I didn’t try it, but perhaps just lowering the master vol might kill it as well.
 

DLC86

Power User
Alternatively just always play with a drummer; I’m pretty sure there’s not going to be any papery buzz to bother you anymore
There will be one more actually, his snare vibrating sympathetically with the guitar ;)
 

yek

Moderator
Moderator
Okay, here is a simplified version of it. I am still hearing the same buzz on Scene 1, but not on Scene 8.
Hearing no buzz at all.

As being said already, the preset level is still a bit hot. Just watch the VU meters in Layout > Zoom. Instead of Cab Level, use Amp Level to set the preset level.
 

guitarnerdswe

Power User
I can kinda hear what OP is talking about, but it's just how certain amps sound to my ears. Like some Marshalls and Voxs have a kind of raspy or crackling quality to them when the note fades out.
 

Mohi

Inspired
Hearing no buzz at all.

As being said already, the preset level is still a bit hot. Just watch the VU meters in Layout > Zoom. Instead of Cab Level, use Amp Level to set the preset level.
That was a great advice .... is it recommended to avoid the "red zone"? I was working on a preset and I don't know if by placebo effect or what, keeping the level barely reaching red it sounded better to me ....
 

Rex

Legend!
That was a great advice .... is it recommended to avoid the "red zone"? I was working on a preset and I don't know if by placebo effect or what, keeping the level barely reaching red it sounded better to me ....
It’s recommended to shoot for 0 VU as a starting point. That’s the transition into the red zone. There’s no harm in poking into the red a bit.
 

greiswig

Power User
Hearing no buzz at all.

As being said already, the preset level is still a bit hot. Just watch the VU meters in Layout > Zoom. Instead of Cab Level, use Amp Level to set the preset level.
I have gone through both patches repeatedly, and can't see any clipping anywhere...until Yek came along with this tip. This seems to be the only place in the UI where the meters show "in the red." The SPDIF into my UAD is hitting at -10db, which gives me plenty of headroom there. The LEDmeters on the AxeFX itself are tickling the yellow on the outputs. None of the meters on the blocks are close to maxing out. It would be REALLY nice to have the block meters also register red if they are clipping! And to have the LED's register it at the same time.

And on all my presets, the cab block level is left at 0db: I use the amp block level as my main source of gain control, because that is the block where most of the gain is.

All of this is helpful, but not to my original issue: I can lower the amp block level 10db, and I still hear that buzz. The parameter that seems to have the most direct effect on it is the negative feedback in the power amp. So I think what I'm hearing is harmonic distortion in the power stage, but it has this odd abrupt end to it instead of a graceful tapering off.

And what's the point of a tweed Deluxe with negative feedback on the power stage? ;-)
 

Rex

Legend!
It would be REALLY nice to have the block meters also register red if they are clipping! And to have the LED's register it at the same time.
"Clipping" is meaningless at the block level. Internally, the Axe has more than 1400 dB of dynamic range. It's almost impossible to make a block clip.


...
I think what I'm hearing is harmonic distortion in the power stage, but it has this odd abrupt end to it instead of a graceful tapering off.
Power-amp distortion can have a pretty abrupt onset.
 

greiswig

Power User
Preset sounds fine here AFTER I turn the levels down. WAY too hot. Everything is clipping. Overdrives my interface which causes a "papery buzz" on low notes. The VU meters are there for a reason.
Cliff, if you have time I’d appreciate your input on the fact that turning up the P.A. negative feedback tones down and eventually eliminates the artifact that I have been talking about if you turn it up enough. I have never played a real tweed Deluxe, or a Maz38. Do they all just do that? I’ve heard that explanation previously on this forum, only to find out later that it was something else in the modeling that wasn’t intentional.
 

FractalAudio

Administrator
Fractal Audio Systems
Moderator
Those two particular amps are "cathode biased Class-A" amps. IMO the designs are poor because... wait for it... they exhibit a papery buzz. The problem with most cathode biased Class A amps is, 1: they aren't really Class A (more like hot Class AB) and 2: They go into Class B operation when they are overdriven. The cathode capacitor charges up and the bias point shifts dramatically. This causes lots of crossover distortion (papery buzz). It's worse on lower notes because lower notes have more energy and charge the cap more.

The is probably the reason Leo Fender switched to fixed bias amps with negative feedback. Fixed bias is just that, the bias point is fixed so the amp doesn't shift into Class B operation when overdriven (not as much anyways, depends on the bias circuit, grid stoppers, etc.). Negative feedback linearizes the amp and reduces the crossover distortion (at the expense of gain). That's why the buzzing went away when you increased negative feedback. Crossover distortion is a unique sound. For cleaner sounds it tends to be objectionable. For overdriven sounds some find it desirable. EVH ostensibly liked his amps biased cold to get some crossover distortion. There are even some amps that have circuits to intentionally generate crossover distortion. Some distortion pedals also do this.

Lowering the Cathode Resistance reduces the crossover distortion as it keeps the amp in Class A operation longer but the tubes run hotter and don't last as long. This is not a problem with our virtual amps though. I forget the actual values but I'm pretty certain if you look at the Cathode Resistance value for those amps it's pretty high. This means the amps are biased somewhat cold to begin with and shift to very cold as soon as overdriven. One reason I like the AC-20 is that it runs the tubes hotter and exhibits less crossover distortion. The worst amp in this regard is the Badger 18. The cathode resistors are very large and the amp shifts into Class B operation early causing a spitty, buzzy distortion quality. This amp, however, is liked by many so that just goes to show that some people like that. It's like fuzz pedals. Some people like that spitty sound. I personally don't like it.

Then there's shared vs. split cathode. If you look at the schematics on the web the Maz-38 is shared cathode. I could never get the model to sound exactly like our reference amp. Finally I traced the entire circuit and our particular amp is a split cathode. As soon as I changed the model to split cathode it was spot on. This is not exposed to the user though (there's a hidden shared/split switch). Our particular amp says "Humbucker" inside the chassis. Not sure if the difference in the cathode circuit is because Dr. Z likes split cathode for humbucking guitars or what.

I could easily make the models more ideal and less buzzy but that's not my call. Accuracy always comes first. Most people want that authenticity so that's why the models are like that. If you don't like it either dial it out by reducing Cathode Resistance, increasing negative feedback, etc. or pick a different model.

tl;dr version. Those amps do that. Pick a different model.
 

notalemming

Fractal Fanatic
Those two particular amps are "cathode biased Class-A" amps. IMO the designs are poor because... wait for it... they exhibit a papery buzz. The problem with most cathode biased Class A amps is, 1: they aren't really Class A (more like hot Class AB) and 2: They go into Class B operation when they are overdriven. The cathode capacitor charges up and the bias point shifts dramatically. This causes lots of crossover distortion (papery buzz). It's worse on lower notes because lower notes have more energy and charge the cap more.

The is probably the reason Leo Fender switched to fixed bias amps with negative feedback. Fixed bias is just that, the bias point is fixed so the amp doesn't shift into Class B operation when overdriven (not as much anyways, depends on the bias circuit, grid stoppers, etc.). Negative feedback linearizes the amp and reduces the crossover distortion (at the expense of gain). That's why the buzzing went away when you increased negative feedback. Crossover distortion is a unique sound. For cleaner sounds it tends to be objectionable. For overdriven sounds some find it desirable. EVH ostensibly liked his amps biased cold to get some crossover distortion. There are even some amps that have circuits to intentionally generate crossover distortion. Some distortion pedals also do this.

Lowering the Cathode Resistance reduces the crossover distortion as it keeps the amp in Class A operation longer but the tubes run hotter and don't last as long. This is not a problem with our virtual amps though. I forget the actual values but I'm pretty certain if you look at the Cathode Resistance value for those amps it's pretty high. This means the amps are biased somewhat cold to begin with and shift to very cold as soon as overdriven. One reason I like the AC-20 is that it runs the tubes hotter and exhibits less crossover distortion. The worst amp in this regard is the Badger 18. The cathode resistors are very large and the amp shifts into Class B operation early causing a spitty, buzzy distortion quality. This amp, however, is liked by many so that just goes to show that some people like that. It's like fuzz pedals. Some people like that spitty sound. I personally don't like it.

Then there's shared vs. split cathode. If you look at the schematics on the web the Maz-38 is shared cathode. I could never get the model to sound exactly like our reference amp. Finally I traced the entire circuit and our particular amp is a split cathode. As soon as I changed the model to split cathode it was spot on. This is not exposed to the user though (there's a hidden shared/split switch). Our particular amp says "Humbucker" inside the chassis. Not sure if the difference in the cathode circuit is because Dr. Z likes split cathode for humbucking guitars or what.

I could easily make the models more ideal and less buzzy but that's not my call. Accuracy always comes first. Most people want that authenticity so that's why the models are like that. If you don't like it either dial it out by reducing Cathode Resistance, increasing negative feedback, etc. or pick a different model.

tl;dr version. Those amps do that. Pick a different model.
Great info! Thanks Cliff!
 

greiswig

Power User
TL;DR Thank you!

PS - I can get rid of more of that buzz by lowering the transformer drive than by lowering the cathode resistance.
 
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