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willjrock

Problematic amp setting

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I believe the issue im having here is from raising the sag level to 10 on the Line 6 doom amp. As a matter of fact i know it is. You can hear best at the very beginning of the track, but ive emphasized the annoyance by playing a passage separately later on. Staccato better exasperates the annoyance....at 17 seconds.

 

Anyway was just wondering why high sag levels do this, if its normal, and if anyone can recreate the phenomenon  :P

 

I guess it would be frustrating if my tonal preference was to keep the sag at 10, but only to find out that Helix is incapable of tolerating such a setting. Surely this wouldnt be modeled? Esp not on a Line 6 designed amp. The couple other amps ive tried do not do this. 

 

Thanks for any intrest here.

 

EDIT: Ok so ive added an attacthment that is not showing up, so here is the public link in the meantime.

 

https://dl.dropboxusercontent.com/u/26654830/example%20D%282%29.mp3

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Not normal. I suggest you transfer it to the bug section.

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Weird yeah - it kind of sounds like a tremolo on those staccato notes near the end... 

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This is only a guess, but here's what might be happening. Sag controls how the power amp responds to being pushed hard. As the amp is pushed, it puts more demand for current from the power supply. When pushed harder, the power supply voltage might "sag" because it can't keep up with the demand. How a power supply reacts to demand depends on the amount of DC resistance in the power transformer, how much iron there is in the core, whether a tube rectifier or diodes are used for rectification, and the size of the filter capacitors.

 

Power supply sag is manifest by a drop in voltage on the filter caps as they discharge in order to meet demand. Then the caps recharge from the rest of the power supply and the amplitude comes back up. At very high sag settings in Helix, you might be getting into a situation where the power amp is essentially oscillating as it tries to keep up with the demand and the filter caps are constantly discharging and recharging.  The time constant of this oscillation is determined by the filter cap values and voltage drop resistors.

 

If that's the case, then simply reducing the sag will eliminate the problem. But let's think a bit more about what you're tying to accomplish with high sag settings. Sag generally has little to do with amp tone, and more to do with feel. Sag essentially results in a unique kind of compression that unlike a compressor in front of an amp, still works even when the power amp is clipping. This is the magic of sag. Higher sag settings will result in more compression. This can have an impact on pick transients and rapid djent playing since the compression attack and release can cut off pick attack. Generally metal tones require amps with power supplies that don't have much sag. Blues tones typically benefit from more sag as that playing style works better with power amp compression.

 

So why do you think you need such high sag settings?

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I believe the issue im having here is from raising the sag level to 10 on the Line 6 doom amp. As a matter of fact i know it is. You can hear best at the very beginning of the track, but ive emphasized the annoyance by playing a passage separately later on. Staccato better exasperates the annoyance....at 17 seconds.

 

Anyway was just wondering why high sag levels do this, if its normal, and if anyone can recreate the phenomenon  :P

 

I guess it would be frustrating if my tonal preference was to keep the sag at 10, but only to find out that Helix is incapable of tolerating such a setting. Surely this wouldnt be modeled? Esp not on a Line 6 designed amp. The couple other amps ive tried do not do this. 

 

Thanks for any intrest here.

 

EDIT: Ok so ive added an attacthment that is not showing up, so here is the public link in the meantime.

 

https://dl.dropboxusercontent.com/u/26654830/example%20D%282%29.mp3

 

First of all, the Helix CAN handle it, just not on that amp model.  I'm not saying it's a bug, it's just not a bug with the Helix.  It's a bug in their modeling of an amp that doesn't exist in the real world.

 

This doesn't surprise me though.  As armsdenj points out there are a LOT of physical interactions in real world amps between the power supply and tubes in higher SAG settings.  Since this is only a virtual amp I can easily imagine a scenario in which digital logic doesn't quite cover what would happen were there to be a real amp.  Since you don't experience this on other amps (that are modeled ideally from real world situations) it's obvious to me where the problem lies.

 

If it were me, I'd report the bug as relating to the Doom amp, and move on to a different amp to address my needs.  There are plenty of them in there....

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This is only a guess, but here's what might be happening. Sag controls how the power amp responds to being pushed hard. As the amp is pushed, it puts more demand for current from the power supply. When pushed harder, the power supply voltage might "sag" because it can't keep up with the demand. How a power supply reacts to demand depends on the amount of DC resistance in the power transformer, how much iron there is in the core, whether a tube rectifier or diodes are used for rectification, and the size of the filter capacitors.

 

Power supply sag is manifest by a drop in voltage on the filter caps as they discharge in order to meet demand. Then the caps recharge from the rest of the power supply and the amplitude comes back up. At very high sag settings in Helix, you might be getting into a situation where the power amp is essentially oscillating as it tries to keep up with the demand and the filter caps are constantly discharging and recharging.  The time constant of this oscillation is determined by the filter cap values and voltage drop resistors.

 

If that's the case, then simply reducing the sag will eliminate the problem. But let's think a bit more about what you're tying to accomplish with high sag settings. Sag generally has little to do with amp tone, and more to do with feel. Sag essentially results in a unique kind of compression that unlike a compressor in front of an amp, still works even when the power amp is clipping. This is the magic of sag. Higher sag settings will result in more compression. This can have an impact on pick transients and rapid djent playing since the compression attack and release can cut off pick attack. Generally metal tones require amps with power supplies that don't have much sag. Blues tones typically benefit from more sag as that playing style works better with power amp compression.

 

So why do you think you need such high sag settings?

great, and informative answer.. thank you for the info on this

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