• We would like to remind our members that this is a privately owned, run and supported forum. You are here at the invitation and discretion of the owners. As such, rules and standards of conduct will be applied that help keep this forum functioning as the owners desire. These include, but are not limited to, removing content and even access to the forum.

    Please give yourself a refresher on the forum rules you agreed to follow when you signed up.

***POWER AMP SETTINGS - Depth, Damp, Sag***

Hello FAS Forum! I have been doing a lot of research on the virtual power amp sections of the Axe-FX Ultra and I'm still working out the kinks.
I am essentially trying to optimize my sound, and it seems that I've narrowed down the last of my tone shaping to the power amp section.
If you have any tips, techniques or suggestions on how to best setup the Depth, Damp, and Sag settings in unison with the master output level,
please feel free to post them here. Thanks!

Below is a link to a recent song I did using the 5150 model. For the rhythms I had all three set to 5, and for the solo I raised the Damp up to 10,
mostly because it seems to add more saturation to the tone. Let me know what you all think!

  • Like
Reactions: MPZ


Fractal Fanatic
You asked for it. Please summarize in understandable terms... ;) May have dated info (like urls) and Dutch mixed in.

- solo-act, 2007: This is just me, but I tend to use the deep as a pseudo "cabinet" EQ to match how hard the speakers are working for whatever tone I'm going after. >> javajunkie: This is what I do as well.
- Cliff, 2/2008: If you increase the depth too much with the deep parameter on, the power amp sim can go unstable, just as a real amp would under those circumstances. I can't say any more as it would be disclosing proprietary information.
- Sebastian, 12/2010: [do you use depth?] Totally depends on:
* amount of gain/distortion (i.e. clean sounds, rhythm sounds, lead sounds)
* if the tonestack is pre or post (if it's pre, the bass control has a very different effect on the sound, compared to depth)
* where the low cut (adv. page) is set; depth can bring back the bottom the low cut removed.
- Clark Kent, 12/2010: I hate depth... they should change the name to boomyness. Whatever it's doing it's wrong IMO.
- Yek, 12/2010: Turn down the Depth parameter for less bass. Depth is the same as what’s called Resonance, Fat, Whomp etc. on real amplifiers. The same as Presence but on low frequencies. Higher values give a fuller, looser sound, while low values can be used to achieve a more focused sound. Note that Depth is non-functional when Power Amp sim is off.

- Cliff: Damp is the amount of negative feedback around the virtual power amp. Increasing it makes the power amp stiffer and tighter. / Damp defaults to value appropriate for model selected.
- BK-Amps, 9/2010: The control does not behave like a real amplifier. "Damp" control on 10 will be ~12db higher in volume than "Damp" at 0! This is not right. [...]
>> Cliff: The Axe-Fx attempts to normalize the volume as you change the damping. Since the overall gain of an amplifier with negative feedback is A = Ao / (1 + Ao * B), the closed-loop gain can be calculated and corrected for. So when you change the damping the Axe-Fx calculates the resulting closed-loop gain and compensates accordingly. However, if you are driving the "power amp" hard, the equation falls apart because it assumes linear operation. Therefore there may be some volume change. This is done since otherwise you would constantly have to adjust your output volume as you change the damping. Unfortunately it is impossible to predict how saturated the power amp is since that depends on input level. The compensation isn't perfect, the idea is to minimize the volume fluctuations, since without compensation the volume would fluctuate wildly. >> Smilzo: Great idea, because our minds judge louder sounds as better ones! / It must be underlined that if the poweramp is saturated, both Damp and Level must be increased to maintain the same level. forum.fractalaudio.com/threads/29243-The-quot-Damp-quot-Control-is-Strange
- Cliff, 5/2007: The DAMP control is the Class A/AB control. It doesn't actually change the class of operation since there aren't really any guitar amps that are Class A. The AC30 is advertised as Class A but it's really just a cathode biased Class A/B biased hot with no negative feedback.
- zap 2007: Does reducing negative feedback allow more 2nd and 3rd harmonics on the Axe-FX as the "Silk" feature of the Rupert Neve Potico Series 5012 (see last par.)? eqmag.com/story.asp?storycode=14187
>> Cliff: Reducing negative feedback increases harmonic distortion including 2nd and 3rd if operating below clipping. This is because feedback linearizes the amplifier. The Axe-Fx has a non-linear "power amp" just like a real tube amp and if you turn down the feedback (damping) then the power amp will be less linear and will therefore introduce some distortion products. The distortion products tend to be low order (2nd and 3rd).
Once you enter clipping, negative feedback can actually increase the distortion products since the onset of clipping is sharper. A power amp with no negative feedback (i.e. AC30) will produce distortion even when not clipping. However, it will go into clipping gently, since the transfer function tends to be smooth. A power amp with negative feedback will produce less distortion when not clipping but will enter clipping more abruptly since the smooth curve is essentially turned into a piecewise linear function with an abrupt gain reduction at the supply rail. setbb.com/axefx/viewtopic.php?p=11678
- Cliff, 2/2010 v9.02: If you set Damping to zero it detects that and changes the Presence control to a shelving filter, since the control would otherwise be ineffective. Set Damping to just greater than zero and you'll hear the filter turn off and revert to a feedback circuit.
- rpurdue, 9/2010: Even though the JVM isn't the mecca of the Marshall line it sounded great on the crunch channel...better than the Axe. It was spongier and seemed more alive. I was determined to emulate this characteristic. After looking at the manual i found the answers right in front of me...the SAG and DAMPING!!! DUH! I thought because I was using a tube poweramp I should set the SAG very low and the DAMP high....BUZZZZZZ WRONG ANSWER!!! As soon as I upped the sag into the 2-3 range and turned off the Damping entirely, there it was! It not only sounded as good as the JVM but better!! It was much fuller and open sounding. I found the Corncob and Marsha BE really nailed it and then some!
- Cliff, 11/2010: The difficulty is that I allow people to adjust the damping so I needed a way to allow for a hi-cut when the damping was set to zero and a presence control when not. So I came up with the dual-function presence control. When an amp has no negative feedback (i.e. AC-30), the speaker impedance has a much greater effect on the tone and causes the tone to be much brighter. Additionally, there is no way to adjust the tone by modifying the negative feedback (because there isn't any). So a non-negative feedback amp classically employs a hi-cut filter in the power amp. The Axe-Fx allows you to turn on negative feedback, even for amp models that don't normally have any. In that case the high-frequency emphasis due to the speaker impedance will decrease and you then may want to increase the highs to compensate so you need a presence control. Thus was born the presence/cut control. At settings less than zero it acts as a simple hi-cut. At settings greater than zero it acts as a presence control if the amp model has negative feedback by manipulating the feedback or by boosting the treble if there is no feedback. thegearpage.net/board/showthread.php?p=9456143
- fuzznut, 12/2010: So I turned up presence all the way, and was playing with the damp parameter to see what effect it had on the presence range. I put damp to zero and... woah! It got louder, very bright and RAW. Cool tone! It is not mentioned in the manual or wiki manual, but searching here revealed that putting damp to zero completely disconnects the feedback loop in the power amp. What I didn't find is, since presence and depth work off the feedback loop, are these controls now shelving filters as when the power amp is disabled? / Having fun with this one! 2 Das Metal amps in parallel. #1 with bass, depth and damp off (bass is flubby with no feedback). #2 normal, initially with mids and high/presence off, adjust output level until bass sounds right in the mix. Then adjust mids & highs on both amps for various mixes. Tight bass, hairy mids and loose highs! Gotta love this black box... >> Cliff: The presence becomes an active shelving filter. I forget what happens with depth. Probably the same thing or nothing at all.
- http://forum.fractalaudio.com/threads/29243-The-quot-Damp-quot-Control-is-Strange?p=428883
- JM: I am not a big fan of the sound of distortion in the power amp portion of the amp block with very high values of damping. To my ears, the transition to distortion is too abrupt and the character of the distortion too harsh. http://forum.fractalaudio.com/share-request-patches/35216-fractal-patch-contest-4.html#post524502
- widrace, 3/2012: I would add that Damp is closely tied to the Sag/Master relationship. Damp to me is the main dynamic adder/subtractor and is dialed in to work with the amount of gain your using. Sag follows as a tool to fine-tune the result. High SAG values act like compression where sustain is added at the expense of dynamics. The combination is everything when it comes to feel at any given gain level. Jay noted that high levels of Damp will cause the onset of break-up to be more abrupt and I agree. If chasing the elusive Robben Ford break-up qualities/mannerism it all starts there. Get this part right before you add any upstream/downstream compression too. FWIW, I generally use Damp settings that are rather high compared to Sag. For live use the Damp/SAG combo is key to correctly fitting within overall dynamics of the band. I like to dial in a bit too much dynamics and trim it with a little bit of high-threshold/high-ratio compression to keep the peaks in order. Same goes for recording. Spend some time twiddling various combinations of only the Drive, Master, Damp and Sag parameters while maintaining a perceived output level. If you do this along with a SPL meter you will find the two don't agree much. The goal is to maximize the perceived levels, minimize the SPL, while keeping the right feel and dynamics to suit. No one but you can do this. http://forum.fractalaudio.com/axe-fx-ii-discussion/48588-i-have-question-about-sag-2.html


Fractal Fanatic
- Cliff: Sag controls the resistance of the virtual power supply. Increasing it causes the power supply voltage (B+) to sag more as you play louder. Makes the amp feel spongier.
- Cliff, 3/2007: I almost always turn the sag up, usually around 5. Many amp models default to around 2 since those amps have solid-state rectifiers. But I like the feel of a tube rectifier which is between 4-6. I usually crank the master volume up too because I like the sound and feel of the "power amp" working.
- Cliff, 5/2007: The sag control is essentially the rectifier type, except that it's variable. A solid-state rectifier will have lower sag than a tube rectifier. But the rectifier is only part of the story, the power tranny affects sag as well. So I just made it so you can dial in the desired amount of sag.
- Cliff, 5/2007: If you want a tighter feel, you can decrease the sag (good for palm-mute chugga-chugga). If, like myself, you prefer it spongy, you can increase the sag and use your picking and guitar volume to control the amount of power tube breakup.
- Finaldo 1/2008: Can the Axe-FX simulate different response times? Here's an example of what I mean. I went to the Egnater amp seminar and built the head, and played on it for a while, got very used to how the amp responded to my playing. Then, when over at a friend's place, I plugged into his Glaswerks, and that amp responded WAY quicker than my Egnater. Some may have called it "stiffer" response, but whatever you call it, there was a HUGE difference, something I had never really noticed about tube amps until that day. I would've thought that this was controlled by the SAG parameter in the power amp, but that sounds like it compresses the tone. Things like response time (I don't know what else to call it) and note bloom don't seem to be adjustable from my tweaking.
> Cliff: The SAG control is for this. But there's more to it. A tube amp will have a finite impedance between the AC source and the reservoir capacitors for the B+. The value of this impedance is dependent upon the power transformer and the rectifier(s). Sometimes there's also a choke or resistor between the B+ and the plates and this will factor in too. An amp with a small transformer and tube diode will have a lot of impedance. Conversely, a large power transformer and solid-state rectifier will yield a low impedance. The Sag control allows you to adjust this impedance. The other part of the equation is the value of the reservoir caps. Small caps get discharged quickly. This, along with a high ac impedance yields a spongier feel as the power amp compresses more and follows the notes quicker. Large caps and/or small ac impedance means the B+ is stiffer and the amp therefore feels stiffer. I'm guessing your Egnater has a small power transformer and small caps and the Glaswerks has a larger transformer and beefier caps. The Axe-Fx hard-codes the cap values for each model. They are not exposed to the user. [B+? Now definable] / The note dependence of sag is due to the speaker impedance. The impedance of a speaker is not a constant 8 (4, 16) ohms but is dependent upon frequency. Typical guitar speakers have a peak in the impedance that can be anywhere from 2 to 4 times the nominal impedance at around 100 Hz. You can adjust this in the Axe-Fx under the ADV tab. There's SPKR RES FREQ parameter that allows you to adjust the resonant frequency.
- Cliff, 6/2008: If Sag is at zero the Power Amp simulation is defeated. The display will show "P.A. Off". With power amp defeated you will get no additional distortion or compression since the power amp is bypassed.
- Cliff, 6/2008: It does behave like a real amp. The more you turn up the master the more it sags. The sag control lets you control how much it sags as you turn up the master. You're not understanding the parameter. The idea of the parameter is to allow people to alter the default amount of sag. For example, a Marshall doesn't sag that much because it has a solid-state rectifier. If you like that sound (as I do) but not the feel (again as I do) you can increase the sag to a get a spongier feel. Conversely you can tighten up, say, a Vox model. The sag control, along with all the other "model" parameters default to the appropriate values for the model when you select the model type (see manual). If you don't care about those parameters then leave them alone.
- [overbodig?] Yek, 12/2010: This parameter models the power supply impedance and therefore how dynamically the power amp simulation behaves. Higher settings simulate higher power supply impedance which leads to a more compressed feel. At low Master Volume settings this control will have little effect as the power amp is not being pushed. As the power amp is pushed the Sag control will have more effect. Turning it to zero disables poweramp simulation for the preset.
- scorch, 3/2012: For those that may still be struggling with the 'sag' concept, permit me to creat a mental picture. Think of the power supply of an amp as a balloon filled with air. It's very full and its very taunt. The power supply has 'filled up' the balloon. Now, you begin banging out power chords and riffing at high velocity. The balloon begins to lose the air...it starts getting 'soft'. The voltage available to the power amp actually begins to drop, causing the clipping of the power tubes to increase and round off earlier. The result is a note that swells or 'blooms' under the fingers instead of exploding at the pick attack like modern metal amps do. It all came down to older power supplys that couldn't keep up the voltage 'pressure'. Us old amp guys love that sound.....metal guys...not so much.


Fractal Fanatic
- Cliff: Master is Master Volume. Sets the volume level into the virtual power amp and therefore determines the amount of power tube distortion.
- Cliff, 5/2007: The master is identical to the master volume on a MV-style amp. It's placed between the preamp and power amp. When you turn up the master and it gets more distorted and more "chewy". That's the power amp section distorting.
- Cliff, 2007: For clean tones the Drive control should be set fairly low and the Master set very high. On a real "Blackface", for instance, the Master is essentially maxed since that amp has no master volume. A Blackface typically achieves full power at around 10-11 o'clock on the volume (Drive). It's also insanely loud. Beyond that the everything starts to saturate and clip. If you set the Master low and the drive high, for clean tones, the low end will tend to get muddy. Good cleans are obtained with little, if any, preamp distortion and a nice amount of power amp distortion. Power amp distortion has a much different character and tends to be glassy and bouncy. Preamp distortion is rougher and more compressed. / Whatever works. The master is the power amp drive. It controls how hard the virtual power tubes are driven. If backing off the master sounds better then do it, there's no rules. However there's interaction. If you turn the drive up the power amp gets driven harder anyways. The two controls balance how much distortion comes from each section.
- Cliff, 2/2008: The amount the power amp sim contributes to the tone is dependent on how hard the "power amp" is being driven. If the master volume is low then the change will be subtle and vice-versa. It also depends quite a bit on the particular amp models. Some models have fairly neutral power amps, others have very colored ones.
- Cliff [not to Jay], 7/2010: Master at 7.02 on the Recto model is WAY too high and will sound muddy. You should be around 3-4, maybe less. This is most likely the source of your lack of "juicy goodness" or "25%" nonsense. [...] I said something to the effect "for old, non-MV amps like Fenders and Plexis you typically want to run the Master at 9 or higher". For modern, high-gain, MV amps you typically want the Master below 5. I've stated this numerous times. Try the Master at 3ish. Turn the drive up and increase the Bass or Depth to get the desired low end. Juicy goodness will ensue.
>> JM: I noticed beginning with 9.0 that I needed to reduce MV settings substantially. Even when the sim represents a non-MV amp, I have reduced the setting quite a bit from where it was pre-9.0.
- Cliff: For ALL the Fender models the Master should be between 9 and 10 if you want authenticity. In general, if the original amp didn't have a master volume then pretty much dime the Master. Of course there are no rules, but running a Fender with the Master below 6-7 will sound pretty thin.
>> yek: With almost all the oldies I crank them up to 10 on the Master and then turn down Drive to about 3.5 or so. I love the tones this way from the Fenders, Plexi, TopBoost, Wrecker etc. Full tones and no farting bass notes.
>> Cliff: That's exactly the way you should do it. With the real amp once you hit around 3.5 it's very loud and the amp is close to full power. Fenders were designed to produce full rated power at around 3.5 IIRC.
- Cliff, 7/2010: For modern MV amp models you typically want the Master set low. I recommend around 3-4.
- SP: Re-initialize the amp block. Turn the output level to whatever you set it at (I set it at -5db). Then turn the drive down to 3.5 and the master volume to 10. Play. Get your drive set first; then EQ. That's it. You are a Fender tweakmaster with version 9.02.
- Cliff: For tight, modern tones be sure to set the Master fairly low. I was doing some tests today and even with the Master at noon there's still significant power amp saturation. If you want that tight, high-headroom sound then I'd set the Master around 2-3. / For high-gain stuff keep the Master below noon. Otherwise you'll get too much power amp distortion.
- andrewsimon, 11/2010: non MV amps should be set at 9.25
- Radley, 10/2009: Cranking the Master volume level seems to incorporate an ever-lowering LPF along with some increased compression (which is pretty much what you will get from a real tube amp). The various suggestions are simply different approaches to 'skinning the same cat' ;)
>> Cliff: The effect of cranking the Master may sound like a variable LPF, but there are actually no changes in any filters. The Master simply sets the level between the preamp and power amp simulation. The power amp modeling behaves like a real power amp. If you push it harder it gets darker. There are no filter tricks like other modelers. For high-gain sounds I start with the Master at noon. Adjust gain and tone and then increase or decrease the Master to get the power amp to the "sweet spot". When you hit the sweet spot it will start to growl. Too much master and it gets muddy. Too little and it gets harsh.
- Cliff, 8/11/2011: The rule of thumb is to start very low. Then bring it up until you hear the power amp compress. The tone will get darker and smoother. Increase or decrease from there to taste. Then adjust the output level accordingly.

You are set for life now ;)
  • Like
Reactions: gpz


To whoever posted all that above, thank you. I now have some stuff to try to see about getting the sounds I've been unable to get lately.
Top Bottom