Wish Two Amp Block Wishes

York Audio

Fractal Fanatic
Vendor
Even though I use the Axe-Fx III every day (literally), I’ve also been incorporating real amps with the Fractal X-Load back into my rig (ones that aren’t found in the unit) and have discovered some things that would be cool to see in the Fractal.

1. The ability to change V1 and Phase Inverter preamp tubes.

Reason: While playing around with different preamp tube combinations, I found that putting a 12at7 in the PI slot opened up the amp a bit more and made distortion less congested. Putting the 12at7 in V1 cleaned up the amp a bit and made the gain sweep more usable. I know that you can kind of simulate this with the input trim, but having the modeled tube give you an accurate level of decreased input trim would be great.

2. Output Transformer “swap” when changing power tubes.

Reason: I know Cliff has said that all power tubes are relatively flat and all basically sound the same, which is why swapping power amp tubes in the Axe doesn’t change the tonality very much. I may be completely off on the technical side of this, but I was under the impression that the relationship of the OT and the power amp tubes are what cause the tonal change when, for example, using a Dual Rec and comparing the sounds using 6L6 vs EL34 tubes. Back when I had an old Dual Rec, I did this and found that the 6L6 had more low end and sounded bigger and meaner while the EL34 had less low end, a more prominent midrange, and more pick attack and felt more “British.”

Whatever the component relationship is that brings that tonal change would be great to see and open up some really cool tonal options for the amp models we love.

EDIT: If the preamp tube wish can happen, adding a 12at7 to the mix would be fantastic!
 
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I think Transformer Match is the answer to your 2nd point...
I do believe you're right that tweaking Transformer Match is a way of doing that, but my wish links the power amp tube type WITH the Transformer Match so you have accurate settings depending on which tube you select. What I'm suggesting is similar to the new impedance curves in the speaker page. Before we had the new accurate ones, it was kind of a "use your ears to tweak the curve" situation. Regardless, it still sounded awesome, but I don't think any of us would have been able to manually tweak those curves by ear and come up with something as accurate as the new ones. Now we just click on a more detailed 4x12 Brit Greenback curve, pick and IR, and it just feels right without having to touch another knob. The new level of accuracy made the cabs feel even better.

To be honest, I don't know what values to set the Transformer Match to in order to accurately replicate different tube swaps, but it would be cool to select the new 6CA7, have it jump to the correct TM setting, and say "whoa! THAT's why Eddie was obsessed with these things!" If it doesn't happen, it's not the end of the world. Just wishin' over here. :)
 
I do believe you're right that tweaking Transformer Match is a way of doing that, but my wish links the power amp tube type WITH the Transformer Match so you have accurate settings depending on which tube you select. What I'm suggesting is similar to the new impedance curves in the speaker page. Before we had the new accurate ones, it was kind of a "use your ears to tweak the curve" situation. Regardless, it still sounded awesome, but I don't think any of us would have been able to manually tweak those curves by ear and come up with something as accurate as the new ones. Now we just click on a more detailed 4x12 Brit Greenback curve, pick and IR, and it just feels right without having to touch another knob. The new level of accuracy made the cabs feel even better.

To be honest, I don't know what values to set the Transformer Match to in order to accurately replicate different tube swaps, but it would be cool to select the new 6CA7, have it jump to the correct TM setting, and say "whoa! THAT's why Eddie was obsessed with these things!" If it doesn't happen, it's not the end of the world. Just wishin' over here. :)
That makes sense - I can get behind that approach!
 
I do believe you're right that tweaking Transformer Match is a way of doing that, but my wish links the power amp tube type WITH the Transformer Match so you have accurate settings depending on which tube you select. What I'm suggesting is similar to the new impedance curves in the speaker page. Before we had the new accurate ones, it was kind of a "use your ears to tweak the curve" situation. Regardless, it still sounded awesome, but I don't think any of us would have been able to manually tweak those curves by ear and come up with something as accurate as the new ones. Now we just click on a more detailed 4x12 Brit Greenback curve, pick and IR, and it just feels right without having to touch another knob. The new level of accuracy made the cabs feel even better.

To be honest, I don't know what values to set the Transformer Match to in order to accurately replicate different tube swaps, but it would be cool to select the new 6CA7, have it jump to the correct TM setting, and say "whoa! THAT's why Eddie was obsessed with these things!" If it doesn't happen, it's not the end of the world. Just wishin' over here. :)

agreed I would love to have that happen like switch XTC to el34
or Uber KT88 and just have all the associated parameters reconfigure
i think Cliff mentioned it before but it would screw up many peoples preset

perhaps keep the ideal mode
and add a second “matched” option
 
I think the biggest issue is the lack of clarity for the parameter values. Everything from power tube mismatch to the variac setting should be in their related unit, mA for bias and mismatch, voltage for variac, ohm for primary inductance, etc.
The biggest factor in power tube's contribution to sound is plate voltage and bias (operating area), primary inductance and secondary (speaker) load/reactance. Switching 6L6 to EL34 is very audible in the recto because of that.
I generally have no idea what the parameters are actually doing and just mess around until it sounds interesting and that's probably fractal's focus as opposed to hardcore tweaking.
 
I think the biggest issue is the lack of clarity for the parameter values. Everything from power tube mismatch to the variac setting should be in their related unit, mA for bias and mismatch, voltage for variac, ohm for primary inductance, etc.

My guess is that at least part of the Axe's internal design is relative/normalized for certain component interactions so that certain changes (e.g. virtual preamp tubes, power amp tubes, transformers, impedances) are effectively relative changes from nominal operating conditions. Exposing voltages, currents, impedances might be fascinating for the electronically-oriented, but are probably TMI for regular users who would ask endless questions like "what's the official voltage or bias or impedance for such and such?" "why is it set to X when I heard the best value is Y?" etc.

In addition, normalizing also probably makes some calculations more stable when changing components (e.g. tubes) or values (e.g. impedance). When I played with the full range of negative feedback, transformer match, and speaker impedance back in 9.00, I got strange squealing and artifacts. Because of that, Cliff reduced the ranges of those relative parameters.

Cliff's response: "There may always be a combination of negative feedback, transformer match and speaker impedance that causes instability just as would happen in a real amp. The Axe-Fx lets you play with things but it can't always protect you from doing things that break the amp just as if you did these same things in the real amp. If you put an 8K transformer in a Plexi, change the negative feedback to the 16-ohm tap and connect a 16-ohm speaker to the 4-ohm output it's going to oscillate. So will the model. I've tried to prevent that the best I could but with great power comes great responsibility."
 
I generally have no idea what the parameters are actually doing and just mess around until it sounds interesting and that's probably fractal's focus as opposed to hardcore tweaking.
I think you've landed on the part that's possibly by-design. @FractalAudio has been saying "use your ears, not your eyes" for as long as I've known the guy now.
 
It sounds like there are quite a few factors at play to accurately emulate swapping power tubes... Transformer Match, Speaker Impedance Resonance levels, etc. And since it’s tied to impedance, the values are probably different for each impedance curve we have, sooooooo I’m probably on Cliff’s s**t list for even bringing this up. Sorry, Cliff.

Maybe the preamp V1 and Phase Inverter wish would be easier to implement. Swapping those tubes in the real world makes a big difference to the amp’s tone and feel and hopefully wouldn’t be as complex to simulate.
 
It sounds like there are quite a few factors at play to accurately emulate swapping power tubes... Transformer Match, Speaker Impedance Resonance levels, etc. And since it’s tied to impedance, the values are probably different for each impedance curve we have, sooooooo I’m probably on Cliff’s s**t list for even bringing this up. Sorry, Cliff.

Maybe the preamp V1 and Phase Inverter wish would be easier to implement. Swapping those tubes in the real world makes a big difference to the amp’s tone and feel and hopefully wouldn’t be as complex to simulate.
Have you tried changing your guitar cable? That will apparently take care of almost anything now ... 😂
 
Have you tried changing your guitar cable? That will apparently take care of almost anything now ... 😂
Well I’ve been using Mogami, but I’ve heard the best tone comes from solid silver core cables wrapped with oxygen-free braided unobtanium with ends made from Mike Tyson’s gold teeth. They’re supposed to be great.
 
It sounds like there are quite a few factors at play to accurately emulate swapping power tubes... Transformer Match, Speaker Impedance Resonance levels, etc. And since it’s tied to impedance, the values are probably different for each impedance curve we have, sooooooo I’m probably on Cliff’s s**t list for even bringing this up. Sorry, Cliff.

Maybe the preamp V1 and Phase Inverter wish would be easier to implement. Swapping those tubes in the real world makes a big difference to the amp’s tone and feel and hopefully wouldn’t be as complex to simulate.

very cool ideas
 
I think you've landed on the part that's possibly by-design. @FractalAudio has been saying "use your ears, not your eyes" for as long as I've known the guy now.

I've seen him say it a bunch too and I don't have a problem with it. I always wished for a real time amp simulator and designer you could use to save on parts when building amps and pedals and maybe some day it will happen.
A bunch of people tried to get Peavery to go that route with Peavalver on the last version beta team, but the dev and company weren't having it. Now look at 'em. I have no sympathy (except for James Brown) :D
 
I edited the OP wishing for a 12at7 preamp tube option if the first wish is implementable. If any of you still have real amps, try a 12at7 in the PI slot and see how it opens up your amp. I did this with one of my Mesa DC-5 amps and recorded it with a 12ax7 and a 12at7, and the 12at7 did wonders for note definition using higher gain settings.
 
Pretty sure the Diezel VH4 also uses 12at7 for the PI or loop. It's a lower gain 12ax7 but with more current capability. You can even use them for a 1 watt power amp, which a few diy forums have done.
12au7 is another possibility for a lower gain drop in replacement, though ideally with all different tube types you would also rebias at least to get the most out of them. Hard to do on a Mesa board hehe.
 
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