Classic signal chain vs the Axe-Fx approach

ozanerkal

ozanerkal

Inspired
Hi all..
This was a question that bothered me even before I thought of buying an Axe-Fx.

In a classic signal chain (that involves a real amp) some effects (drive, comp, wah etc.) go BEFORE the amp, and some others (reverb, delay, chorus etc.) go in the FX Loop which means AFTER the preamp but BEFORE the power amp and speaker.

With the Axe-fx the common approach is to place the "AFTER" effects at the end of the chain, even after the Cab Block.

What I'd like to know is, can the Axe-Fx model the classic signal chain (without using a real power amp and cab) and would that would make a difference?

If this has been discussed here before, I'm really sorry, just give me the link and forget this :)
 
You can place reverb or delay or what have you before the Cab block and after the Amp block to do what you're talking about. As far as I know placing EQ before or after the Cab block doesn't make a difference, but effects have the tonal variance depending on where it's located in the chain.

To me having effects like delay and reverb going before the Cab block is what I familiarize as a more live tone, whereas after the Cab block is what I recognize as a studio sound. With the Axe-Fx you can have your cake and eat it too.
 
You can place the effects blocks wherever you want.

Your sig line says you own the XL already, so just install Axe Edit, if you haven't already, and you can quickly and easily move blocks around (this is something I find far easier in Axe Edit than using the front panel)

Experiment with putting a reverb before the amp vs after it, try a flanger before the amp vs after the cab; totally different sounds.

That is the cool thing about the Axe, its nearly limitless in terms of flexibility and routing. The presents are simply one variation of that. You can go into parallel routings instead of series etc. Sky is the limit
 
It has been discussed several times in the past , Cliff has said several times (since the Standard/ Ultra ) he won't be separating preamp and power amp to insert effects , ( that would make the code too vulnerable ) there is a difference between the insert being placed there (as a real amp would have) as opposed to after power amp and before speaker, but probably not something you would notice unless you A/B them isolated .
 
The OP is referring to "Classic signal Chain" as to put the effects between the Preamp and the PowerAmp. You can't do that in the Axe-FX II. You can put the effects before the whole amp (preamp+poweramp) or after.
He's asking if there is an audible difference to put the effects between the preamp and poweramp vs after the whole amp (preamp+poweramp).

I would say that there is a difference, but not a drastic one. It depends if your tone is more preamp distortion oriented or poweramp distortion oriented.

Using the effects in the Axe-Fx II it's like mimic what you'll doing in a studio... Setting your amp, micing your cab and use outboard effects, but instead of outboard effects you're using effect blocks after the cab.
Of course you can put the effects between the amp block and the cab to get a different flavor.

EDIT: You beat me RDH ;)
 
The ideal location for delay, reverb, etc. is after the power amp. Real tube amps have the fx loop between the preamp and power amp out of necessity as it is impossible to do otherwise. IOW it's a compromise that the AXE-FX does not have to make.
 
But as with all things guitary, isn't "compromise" subjective? If it's not perfectly ideal, I can see the appeal of having the option of putting them between the pre and power amp.
 
FractalAudio said:
The ideal location for delay, reverb, etc. is after the power amp. Real tube amps have the fx loop between the preamp and power amp out of necessity as it is impossible to do otherwise. IOW it's a compromise that the AXE-FX does not have to make.
Click to expand...

Not to mention many of use use to slave amp heads down to line level to get the amp fully in between, then reamp the signal post effects. At the height of the insanity I had four multichannel anps slaved, feed through a 22 space rack of effects and then triamped out to three 4x12s with the middle being the dry, powered by a tube power amp to keep that signal pure analog.
 
FractalAudio said:
The ideal location for delay, reverb, etc. is after the power amp. Real tube amps have the fx loop between the preamp and power amp out of necessity as it is impossible to do otherwise. IOW it's a compromise that the AXE-FX does not have to make.
Click to expand...

Who can say it better than the man himself..
Honestly, I always thought that separating pre and power amp stages was something to come with a new firmware someday, or a new device...
The answer is clear as you say that this is what was intended.
Thank You
 
You could try a test to simulate this. Use two similar amp blocks and put your effects between. The first has the pre cranked with MV low, the second has the pre very low with the MV cranked. You might get it to work, by playing with levels and eq. Or just put your effects after a single amp block and use the drive parameter of the effect to approximate the PA distortion?

But I'm with cliff on this. This was only done because it's not feasible to put effects after the poweramp section in the real world.
 
Randy4Guitars said:
You could try a test to simulate this. Use two similar amp blocks and put your effects between. The first has the pre cranked with MV low, the second has the pre very low with the MV cranked. You might get it to work, by playing with levels and eq. Or just put your effects after a single amp block and use the drive parameter of the effect to approximate the PA distortion?

But I'm with cliff on this. This was only done because it's not feasible to put effects after the poweramp section in the real world.
Click to expand...

was thinking about the same thing.. just for the sake of trying.. :)
 
A true "classic" signal chain was a guitar plugged straight into an amp with a mic on it and some plate reverb added to it on the mixing board in the studio.
Then in the 50s guitar amp manufacturers realized that they could "model" a studio reverb by using springs inside the guitar amp so guitarist could use reverb in a live setting.
Later on they did things like impeding the travel of the recording tape to create quasi flanging effects, again post-mic.
Multi-head recorders or several recorders ganged together allowed for things like echo, again all post-mic.

In the 1960s and 70s effects pedals started to come on the scene ad these all had to be placed pre-preamp.
So any time-based effects like echo would be distorted by the guitar amp's preamp and power amp unlike the studio effect that the echo pedal was "modeling".
Of course this became a standard too, but that's another story.
Other issues involved the signal path sucking the tone of your guitar out before it even reached the input of your amp due to capacitance effects and bad buffer amp circuits inside the pedals.

Then in the late 70s Mesa came out with the Boogie which featured a circuit for distorting the signal within the preamp of a guitar amp while the power amp stayed nearly perfectly clean.
By the early 80s Mesa realized that if time-based effects (reverb, delay, flange, chorus, etc.) were place between a hi-gain preamp and a clean power amp that certain of the old studio based effects could be modeled and the effects loop was born.

This effects-loop system doesn't work so well with amps where the power amp is being driven into distortion because then those time-based effects are also distorted.
If using a low watt power amp and driving it into clipping was essential to your tone then your only option was to mic your amp in an isolation box (or put a load resistor on your amp along with a slave out circuit and an speaker emulation circuit) and send that signal into your time-based-effects and then fold that back into a clean power amp and then out to some sort of full range speakers.
Of course there were several other flavours of this approach as well, but that gives you the gist of it.
That's a lot of gear to take to the Bar Mitvah gig you were playing that Saturday.

The moral of the story is that the effects loop paradigm only works well with preamp-gain-oriented hi gain amps and kind of sucks for non-master volume oriented hi-ish gain amps.
The H&K Cream Machine was the first guitar preamp device I ever saw that had a little tube power amp that you could push and then slave out to some time-based effects and then monitor with whatever.
But it had no channel switching and was a one-trick pony.

The modelers, like the Line 6 stuff that came out in the 90s, solve all of these issues by simulating the entire signal path, including the power amp distortion, in software .
The disadvantage was that they sounded like shit.
Enter Cliff Chase and the Axe-FX (circa 2005?).
*All* the above problems solved - and guitarists can now easily achieve the true "classic" signal path in a live setting with state of then art tone along the entire signal path whether monitoring through guitar cabs or FRFR cabs.

It might be a nice option to be able to put effects between the Axe's preamp sim and the power amp sim, but I'd probably never use it.
If I want my reverbs and delays and choruses to distort I can always place them in front of the Amp Block.

And as far as placing time-based effects in front of or after the Cab Block is concerned it really doesn't matter although intuitively you'd think it might.
This was one of my first concerns back in 2008 when I bought my Ultra but I was set straight quickly by several forum members including Jay Mitchell.
Search the forum for "LTI" or "Linear Time Invariant".
 
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This has been brought up before in the wish list. You can come close to a classic signal chain buy using AMP 1 Block into a FX Block into AMP 2 Block into a Cab Block.


Here's an old thread about it: http://forum.fractalaudio.com/axe-f...mps-adding-separate-poweramp-simulations.html


I place a lot of FX between the AMP Block and Cab block bc when I started using FRFR cabs and recording, I noticed a lot of high end that I never heard when playing through a regular guitar cab. By placing FX Blocks between the AMP and Cab Blocks, it makes the FX sound more realistic to me.

A good example is Factory Preset 375 - Diamonique Rain. Try putting a Cab Block at the end of the Layout grid and then try putting it before the FX. You'll hear a huge difference when listening through FRFR cabs or Studio Speakers. Then try disabling the Cab Block and play through a regular guitar cab. It will sound similar to putting the FX Blocks before the Cab Block.
 
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That being said, it's because of the physical limitations of an amp, and I see why it is the way it is in the Axe...which is the better way.
 
There isn't any difference with a reverb or similar block before or after the Cab block, unless the Drive parameter in the Cab block is used. As stated above, amp effect loops are basically a compromise to try to add "post" effects like they are added in the studio. It's much cleaner to add reverb after the power amp so the reverb tone isn't changed.

If you want to change the reverb sound only, use the low and high cuts in the block, or put it in an parallel row and put an EQ block after it.
 
Chris@AxeFxTutorials said:
There isn't any difference with a reverb or similar block before or after the Cab block, unless the Drive parameter in the Cab block is used. As stated above, amp effect loops are basically a compromise to try to add "post" effects like they are added in the studio. It's much cleaner to add reverb after the power amp so the reverb tone isn't changed.

If you want to change the reverb sound only, use the low and high cuts in the block, or put it in an parallel row and put an EQ block after it.
Click to expand...

Lol are you just saying things without having tried it, or do your ears not work? Reverb and other effects will have a difference depending on if it's before or after the Cab block even without the Drive parameter. Go try it.
 
The one part of all this I disagree with is the Mesa Mark series EQ sections. The EQ in that case should be able to be placed between the preamp and poweramp because the curve of the graphic EQ will affect how the power tubes distort. Ridiculous amounts of bass and nothing else will distort differently than ridiculous amounts of treble and nothing else.

Aside from that, basically all external effects are better outside of the amp than in the loop. And even then, you can always just place the Cab block after everything to get a decent simulation of "classic" effects in the fx-loop tone.
 
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