Workaround for "Power Amp only"

RB_Guitar

Inspired
Hi fellows,
as an owner of a tube preamp (Engl E530) sometimes I'd like to connect it to my Axe Fx Vintage Standard and use an amp sim to get some power amp only coloration. In my former attempts I chose a quite clean amp and tried to fiddle around with the tone stacks, amp EQs and sag=0 to get the preamp flat. But this is hard to tell by ear and the results were not so promising.

Yesterday I had an idea and would like to ask if anybody has done this before and what you think of this approach:
1. Select a clean amp model as Amp2 which you like as the power amp
2. Set amp drive fairly low, let's say 0.5 and set sag=0 to disable the power amp. Leave all other settings at default.
3. Now send some white noise through this patch and record it as an impulse response.
4. That's the tricky part for me: invert the measured impulse response to defeat the coloration of the tone stack/preamp.
5. Now we could choose another amp which is our preamp(external or Axe Sim with sag=0) and put the inverted IR and the Amp2 with low drive but sag > 0 after the preamp. Set the master volume and other power amp parameters on amp2 to taste.

What do you think? I don't know if this has been discussed, my search is limited to 10 results.


RB
 
Last edited:
Hmmm, I tried a PEQ but got nowhere near. I'm very slow but will give this a whirl. Am thinking of using the RedWire multi ir 'click' tool but instead of using the ir's, route it through the AXE FX. Hoping there is an inverter on the DAW somewhere.........?

The only thing I can think of is the IR is linear and the Amp pre is not although the settings are static when you drive the other pre in to it everything may change?
 
Of course this can only work with a clean amp model and static settings, especially for preamp drive. When you alter any preamp parameter you have to measure the IR again.
And I would set the inverted IR before the second amp because only this way your "real" preamp signal hits the power amp without any alterations

Does anybody know tools for white noise and for interting an IR? So +3dB will become -3dB at the same frequency. I'm using Reaper btw.
 
I meant the signal input from your external pre but ok. I'll leave ya to it :)

I think now I got your concern. As far as I understand you have to avoid all nonlinear changes between your external preamp and the virtual power amp. The only nonlinear part I could identify here is the drive parameter, so keep it low and your external signal doesn't change. If you want to push the virtual power amp you can use the IRs volume as "channel volume".
 
Thank you for your replies and ideas!
I fiddled around with the tonestack calculator, but even the Fender with Bass=0, Mid=10, Treb=0 was not nearly flat. And the Marshall, which I am after, had a huge drop in the low frequencies.
Of course I can get close, but will continue my approach. I first need another coax cable to connect my Axe in both ways to the DAW. I'll report when I get results.
 
Back
Top Bottom