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Trainwreck Express Tweaks

FractalAudio

Administrator
Fractal Audio Systems
Moderator
A real Trainwreck Express is a fizzy, spitty amp. Some people like this. The same people who like fuzz pedals and that quasi-half-wave rectified sound. Personally I like more clarity.

The reason the Express is like this is primarily due to the last triode stage before the phase inverter (PI). This stage is biased very cold and drives the PI very hard due to the lack of any limiting resistor (grid stopper) between the triode and PI.

The lack of a grid stopper resistor and large coupling capacitor create significant bias excursion (blocking distortion). It appears the designer attempted to minimize the bias excursion by biasing the triode cold which limits its positive excursion and therefore limits the PI grid conduction. Despite the cold bias point the PI grid is still heavily overdriven resulting in massive blocking distortion.

The Axe-Fx allows you to reduce the amount of block distortion via the PI Bias Excursion parameter. Simply turn this down and the spittiness will go away. You can then also rebias the triode via the Preamp Bias parameter. Values closer to zero result in a more symmetric waveform.
 

pharmd07

Inspired
I find the bass in Trainwreck amps to be pretty loose. Will this improve with your suggested modifications?
 

Admin M@

Administrator
Fractal Audio Systems
Moderator
It's a bit funny to me to learn so much about this amp now. Many years ago, I played through a Trainwreck on a recording, because the studio here in NJ had one and I was told that it was a great amp. As we dialed it in, I thought it didn't sound very good... but I felt like one of the onlookers of the emperor's new clothes, and I didn't say anything! Studio time was expensive. Engineer and bandmates apparently thought it was "fine". Away we went. In retrospect, I always wondered if there had been something wrong with the amp. I guess I blamed my dissatisfaction with that session on other things.

Cut to today. Now, when I play this model (with the default settings and new knowledge) I experience things in a new light: the I get the same "weird" effect: blocking distortion makes it feel like I can't dig in without what I'd call an unpleasant "spitty" tone.

Cliff's suggested tweaks do indeed improve this amp model in my opinion. If only the Axe-Fx III had been by my side in 1989!
 

WW Audio

Inspired
In Axe Edit, there's a PI Bias Exursion setting in both the Preamp and Power Amp pages. With the Express model, the default Excursion on the Preamp page is 22%, the Power Amp page is 81%. To my ears, turning down the one in the Power Amp section seems to reduce the fizzy spitty stuff the most. Is this the one referenced in the OP?
 

pitta

Inspired
Would it be possible to create a FAS Wreck2 Model with an optimized Trainwreck circuit, please?
Otherwise, presets with these settings would likely be reset by future firmware upgrades and would require additional preset maintenance.
Thanks for considering.
 

FractalAudio

Administrator
Fractal Audio Systems
Moderator
In Axe Edit, there's a PI Bias Exursion setting in both the Preamp and Power Amp pages. With the Express model, the default Excursion on the Preamp page is 22%, the Power Amp page is 81%. To my ears, turning down the one in the Power Amp section seems to reduce the fizzy spitty stuff the most. Is this the one referenced in the OP?
Yes.
 

Joe Bfstplk

Power User
It's a bit funny to me to learn so much about this amp now. Many years ago, I played through a Trainwreck on a recording, because the studio here in NJ had one and I was told that it was a great amp. As we dialed it in, I thought it didn't sound very good... but I felt like one of the onlookers of the emperor's new clothes, and I didn't say anything! Studio time was expensive. Engineer and bandmates apparently thought it was "fine". Away we went. In retrospect, I always wondered if there had been something wrong with the amp. I guess I blamed my dissatisfaction with that session on other things.

Cut to today. Now, when I play this model (with the default settings and new knowledge) I experience things in a new light: the I get the same "weird" effect: blocking distortion makes it feel like I can't dig in without what I'd call an unpleasant "spitty" tone.

Cliff's suggested tweaks do indeed improve this amp model in my opinion. If only the Axe-Fx III had been by my side in 1989!
I had my first experience with a Marshall through a hot-rodded one in a small studio in Hamilton Square (near Trenton) in 1987. I should have picked up one of the Park heads and a 4x12" from The Music Box on 33 instead of the '70s Twin Reverb....
 

Freds55

Experienced
I never heard a real Trainwreck amp but the sim is amazing (Liverpool version)
In this video the sound is so creamy...
Maybe I combined the amp with wrong cabinet but the result is perfect in my opinion :D

Marco that was stupid good!!!
Awesome sounds and picking. You really are a talented musician my friend:)
I really enjoyed your video as alway.... thanks for sharin.
 

FractalAudio

Administrator
Fractal Audio Systems
Moderator
Another simple tweak is to simply turn the Master Volume down. This will reduce the phase inverter overdrive.

The models also make good clean patches if you turn the Input Gain way down. You may want to turn the Bright Switch off in these cases. I dialed up a fantastic clean yesterday by setting Input Gain to ~1.3. Very dynamic and crunches just a bit when you dig in.
 
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