FX loop location in the signal chain ?

  • Hi everyone,

    Where is located the effect loop in the signal chain of the Bias Head Processor ?
    Between the "preamp stage" and the "tone stack stage" ?

    Thanks for your help


  • Up !

    Nobody knows ?

  • I actually knew the answer to this at some point as I recall testing it out using a signal from my phone into the FX return. I can say that the Output knob is definitely placed before the FX Send, because it has zero effect on the signal coming in through the Return.
    I'm guessing that it's something like Power Section / Output knob -> FX -> Amp Sim/IR -> out. I can do some more tests next time I have my amp handy.

  • @Ash-Wolford
    Tanks for you answer.
    So your feeling is that the loop is placed after the power section...
    Strange... I was wondering Preamp -> FX -> Power Section...

    Something like this :


    Hi Felix, do you have the answer ?

  • Moderator

    @serge-cattoul Yes it's after the power section!

  • @Felix
    Thanks for your answer.
    So in my case (I use the Head Processor) the fx loop is useless...
    If I put some effect pedals like reverb, chorus,... after the "line out" (unbalanced) it's the same than using the effect loop?
    Could you confirm ?

  • @serge-cattoul I believe the line out would be after the power section since that's presumably going out to PA/FRFR?

    I use the head with the effects loop, what's happening when you use it?

  • @Liam
    Hi Liam,
    I use it also, with only 1 effect pedal (Eventide H9) in the fx loop, and I had to decrease its outpul level otherwise the sound was crappy... I didn't have to do that before using the Bias Head Processor (this one replaces a Tech21 Fly Rig 5).
    So I try to understand why I have to do that.
    The Bias Head Processor is new for me, I have it for 3 weeks now, and I would like to understand the signal flow.
    Don't forget that I'm talking about the Processor Head, not the Powered one...

    As you know, the "classic" implementation of a FX Loop in Guitar amplifier is :

    • Guitar->preamp->send to external FX

    • Return from external FX->Power Section->Cab/Speaker

    Why is it implemented differently in the Bias Head ?

    My idea is that, the signal processing being digital, from the head "input" to the head "line out", if you want to insert a FX Loop in the half of the chain, you need to convert the signal to analog before the "FX Send", and convert it again to digital after the "FX return".
    With the FX Loop placed after the power section (incuding the speaker sim), you just have one analog signal that is either sent directly to the PA/FRFR (through the line out) , or if you use the FX Loop sent to the external effects and then to the line out... no more digital processing needed !

    I will test it this way : I will compare these 2 configurations and see what's different :

    • my effect pedal connected to the "Send" output and the output of the pedal connected directly to the PA/FRFR. If I can modify the ouput level with the Cab Master Level, then I can conclude that the "FX Send" is the same signal than the "Line Out".

    • my effect pedal connected to the "Send" output and the output of the pedal connected to the "Return" input, line out to the PA/FRFR. (that's my current config).

    It's not a question of sound quality. Even if it's not easy to "master" Bias Amp 2 software, I'm happy with the sound I get, even more since I upgraded it to the "Elite" version allowing me to use the Celestion IR's.
    But, once again, I really want to understand the signal flow.

    Sorry being so long...

  • @serge-cattoul Ahhh, I think I get what your saying but I'm not too sure I can help unfortunately. Hopefully Felix can help a little more, hope you get it sorted!

  • @serge-cattoul if i'm not mistaken, FX is after the power section but before the cab sim / IR, so you still get the proper cabinet coloration. Thus it's not exactly pointless if you're using the cab section.

    I can't speak with authority, but I imagine the reason they do it this way is because modulation effects usually sound best when placed after all distortion effects -- which would ideally include the amp's power section, but that's not normally possible for obvious reasons. Normally with amp heads, post-preamp is the last place they can feasibly be placed without outright destroying the effects units.
    With the BIAS stuff however, the power section is modeled (even in the powered units the actual poweramp is after the cab sim), so they can safely move the FX send after it and before the cab sim for the most efficient usage of effects. This is probably why you have to change levels on your effects compared to normal amps -- the normal amps might be crushing the level change from the effects units via the power section, while it's free to apply whatever level changes it likes with the BIAS unit.

  • Felix said it's after the power section.

  • So I have started testing...
    I have connected my guitar directly in the "Return" input of the FX Loop, and as I expected, when I change the Cab Level, there is no changes in the sound volume...
    I have also connected the send output to my active speaker, and this time changes of the Cab Level affect the sound. The difference between the send out and the line out is that the line output is louder.
    So my conclusion is that the FX Loop is placed after all digital processing, cab SIM included.