Using output level of multi-FX unit in FX Loop as an attenuator??

Discussion in 'Amps and Cabs' started by Deuterium, Mar 13, 2015.

  1. Deuterium

    Deuterium Member

    Messages:
    773
    Joined:
    Sep 19, 2005
    I apologize in advance if this is a stupid question...

    I use either a Digitech GSP1101 or a Rocktron Xpression in the FX loop of my tube amp heads (Eganator Rebel or Marshall Vintage Modern).

    I have always had a question as to using the rack FX unit's output level to control the volume of the amp. Specifically, the question is...should I adjust the rack FX unit for maximum output level, and control volume on the master volume of the amp...or should I crank the amp's MV, but control volume by turning down the output level on the rack FX unit?

    My original thinking was that if I increased the MV on the amp, I would be pushing the power tubes more...and that I could tame the overall volume level with the Multi-FX output level. In fact, at one point, I couldn't understand the demand for amp attenuators, given that most amps have an FX loop, and one could use a prosumer FX unit, in the amp's FX Loop, to control the output signal (and volume) to the amp's power section.

    Now, however, I am not so sure this is ideal. I mean, when doing this, the Multi-FX unit isn't really acting like a true attenuator. Also, even if the MV on the tube amp is set high, but the signal coming from the Multi-FX into the amp's FX Return is very low, I imagine I can't be pushing the power tubes very much at all. Is this accurate?

    So, I guess my real question is what is the best way to set output levels to control volume, when using a rack Multi-FX unit in a tube amps FX loop (given the tube amp has a Master Volume)? Am I compromising tone by using the output level on my Xpression or GSP1101 to control over-all volume?

    Thanks in advance for any and all input and guidance.
     
  2. Roccorobb

    Roccorobb Member

    Messages:
    608
    Joined:
    Nov 12, 2013
    Location:
    Virginia Beach
    I would control volume with the amps MV and not the fx unit.
    Most MVs come after the fx loop. They are (hopefully) designed to control overall volume in an ideal way for that amps circuit, and probably expect a fairly strong signal.
    Controlling vol from an active fx unit can work, but it may introduce more noise.
    You are correct in your 2 conclusions that:

    1 - controlling vol from the fx loop is not the same as a power attenuator (which bleeds signal to a load *after* the power section)
    2 - maxing amp MV while reducing vol @ fx unit doesn't push your power tubes any harder than the other way around
     
  3. LPVM

    LPVM Member

    Messages:
    2,071
    Joined:
    Jan 21, 2009
    Location:
    Dutchess County NY
    That's the same as running a volume pedal in your loop which I do often. Whatever works for you, there are no rules here.
     
  4. 8len8

    8len8 Member

    Messages:
    9,549
    Joined:
    Dec 25, 2010
    Location:
    Chicago
    Doing so would reduce the signal going to the power tubes. That's ok if you don't want power tube distortion.
     
  5. Deuterium

    Deuterium Member

    Messages:
    773
    Joined:
    Sep 19, 2005
    Thanks for the replies, everyone. Very much appreciated. Thanks for confirming my suspicions. That is, if I specifically want to push the power tubes (in order to increase the contribution of power tube distortion to my overall tone), I need to look towards an attenuator or something like the Fryette Power Station.
     
  6. slybird

    slybird Member

    Messages:
    5,363
    Joined:
    Feb 8, 2014
    I program my rack effects to boost and attenuate. I set the units to -9db clean (effects off) and then adjust output until there is no volume difference between loop on/off. After that I will set up a CC for volume changes if they are needed.
     
  7. drbob1

    drbob1 Silver Supporting Member

    Messages:
    21,974
    Joined:
    Aug 9, 2004
    The Marshall is designed for the output stage to stay pretty clean, so it would work well in that case. I'm not sure about the Egnator. But yeah, if you want to try and get some power tube crunch, an attenuator is the only way to go, and the Power Station is one of the best!
     
  8. joeprs

    joeprs Member

    Messages:
    1,517
    Joined:
    Jan 6, 2002
    Location:
    NV
    I agree with this. But do what sounds best to your ears.

    I might add, if you put your multi-FX unit in front of the amp, not using the loop, you could push your volume on the amp and MV as high as you want and lower the volume on the FX unit to keep the level where you want it. I used to run my Digitech RP2000 this way with good results, at least to my ears. Plus, I could raise or lower my volume w/o having to go to the amp, when I was on stage. Keep in mind, you might like this, or you may prefer using the loop. There really aren't any rules here, do what sounds best to your ears.
     
  9. Mark Robinson

    Mark Robinson Member

    Messages:
    7,087
    Joined:
    Sep 9, 2002
    Location:
    Redondo Beach, California
    Compare the results and decide with your ears. I have run an Intellifex in the loop for a long time.
    First I go to the input relationship of the send from the amp and the input of the effects unit and make sure I've got ample signal in the unit and some headroom so as to avoid clipping in that stage. Make sure you try the plus 4/versus -10 switch if you have that option in the effects unit. If you have a better match one way, you'll hear it and possibly see it in the input metering.

    Then what I do is get a reference for how the amp sets up with nothing in the loop, and I will go back and forth once in a while with just a cable or the loop unplugged and compare that volume to the volume with the effects unit in line adjusting the output of the effected signal to match the amp signal path with no effects in the loop. So then I know where unity gain is. But I actually don't care where unity gain is, I'm just looking for what sounds natural and the best to my ears. But it's nice to know. Its possible to starve the amp for signal and wonder what happened and it's possible to bombard the return section and ruin your sound too. So knowing where you are in volume, with reference to the natural volume of the amp is useful.

    Then you use your ears and I have found that I will often bring the effects loop signal in pretty low to play quietly.

    In a live playing situation, you have some flexibility. If you have a multichannel amp, keeping the master up, will usually help out the clean channel, more than it hurts the dirty channel.

    So compare the sound of a hot return signal with the master down, to the sound of a lower return signal and the master volume up. It is likely that you run into some hiss or noise increase one way or the other depending on the quality of your effects unit and your amp loop. Use your ears and have fun with it. There are times with good loop design where they will sound pretty identical, other times not so much.
     

Share This Page