1. We would like to remind our members that this is a privately owned, run and supported forum. You are here at the invitation and discretion of the owners. As such, rules and standards of conduct will be applied that help keep this forum functioning as the owners desire. These include, but are not limited to, removing content and even access to the forum.

    Please give yourself a refresher on the forum rules you agreed to follow when you signed up.
    Dismiss Notice

Mesa Mark IV Pentode/Triode Switch?

Discussion in 'Axe-Fx II Discussion' started by KH2203, Dec 24, 2016.

  1. KH2203

    KH2203
    Expand Collapse
    New here

    Joined:
    Mar 10, 2011
    Messages:
    41
    Likes Received:
    32
    Location:
    Omaha, Nebraska USA
    Merry Christmas everyone!

    Spent some time today with my Axe FX II trying to really nail the tone of my Mark IV. So far, I've managed to come really close but I'm having trouble getting the last bit of "feel" right where I want it. For the particular tone I'm currently after, I have my Mark IV's rear panel Pentode/Triode switch set to Triode. Does anyone know what the current USA Lead amp model is set to by default? If modeled based on this switch set to Pentode, is there a trick to simulating it set to the Triode mode? I think if I can work out this last little bit, I'll have the Fractal right where I want it.

    I've searched the forum looking for some answers but haven't come up with much. Any help/suggestions are greatly appreciated!
     
  2. unix-guy

    unix-guy
    Expand Collapse
    Legend!

    Joined:
    Aug 3, 2013
    Messages:
    10,827
    Likes Received:
    6,615
    Location:
    Vacaville, California
    I don't know the answer, but I would try playing with Power Amp tube type...
     
  3. firmani99

    firmani99
    Expand Collapse
    Inspired

    Joined:
    Jul 11, 2015
    Messages:
    293
    Likes Received:
    152
    I'd be curious what it is defaulted at also.
     
  4. soheil

    soheil
    Expand Collapse
    Forum Addict

    Joined:
    Oct 3, 2012
    Messages:
    1,427
    Likes Received:
    625
    Location:
    Iran
    +1
     
  5. mr_fender

    mr_fender
    Expand Collapse
    Fractal Fanatic

    Joined:
    Mar 31, 2014
    Messages:
    3,231
    Likes Received:
    2,311
    To my ears, Pentode mode sounds louder, tighter and punchier while triode mode sounds more pushed, compressed, and loose. On my Mark IV, Pentode mode sounds better for loud playing and triode mode sounds better for low volume playing. Makes it sound more like it's cranked at lower volumes. I find that the master volume in the Axe models gives a similar difference. Set low, it is tighter and more clear and punchy. Set high it's looser and more compressed. YMMV.
     
  6. Jean-Pierre Brunod

    Jean-Pierre Brunod
    Expand Collapse
    Inspired

    Joined:
    Mar 12, 2012
    Messages:
    209
    Likes Received:
    85
    Location:
    Rome, Italy, Italy
    If I remember correctly, after you've changed your tube type to EL34 / 6L6 you should play with the transformer match parameter to get that pentode/triode sound. This is because the Axe automatically adjusts the bias according to the power tube selected and so that "typical tube-change" sound is missing.
     
  7. FractalAudio

    FractalAudio
    Expand Collapse
    Administrator
    Fractal Audio Systems Moderator

    Joined:
    Jul 29, 2008
    Messages:
    12,937
    Likes Received:
    85,456
    There isn't any way to run the virtual power tubes in triode mode... but you can change the Power Tube Type to "300B" which is a triode.

    When you run a pentode (or beam tetrode) in triode mode you connect the screen to the anode which effectively defeats the screen. This lowers the output impedance of the plate significantly which, in turn, lowers the output impedance of the amp itself making the voltage output less dependent on the speaker impedance. Using the 300B tube type should get you pretty close.
     
  8. AdmiralB

    AdmiralB
    Expand Collapse
    Inspired

    Joined:
    Sep 4, 2008
    Messages:
    489
    Likes Received:
    146
    Location:
    Central Indiana
    This makes sense to me. Oddly enough, the 300B is the one 'choice' in the tube selection matrix where I actually hear a difference - and even it is subtle.

    Which matches my experience with real amps with tied screens. You get tone changes because the impedance is different, and because - for a given volume level - you have more compression. Not that triodes have a 'sound', at least IME.
     
  9. pima1234

    pima1234
    Expand Collapse
    Fractal Fanatic

    Joined:
    Nov 24, 2012
    Messages:
    3,025
    Likes Received:
    1,483
    Location:
    Michigan
    Power tube changes are so much about the break up and feel, at least in some ways.

    Otherwise, the sound of an amp is largely about its circuitry and the speaker cab.

    I have owned amps with a Pentode/Triode switch, and hadn't thought about trying to replicate that on the AxeFX until now. Cool
     
  10. KH2203

    KH2203
    Expand Collapse
    New here

    Joined:
    Mar 10, 2011
    Messages:
    41
    Likes Received:
    32
    Location:
    Omaha, Nebraska USA
    Thanks all for input and helpful comments. I gave the "300B" tube type a try and definitely noticed a change in feel. In my continued tweaks to fully match this sound, one thing I totally left out of of my Fractal chain was the fact that I was recording my Mark IV through my UA Apollo with the API Unison Preamp plugin running. That was definitely adding a bit more gain and some "sauce" that I really liked and turned out to be contributing more to the missing feel than the Pentode/Triode thing. So ultimately, I left the tube type at the default 6L6 and added just a touch of preamp gain in the CAB block (set to transformer type - which I think is similar to the API 212L plugin I'm using on the UA). That got me so close that I really can't hear (or feel) the difference anymore.

    I really can't say enough about the Axe FX. I started almost 6 years ago with a Standard and have had my Axe FX II for the past several years and have never really been able to dial in a better Mark IV sound that I could get with my actual head. Always loved the sounds I could get from other amp models in the box, but just never really settled on "my" Mark IV sound the right way until now.
     
  11. barhrecords

    barhrecords
    Expand Collapse
    Axe-Master

    Joined:
    Mar 26, 2010
    Messages:
    8,968
    Likes Received:
    5,891
    Location:
    34.673, -86.745
    From that description, would lowering the low / high resonance in the amp block spkr page produce a similar result?

    Trying to think through making the voltage output less dependent on speaker impedance.
     
  12. FractalAudio

    FractalAudio
    Expand Collapse
    Administrator
    Fractal Audio Systems Moderator

    Joined:
    Jul 29, 2008
    Messages:
    12,937
    Likes Received:
    85,456
    Yes.
     
    barhrecords likes this.

Share This Page