Mid range boosting tubes...is it a thing?

Discussion in 'Amps and Cabs [BG]' started by 707GK, Sep 14, 2018.

  1. 707GK


    Jun 13, 2013
    A while back, I sold my Ashdown LB30 and regretted it from day 1. So recently, I saw a used CTM-30 and bought it, and I love this little amp. The stock Ruby tubes break up really easy and I remember my LB30 having JJ’s and it didn’t have this problem. So I will be re-tubing it very soon!

    Now, my question is are there any tubes that will affect my midrange? I also have a CTM-100 and it has some of the nicest, creamy, tubey midrange I have ever experienced playing through an amp. The CTM-30 is a bit mid scooped and I am wondering if there are any tubes (reasonably priced) that will help this, or is it just part of the amp itself?

    I’m leaning towards all JJ’s as I have read it is more just how the amp is voiced than anything else, and JJ’s are reliable and consistent in my experience. I’m playing a EBMM Sterling through a Philosophers tone compressor, and using Greenboy Bassic cabs. So there is a slight dip in the 500hz range on the cabs which I try to balance out by boosting the midrange control on the Sterling, which is roughly in the same frequency range.

    The CTM30 just feels a bit boomy unless I cut the bass, and then it feels a bit thin (in a variety of different size/shape rooms, the result is always roughly the same). The low end on the 100 is very crisp and not muddy at all, in any room I have played it in and the midrange is just about perfect. Is this just a difference between KT88 and EL84 power tubes?

    Thanks in advance.
    Last edited: Sep 14, 2018
    FronTowardEnemy likes this.
  2. FronTowardEnemy

    FronTowardEnemy It is better to go unnoticed, than to suck Supporting Member

    Sep 19, 2006
    Chicago Illinois
    I have the LB30 and I swapped out my tubes for some Tube Dr. EL34s in the power section and Tung Sols in the preamp.

    I have a Fender Super Bassman, which I find has a wonderful tone all the way around as well as perfect midrange through my GB Uber 410, Tech 21 B410, and Avatar 212.

    Like you, I found the bass to be a bit boomy and not so tight with the LB30, though the midrange was not too bad.

    I did find out through trial and error that setting my mid control to around the 11:00 position and the bass just a hair above full counter clockwise, that I was able to create a nice cut through the mix with tight lows and punchy midrange.

    I think no matter what tubes you put in it, you are going to find that this amp has a baked in tone. I love it though and will never ever give it up. It is a beastly little bastard. I play Fender P and J basses. I tend to like my LB 30 the best through ceramic speakers like my Tech 21 B410.

  3. BassmanPaul

    BassmanPaul Inactive

    The voicing of an amplifier is something that the designer builds in. It doesn’t matter what particular tubes he uses to reach his/her goals.

    Comparing a KT88 to an EL84 is like comparing a Ferrari to a VW Bug.
  4. 707GK


    Jun 13, 2013
    Thanks for the replies! I will have to keep messing with the tone controls to what was recommended above. I figured it was a baked in tone and swapping tubes would only help the breakup point and not the tone. I like it a lot for low volume rehearsals and hope to use it for gigs if I can figure out how to get rid of the mid scoop.
    FronTowardEnemy likes this.
  5. FronTowardEnemy

    FronTowardEnemy It is better to go unnoticed, than to suck Supporting Member

    Sep 19, 2006
    Chicago Illinois
    Also mess around with the mid switch. It can add serious lowmid to the tone. I use it in the less bassy mode, down position on the LB, and it makes a world of difference with the low end.

    This is how I run it with a Fender RW P bass with AVRI 63 pickups in it.
  6. Not true -- at all. Many tube amps are designed, and designers tweak the circuits, based on the tubes they are using. This is especially true in amps we see and use, and preamp sections using 12A*7s are no exception.

    OP: JJs, compared to MIC Rubys (and current production MIR Tung-Sol, for that matter) will display more midrange. ALso, they are relatively inexpensive, so it won't hurt your wallet much to try a 12AX7 and 12AU7 and see how they work for you.
  7. BassmanPaul

    BassmanPaul Inactive

    Sorry Dave but what I say is very true. :D
    agedhorse and SirMjac28 like this.
  8. Maybe that's how it works for you?
    Then maybe you could explain why amp designers and builders have used certain brands of tubes, and/or refined their their circuits based on the sound and response of certain tubes? Maybe even why some tubes of the same type sound different than others?
  9. Wasnex


    Dec 25, 2011

    LB30/CTM30 use 12AX7s in the preamp and the CTM100/300 uses 12DW7s. The voicing and gain characteristics of these preamps are drastically different.

    The LB30/CTM30 preamp is almost identical to Ashdown's old Dual Tube preamp. The Dual Tube preamp was a bit scooped and the lows were a bit woolly sounding to my ears. These amps use a Fender tone stack with a few mods. Pretty sure the architecture of the tone stack in the big CTMs is almost identical, but some of the component values are changed so these amps sound and behaves a bit different from the earlier Dual Tube series. The Dual Tube preamp was optimized to be clean while the preamp in the CTM100/300 is high gain and designed for distortion. The CTM100/300 also has a strong low mid push like a Ampeg SVT that can be emphasized with push buttons on the front panel.

    The EQ in all of these amps is intended to be extremely interactive. The controls have a tendency to dominate each other; when one control is dominant, adjusting the other controls makes no difference. You can get a wide variety of sounds but the controls are not very intuitive. IMHO great sounding amps but, from a functional standpoint, the worst tone controls ever. YMMV.

    I haven't done any tube rolling in a Dual Tube preamp, but I believe the stock preamp tubes were JJ ECC83s. This tube is often described as mid heavy. I would describe it as narrow bandwidth...it doesn't do deep or high so it is perceived as lots of mids. This is a fairly low gain 12AX7 but it tends to break up easily and sounds a bit fuzzy and woolly to my ears. Every time I have rolled tubes in a bass amp with JJ ECC83s, they came out because I thought they sounded horrible. A few have found a new home in guitar amps.

    If you want to tighten up the lows I suggest trying a Russian Mullard 12AX7/ECC83 in V1 and a JJ ECC803S in V2.

    The Mullard is very smooth sounding and emphasizes clear tone and thick, deep bass. Seems to extend the highs and lows, boost the bass and mid bass, and has a dip in the high mids reducing clank and fret noise without gutting the sound. The low end produced with this tube was drastically punchier, tighter, and more focused than everything else I have tried. The highs tend to be smooth and a bit glassy.

    The JJ ECC803s has a tight, articulate, muscular sound and a relatively warm and even response with a bit of upper mid-range shimmer and slightly lean bass. It doesn't go as high or low as the Mullard but has a wider response than the JJ ECC83s.

    The Mullard ECC83 and JJECC803S together seem to create a nice synergy and have been a reliable combination in several of my bass amps. But the combination is not always my top choice. Different tonal priorities would require a different choice of tubes. My normal goal is for my amps to be capable of producing clear/tight lows, articulate mids, soft/smooth high mids, and slightly glassy highs with relatively neutral EQ settings. Also, keep in mind that tubes respond to circuit conditions, so they may behave a bit different from amp to amp, or even when you move them around from position to position within and amp.

    One characteristic where the JJ ECC83s is superior...it's a small plate tube so it should be able to tolerate more physical abuse and be less likely to go microphonic. The Mullard ECC83 and JJ ECC803s or both long plate tubes.

    Good luck!
    Raymundo49 likes this.
  10. BassmanPaul

    BassmanPaul Inactive

    Dave, you’re missing the point. Still, there have always been spreads in tube parameters even back in the hey day. nowadays who knows what you are going to get with manufacturers playing fast and loose with specifications. Anyone using tubes most likely goes through whole batches of tubes to find the ones that suit their design criteria.
    Last edited: Sep 14, 2018
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  11. Wasnex


    Dec 25, 2011
    The designer does bake in a voicing, but the voicing may respond to tube rolling. Some amps respond pretty noticeably to different models of 12AX7s, but with some amps it hardly makes a difference. I suspect the little Ashdown will respond in a noticeable way, but it won't be dramatic unless one of the existing tubes is bad.
  12. SirMjac28

    SirMjac28 Patiently Waiting For The Next British Invasion

    Aug 25, 2010
    The Great Midwest
    I think you're better off getting a preamp pedal
  13. ptensioned


    Jan 12, 2013
    Hamilton, ON
    One thing to note, just in case it hasn't been considered: Ashdown says the CTM-30 has a 'traditional' tone stack, which usually means Fender. If you set your knobs all in the middle, you end up with a heavily scooped EQ. Barring some variance, flat is closer to 0-10-0, bass-mid-treble. You might be able to get some mids back for free by turning down the bass and treble, and turning up the volume a nudge...
    707GK likes this.
  14. Ross W. Lovell

    Ross W. Lovell

    Oct 31, 2015

    If you knew the QC and the way they built tubes, the word consistent would be the last one used, especially on preamp tubes.

    They do however customize their circuits to achieve the voicing they desire based on the tubes they have decided to use.
  15. two fingers

    two fingers Opinionated blowhard. But not mad about it. Gold Supporting Member

    Feb 7, 2005
    Eastern NC USA
    Start with lows at 0, mids at 10, and highs at 0. That should be close to "flat" on the Ashdown.

    Keep in mind that the controls "mess with each other" a LOT. You'll need to experiment a lot.

    I love my LB30. With a large cab (4-10 or bigger) it's pure magic.
  16. agedhorse

    agedhorse Supporting Member Commercial User

    Feb 12, 2006
    Davis, CA (USA)
    Development Engineer-Mesa Boogie, Development Engineer-Genzler (pedals), Product Support-Genz Benz
    I think your opinion, based on my experience, has a little bit of truth combined with a whole lot of internet mythology. The little bit of truth is often well overstated by those selling tubes, as well as those recreationally playing with tubes, ie. in place of drinking beer or wine or smoking cigars, etc.

    Generally, amp designers will test a variety of tubes to see how the circuit responds, and choose a tube that performs well with respect to a variety of parameters. This may include consistency across say a sample of 50 tubes of a particular model, microphonics, self noise, hum (primarily for AC heater models), and most responsible designers will develop and analyze ageing curves from which to extract expected lifetime models, and will also look at historical failure rates. For example, I will stay away from a particular tube that has a wide parameter spread, or a significant widening of parameters across the ageing curve, I don't care how fabulous one tube might sound if others that are not close would result in a player getting a mediocre amp also.

    Or, a designer will design a circuit to minimize the uncontrollable spread so that they don't have to test 50 tubes to get 10 acceptable ones. That would make buying replacement tubes that much more of a gamble in a world where the odds are already against them buying tubes.
    BassmanPaul, coreyfyfe, Mili and 2 others like this.
  17. 707GK


    Jun 13, 2013
    Awesome! I will try cutting the lows and highs while boosting the mids a bit. Will also try some different tubes as these Ruby tubes break up so early and instantaneously compared to the JJs I had in my LB30, which seemed a lot more “linear” or predictable.

    I do like the tone controls as they are very interactive with each other. I’ll just need to spend some time dialing it in. I suppose I was just spoiled with the 100, where I could plug in, everything at noon, and call it a day.
  18. Is the 12AX7 a gateway tube?
  19. Bassheart365


    Oct 19, 2014
    Northern California
    "A good bassist determines the direction of any band." - Ron Carter
    Telefunken. That is all.
    Spacecase likes this.
  20. 40Hz

    40Hz Supporting Member

    In this particular instance, I think so too. That or an outboard EQ.
    SirMjac28 likes this.
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