5751 for DSL40CR headroom?

Discussion in 'The Workbench' started by SkyMonkey, Jul 27, 2019.

  1. SkyMonkey

    SkyMonkey Well-Known Member

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    Hi guys. I am thinking of ordering a 5751 in an attempt to improve the useable headroom of the Ultra Gain channels of my DSL40CR. At the moment with the stock tubes it is pointless turning the gain above 6 on the dial. After that the sound just gets mushier and the volume seems to dip out when palm muting.

    So would a new JJ tube like the 5751 or an ECC83MG shift the maxing out of useable headroom to somewhere like 8 or 9 on the gain dial?

    Also I am not sure which position to try one of these tube in.
    Anyone tried this?
    P.S. I cannot roll any of the tubes yet as my collection so far is only 1 ECC83 from 1997 that I removed from a Valvestate VS65R!

    Cheers.
     
  2. Guitar-Rocker

    Guitar-Rocker Well-Known Member

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    While you're gain factor possibility will be lowered with a 5751 (100 with 12ax7, 70 with the 5751), I doubt there would be much difference in headroom, that would be noticeable. But give it a try.
     
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  3. pedecamp

    pedecamp Well-Known Member

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    I got a couple 5751's to do the same thing with a Peavey 6505mh I had and it was hardly noticeable. I would try something else like a 12AY7 or 12AU7.

    [​IMG]
     
    Last edited: Jul 27, 2019
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  4. ampmadscientist

    ampmadscientist Well-Known Member

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    The tube lowers the input sensitivity, but does not change the headroom at all.

    It's the V1A cathode bypass capacitor, not the preamp tube.
    The capacitor allows too much subsonic low frequency to pass through, creating overload / over-compression in the lower frequencies.

    With a schematic (which we don't have) some solutions could probably be created...
     
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  5. pedecamp

    pedecamp Well-Known Member

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    Or if he wants more head room use the clean channel! :yesway:
     
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  6. SkyMonkey

    SkyMonkey Well-Known Member

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    One of the things I hoped it might do is increase the difference between OD1 and OD2.
    OD1 has too much gain when I set OD2 where I want it. But also it just seems a bit of a waste when the useable gain tops out a notch 6. I suppose this may not be the case for single coils and they could go a bit higher?

    I wasn't expecting a capacitor to be the problem. So too much subsonic signal (that we probably cannot actually hear) might be the reason for the early gain compression.

    I might try a JJ ECC82 (12AU7) just for the hell of it, only costs £10, and I should start a tube collection at some point. If I do I get one will report back.

    BTW which position is best, V1 or V2? Or is there any difference?

    Cheers guys
     
  7. ampmadscientist

    ampmadscientist Well-Known Member

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    If the cap is decreased there will be much less muddiness and much less subsonic compression.
    V1 is where the problem starts out.
    But it's harder to analyze because no schematics.

    The headroom remains the same because the power supply is still the same.

    Different tube will make the amp more or less sensitive but does not actually alter the headroom.
     
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  8. SkyMonkey

    SkyMonkey Well-Known Member

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    I think I may be using the word headroom in the wrong context here! I am meaning being able to take the Ultra OD2 gain dial higher than notch 6 without the tone mushing and compressing out (up to 8 or 9 maybe).
    Can you state what you mean by headroom please AmpMad?
     
  9. BftGibson

    BftGibson Well-Known Member

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    did quite a bit of recording with CR...into GT75/V30 cab & greenback cab tho..biggest dif i ever heard in an amp..getting it out of the enclosure.....a stiffness was gone....looked quick at my notes..highest we got gain was noon on any, always had MV dimed also makes a dif..it stays tighter..now ..my 100h had my tech do some mods..gain usable without fizz the whole way but we brought the amp down a bit, still heavy as needed but very much more control. The MV was usable the whole sweep.I like both amps. but the mods really made that 100h go into dif territory. maybe one of the most controllable versatile amps i ever experience. Again tho..no need for gain past noon..it didnt do much beside add fizz & at noon it had a ton of gain..only thin out after that point
     
  10. BftGibson

    BftGibson Well-Known Member

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  11. stickyfinger

    stickyfinger Active Member

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    JJ has a tube that works great for this application. Forget the name though..

    One half is a 12ax7 and the other is a 12ay7 (I think)
    With this it doesn't effect the clean/crunch gain but lowered both lead/OD channels gain.
     
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  12. ampmadscientist

    ampmadscientist Well-Known Member

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    Headroom just means that when you amplify a signal the amp stage has not maxed out to point of distortion.

    Let's say that Guitar into V1A:
    72 volts output, and the stage can be driven to 120 volts out, before distortion (clipping) occurs.
    You still have headroom in that stage.

    But what is really happening:
    The lowest frequencies are being amplified (example 20 Hz).
    And when that 20Hz hits the compression stage, it makes the amp sound muddy.
     
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  13. Cadorman

    Cadorman Well-Known Member Premium Member

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    I have 5751s in V1 and V2 of my TSL100. Works great. If you really want to use a lot more of the gain knob without distortion a 12AY7 may be what you are looking for. Just depends on how much breakup you want.
     
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  14. SkyMonkey

    SkyMonkey Well-Known Member

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    Hi stickyfinger. There is JJ tube in their catalogue called the ECC832 - 12DW7 which is a combined double triode.

    "ECC832 is 12DW7 pre-amplifying double triode. It combines 12AX7 and 12AU7, where the 12AX7 is used as 1st stage and the 12AU7 as 2nd stage."

    I have found some reviews on Amazon that make this sound like a good candidate.

    As I have no tubes so far, to speak of, I am going to get a selection of JJs to experiment with.
    Thinking of:
    ECC83s 12AX7 tested for Phase Inverter (V4?)
    ECC832 12DW7 to try in V1
    12AY7 - 6072 to try in V1 or V2 with 12DW7
    ECC82 for lowest gain option in V1.

    Cheers guys. I will report back.
     
  15. ampmadscientist

    ampmadscientist Well-Known Member

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    The problem is the circuit design not the tubes.
     
  16. Chris-in-LA

    Chris-in-LA Well-Known Member

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    Not sure why it matters where it mushes out. Just set the knobs where the amp sounds good to you and forget about what number they’re on.
     
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  17. SkyMonkey

    SkyMonkey Well-Known Member

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    I think I have started this thread off on the wrong footing by my misuse of the word HEADROOM.

    I am also trying to see if the OD1 and OD2 gain levels can be made to be further apart. To my ears they have very similar gain levels. I don't know if this is just a peculiarity of my amp or DSL40CRs in general. Just my own crackpot theory that because the 2 voicings use the same gain setting (i.e. only one shared gain knob) they are maybe pushed closer together gain-wise because only half the sweep of the gain knob is useable on the Ultra channels. If more of the gain sweep is useable might the resultant gain of the OD1 be lower in comparison to OD2.

    No one has replied yet as to whether they have tried anything similar with this particular amp, so I am assuming no one has.

    I may be on a hiding to nothing, but it is a relatively cheap experiment, and with all the threads I have read about tube rolling I think the only way to actually understand the differences is to do it myself.
    As I said in my original post, I have only got one crappy "no-brand" ECC83 that came out of a 1997 MkII Valvestate, so a collection has to start somewhere.

    :fingersx:
     
  18. BftGibson

    BftGibson Well-Known Member

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    on Ultra my mind set has always thump green..more gain quickly on red..i use them that way... set my red up darn close to my SLX witch is always my go to lead sound.its freakishly close..but again gain, way lower..that gain on Ultra is being used like immediately..there is a ton of movement in small increment from just barely on to noon..after noon its just saturation..if you are trying to stay tight.it wont help at all...use the ears...also get the MV up then set..if a DSL is used too low it is not designed to do much..but MV up..it becomes an animal...hey what pickups are you using..if they real hot it will influence a lot..can be an instant fizz fest from the door with too much gain. have been using way less gain & less hot pups & seeing the tone thicken up & also very clear
     
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  19. ampmadscientist

    ampmadscientist Well-Known Member

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    Lots of people have tried it...the complaints of muddiness in this amp are pretty frequent.
    Well, it is an issue (in a way) with "headroom."
    Just related to low frequency headroom as opposed to overall.

    But what players don't understand is that using different tubes doesn't change the headroom.
    That misunderstanding is pretty wide spread.

    See? I will explain this a little more for those who are interested.

    The Marshall sound is crunchy compressed highs and clean lows.
    That's what makes a Marshall sound like a Marshall.
    But in the design of this amp, the lows were not maintained as "clean." It's different than other Marshall amps in that respect.

    To accomplish this:
    the lows are intentionally rolled off in the first stage of the preamp. Like this: /
    The higher the frequency, the less roll off.
    The lower the frequency: the more roll off.
    This is how the traditional Marshall preamp maintains clean lows.

    But in this amp: the lows were not rolled off. Result: too much distortion in the lows, which sounds like mud.
    It's sounding more like a Mesa Boogie rather than --- what a Marshall sounds like.
    Not the British sound anymore.
     
    Last edited: Jul 28, 2019
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  20. SkyMonkey

    SkyMonkey Well-Known Member

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    Hi BftGibson.

    I won't list my pickups as they are all in my signature, but as you can see they are generally on the high output side. Generally they are set at about 4mm clearance from the strings. I am a metalhead at heart, hence the high Ultra gain setting I keep quoting (notch 6, between 1 and 2 O'clock). At this setting I get upto but not over the point of mush compression and can still use overdrive to push for more harmonics. But the Ultras are too together close for what I want them for.
    Ideally I want to set and forget OD1 for rock and OD2 for metal, but there is not enough distinction to my ears.
    Don't get me wrong, this is the best amp I have ever had for what I want out of it. I just want to see if I can tweak it to suit me slightly better. The range of tones from my different guitars keep things nice and varied, and the tones are lovely and fat, especially with the new speaker.
    I will try using the MVs higher though. I am guilty of keeping them low. I guess as I am not a gigging musician I tend to keep the MVs low at bedroom levels, and set the gain and channel balance with the channel knobs.
    I am also running my DSL with a BOSS GT-100 in 4CM, which adds extra layers of gain/volume/boost/overdrive complication. :scratch:

    I do love to tweak though. :hmm:
     
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