Making an 18 watt sound more like a Marshall, less like a Vox?

Discussion in 'Shock Brother's DIY Amps' started by itsGiusto, Aug 17, 2019.

  1. JD0x0

    JD0x0 Poster Extraordinaire

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    The tone control on the 18 Watt is just a high frequency roll off. The amp doesn't have the mid 'scoop' that the Fender/Marshall/Vox tonestacks have, so rolling the highs off leaves you with flat mids and rolled off highs, which might be where some of the nasally-ness comes from.

    Consider getting rid of the two inputs on the normal channel and instead cascading V1a and V1b and putting a plate driven tonestack between the stages, OR convert the 'low' input into a cathode follower that follows the first gain stage, and run a buffered Marshall tonestack. To get more of that voicing and the ability to cut out some mids for less nasally mid frequencies. Additionally, you can wire a 'tonestack lift' to a push pull, so you can bypass the stack for more gain, and a tone closer to stock (with the tone control rolled up)
     
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  2. David Barnett

    David Barnett Doctor of Teleocity

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    It's sort of its own thing really. The output stage is a generic cathode bias EL-84 PP, as published in Mullard manuals and used in lots of hifi amps, juke boxes, projectors, DIY articles in magazines, and anywhere the Brits might need a 10-18W audio amp in the late 1950s. I suppose the way the trem is applied is sort of AC10-ish but there are no pentodes in the preamp.

    I don't think Charlie Watkins was copying entire circuits from his competition, unlike Ken Bran who blatantly lifted the 5F6A Bassman and Watkins Dominator circuits whole to create the JTM45 and 1974.
     
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  3. Zepfan

    Zepfan Poster Extraordinaire

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    The 18watt isn't going to do Plexi tones very well.

    I've always liked the Creambacks over the Greenbacks when it comes to Celestion's. Closing the back will help get you more Beefy tone and the 9" wide/depth cab probably isn't helping the situation.
    Cab construction material makes a big difference too. What type of material is the Cab made of?
     
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  4. jsnwhite619

    jsnwhite619 Friend of Leo's

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    Yeah, no way I'd build a cab only 9" wide if it's bigger than a Champ. Add in a plywood cabinet, and it's just going to get brighter. Compare the standard Fender vs. Marshall differences with that and I think you know what you're going to get.

    A lot of classic amps and classic sounds where designed around being played wide open. It's hard to build a Swiss army knife amp without a lot of buttons and switches. Some apps sound great at low volume. Some sound great when you have it cranked wide open. The same thing that keeps the low volume sounding great usually makes the high-volume sound bad. And the other way around. if it holds together enough to sound great wide open, it will probably sound thin or choked at low volume.

    I always say it's like a bag of golf clubs... How hard and far do you need to hit it? It's hard to get the most out of a driver if you never leave the Putt-Putt course.

    Sent from my XT1585 using Tapatalk
     
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  5. telemnemonics

    telemnemonics Doctor of Teleocity Ad Free Member

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    ...I put some comments in italics inside your quoted post...

    Well yeah, the 18w is a cathode biased el84 amp, so is vastly different from the 50/100 Marshalls.
    Yet it is a classic Marshall circuit.
    A 5e3 is vastly different from a 5f6a yet both are classic Fender circuits.
    The 50w Marshall is much like a 5f6a and you would not make a 5e3 sound like a 5f6a any more than you would make an 18w sound like a 50w Marshall.

    You could certainly find numerous people on the internet who will tell you a bunch of mods to get closer, but you will just never get there.
    Again, any more than you could mod a Tweed Deluxe to sound like a Tweed Bassman.

    There was also a 20w Marshall which was basically a fixed bias version of the 18w, but while it was more punchy like a 50 it wasn't really a great amp compared to the classic 50/ 100.
     
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  6. Guitarteach

    Guitarteach Poster Extraordinaire

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  7. Zepfan

    Zepfan Poster Extraordinaire

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    I never liked plywood for anything music related. You need at least a 12" deep cab IMO.
    I found an old Silvertone amp and the original cab(pressed fiberboard) was in terrible condition and I wanted to build a new cab for it. I removed the guts and temporarily put everything in a old 3-way stereo speaker cab. That was a few years ago and I don't want to change it, the Pressed Sawdust boards gave that wimpy thin sounding amp some meaty tone. Still has the original tubes and Fisher P12Q speaker. It's a keeper.
    The material can be a big contribution to the sound as well as the dimensions. Some times the material you discount will surprise you. That old speaker cab I used was 12" depth/width and closed back with air ports. Something to think about and using ports that can be closed or partially closed can be a big help.
     
  8. itsGiusto

    itsGiusto Tele-Meister

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    Well, I always play it "wide open" (usually on 8), but I use an attenuator to get it down to hearing levels. Though when recording it, I don't use an attenuator, and it still sounds nasally.
     
  9. telemnemonics

    telemnemonics Doctor of Teleocity Ad Free Member

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    There are lots of claims online that el84 tone is different from other power tubes in ways like you describe.
    I have an 18w TMB with el84 and an 18w TMB with 6v6.
    They sound pretty much the same, and the el84 with TMB does not have a "nasal spike in the upper mids and lack of bass depth".
    I run the bass below noon and it is still huge compared to the stock 18w, which does have those tonal problems you attribute to el84s.
    It's the circuit, not the power tubes.
    Not just according to me though, plenty of builder agree that we associate tone with tubes that came in classic amps and assume those tubes made those tones. I suppose the thin shape of the el84 also suggests thin tone.
     
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  10. itsGiusto

    itsGiusto Tele-Meister

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    Hah, yeah, it's good to hear you say that, and that's part of what I wanted to hear about in starting this thread, whether EL84 are just nasally or if that's a myth. Honestly in all my listening to people swapping out different tube types into the same amp, it never sounds that different to me, so I'm more of the belief that it's more about the architecture surrounding the tubes as opposed to the tube-types themselves that matter.

    BTW, I've found a few different TMB 18 watt schematics out there. Do you have one particular one you recommend?
     
  11. telemnemonics

    telemnemonics Doctor of Teleocity Ad Free Member

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    Are you playing a stock 1974x with a G12M20?
    That's just IMO a lousy example of what an 18w Marshall can sound like.
    The lack of bass in that circuit makes it sound like crap to my ear.
    Some like it but I find it thin and nasal with not enough gain.
     
  12. itsGiusto

    itsGiusto Tele-Meister

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    Yeah, I think that's the one, though not sure exactly about the speaker.
    Is that circuit different in some way from other 18 watts that makes it less bassy?
     
  13. telemnemonics

    telemnemonics Doctor of Teleocity Ad Free Member

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    The two I have are the old basic Ceriatone schematic, but there may be newer circuits with switching options that would make them more versatile.

    I'm actually playing a different amp now which is a Tiny Terror preamp (designed to sound like the 66 Plexi 100 Angus Youndg used) into an AC30 power amp.
    I'm also not cranking amps as much, and instead using muffs and Tone Benders for my dirt.

    So YMMV!
     
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  14. telemnemonics

    telemnemonics Doctor of Teleocity Ad Free Member

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    Way way way less bassy than the TMB, which has two more gain stages, one for the tone stack and one just for the sake of gain.

    To me the stock Marshall 18w with volume and tone knobs is hardly even similar in sound to the TMB version.
     
  15. itsGiusto

    itsGiusto Tele-Meister

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    I don't think Ceriatone has schematics anymore on their site, just layouts. Do you have a schematic you could link me to?
     
  16. dogmeat

    dogmeat Tele-Afflicted

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    Hoffman 18W Plexi
     
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  17. Asmith

    Asmith Friend of Leo's

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    Most values are different, V1 has different resistors and cap, all the decoupling caps are lower in value. The gain(volume) and tone circuit is different. Half the PI resistors are different values and the power section is missing the vox cut control. Also a vox would typically have a choke which is fairly significant. Overall Id say the marshall is voiced to be brighter but with such a basic tone shaping mechanisms in that amp what your hearing is mostly pickups and the speaker.

    I guess I didnt see any vox specific design elements, if you asked someone to design an amp with an el84 push pull outplut, a ltppi and a single stage preamp youd get something that looks like that every time but resistor values and especially caps will dictate the voicing. So your 18 watter is a marshall sound but its clear its not the one you want.

    If you wanted a plexi you should have got something closer to a plexi. Turning that 18 watter into a plexi isnt impossible but it would be a challenge, especially if you dont have some amp design experience. Youd have to change the gain structure drastically while sacrificing a triode somewhere in the plexi schematic (I would ditch the cathode follower). Then youd want to add a TMB tone stack and a presence control.

    Regarding cathode vs fixed bias the differences are the fixed bias will get you extra clean head room and when it distorts it will sound like harder clipping but until you reach output distortion you wouldnt be able to tell which is which. So I probably wouldnt go to the hassle of making that conversion, cascading preamp triodes, TMB tone stack and presence will get you most of the way there and it will sound drastically different to the current amp.
     
  18. itsGiusto

    itsGiusto Tele-Meister

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    People always say you can just substitute a choke for a resistor to simulate it, so I'm not sure it's too significant. Besides, Marshalls usually have chokes, so the lack of a choke doesn't make it more Marshally, it just makes it less of both.


    Design elements similar to Vox:
    No NFB
    No presence control
    Cathode-biased EL84 output stage
    Architecture of single preamp stage into PI into power stage



    Whether or not it's a vox sound is somewhat separate from the question of whether it's a Marshall sound. Even if it has key differences from Vox, I still don't see a reason to think it's a Marshall sound. Is it the sound people think of when thinking of Marshal amps, or is it similar to that sound? Can you point me to what parts of the circuit you think are particularly Marshally?

    What specific changes to the gain structure would I have to make? Why would I have to sacrifice a triode, couldn't I just get rid of the tremolo circuit and use those triodes?
     
  19. itsGiusto

    itsGiusto Tele-Meister

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    By this same argument, do you think that the solid-state Fender amps of the 60s are "classic fender circuits" that most people would hear and think of as "classic fender tone"?
     
  20. telemnemonics

    telemnemonics Doctor of Teleocity Ad Free Member

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    A google search found their ef86 versions but not the plain jane TMB schematic.
    Plenty of layouts, and I think the schematic was the same from Weber and others selling TMB kits.
    My TMB with el84 was from a Weber kit with some parts upgrades including a spendy MM OT.
    That one also lacks a MV but I really don't find the MV on these low gain circuits very useful.
    Some do use and like MV with low gain vintage amps though.
     
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