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. itsGiusto

    itsGiusto Tele-Meister

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    Looking at the schematic for a Marshall 18 watt (https://www.thetubestore.com/lib/th...Marshall/Marshall-18-Watt-Schem-Schematic.pdf) it seems to me to have many characteristics typically associated with Vox amps, not Marshall. I've always thought the 18 watt had a more nasally tone, like a Vox, less the beefy, warm tone of a plexi.

    Has anyone ever tried experimenting with things like changing the power tubes to be fixed bias instead of cathode biased to make it sound more Marshally? Would this work, or would it fail to make enough of a difference, since it's using EL84s instead of larger tubes like KT66s or EL34s?

    Another possibility might be adding in a presence knob and a TMB tone stack? Or maybe using a closed-back cab?
     
    Last edited: Aug 17, 2019
  2. jsnwhite619

    jsnwhite619 Friend of Leo's

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    I k ow a guy that builds and loves 18 watt Marshall amps. I don't know how much he tweaks, but his demo videos leave nothing wanting for Marshall tone. Have you built one yet?


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  3. itsGiusto

    itsGiusto Tele-Meister

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    No, haven't built one, but I have owned one (1974x) for 6 years. It's a good tone live, but like I said it's a little nasally, hasn't been great for recording because of the slightly anemic sound, and honestly I don't think it sounds that much different than my Vox.
     
  4. jsnwhite619

    jsnwhite619 Friend of Leo's

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    What type, size cabinet and what speaker?

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  5. itsGiusto

    itsGiusto Tele-Meister

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  6. jsnwhite619

    jsnwhite619 Friend of Leo's

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    Have you tried it through a different speaker? I love a lot of classic albums recorded with them, but for my ear and playing, I hate Celestions. I can't and don't play cranked very often, so that isn't a selling point for me. I just don't like them. Maybe try a different speaker and see?

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  7. itsGiusto

    itsGiusto Tele-Meister

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    What would you recommend for a more Marshally sound than a greenback?
     
  8. jsnwhite619

    jsnwhite619 Friend of Leo's

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    Don't know -- that's why I'm on a Fender forum! Haha. ;-)

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  9. itsGiusto

    itsGiusto Tele-Meister

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    Well, then what would you recommend in general for a less nasally sound?
     
  10. telemnemonics

    telemnemonics Doctor of Teleocity Ad Free Member

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    I have three 18w Marshalls, two TMB, which is an improvement and gets more crunch compared to the stock V & T circuit.
    Not Voxy sounding but also not classic 50/100w Plexi/ metal panel sound either.

    If you want to build for that sound I'd build that corcuit but with a pair of 6v6 or el84 power tubes.
    Not worth tweaking the 18w Marshall preamp if you're strting from scratch and have to experiment.
    Just build the amp you want.

    One of my 18w has 6v6 power tubes and sounds like an 18w regardless of the "American" tubes.
    Use whatever power tubes you have access to, but consider that going with 6v6 allows swapping in 5881 for more headroom if desired as long as you choose a PT that can serve them. Maybe a bigger OT as well, or not.
    Better still build a Plexi/ JTM45 with a quad of 6v6 and then you can just pull two power tubes for half power and earlier breakup.

    Otherwise an 18w is much better with the TMB, I don't even use the stock one at all.
     
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  11. telemnemonics

    telemnemonics Doctor of Teleocity Ad Free Member

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    Regarding the nasal GB sound, I never use them either, go for Golds, Blues, 65w Creambacks, Classic Lead 80, whatever the 85w Celestion was called is good, skip the T70 but the 75w from the '80s is supposed to be OK too.

    Greenbacks are nice in 30w and cool in 20w but I never liked the 25w generic nasal crunch speaker.
    Might try the G12H30 55hz Heritage GB if you want bigger bottom.

    Not sure you want a V30 which some hear as fizzy and I might hear as a bit nasal, have a bunch in boxes but got tired of them years ago.

    I do not hear nasal from an 18w TMB into Celestion Golds or Red Fangs, nice clear fat cleans and thick snarling distortion, just not the sort of creamy thing a good Plexi can do, and not quite as brutal either, maybe just less loud.
     
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  12. jsnwhite619

    jsnwhite619 Friend of Leo's

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    Nasally is how I would describe Celestions. I don't know Marshall amp, but I love Eminence. Do some research - I don't know if those are bright or dark amps - but Eminence GB128 sounded great with my 5e3. Their 1258 sounded the best if anything in that power level. Both on the brighter side. Cannabis Rex is a little darker and smoother. All American voiced though. Everyone I know seems to put Celestion in everything. Never heard one I loved yet. I like the big open American tone. Pinched & nasal is how I would describe Celestions. Gold, Blue, Vintge 30....I've installed them for people, but not a single one I would keep.


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  13. itsGiusto

    itsGiusto Tele-Meister

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    I can try adding TMB, maybe that'll help. But why not also add presence to make it even more Marshally?

    Why do you say "Plexi/ JTM45 with a quad of 6v6"? Is there a version of plexi with 6v6s?

    I have the 20w greenback, which is what comes in the 1974x.
    Looking at Creambacks, this video makes it sound even more nasally and midrange-focused than greenbacks:


    Before we decide that the best thing for me to do is to spend lots of money auditioning speakers, I want to pose a question to you all:

    Why do you insist that the 18 watt is Marshally?

    Have you AB-ed it against a Vox AC15 or AC30 like I have? Most importantly, have you examined the schematics? I want to know what about the circuit makes it not just a Vox with more gain, like I believe it to be. I don't see anything in the circuit to make me think otherwise, the architecture basically looks like a Vox with small tweaks. Just because this amp was produced by Marshall doesn't mean it necessarily sounds more like classic Marshall tone than Vox.

    Attached are some schematics for reference.
     

    Attached Files:

    Last edited: Aug 17, 2019
  14. Asmith

    Asmith Friend of Leo's

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    Personally I'm struggling to see the vox in that circuit other other than the gain structure is similar to an AC15 (normal channel) but most of the component values are different meaning should be voiced differently and thats whats important. A lot of vox amps come with greenbacks too so maybe youre hearing the vox in them.

    If you want a plexi tone then youd want a different gain structure and a more sophisticated tone stack (known as a FMV or fender marshall vox). A typical plexi circuit looks a lot more like a vox circuit (top boost).

    Both are 2 cascading triodes,
    followed by a cathode follower,
    into a FMV tone stack (TMB instead of Vox's TB),
    into a LTP phase inverter,
    into a PP cathode biased output (but with a presence control).

    To get it like a plexi it would basically take a rebuild in my opinion. With the preamp valves (triodes) currently availiable I would setup an input similar to a JCM 800, where the high input is a triode cascaded into the low input (but the high input schematic would be made identical to plexi input). Id skip the cathode follower since you dont have a triode to spare and put a plexi TBM tone stack in and then send that to the PI and power amp. Id also add a presence control to as well.

    Without messing with the circuit too much Id advise looking at a speaker swap as othera have said, they play a big role in the voice of an amp.
     
  15. David Barnett

    David Barnett Doctor of Teleocity

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    The G12H30 sounds pretty "meaty" in my 1974 clone.
     
  16. telemnemonics

    telemnemonics Doctor of Teleocity Ad Free Member

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    You're thinking in circles and I cannot follow.
    If you don't want the thick mids of Celestion, why do you want the thick mids of Marshall?

    I suggested a 6v6 Plexi/JTM45 build because that is the Marshall circuit you say you like even though you also say you don't like thick mids, and I have to assume you want to build an amp you don't like (18w) rather than the amp you do like ("Plexi") because you want less wattage.
    Hence the suggestion for a Plexi/ 45 with 6v6 instead of an entirely different amp that you have to randomly mod hoping to make it sound like the amp you do like.

    WRT the 20w GB, I consider it a special effects speaker, not versatile.
    All nasal mids with no bottom or top.
    I don't like the 65w much but they are more neutral and versatile.

    I'd say if you put new Celestions in cabs for people and didn't like the sound of any of them, it may be due to being new.
    Breaking in new Celestions is torture, they sound awful for 10 hours or so of fairly loud playing.

    As far as us insisting 18w Marshalls sound marshally?
    Well, they are indeed Marshalls, so whatever the sound, it is a marshally sound!
    I've owned a dozen vintage Plexi and early metal panel Marshalls and they do not all sound the same.
    I vastly prefer the '67 100w circuit over the later 50 and 100 as well as over the earlier 45/ 50.
    I would not kick a '66 Plexi 100 out of my bed though!

    Compared to Vox?
    Marshall in general dials in thicker in the low mids and faster with more punch.
    But the stock 18w Marshall is less thick, has less low mids, and is not fast and punchy like a 50/100 Plexi.
    (this is compensated for by a thick nasally 20w GB, but at a loss of other things I like, so it isn't an amp/ speaker I want)

    So aside from the speaker I suppose that moves it more in the Voxy direction.
     
  17. itsGiusto

    itsGiusto Tele-Meister

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    What I want is simple: I want a Plexi or a JTM45, but I don't want to have to play ridiculously loud, so I don't think it makes sense to actually build a real one. I'm thinking of trying to emulate a plexi using lower-wattge tubes. Using 6v6s sounds like the sort of thing I'd like, but you confused me before in the way you phrased it. You made it sound like JTM45 canonically uses 6v6s, which is not true. But I guess you were talking about some sort of DIY mod-circuit that uses 6v6s instead? I'm still not sure what you mean by that. Also, 6v6s have the same power as EL84s (I think), so I could probably just use EL84s instead.

    I don't know where you got that I don't like thick mids, I do like them. But I find the 18 watt to be upper-mids focused, which is what I'd call nasally, not lower-mid focused like a plexi. I want syrupy, maybe throaty, not nasally.

    This isn't quite true. When people say "I want a Marshall amp" usually the first thing people think of is a Plexi, not an 18 watt. For example, Marshall has also made the Valvestate, and some solid state amps, but I don't think that anyone thinks of those amps as being classic-marshall tone.

    As far as looking at the circuit is concerned, I see more similarities between the 18 watt and the vox than I do the 18 watt and the JTM45.
     
    Last edited: Aug 18, 2019
  18. David Barnett

    David Barnett Doctor of Teleocity

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    It's a clone of a Watkins Dominator.
     
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  19. itsGiusto

    itsGiusto Tele-Meister

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    Yeah, I know. The question is whether the Watkins Dominator is based on an AC15/30, or at least pretty similar. To me, it seems to be.
     
  20. itsGiusto

    itsGiusto Tele-Meister

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    Some of the component values are different. Mostly it seems to be that the 18 watt tubes are biased hotter, and the coupling caps are lower. Are there other significant differences I'm missing? Please point them out so I can see.

    I'm basing this conclusion on both looking at the circuit, and AB-testing my two amps, one an 18 watt, and one a Vox. I played them each though the same speakers (a 20w greenback, and then an alnico blue), and couldn't really tell the difference between the two, when plugging into the same speaker.

    How much role does the cathode vs fixed bias play in the voice of the amp? That and the lack of NFB/presence are very similar to Vox amps.
     
    Last edited: Aug 18, 2019
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