Plug Ports On Haze 40?

Discussion in 'Marshall Amps' started by Adey1981, Sep 15, 2018.

  1. Adey1981

    Adey1981 New Member

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    Hello there. I have a Haze 40 which on the whole Im happy with, but the bass is too loose and flabby. One suggestion I've come across is to plug the ports on the back.

    Is this safe to do?

    Also, is the amp chassis isolated from the speaker enclosure? Meaning if I block the ports will the top vent still be acting as a port? Obviously I cant block the vent due to heat. But im worried that if I block the ports, the amp would still be ported, but at a different resonant frequency, and could this cause speaker over-excursion and damage it?

    Thanks
     
  2. Dogs of Doom

    Dogs of Doom Moderator Staff Member

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    does yours look like this?

    [​IMG]
     
  3. MarshallDog

    MarshallDog Well-Known Member

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    The chassis electronics will still be vented but DONT block the ports as they do help vent out some heat. If they are blocked, the tube heat will biuld within the cab and may overheat the electronics. I used to own one.

    Try different tubes or speakers but DONT plug the ports IMO or you are asking for issues.
     
  4. Dogs of Doom

    Dogs of Doom Moderator Staff Member

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    it looks like they are using the speaker air pressure to blow out heat... :)...

    yeah, as a standard practice, I wouldn't either. If you get too much heat, inside the speaker cabinet, too, you could overheat the voicecoil & burn up the speaker...
     
  5. Adey1981

    Adey1981 New Member

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    Doe this also mean the amp can't be used with an extension cab? With a extension cab the only heat management would be the heat rising up through the top vent?
     
  6. ampmadscientist

    ampmadscientist Well-Known Member

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    On the wrong side of the tracks.
    The vents cannot be plugged.
     
  7. Adey1981

    Adey1981 New Member

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    By vents do you meant ports?
    In that case I won't do it, I was dubious about it anyway, it was juat something someone suggested on another forum.

    So can the amp be used with an external cab?
    If I build a sealed cab can I put the stock speaker in it or would it overheat?
     
    Last edited: Sep 16, 2018
  8. renips

    renips Well-Known Member

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    I own this amp. You can use it with another cab. Just unhook the speaker wire and get an extension to lengthen the speaker wire. I use this with my 4x12 all the time. It sounds killer.
     
  9. JohnH

    JohnH Well-Known Member

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    The ports need to be open to help vent tbe heat. Cool air coming in low helps hot air get out the top.

    I dont think the speaker movement does much cooling though, so ok to use an external cab
     
  10. Adey1981

    Adey1981 New Member

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    I've used a 4x12 too and yes it sounded amazing, like a new amp.

    Thanks John, that's exactly the clarification I needed.

    Thanks all, I'll build myself a cab and see how it goes, cheers
     
  11. MarshallDog

    MarshallDog Well-Known Member

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    That would be fine. You just want an open path to allow the heat to escape as it builds.
     
  12. Dogs of Doom

    Dogs of Doom Moderator Staff Member

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    no, what I'm saying is that, by closing off the ports, you are creating a tube oven, that will get the speaker coil extremely hot.

    Speakers can get hot & the mfgr's are always looking at ways to make them more efficient & also keep the voice coil cool. There's a lot of different designs. You'll notice these things more prominently discussed w/ bigger bass speakers, but, the same theory applies to guitar, as many guitar speakers blow. How do they blow? By running them hot & (over) heating the voice coil...
     
  13. Adey1981

    Adey1981 New Member

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    Just an update, for anyone interested.
    I've just bought a Vintage 30 and I'll see how that goes, theV30 is a popular upgrade for the Haze, and is supposed to alleviate the issues with this amp, i.e flabby bass, and no bite/punch.

    Cheers!
     
  14. jamesm

    jamesm Active Member

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    As above, the holes in the back are for ventilation and also tuning. They are sized such that there is a slight hump in the response at about 150Hz which is where the slightly 'undersized' 4x12" has a hump. If you want to reduce the bass, then a larger hole is what is needed. The standard Marshall combo has about 1/3 or more of the back open. This is how it was designed initially, but due to fears that someone might reach inside and burn themselves on the valves, it was decided to close the back up.
    The amp was designed with a heavy magnet speaker (a variation on the G12H) but this was pulled late in the day. The Vintage 30 is an excellent choice as it is close to what was originally supposed to be there.
    I always have both bright buttons pressed. Marshalls are almost by definition 'built in bright'. They were only there because the Hotrod Deluxe had bright switches and the marketing guys insisted. The same goes for the 40 watts output. If this amp was a 50, the EL34s would have been in a edgier part of their transfer curve and that would give it more aggression, but 40 watts was seen as a magic number as so many HRDs were selling.
    There are also some brightness mods that are highly recommended (mostly consisting of removing a couple of capacitors). These are possible for a tech to do without removing the PCB, so shouldn't cost too much.
     
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