Studio Vintage: High treble channel hiss?

Discussion in 'Marshall Amps' started by Robus, Jun 5, 2019.

  1. Robus

    Robus Well-Known Member

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    I'm finding the high treble channel very noisy. Just barely cracking the volume know open introduces a kind of white noise hiss which is very pronounced. I don't hear this on any demo vids on this amp.

    How loud should it be?
     
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  2. solarburnDSL50

    solarburnDSL50 Well-Known Member Platinum Supporting Member

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    A noisy tube maybe? I've had tubes ring, hum, crackle/static and create white noise.

    That would be an easy fix it you have spares to check with. Otherwise I don't know. Hope the fix is simple.
     
  3. Georgiatec

    Georgiatec Well-Known Member VIP Member

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    Looking for something I don't remember what.
    Yeah, most likely a pre-amp tube. Have you had the amp awhile and it's just started doing it, or is it new. I would just take it back to the dealer if new? If it's over 90 days old change the pre-amp tubes and see if the noise goes away. It should be pretty much silent at lower volumes.
     
  4. Ufoscorpion

    Ufoscorpion Well-Known Member

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    its obviously because it's been recently made in Bletchley , if you've ever been there or Milton Keynes you will know where I'm coming from . You're probably not allowed to work in the Marshall factory unless you've got three nipples and webbed feet , lol .
     
  5. Ufoscorpion

    Ufoscorpion Well-Known Member

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    Actually as everyone else says , probably a tube .
     
  6. assaf110

    assaf110 Well-Known Member

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    :)
    I had the same (high treble channel, even if it's barely on, like 1 on the knob). Like a high pitch whistle sound Not exactly white noise. Gets worse when switching to 20W or turning up the volume knob.
    Rolled all of the pre-amp tubes (NOS mullard i63, JJ gold pins, JJ balanced in PI) - no change.
    Was going to ask the same question here, i tried to unplug the input - suddenly silent! (well, almost...).
    I found out it's noisy when ever i jumper the channels :rolleyes: even if there is no other input, and also one of the pedals was noisy, as soon as i unplugged the power supply to that pedal it went away.
    Do you jumper the channels? have anything plugged in?
    I guess that since the high treble has more gain, every little noise gets boosted. Still, noisier then i would have hoped.
     
  7. ampmadscientist

    ampmadscientist Well-Known Member

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    1. The hiss noise is normal in all modern tube guitar amplifiers. It is caused mainly by resistors and layout used / the circuit design. A elevated symptom of this is microphonic whistling and ringing oscillations.

    2. A lot of times you will hear people tell you to change tubes, but the inherent problem will still be there (more or less of it) depending on which tubes you stick into the sockets. Realistically the real problem never goes away completely, although you may get some varying degree of improvement.

    3. Builders could use better parts, but these parts cost so much that manufacturers try to stay away from them. (such as bulk metal foil resistors, improved shielding, etc)

    4. The only solution that is commonly used : kill the response of the amplifier (take away the highs) then the hiss will be reduced. You could probably tell that the tone is reduced also ! But this was the only cheap / easy / practical solution that manufacturers could realistically implement.
    Musician responds with: noise gate, EQ, reduce the gain, etc...but all of this still injures / compromises the tone one way or another.

    5. Future of noise. Eventually tube guitar amps will progress into lower noise with less tonal compromise,
    just as tube hi fi amplifiers have done, today.
     
  8. Trapland

    Trapland Running Into Walls Silver Supporting Member

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    This is one reason I’ll probably change mine to Bass spec. I’m just waiting for someone else to map out the board so I don’t have to.
     
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  9. Robus

    Robus Well-Known Member

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    Are you experiencing the same issues as I described in the OP?
     
  10. ampmadscientist

    ampmadscientist Well-Known Member

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    If you had the schematic it would be possible to start planning out some measures...without a schematic you are basically faced with drawing your own.
    But I will give you this:
    about 70% of the hiss is caused by 1 part. A better resistor which replaces it costs about $20 for 1 resistor.

    There are basically 2 approaches to reducing hiss:

    A. Anamorphic approach:
    Interferes with the pure tone of the amplifier, this is the most common approach. Example: install snubber caps to reduce high frequency response.
    This in turn reduces the hiss (because you killed the highs). "an intentional distortion."
    But...almost everybody uses this method - cheap and simple.

    B. Amorphous method:
    Does not change the pure tone, does not reduce the frequency response of the amplifier.
    "without definite character...."
    Example: you are using resistors which produce much less noise, but you are not changing the value of the resistor.
    You are reducing the switching noise of the diodes in a rectifier, but the rectifier still works the same as before.

    Therefore any change to the amplifier "could be" Amorphous. "Without interfering with the original tone."
    However, to make an improvement you are going to make a change in the amplifier somewhere.
     
  11. Robus

    Robus Well-Known Member

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    ampmadscientist, are you suggesting by the symptoms I described you suspect this is normal behavior for the amp? I've never had a plexi so I don't know is supposed to sound like. What happens is that cracking the volume knob of the high treble channel even a slight amount introduces a very noticeable hiss. This gets louder as that volume knob turns up. The normal channel volume knob is very quiet all the way up to max.
     
  12. ampmadscientist

    ampmadscientist Well-Known Member

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    Is this amp a plexi basically with a smaller power amp?
    Can you take detailed pictures of the insides?
     
  13. Robus

    Robus Well-Known Member

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  14. Ufoscorpion

    Ufoscorpion Well-Known Member

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    My evh lbx is fairly noisy on the blue channel , but it is very high gain and has to be expected . A correctly set gate helps no end with no tone compromise . But bottom line is if you can't hear it when you're playing it ain't a problem is it !
     
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  15. coolidge56

    coolidge56 Well-Known Member Double Platinum Supporting Member

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    Try a Preferred Series 7025 from thetubestore in V1. I rolled some tubes in my studio SC and that lowered the noise floor significantly vs the factory 12ax7. I tried other factory tubes in V1 and some EH golds which are typically pretty quiet but the 7025 was the king in V1. No improvement on noise in V2 but the EH gold lowered the noise a touch more in V3. Impact was 90% V1 and another 10% lower in V3.
     
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  16. trovador

    trovador Well-Known Member

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    some hiss is normal when the volume is past 5
     
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  17. peterplexi

    peterplexi Active Member

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  18. peterplexi

    peterplexi Active Member

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    Snip the bright cap
     
  19. Sacalait

    Sacalait Well-Known Member

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    My SV20 makes noise at idle once you turn up the volume past off. It doesn't increase as you increase the volume but it is present and a noise gate on the front won't help. I have tried a noise gate in the effects loop and it DOES help- so there is a workaround. It's the only issue I've had with the amp but it's not a game changer for me whatsoever. And I have changed the tubes.
     
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  20. tallcoolone

    tallcoolone Well-Known Member

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    Shoot a quick vid of the issue and post it would be my suggestion.
     
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