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Thread: Orange noise

  1. #1
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    Orange noise

    I have a AD 200 bass mk 3 here with a loud buzz. I can kill it with the MV and by pulling v2 or v3 . The only scem i can find is on prowess amps but its not correct to this amp. This pcb is dated 2006. (ill try calling Orange tomorrow) , I tried clipping in a 50uf filter cap at all the plates v1/2/3 - it doesnt affect the noise unless i clip it to the plates of V1--but then i have almost no volume .

    i did find about 18 vdc at the grids of V2 -- that shouldnt be there, yes ?

    the shielded cable grounds are good




    side note = theres a cap in here , that i think is a coupling ( traces are on both sides of pcb-cant see the bottom) , but its got strange labeling. Can someone decipher this ?

    R60 MKT 400 A9 10MRL19

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  2. #2
    don't forget the joker g1's Avatar
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    You found 18V at the grids, what was at the cathodes and plates?
    How about a pic of that component with the marking.

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    Supporting Member The Dude's Avatar
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    Quote Originally Posted by g1 View Post
    You found 18V at the grids, what was at the cathodes and plates?
    How about a pic of that component with the marking.
    pin 3 33vdc
    pin 8 33vdc
    pin1 202vdc
    pin 6 198vdc

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  5. #5
    don't forget the joker g1's Avatar
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    With the cathodes at 33V, the 18V at the grids is not necessarily a problem.
    Without some kind of schematic, even close, it's all guesswork as far as hum.
    Sometimes there are DC heaters for the early preamp stages. See if you can find out if there are AC or DC heaters on the preamp tubes.

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    all heaters are AC --all tubes

    orange wont send me a scem. any authorized guys on here ?


    heres a vid of the noise =

    https://vimeo.com/259402089

    edit---the amp owner knows a rep there , so hes trying to get me the scem.

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    Last edited by Valvehead; 03-10-2018 at 12:12 AM.

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    Senior Member Pedro Vecino's Avatar
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    It's obvious, but have you tried a new 12AX7? Sometimes I have seen that noise (with more bass component) in defective tubes. Specifically in ECC83 JJ and Tesla E83CC (same type of construction).

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    yep--swapped out every tube.

    i cant get directly to the filter caps-they are vertical pcb and some of the traces are on the bottom .. so i clipped in a 50uf at all the plates of the preamp tubes. Would that cover it , or do i need to get directly to some of the caps "first in line" ? if that makes sense

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    Lifetime Member Enzo's Avatar
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    Ok, your funny voltages look like they are on a LTP phase inverter. The plate voltages are close, the cathodes are the same. probably wired together, and the grids have the DC the cathode has, but your meter cannot read it due to the high resistances. Looks normal then. Instead of measuring pins 2 and 7 to ground, try measuring 2 to 3 and 7 to 8. I bet you only get a volt or two.

    You can't tack a filter cap on the tube plates, that acts like a giant tone control rolling off your audio.

    Pulling V1 stops the noise? Pins 2 and 7 are grids. Try grounding each of those one at a time. Either kill the hum?

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    .........

    Quote Originally Posted by Enzo View Post
    Ok, your funny voltages look like they are on a LTP phase inverter. The plate voltages are close, the cathodes are the same. probably wired together, and the grids have the DC the cathode has, but your meter cannot read it due to the high resistances. Looks normal then. Instead of measuring pins 2 and 7 to ground, try measuring 2 to 3 and 7 to 8. I bet you only get a volt or two.


    YES--THATS WHAT I SEE


    You can't tack a filter cap on the tube plates, that acts like a giant tone control rolling off your audio.

    Pulling V1 stops the noise?


    NO--PULLING V2 /3 KILLS THE BUZZ

    Pins 2 and 7 are grids. Try grounding each of those one at a time. Either kill the hum?

    ON V1-- GROUNDING GRIDS -- 2. NO STILL HAS LOUD BUZZ 7. KILLS VOLUME-- STILL BUZZ IN BACKGROUND / QUIETER

    V2-- 2. KILLS BUZZ 7.KILLS VOLUME, STILL BUZZ IN BACKGROUND / QUIETER

    V3 2. KILLS BUZZ 7. KILLS VOLUME , BUZZ STILL IN BACKGROUND -QUIETER

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  11. #11
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    I'm thinking you are experiencing an imbalance somewhere in the phase splitting circuit?

    Here you have some unofficial schematics:




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    i think i have found the correct scems.....pm me for link

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    Try measuring heater (ac) voltage on preamp tubes, ground to pins 4/5 and ground to pin 9. They both should be around 3.15V AC

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  14. #14
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    3.89vac

    3.34 vac

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    You said you can kill the buzz with the master. That leaves only V1 ahead of it so you can concentrate on that area.
    How about with the gain all the way down, does the master still bring the buzz in and out?

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  16. #16
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    Quote Originally Posted by g1 View Post
    You said you can kill the buzz with the master. That leaves only V1 ahead of it so you can concentrate on that area.
    How about with the gain all the way down, does the master still bring the buzz in and out?

    gain on 0 ...buzz still there , just quieter

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  17. #17
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    Have you tried other tubes in V1 position?
    And instead of clipping that 50uF cap to the plate, clip it to the other side of the plate resistor. Any effect on the buzz?

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  18. #18
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    [QUOTE=g1;482825]Have you tried other tubes in V1 position?

    yes


    And instead of clipping that 50uF cap to the plate, clip it to the other side of the plate resistor. Any effect on the buzz?

    no effect

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    Senior Member SoulFetish's Avatar
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    Nobody’s made a “white/pink” noise joke yet??

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  20. #20
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    Don't miss your chance!

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    The voices in my head are idiots!

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    Senior Member SoulFetish's Avatar
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    Okay, okay.... How ‘bout this one:
    Orange noise (the worst kind of noise), is also known ass 1/Sl noise due to it’s tendency to improve linearly with skill level.


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    Last edited by SoulFetish; 03-14-2018 at 12:30 AM.
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  22. #22
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    So, of the schematics you received, none of them show the tone controls. But there is the d'Uur power amp drawing like in post #11. (edit: nevermind I see the pots are shown on the separate front panel board and what I thought were pots on the main drawing are connectors to the pots. Even so, the drawing in post #11 is accurate enough for everyone to work from)
    With master up, does turning all tone controls down to zero reduce or remove the buzz?
    Is this a circuit board amp? Are the tube sockets wired or mounted on the board? Can you post some pics of inside the chassis?
    What does the owner say about the history of the fault, just showed up overnight, or appeared gradually?

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    Last edited by g1; 03-14-2018 at 01:36 AM.
    The voices in my head are idiots!

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    Supporting Member The Dude's Avatar
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    Have you tried Enzo's suggestion in post #9?

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  25. #25
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    yes post 10

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  26. #26
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    Quote Originally Posted by g1 View Post
    So, of the schematics you received, none of them show the tone controls. But there is the d'Uur power amp drawing like in post #11. (edit: nevermind I see the pots are shown on the separate front panel board and what I thought were pots on the main drawing are connectors to the pots. Even so, the drawing in post #11 is accurate enough for everyone to work from)
    With master up, does turning all tone controls down to zero reduce or remove the buzz?
    Is this a circuit board amp? Are the tube sockets wired or mounted on the board? Can you post some pics of inside the chassis?
    What does the owner say about the history of the fault, just showed up overnight, or appeared gradually?
    yes-pcb amp
    sockets are pcb
    turning down tone controls doesnt really affect it---the Gain pot does

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  27. #27
    Supporting Member The Dude's Avatar
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    Quote Originally Posted by Valvehead View Post
    yes post 10
    Apologies. Missed that one.

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  28. #28
    Supporting Member The Dude's Avatar
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    Just watched the video you posted. It sounds a lot like noise from a ballast- florescent lights, neon lights, etc. Are there any nearby? If you had say a bad input or loop switching jack or an open circuit somewhere and were near the right source, it might sound something like that. Grasping at straws a bit, I know.

    Edit: Make sure your AC plug ground is making it to chassis ground.

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    Last edited by The Dude; 03-14-2018 at 03:18 AM.
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  29. #29
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    That crossed my mind too but i unplugged the lights to check that

    i will check the amp ground

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  30. #30
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    ac ground is good ...tried a ground lift too

    also took the amp out to my garage to try it on different power

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  31. #31
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    Im starting to think either filter cap or coupling cap ?

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