Questions about Valvestate 8100 and 8200 bi chorus

Discussion in 'Marshall Amps' started by Captaidy, Nov 2, 2019.

  1. Captaidy

    Captaidy New Member

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    Hi all,

    I'm not a great reader of schematics so I wondered if anyone on here would be able to help with these questions?

    1. The valvestate 8100 doesn't have a presence control. Is there anything in the schematic that indicates that in the power amp stage there is any presence added or anything that would make the amp brighter when the signal goes through that stage?

    2. I've always thought that the bi chorus 8200 was just the chorus version of the 8100. I have both heads and they do sound different to each other (both great). Not completely different but definitely different. Am I just hearing a slight difference that would be normal say if you had two amps of exactly the same type next to each other (but maybe one was a bit older or one had been serviced recently with some pots replaced) or are they fundamentally different heads from the start?
     
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  2. South Park

    South Park Well-Known Member

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    The presence is a feed back off of the output transformer that goes into the phase inverter. You do have a output transformer to work with. Try a different guitar for the tone you want
     
  3. Captaidy

    Captaidy New Member

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    I'm happy with the tone and these are wonderful amps. I'm just learning a bit more about how they work.

    So am i correct with my understanding that there is something in the power amp section of the 8100 that adds presence (just that there's no presence control) ?
     
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  4. South Park

    South Park Well-Known Member

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    If Marshall did not put one in thar is no circuit for it. Not sure if the feed back circuit for solid state would work.
     
  5. johan.b

    johan.b Well-Known Member

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    The 8100 and 8200 are completely different in their build up of the preamp. To my ear, the 8200 has a leg up in the tone department, but I guess that depends on what style music you're using it for.
    J
     
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  6. Captaidy

    Captaidy New Member

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    Thank you johan.b, after looking at the schematics and seeing that they looked different (to me anyway!) then I was thinking that must be the case.

    I think because they were released at the same time I've just always assumed they were the same apart from the built in stereo chorus on the 8200.
     
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  7. SkyMonkey

    SkyMonkey Well-Known Member

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    I know my VS65R is the later Valvestate Mk II series, but I changed out the valve for a JJ ECC83S and it did improve the tone a small amount.
    Maybe some of the differences you are hearing are the valves.
    If the tubes are the originals, they could be over 25 years old! They do age.
     
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  8. wakjob

    wakjob Well-Known Member

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    Usually there's a small capacitor around the last op-amp in a preamp before it goes onto the power section. That cap is used to control high frequency oscillations...

    I've lowered those to make the overall sound brighter,
    acting like a faux Presence control.

    Can't seem to find a way to do that on the 8200 looking at the schem.
     
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  9. South Park

    South Park Well-Known Member

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    Thar is a feed back circuit with tone shaping with op amps. You might be able to mod it. Solid state is a whole different ball game then tubes.
     
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  10. Mitchell Pearrow

    Mitchell Pearrow Well-Known Member VIP Member

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    Welcome to the forum, a trick that was used on the AVT50H was to unplug the reverb, and that reverb knob could be turned up similar to a presence control, when I tried it I really didn’t hear much difference.
    YMMV as always but it might make a difference on your particular amp. Can’t hurt, and easily plugged back to normal.
    Cheers Mitch
     
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  11. South Park

    South Park Well-Known Member

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    Thar is some ways you can tone shape a ss amp. Or put a eq in the front of it or different pickups. When trying out a amp play it with guitars with different pickups to see what tones you can get out of it
     
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  12. Captaidy

    Captaidy New Member

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    Thanks for all the responses! I think what I was getting at with question one could apply to any valvestate amp really and I was wondering how the power amp section right after the master volume affects the tone rather than just making it all louder. I know most of the tone shaping goes on in the preamp with various resistors etc. But what about in the power amp section?
     
    Last edited: Nov 3, 2019
  13. South Park

    South Park Well-Known Member

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    Ss might have some tone shaping in the power section You can do things different with ss. You have a lot of feed back circuits the out put is feed back into the input it controls the power . When you try new things for that amp study the specks . So when find thing you like you will know why
     
  14. wakjob

    wakjob Well-Known Member

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    Upgrading some components will "enrich" the overall timbre.

    But external gear like pedals and utilizing the FX Loop will get just about the same results...no need to go inside.

    If you nab a cheap dual rack EQ, you could use one side to reshape things at the input...and use the other side to shape the output through the Loop.
     
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  15. South Park

    South Park Well-Known Member

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    What a lot of people don’t get is when you change one thing in the signal chain. It alters the whole chain not just one thing. Its not just the power you are ramping up it is certain frequency’s. So gain and tone work together
     
  16. Captaidy

    Captaidy New Member

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    I've only ever done as much as change tubes in an amp, never any fiddling around with any of the components inside. Not experienced enough in that field. I do find it fascinating reading and learning about how amps work though (hence this thread). The sound of a tube screamer in front of a cranked Marshall is where it's at for me.
     
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  17. wakjob

    wakjob Well-Known Member

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    It was curiosity like yours that got me into so much trouble.
    :naughty:

    I got sick of looking at the inside of pedals or amps that I didn't quite like something about, and not understand what I'm looking at...or how to change it.

    So I edumbacated myself.
     
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  18. Captaidy

    Captaidy New Member

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    I can see how that could happen to someone!
     
  19. Jon C

    Jon C Well-Known Member

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    Edumbacashun is impotent!!
     
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  20. South Park

    South Park Well-Known Member

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    to get into this stuff is to go to school for it.it took me three years in night school . You start at the basics and go from thar.
     
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