Tuesday 2 October 2018

Marshall JCM800 Super Lead

Next up we have the Marshall JCM800 Super Lead.



With a switch to go between channels


With 2 separate inputs like the amp


With both channels jumpered


22 comments:

  1. This comment has been removed by the author.

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  2. If I build the version with the switch to go between the channels, is the center position jumpered with an on/on/on?

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    1. Well it shouldn't be because in a real 2204 the low input skips the first triode while the high input goes into the first triode which then goes to the second triode. So the first two tube stages are used in series rather than the typical parallel of the Bassman and Plexi. The switch should really be only two positions. And I don't know of anybody who uses the Low input because it is a LOT lower than the high input. The first triode is used pretty much as a clipping stage - it's not a normal gain stage.

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  3. Comparing with the Laney Supergroup 100 MKI Preamp layout, it's very similar. With all of these preamp circuits being virtually the same, one could probably build the vero with sockets where the modifications happen. I built the Laney with the middle, polarized caps socketed. If I toss in the JCM800 values, should I expect more low-end?

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    1. You’re dead on. As I mentioned in the Fender Bassman preamp all these amps are basically the Fender Bassman with value changes giving them their distinctive characteristic. The Laney is much thicker sounding compared to the Marshall, which is one of the reasons Tony Iomi used a treble booster in front of his Laney Supergroup.

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  4. I marked it verified because I've built the other preamp layouts which are identical aside from value differences due to being from different amps.

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  5. Verified, built the option with the switch.

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    1. Oh and either I wired the treble pot wrong or it is backwards.

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  6. Is the electrolytic capacitor a 680uf or 680nf? 680nf is very hard to come by.

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    1. very good question.. My guess would be uf but that is just a guess... I am making it as soon as I get some parts in and that is what I am going with so I will update you.

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    2. it's 680nF. you do not need to use an electrolytic. the amp used an electrolytic, which the layout was designed around.

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    3. awesome! thank you very much!

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    4. btw thank for the layouts too!

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  7. Could I wire this with a dpdt on off on switch and have high, low and bridged?

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  8. the reason the low inputs were there was so you could use an ab box. kinda old-school channel switching, gave ya a built in "lead boost".

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  9. Hello, where I can get the schematic of this jfet version, please?

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  10. I built the jumpered version and it works great

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    1. Hello Fred, can you post or send me any audio or video demo from this project? i am interested but havent found any on the web. Thanks in advance.

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  11. I built mine, sounds very low and doesn't make any distortion, any guesses?

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  12. This comment has been removed by the author.

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  13. Hello ! Just finish my first preamp and have some question.

    Mine is not really high gain, just have a soft distorsion.
    Q1 and Q2 is biased to 6,5v and Q3 to 4,5 v
    What Can i change ? Bias Q2 around 4,5 - 5v ?
    Thanks !

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