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Turning a Champ into a Champ Micro

Discussion in 'Shock Brother's DIY Amps' started by Goudacris, Jan 24, 2021.

  1. robrob

    robrob Poster Extraordinaire Ad Free Member

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    Have you tried disconnecting the NFB? Sometimes the NFB squeal will only come on at high volumes.

    I also recommend you separate your preamp grid and plate wires. They can interact.

    You can try alligator clipping 1000 or 470pf cap in parallel with the preamp plate load resistors. This will filter out some very high frequencies and may help you find the problem triode.
     
  2. Bitsleftover

    Bitsleftover Tele-Holic

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    Not a great pic, and not very pretty because it was a way-after thought!
    9C8C822B-7A6B-4C18-8107-BAA9B09CAB72.jpeg
     
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  3. Goudacris

    Goudacris TDPRI Member

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    Success!

    Disconnecting the NFB eliminated the MV triggering the oscillation. Then I went to play through it and noticed some thick rumbly feedback with higher volume on the low frequency, Then I tried to get as much space and insulation between all the leads on V1 and V2, and that solved that. I still have some faint intermittent pop and crackle, but it's hardly noticeable, and I'm sure it's simply subpar lead dress.

    Many thanks!

    I was thinking of building one for a friend. I have fiberboard that's about 1.6mm thick, and 2mm turrets. I tested putting one turret in and it's fairly secure, but it does move up and down slightly. Will this be a problem? can I do anything to secure the board without going through major hoops or buying a thicker (more expensive) board?
     
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  4. robrob

    robrob Poster Extraordinaire Ad Free Member

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    Crackle and pop is usually a bad solder joint or possibly a bad tube.

    Did you swap the output transformer primary wires to fix the NFB?
     
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