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Fender Red Knob Champ 12 with 100Hz Hum

Discussion in 'Shock Brother's DIY Amps' started by jimi00, Feb 9, 2013.

  1. robrob

    robrob Poster Extraordinaire Ad Free Member

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    I am not familiar with this amp but yes, C101, C102 and C103 are the power supply filter (reservoir) caps.
    Larger filter caps can help tighten up the low end.
    Changing C101 and C103 to 220uF 350V should be plenty to feed the unaltered C102.

    [​IMG]
     
  2. jimi00

    jimi00 TDPRI Member

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    Hi MaxRite,

    Everything went fine, the amp behaved perfectly after that. Just make sure your tech understands this is not just about putting in new caps in C101 and C103, but replacing them with higher capacitance ones. As suggested, you can probably leave C102 alone (which, if my memory serves me right, was a ***** to get to).

    Enjoy!

     
  3. MaxRite

    MaxRite TDPRI Member

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    Hey, thanks Robrob and Jimi00 for the quick reply!!
    Does tight bass stand for less bass frequencies or just a more focused bass?
    Being the first option not much desirable to me in this particular amp
    But also I guess we're talkin' details here, right?
    Jimi, have you noticed changes in the bass department of the amp?
    And, Bob, what I see in the schematic you posted, are mod suggestions?
    I wouldn't want to adventure too far into modding my Champ 12, which I already like as it is...

    Thanks
     
  4. robrob

    robrob Poster Extraordinaire Ad Free Member

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    More focused, less sloppy bass.
    I just used the schematic but those mods affect the voice so just ignore them.
     
  5. jimi00

    jimi00 TDPRI Member

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    I, for my part, didn't notice any difference in the amp's sound signature. If your old caps are really washed out then their replacement will likely tighten the bass, but by no means would you lose any frequencies.
     
  6. MaxRite

    MaxRite TDPRI Member

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    You guys are so cool!..
    Thanks a lot!
     
  7. MaxRite

    MaxRite TDPRI Member

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    Job done! It DOES work!
    THANKS!
     
  8. robrob

    robrob Poster Extraordinaire Ad Free Member

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    Sweet, congrats.
     
  9. TommyV

    TommyV NEW MEMBER!

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    This is a post i found from another site, maybe this helps. Red Knob, success!
    Big update on this thread! I have finally received the 350V 220uF caps. I have replaced C101, C102 and C103, and guess what? When I powered it on the first time, for a moment I thought I made a mistake in re-assembling because it had to stick my head IN the speaker to hear anything . THE AMP IS DEAD QUIET AS FAR AS 100 HZ GOES!! This is fantastic news for all the Champ 12 lovers out there. A very slight 50 Hz hum is still to be heard inches away from the amp but this is so faint that it would not even be a concern for studio or recording use.
    The only point of caution I would give concerns the size of the new caps which are twice as wide as the original. Don't let that fool you, they fit perfectly in length.
     
  10. boppy

    boppy Tele-Meister

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    I had the same issue as OP...loud hum independent of volume whether or not anything was plugged into the amp.

    I swapped caps 101-103 with 3 350v 100ufs.

    Almost dead quiet now.

    Thanks for a great fix and a very useful thread...
     
  11. multivoxmx2000

    multivoxmx2000 NEW MEMBER!

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    Hey everyone, thank you so much for all your inputs.
    I guess this thread is a bit old, but I'll give it a shot.

    I still have the original power supply section caps (47uF 350V 85°C).
    I want to try and change them but it seems hard to get caps that meet the requirements.
    I suppose that, aside from respecting the specs, quality of the caps, tolerence etc. are important.

    @jimi00, your seller on ebay doesn't have these any more or any that could fit the requirements (i contacted him), I saw these and theseonline that look OK, but I'm pretty sure won't fit in... would you know any good supplier ?
    @boppy, could you give us the reference from your caps please ?

    Thanks again.
    I'll post pictures if I manage to do this.
     
  12. Mongo Park

    Mongo Park Tele-Afflicted

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    multivoxmx2000 likes this.
  13. boppy

    boppy Tele-Meister

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    multivoxmx2000 likes this.
  14. multivoxmx2000

    multivoxmx2000 NEW MEMBER!

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    Thanks a lot to both of you, I'll post the results of my experiments here.
     
  15. Dave Yeats

    Dave Yeats Tele-Holic Silver Supporter

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    Just want to +1 everything in this thread. Had the same issue with an ‘87 (red tolex) Champ 12 I just acquired with a bad hum. Replaced C101, C102 and C103 with Tube Amp Doctor 220uF 350V Electrolytic Capacitors. Tight fit, but solved the hum issue and the amp still sounds good.
     
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