1. Win a Broadcaster or one of 3 Teles! The annual Supporting Member Giveaway is on. To enter Click Here. To see all the prizes and full details Click Here. To view the thread about the giveaway Click Here.

Champ 12 Upgrades

Discussion in 'Amp Tech Center' started by oldlefty, Dec 4, 2020.

  1. oldlefty

    oldlefty TDPRI Member

    Age:
    70
    Posts:
    52
    Joined:
    Sep 18, 2020
    Location:
    Oswego NY
    I have my Champ 12 opened up to do the Torres input jack upgrade. "While I'm in there..." there are a few other things I'm going to do, looking for other suggestions. I really only need the normal channel (plenty of pedals get anything else I want), but I wouldn't mind trying to tame the distortion channel a bit. Years ago I did put in the Torres mod that links up the two preamp tubes with a few resistors and caps. I think its purpose mainly was to try to balance the two channels (a little more normal, a little less drive)?

    I want to recap while it's open, at least the four big 47s- most likely go up to 220? Any need to do the other four smaller electrolytics?

    I can't find any smaller value pots that will fit in for the two 1M drive channel pots, but I do have some 330k resistors that I can put in across the outer lugs- I think that's a known mod to give those pots a more usable range?

    I'll try playing with the reverb trim pot, but again I have a decent reverb pedal so no biggie.

    I wanted to replace the power switch with a typical Fender toggle, but after looking it over it's a bit tougher than I thought- faceplate-wise. Like fitting a round peg in a square hole...

    I've printed out two or three marked up schematics of other guys mods, but I don't want to just start changing things "willy nilly".

    Suggestions?

    This link was very helpful, particularly for tracing out the signal path (good ol' robrob again):

    https://www.tdpri.com/threads/explain-the-champ-12.691445/

    [​IMG]

    (ignore the stuff to the left, also building the Smallbear Maestro FZ-1 clone).
     
  2. dougstrum

    dougstrum Tele-Afflicted

    Posts:
    1,948
    Joined:
    Oct 6, 2015
    Location:
    blu ridge mtn cabin
    Nice little amps, changing the input jacks is a good idea. I did mine when the plastic ones quit. No need to up the size of the filter caps, but never a bad idea to replace the "illnoise" with better caps.

    Had thought about mods, but other than speaker swap feel they are fine as is. Of course I never use the drive channelo_O
     
  3. Lowerleftcoast

    Lowerleftcoast Friend of Leo's

    Posts:
    2,620
    Joined:
    Dec 30, 2019
    Location:
    california
    The Champ 12 distortion channel uses the gain produced by the V1 12AX7 preamp tube. Basically the way the clean channel works in the Champ 12, is to let some of that signal voltage go to ground. There are several ways to change the distortion channel. Some ways of changing the distortion channel will change the clean.

    My initial thought was to allow *some* of the gain to bleed to ground. I figured a couple 1M trim pots to bypass the LDR1 resistors. Dial in the amount of bleed. (When the pedal switch is on the Clean Channel nothing would be different.)

    Other things to try...
    Try a 12AY7 in V1

    Reduce the 22uF bypass cap on V1A or trade it with the .68uF on V1B.

    The function of LDR1 is explained by FenderLover in post#8 of the thread you referenced: https://www.tdpri.com/threads/explain-the-champ-12.691445/
     
    oldlefty likes this.
  4. Obsessed

    Obsessed Telefied Silver Supporter

    Posts:
    25,828
    Joined:
    Nov 21, 2012
    Location:
    Montana
    Did you just purchase the Torres input jack kit?

    BTW, I have been afraid to chase the "gain channel" mods, because I didn't want to ruin the primo clean channel.
     
  5. oldlefty

    oldlefty TDPRI Member

    Age:
    70
    Posts:
    52
    Joined:
    Sep 18, 2020
    Location:
    Oswego NY
    No, I got it 6 or 7 years ago (while he was still selling kits). "Just getting around to it..." :D
     
    Obsessed likes this.
  6. oldlefty

    oldlefty TDPRI Member

    Age:
    70
    Posts:
    52
    Joined:
    Sep 18, 2020
    Location:
    Oswego NY
    I was thinking about that cap swap.

    And I've read how the amp is very responsive to tube changes.
     
  7. Obsessed

    Obsessed Telefied Silver Supporter

    Posts:
    25,828
    Joined:
    Nov 21, 2012
    Location:
    Montana
    Darn, I was hoping ...
     
  8. oldlefty

    oldlefty TDPRI Member

    Age:
    70
    Posts:
    52
    Joined:
    Sep 18, 2020
    Location:
    Oswego NY
    OK, I replaced all the electrolytics. Upped the filter caps from 47 to 100uf. The MOD caps were the only ones I could find with the same dimensions for the tight real estate of the boards- any experience with them?

    I changed the tone stack caps to 150 pf mica, .047uf, and .022uf as per the Premier Guitar article.

    I replaced the plastic jacks with switchcrafts, and I put 330k resistors across the two drive pots give them a little more operating room.

    I was toying with the idea of making the Torres mod that I had put in years ago switchable by adding a mini-toggle on the back panel, but now I'm not so sure. Looking at it a little closer (and with my newfound amp understanding- danger danger....), I think all it is is an additional cathode resistor and cap for both V1B and V2A? I don't know if they're working together, or both can be independent of each other? You really would need two switches one for each resistor/cap right? And it might just be snake oil anyways?

    [​IMG]

    [​IMG]

    Torres mod:

    https://torresengineering.stores.yahoo.net/redcham12kit.html

    [​IMG]
     
  9. oldlefty

    oldlefty TDPRI Member

    Age:
    70
    Posts:
    52
    Joined:
    Sep 18, 2020
    Location:
    Oswego NY
    Done. Sounds really nice! Quiet as a church mouse. Distortion channel is much more usable, pots have enough range now that you can start off with just a hint of "edge", and balance it with the normal channel. I'm liking the normal channel mid boost setting.

    The other improvement I added was the Torres tube set that I had ordered years ago but never put in. I don't know what the 6L6 is, the preamp tubes are a Mullard and a Sovtek.

    At some point I might try removing the "Torres mod" from the preamp tubes to go back and hear it now without it. Many say it helps the distortion channel at the expense of the normal channel.
     
  10. schmee

    schmee Doctor of Teleocity

    Posts:
    13,354
    Joined:
    Jun 2, 2003
    Location:
    northwest
    So it's quiet now? On mine I went to 100uf for the three together on the smaller board and it wasn't very quiet, then I read more and went to 220 uf and it's quiet.
     
  11. oldlefty

    oldlefty TDPRI Member

    Age:
    70
    Posts:
    52
    Joined:
    Sep 18, 2020
    Location:
    Oswego NY
    Yeah, very quiet. With my 70-year-old ears I have to get down on the floor with my ear near the speaker to hear any hum.
     
  12. Robster

    Robster Tele-Afflicted

    Posts:
    1,009
    Joined:
    Feb 14, 2009
    Location:
    Marietta, GA
    I worked on one of these a couple months ago. Input jacks were broken, weak reverb. I replaced the jacks and found someone did a poor job of adding in another old filter cap. I removed that and replaced the 3 filter caps with 80uf ones and had no hum. I also found 3 or four resistors that had gotten so hot I could not see their colors.
    I found a schematic and replaced them. Clean channel was great, no hum, distortion channel was very usable too.
    Tweaked the reverb adjustment and got it sounding very nice.
     
    oldlefty likes this.
IMPORTANT: Treat everyone here with respect, no matter how difficult!
No sex, drug, political, religion or hate discussion permitted here.