BF Fender mid resistor SOLVED

Discussion in 'Amp Tech Center' started by schmee, Aug 18, 2019.

  1. schmee

    schmee Poster Extraordinaire

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    Quick question, the resistor soldered on the Bass pot back is the one that controls the amount of mids right? Do I go up or down in resistance for less mids?

    Dont really want to add the mid pot mod on this one.

    For some reason my BFD just seems very middy lately to me compared to myt BFDR. Maybe it's my imagination. They both have the same speaker. I'm going to check all the values of the related tone caps and that resistor. But may just adjust it.
    [​IMG]
     
  2. Wally

    Wally Telefied Ad Free Member

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    If you increase the value of that resistor, you 8ncrease the midrange content.
     
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  3. Wally

    Wally Telefied Ad Free Member

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    Regarding that 6G9 schematic, that treble pot has a tap at 70K. Ime, that does something interesting in the mid range.
     
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  4. David Barnett

    David Barnett Doctor of Teleocity

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    That 6G9 is not a Blackface layout.
     
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  5. Phrygian77

    Phrygian77 Tele-Afflicted

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    Which channel(s) did you compare? The tremolo channel on the DR is going to sound a brighter, not just because of the bright cap, but also because of the 10pF bypass on the 3.3M reverb mixing resistor. A non-reverb Deluxe cabinet is also slight smaller.
     
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  6. Wally

    Wally Telefied Ad Free Member

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    Although, some of these 6G amps were installed in BF cabs....Tuxedo amps, right?
     
  7. LudwigvonBirk

    LudwigvonBirk Tele-Holic

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    Right (as usual!)

    Increasing the tone pot resistor value means LESS gets shunted to ground.
     
  8. schmee

    schmee Poster Extraordinaire

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    Sorry, whoops posted the wrong schem! But, the BFD has that same resistor on the Bass pot.
     
  9. schmee

    schmee Poster Extraordinaire

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    Yeah the bright cap is long gone on the BFDR. But I agree, that amp has always been a little brighter than the BFD which is more like playing the normal channel I suppose. I take one of 3 similar amps to gigs, but it seems when I take the BFD lately it sounds very middy to me and I end up teasing out the mids with an EQ or etc. I would like to just lessen the mids maybe 5-10%.
     
  10. David Barnett

    David Barnett Doctor of Teleocity

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    I have a blackface non-reverb Deluxe-Amp, a '63, and I've found that the choice of speaker effects how useful the tone controls can be. If the speaker has some annoying frequencies, then often there is just one sweet spot for the controls, to try to sweep that problem spot under the rug.

    I had a Fender-Utah speaker in mine, which had a really annoying peak somewhere in the upper mids. I replaced it with a Reverend Alltone, which had better mids but an annoying spot up top. Finally I tried an Eminence EJ-1240, which seems a lot more even-handed to my ear. It allows me to actually USE the tone controls for preference, rather than for damage control.

    So I wonder if maybe you just don't like the speaker in your BFD?
     
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  11. Phrygian77

    Phrygian77 Tele-Afflicted

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    I play mostly non-reverb amps. The PRs I've built always sounds a bit brighter than my blackface Bassman combo, but I've also had to run the bass control lower on those PRs also. I did a 47pF bright cap on the Bassman, and I use it occasionally. My latest Vibro Champ build is a bit darker than any of them (it has a 6.8k mid resistor instead of a 15k). My 1967 super reverb is about the brightest (and loudest) of all, but I think that's mostly the CTS speakers.

    On the blackface amps, a fixed 6.8k mid resistor is the equivalent of a 10kA mid pot turned up fairly high.

    I think, all of this works really well for vintage voiced pickups.
     
  12. aerhed

    aerhed Friend of Leo's

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    Have you tried bumping bass and treble? It's about the same as dropping mids. Our ears get deceived by the volume change somewhat. Or go ahead and drop the resistor.
     
  13. schmee

    schmee Poster Extraordinaire

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    It's a good thought. I did bump the treble saturday night further than usual. On these low watt Fender amps though, bumping the bass above about 4 just adds breakup really, not more bottom.
    I need to open it up. Maybe that old 6800 ohm resistor has aged to the point where it's a lot higher resistance. I could put the mid control in, but every time I do that I end up just leaving it in one place anyway! And the DR or hot rod Princeton aren't too middy for me.
     
  14. schmee

    schmee Poster Extraordinaire

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    I thought I would wrap this up. I found the issue. (I think!)
    The 6800 ohm resistor actually measured 10500! A damn modern carbon comp resistor. Many are way off. I dont use them that much any more, but replaced this one a couple years ago. Testing CC ones in my stock revealed ones from 7.5k ohms to almost 9k ohms, brand new.
    I put a good metal oxide resistor in, all mine tested near dead on spec in metal oxide.

    I guess the middiness in this amp wasn't my imagination !
     
  15. David Barnett

    David Barnett Doctor of Teleocity

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    I love a happy ending.
     
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  16. FenderLover

    FenderLover Friend of Leo's

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    CC's are mostly a PITA. Their mojo isn't on my radar.
     
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  17. corliss1

    corliss1 Friend of Leo's Platinum Supporter

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    I only use them if a knowledgeable customer insists when I'm doing vintage restorations. Other than that, I don't even keep them in stock.
     
  18. King Fan

    King Fan Friend of Leo's Ad Free Member

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    I’m def not going to defend CCs. You guys know way more'n me.

    In the small vintage circuits I build I’ve put 'em in the very few spots where Mr. Keen points out they may have EE mojo. May be a thing, may not...

    http://www.geofex.com/article_folders/carbon_comp/carboncomp.htm

    If that had been a vintage CC that tested good, of course, we wouldn’t be having this discussion. But I don’t think there’s any way CC 'mojo', even if it’s real, works in a shunt location like we’re discussing here.


    Sent from my iPad using Tapatalk
     
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  19. D'tar

    D'tar Friend of Leo's

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    Good ears Schmee! trust your instincts right! Glad it turned out a simple fix.


    Funny thing.... To me anyway... is #4 here from the link above. Most builders I see using CC will overkill the power rating in hopes of quieting down the noise associated with CC. This in turn negates the very reason for using them.

    MR. KEEN,

    "4. resistor power rating should be the minimum needed to work for a reasonable life in the circuit to maximize resistor distortion. Maybe a good guideline is that the dissipation should be selected to be as close to two times the average dissipation as possible.
    5. as a corollary to the power guideline, we should be prepared to replace CC's every few years as the life at high temp makes them drift and get noisy(-er)."
     
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  20. corliss1

    corliss1 Friend of Leo's Platinum Supporter

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    That is interesting since Aiken says this about contact noise:

    "Contact noise Contact noise is dependent on both average DC current and resistor material/size. The most significant contributor to noise in guitar amplifiers is the use of low-wattage carbon composition resistors. Since the noise is proportional to resistor size, the use of 2W carbon comp resistors will improve the performance over that of 1/2W resistors. Studies have shown a factor of 3 difference between a 1/2W and a 2W carbon comp resistor operating at the same conditions."

    The confusion/opinions are another reason to not use them :D
     
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