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.

Taming High Gain Deluxe Reverb

Discussion in 'Amp Tech Center' started by carlbob, Apr 10, 2021.

  1. carlbob

    carlbob TDPRI Member

    Posts:
    10
    Joined:
    Aug 26, 2020
    Location:
    Texas
    I bought a 1979 DR (push boost model) that was modded by running the “boost” from the reverb input, via a pot, to the tone circuit. The vibrato channel went from strangely clean to awful, by adjusting the pot. So I disconnected it and all of a sudden it was so gainy! No headroom at all on the channel. I then put a 12ay7 in V2 and at7 in V4 (reverb recovery?). I now have what is a crazy good gain structure. But the bass is still somewhat flubby at volume. Two questions: how to restrain the bass, and would you fix the high gain “problem” or leave the lower gain tube substitutes? The speaker is a V30. (It may have other mods but haven’t gone through it carefully.) Thanks for any advice/opinions.
     
  2. archetype

    archetype Fiend of Leo's

    Posts:
    5,904
    Joined:
    Jun 4, 2005
    Location:
    Williamsville NY
    I'd fix it by taking it to a proven, good amp tech and have it put back to the stock circuit.

    Messing with it is unlikely to make it right, unless you're relying on luck as a troubleshooting technique.
     
    lil scotty, Wally, SoK66 and 3 others like this.
  3. Engine Swap

    Engine Swap Tele-Afflicted

    Posts:
    1,453
    Joined:
    Nov 28, 2014
    Location:
    Chicago
    This.
     
    AlbertaGriff likes this.
  4. AlbertaGriff

    AlbertaGriff Tele-Afflicted

    Posts:
    1,881
    Joined:
    Mar 2, 2016
    Location:
    Canada
    Sounds like it sounds awful. It's worth having it put right and doing the proper maintenance at the same time.
     
  5. Jay Jernigan

    Jay Jernigan Tele-Afflicted

    Posts:
    1,559
    Joined:
    Feb 11, 2013
    Location:
    10-uh-C
    I had my BFDR rebuilt (is that the proper term?) and I have to use the second input on channel two (I don't know about#1) in order for it to be clean in front.
     
    Tommy Biggs and carlbob like this.
  6. radiocaster

    radiocaster Poster Extraordinaire

    Posts:
    8,424
    Joined:
    Aug 18, 2015
    Location:
    europe
    Lower gain tubes usually give more bass.

    Maybe you could try an Electro-Harmonix 12AY7 because their 12AX7 is unusually bright, although I can't guarantee that it would do what you want.
     
  7. carlbob

    carlbob TDPRI Member

    Posts:
    10
    Joined:
    Aug 26, 2020
    Location:
    Texas
    Thanks archetype. I’m leaning in that direction.
     
    Engine Swap likes this.
  8. carlbob

    carlbob TDPRI Member

    Posts:
    10
    Joined:
    Aug 26, 2020
    Location:
    Texas
    Actually it sounds pretty good. It’s just the bass flub at high volume I’d like to tighten up. A previous owner has replaced all the electrolytics with F&T. And a couple other caps. I haven’t checked if the values are stock. If they are, this thing was born a gain monster because it has no headroom with the Sovtek AX7s it came with when I got it.
     
  9. carlbob

    carlbob TDPRI Member

    Posts:
    10
    Joined:
    Aug 26, 2020
    Location:
    Texas
    thanks radiocaster. I didn’t know that about lower gain tubes. I have at least a couple other ay7’s to try but not the EH.
     
  10. SoK66

    SoK66 Tele-Afflicted

    Posts:
    1,487
    Joined:
    Oct 2, 2007
    Location:
    Four Corners USA
    Take it to a good tech and ask to have the Pull Boost BS eliminated. Involves rewiring the reverb driver circuit to AB763 specs, replacing the Vibrato channel pull pot with a 1Meg audio pot and a few otehr changes, like component values in the PI circuit. It'll be a desert island amp when he's done.
     
  11. corliss1

    corliss1 Friend of Leo's Platinum Supporter

    Posts:
    4,785
    Joined:
    Sep 13, 2008
    Location:
    Lansing, MI
    And...after it's back to a more stock setup, you could add a tone stack lift or "raw" control if you wanted an option for more gain. Easily reversible, use the extension speaker jack.
     
    carlbob likes this.
  12. Dacious

    Dacious Poster Extraordinaire

    Posts:
    9,622
    Joined:
    Mar 16, 2003
    Location:
    Godzone
    Most small Fender amps don't do 'everything dimed'. If you push treble high high you will get unpleasant harsh distortion. Mostly, you can get to 6 treble, 3-4 on the bass before it starts to crap out - depending on guitar and input 1 or 2.

    In the Fender-Marshall-Vox tone stack the treble acts as a master eq control. If you turn it too high it will over-enhance the mids and bass, which turns everything to mud, at which point you turn the treble higher and make things worse.....
     
  13. carlbob

    carlbob TDPRI Member

    Posts:
    10
    Joined:
    Aug 26, 2020
    Location:
    Texas
    Thanks, SoK66. The “boost” was modded by a previous owner so it was variable via a pot. Didn’t sound great. I removed it.
     
    SoK66 likes this.
  14. carlbob

    carlbob TDPRI Member

    Posts:
    10
    Joined:
    Aug 26, 2020
    Location:
    Texas
    Yeah on this one I leave the treble on 3. Bass on 6 or 7.....it turns out the flubby bass at high volume was related to my Strat pickups. When I plugged in my LP with Throbaks, bass was not an issue at all. And it sounds freakin glorious.
     
  15. Lowerleftcoast

    Lowerleftcoast Friend of Leo's

    Posts:
    3,468
    Joined:
    Dec 30, 2019
    Location:
    california
    Ime the V30 would want to be removed if the amp was put back to stock or black faced.

    It would be helpful to know what mods have been done to the amp and what the schematic looks like in the current configuration.

    You like the gain the way it is now. There are several places where bass can be reduced.
    Typically the cathode bypass capacitor on the first gain stage(s) will be reduced. 4.7uF to 10uF rolls off sub bass frequencies without a reduction in audible bass for the most part. 2.2uF rolls off the low bass and maintains most guitar frequencies. 1uF to .68uF rolls of some guitar frequency bass. Marshall used .68uF on some of their high gain amps.
    AFAIK the 25uF or larger cathode bypass caps were chosen to reduce noise (S/N ratio) and provide full range signal amplification. My ear does not detect a difference in noise when smaller cathode bypass caps are used on a guitar amp.

    The coupling caps and tone stack caps form RC filters. The RC filters can be adjusted by changing the cap and/or the resistor.

    As a general rule bass is reduced early in the signal path or late in the signal path but not both. Marshall and Fender designs seem to follow opposite ends of the general rule. Marshall would reduce bass early. Fender would reduce bass late.
     
    carlbob likes this.
  16. carlbob

    carlbob TDPRI Member

    Posts:
    10
    Joined:
    Aug 26, 2020
    Location:
    Texas
    those are very helpful points, @Lowerleftcoast , thanks. over the next couple weeks I plan to find out what mods remain. I did find the bass more tamed with my LP, but of course the headroom comes down quite a bit. And my Strat neck pickup still causes lower frequency overload.
     
IMPORTANT: Treat everyone here with respect, no matter how difficult!
No sex, drug, political, religion or hate discussion permitted here.