Headroom & EQ help, PLEASE!!!

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by DocRock, Feb 23, 2006.

  1. DocRock

    DocRock Supporting Member

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    Hey all,

    I just recently made the switch from a Dual Showman Reverb to a Bandmaster Reverb. I'm running into an 8-ohm THD 2x12 cabinet. The reason I made the switch was because I found that I simply had to run the DSR way too loud to get anything out of the output section. I even tried pulling two of the 6L6's and that helped a little...but not enough. It was still way too loud, even for stage use.

    I switched to the BMR because I liked the overall tonality of the amp, and found that I could get the output section to "give up the goods" at a much more reasonable stage volume. Still too loud for "bedroom" applications, but much better in a band setting.

    Here's the problem I've run into. The BMR breaks up a little too easily, and while I like the tone, I find that it doesn't have the bottom end that the DSR had. I don't think I can go back to the DSR for the forementioned reasons. That had too much headroom, actually. I'm trying to see if I can get to a sweet spot in between the two extremes. Without doing any invasive mods to the amp's original circuit, is there anything I can do to tighten up the bottom end of the BMR, along with giving it just a tad more headroom?

    Any input would be sincerely appreciated.

    Thanks everybody,

    Doc :)
     
  2. brad347

    brad347 Member

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    buy the following tube types:

    12AT7
    12AU7
    5751

    Try swapping each of these into the first (or second, depending on which channel you use) preamp slot.

    What kind of rectifier is in that amp?

    If it is a tube rectifier and there is NOT a 5AR4/GZ34 tube in there (look at the actual tube and not just the tube chart) then try getting a 5AR4 tube and re-biasing your power tubes.
     
  3. brad347

    brad347 Member

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    by first or second preamp slot I mean, facing the rear of the amp, the first two from the right.

    The subs will change the tone and the gain to a degree.

    The rectifier swap (if applicable) might be your best bet. Don't know when your amp is from but if it happens to have a 5U4 or something in there, going up to a 5AR4 and re-biasing will give you a touch more headroom and clarity, especially in the bass frequencies.

    It also sounds as if your power tubes might be tired... if it already has a good rectifier, try swapping your power tubes and re-biasing.

    Old and tired power tubes will often sound flubby in the bass and lose some power.
     
  4. DocRock

    DocRock Supporting Member

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    Thanks so much for your response to my headroom/eq question about my Bandmaster Reverb. It's a 73-74 yearwise, non-master volume. Looks like the previous owner had already changed the rectifier tube. The chart calls for a 5U4-GB, but there's a GZ-34/5AR4 in there right now, with a pair of pretty new-looking Sovtek 5881-WXT in the output. Maybe the output tubes are too old. What do you like?

    As for the pre-amp tubes, I had a 5751 so I tried it. It did help out a lot. I wasn't sure which slot to put it in, because I don't use the "normal" channel...only the "reverb/vibrato" channel. The tube chart reads, from left to right: 5U4-GB, 6L6-GC, 6L6-GC, 12AT7, 7025, 7025, 7025, 12AT7, 7025, 7025.

    When looking at the back of the amp, there are 3 pre-amp slots on the far right, followed by a little square-shaped thing (looks like a miniature transformer or choke of some kind), followed by 4 more pre-amp slots in the middle, and then the 2 output slots and, on the far left, the rectifier slot. I took this to mean the the 1st three pre-amp slots (7025, 7025, 12AT7) were for the normal channel. Then, after that little square thing, the remaining 4 pre-amp slots (7025, 7025, 7025, 12AT7) were for the reverb channel. Since I only use the reverb channel, I swapped the 5751 into what I thought was "V1" of the reverb channel. Was that incorrect? Does the pre-amp tube farthest to the right govern BOTH channels? If so, then I guess that's where I'm supposed to swap? Or is my intuition of where "V1" of the reverb channel was correct?

    Thanks again for your help...I really do appreciate it!!!

    Doc :dude
     
  5. brad347

    brad347 Member

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    Doc, see the PM I sent you. Second from right is the preamp tube for the reverb channel.

    I recommend ditching the 5881s... see my PM

    Good luck :)
     
  6. DocRock

    DocRock Supporting Member

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    I'll check it out. Thanks again so much for your help!!!

    Have a great weekend,

    Doc :BEER
     
  7. deeval

    deeval Supporting Member

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    Try using the 2nd input on the amp,this is about 6db lower gain and then you can turn the volume level a bit higher and should give you extra head before breakup,also some speaker experimintation would help also.:JAM
     
  8. DocRock

    DocRock Supporting Member

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    Thanks so much for the tip!!! What kind of speakers would you recommend trying out? It's funny, the speaker does so much to give final shape to the sound, yet it's something I've never learned that much about. I'm not even sure where to start.

    Anyway, thanks again!!!

    Doc :dude
     
  9. deeval

    deeval Supporting Member

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    Depending on what type of music you are playing to achieve the tone you want.
    You will have to try different spkers,I have experimented with alot of them to get the tones I want,Also have you tried using a quality amp attenuater to keep some of the headroom and being able to drive the amp harder?
    It will take a few bucks and trial and effort to get what you want and then you will have so much gear you will be selling it after awhile.
    Its becomes an obsession,and then you will still not be content.:horse
     
  10. DocRock

    DocRock Supporting Member

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    Thanks, guys, for the valuable input! Another thing I had heard was that simply changing the output transformer to something a bit beefier could do a lot to tighten up the bass response, as well as improving the amp's overall overdrive response. A couple different people suggested changing the Bandmaster OT to a Bassman OT. I've read posts from other BMR guys who have done that and never looked back. What do you think of that idea? Seems like it would be pretty inexpensive to do. I've heard good things about Heyboer. Any thoughts?

    Thanks again,

    Doc :)
     
  11. donnyjaguar

    donnyjaguar Member

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    Isn't the bandmaster the one with the small output transformer? If so, the reality is there just isn't enough iron, and resultant magnetic permiability, in the output tranny to properly amplify the lower-frequencies. Swapping tubes and speakers is only going to bring a little symptomatic relief. I'm considering doing this swap with one of my under-tranny'd heads. The dilemna is, do you spend money to modify it to make it more useful and then risk reducing its collector value?
     
  12. DocRock

    DocRock Supporting Member

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    Thanks for the input!

    I see what you mean about the collector value. I'm going to hang on to the original wimpy OT in case I ever decide to sell the amp. But in the meantime, I am gonna try and make this thing more useful to me, as I do gig with it.

    What do you think of Heyboer products? Any knowledge or experience with them?

    Thanks again,

    Doc :)
     
  13. brad347

    brad347 Member

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    I recommend a few extra $$$ for a Mercury Magnetics transformer. You won't look back, and even "vintage amp snobs" tend not to frown when they see a MM tranny in there...
     
  14. DocRock

    DocRock Supporting Member

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    Hey Brad,

    Thanks again for your responses. This whole techical discussion of swapping OT's is *very* new to me. I've been going largely on what I've been hearing. Some have said that MM is the best money can buy, some have said MM is overpriced. I haven't heard anything bad about Heyboer yet. I did some pricing on the net, and noticed that the MM costs DOUBLE what an equivalent Heyboer would cost. I realize tone is a very subjective phenomenon, but I wonder if MM sounds twice as good as a Heyboer. Do you have any experience with Heyboer? Is it good stuff?

    Thanks,

    Doc :)
     
  15. brad347

    brad347 Member

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    I don't have much experience with heyboer. I'm pretty sure that the MM probably doesn't sound "twice as good" even though it IS "twice the price."

    It all depends on you. I'm a perfectionist, I would always spend more to get a sound that was even a little bit better.

    Do you know how they Heyboer trannies are made? Interleaved, etc?
     
  16. DocRock

    DocRock Supporting Member

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    Well, the Heyboer site sucks. It has almost *ZERO* information on it. I'm told that they're made the "old school" interleaved, paper bobbin style.
     
  17. brad347

    brad347 Member

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    interleaved paper bobbin... probably a ok.
     
  18. DocRock

    DocRock Supporting Member

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    Thanks again, Brad. I'll post once I've done the tranny swap and let you know how it turned out.

    Best,

    Doc :dude
     
  19. brad347

    brad347 Member

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    good luck! I'd love to know how it turns out.
     
  20. Shea

    Shea Member

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    Heyboer trannies are good. They recently wound me a replacement OT for a Fisher stereo, and it sounds just as good as the remaining original one.

    One potential drawback to putting a Bassman OT in a Bandmaster Reverb is that you'll probably have to drill extra holes in the chassis, unless you can fabricate some kind of adapter plate.

    Shea
     

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