Old Ampeg extremely boomy…

Discussion in 'Amps and Cabs [BG]' started by punkrot, Sep 8, 2020.


  1. Tube amp with gain + master volume

    6 vote(s)
    33.3%
  2. Jumpered tube amp with blended dirty channel and clean channel

    2 vote(s)
    11.1%
  3. Clean amp with dirt pedal

    10 vote(s)
    55.6%
  1. punkrot

    punkrot

    Sep 8, 2020
    Hiroshima, Japan
    I am essentially unendorsable.
    Hello Everyone,

    Longtime fan, first time posting. I have a two-part question for all you glorious bass gods.

    I have an Ampeg Jupiter B-42X 55W all tube head (circa 1969). Normally these old guys have two identical channels, but mine’s been modded so that one channel is very high gain with separate gain and master volume controls. Both channels have treble and bass controls, switches for ultra-low and ultra-high (not sure if these boost or just re-shape the EQ). There are also bright and normal inputs for each channel. No mid controls, and no effects loop.

    Question 1:
    The amp has a very overly-bassy, boomy sound. I’ve tried it with a few cabs, same problem in all cases. Do y’all think it needs a retube and/or rebias? Or is this just how these old Ampegs are? What can I do to tame the mega-bloat? I had it retubed over a decade ago, and I used it a little in very low-volume practice situations for guitar, but it's been sitting for most of that time. I recently swapped the rectifier tube for an NOS since the previous one died.

    Question 2:
    Ideally, I’d like to run the channels jumpered, with the original channel clean/cleanish and bass-focused, and the modded channel gritty as hell and mid/treble focused. For those not familiar, jumpered channels on these old beasts run parallel, not stacked, so you get both channels blended (one doesn’t boost the other). Is this a good way to get brutal distortion with reasonable clarity, or should I just run a clean channel with a dirt pedal?

    Bass is in drop A. But the amp is boomy on all strings. Even the drop A baritone guitar sounds boomy through it.

    Thanks in advance for any help!

    P.S. If it matters, I'm playing melodic crustpunk (His Hero is Gone, Acursed, Martyrdöd, Exul, etc.). So filthy and heavy yet somehow still musical is the goal. Looking for a usable live sound.
     
    SherpaKahn and xJasonSmithx like this.
  2. Jim C

    Jim C I believe in the trilogy; Fender, Stingray, + G&L Supporting Member

    Nov 29, 2008
    Bethesda, MD
    OK, I'm old. Crustpunk? Did you just make that up?

    I've not found old Ampeg's to be boomy. Perhaps it's worth spending $75ish dollars for a tech to see if anything other than the input and gain structure has been altered. I'm assuming this is the guitar version of a B-25 like this: Used Ampeg "Jupiter" B-42X guitar amp
     
  3. punkrot

    punkrot

    Sep 8, 2020
    Hiroshima, Japan
    I am essentially unendorsable.
    That's the very amp. Is it for guitar? I thought it was a bass amp that could handle guitar. Maybe it's the other way around? No idea…

    And no, I didn't make it up. The term "crust punk" was came about from the "Ripper Crust" EP by UK crusties Hellbastard back in 1984. The genre has had many permutations since. The melodic stuff hit in the 90's. It was originally called "melodic crust," but then the term "neocrust" got applied somewhere along the way. Anyway, it's a real thing, is all I'm saying. It's also always been staunchly underground.
     
    pie_man_25 and Jim C like this.
  4. punkrot

    punkrot

    Sep 8, 2020
    Hiroshima, Japan
    I am essentially unendorsable.
    As for the modification, the amp retains one completely unaltered channel, and at the bottom of the gain dial the second channel is basically indistinguishable from the first. When you crank the gain it gets super hairy though. There's a custom footswitch for channel switching as well (obviated when jumpering).

    The mod was commissioned from a reputable vintage-specialized amp tech in Portland (Leighton Audio, now defunct). He also fixed bunches of other stuff that needed TLC at the time.

    I think you're onto something with having a tech give it a go-over. It probably just needs a tune up.

    But whether or not it's suitable for this bass project is another matter. If it's a guitar head, will it work well as a bass amp, particularly for a bass tuned to a bowel-loosening drop-A?
     
  5. Jim C

    Jim C I believe in the trilogy; Fender, Stingray, + G&L Supporting Member

    Nov 29, 2008
    Bethesda, MD
    The Ampeg V4 is a 100 watt guitar head and the V4B is the bass version.
    If you search, you will find the small difference between them is (as I remember) is a capacitor or two.
    Many guys don't touch the guitar version and say they sound great as is for bass.
    I would think this would apply to your amp too.
    I would go to an authorized Ampeg repair facility and make sure they have the schematic.

    @beans-on-toast is highly knowledgeable about these Ampeg amps and can possibly shed more light on these tech details.
     
  6. punkrot

    punkrot

    Sep 8, 2020
    Hiroshima, Japan
    I am essentially unendorsable.
    Awesome, thanks for the info. I live in Hiroshima, so I have no idea if there's an authorized Ampeg repair facility.

    I do know a guy, though…
     
  7. sunbeast

    sunbeast Supporting Member

    Jul 19, 2006
    Denver, CO
    I think these were designed to be paired with a 16 ohm cabinet, so running it with a modern cab in some lower impedance would not be ideal and would change the tone. I read that the preamp is quite similar (if not identical) to the B25 amps, which I’ve seen some bassists use live and sound great with.
     
    bobyoung53 likes this.
  8. punkrot

    punkrot

    Sep 8, 2020
    Hiroshima, Japan
    I am essentially unendorsable.
    It has outputs for 8 Ohms and 16 Ohms. The cabs I've hooked it up to were all 8.
     
    sunbeast likes this.
  9. beans-on-toast

    beans-on-toast

    Aug 7, 2008
    Question 1: A general checkup by a tech that knows these amps wouldn't be a bad idea. Have the power tube bias checked. On this amp you have to change a resistor to change the bias so it often wasn't optimally set. These amps can run a bit cool in terms of bias and they still sound good, good for tube life. It would also be good to have the tone stage checked out. The components in the PEC modules (the tech should know what these are) tend to drift out of spec with time. Check the input jacks for oxidation where the jack touches the chassis. THis is the main ground and often needs to be cleaned.

    Question 2: Jumpering the channels is fine, more tonal complexity. In addition, I would use a pedal to overdrive the first stage.
     
    AstroSonic, Al Kraft and Wisebass like this.
  10. BogeyBass

    BogeyBass Inactive

    Sep 14, 2010
    running channels parallel is not a good way to get distortion.
    it has gain, it will distort

    Most likely the problem, its running 2 tone stacks/ tone controls all the time.
    any hard core ampeg collector would immediatly remove the mods.
    Knowing the classic Ampeg 2 band tone stack well. There is slight mid cut.
    running a mid cut x 2 would be boomy muddy bass.

    Too get clean deep crunchy distortion, guitar pedals or even bass pedals.
    those pedals highpass the signal first. removes the bass. bass signals distort and bloat and sponge out the distortion.
    then after the gain stage or numerous gain stages. The bass is added back.
    after the distortion, not full boosted tonestack into tonestack to create distortion

    the real key to distortion is multiple pre filtering , and post filtering.
    running 2 channels with full boosted EQ sections, just pounding the phase inverter for distortion.
    with boosted tonestack. is not going to be good distortion and be way to much EQ

    its a 100 watt amp, you just run a normal channel and turn the thing all the way up for distortion.
    if you want high gain, high sustain distortion, then yes a well designed pedal does that better.

    in the end its a combination of the pedal sustain and the amp distortion that makes the magic.
    for the most part a pedal could still remove some bass, and the amp tone controls are used to boost it back
    after all the gain and distortion gets made.

    basically yes remove the mods, use a pedal for high sustain distortion.
    another always on distortion trick is always on EQ after the distortion.
    you do slight cuts where all the gain is, and clean up the fizzle. and do magic mid boost to some frequencies.
     
    Last edited: Sep 8, 2020
  11. BogeyBass

    BogeyBass Inactive

    Sep 14, 2010
    in the meantime since you have 2 channels running for gain.
    run your bass into channel 1 keep the bass and treble, almost straight up or slightly down.

    then i assume as you turn up the volume on channel 2 its even more gain.
    keep the tone controls almost fully cut. just use it for gain not EQ
     
  12. punkrot

    punkrot

    Sep 8, 2020
    Hiroshima, Japan
    I am essentially unendorsable.
    Sounds like the tech is in this amp's future. I can clean the jacks myself, at least. But there's no way that's all that's going on.

    This was my first real guitar amp, and I used it with a Landmine Distortion pedal. It sounded great and had a luscious clean tone. Definitely something seems off now with the boom-city thing. So everything you're saying makes loads of sense in terms of stuff drifting.

    Thanks again!
     
    beans-on-toast likes this.
  13. I've been using the b25b for 30 years, basically the dedicated bass version of your amp.
    Never had an issue of "boominess ". Mine stays crystal clean all the way to 5.
    At 6, the dirt kicks in, and at 7 its growling.
    I'm no Amp tech... but if your getting mud..something ain't right.
     
  14. punkrot

    punkrot

    Sep 8, 2020
    Hiroshima, Japan
    I am essentially unendorsable.
    Thanks for the reply.

    The idea with the parallel isn't to get more distortion, it's to blend an undistorted or mildly distorted bass-heavy tone with a distorted mid-heavy tone. But yeah, probably a pedal is going to get me there with a lot less trouble, less things to tweak around with, and less stuff to go wrong.

    As for the boom, each channel does the bloated thing individually as well as together. Like, same bloatedness, which is why I thought maybe it was tube related. But from what folks are saying, it sounds like other stuff could be off kilter too.

    When the mod was put in, the tech fixed a bunch of stuff that was out of whack, and he did it using all period-correct (to the extent possible) components. The mod is actually very simple, and was added in such a way as to not mess with the underlying amp. Basically, the tremolo feature was busted, so he turned one of the two controls for it into a master volume. Easy to remove without harming anything. The footswitch for the two channels involved drilling a couple jacks into the back plate though. But in all honesty, the amp was thrashed to $h*t when I handed it over to him — it had been given to me after a long, unhealthy life of gigging in punk bands and was, at that time, non-operational. It even had a cable plug broken off in one of the jacks. He gave it a lot of love, and it showed in the sound I got out of it back then.

    I'm just wondering if I should resurrect it again as a bass amp, or if it's not really ideal for this application.
     
    Last edited: Sep 8, 2020
  15. punkrot

    punkrot

    Sep 8, 2020
    Hiroshima, Japan
    I am essentially unendorsable.
    That's what I'm thinking. And I wouldn't say mud, just a sound like the bass is cranked to hell even when it's not. Like a standing wave in the low end.
     
  16. punkrot

    punkrot

    Sep 8, 2020
    Hiroshima, Japan
    I am essentially unendorsable.
    The channels don't stack, they're parallel. One has a master volume, the other doesn't. The original purpose for the mod was to have footswitchable clean and dirt channels for guitar. But with bass, I'm wondering if mixing clean and dirt will get me a good, usable heavy bass tone for a live setting. It would be nice to know the low down on that before sinking several hundred into a retube and whatever else the tech needs to do to this poor old gent of an amp.
     
  17. Jim C

    Jim C I believe in the trilogy; Fender, Stingray, + G&L Supporting Member

    Nov 29, 2008
    Bethesda, MD
    Just out of curiosity, what cabinet are you using and does it sound less boomy with a different amp and your bass?
    It's a 50 watt amp so it's only going to get so loud before distortion and generally speaking, a cabinet with more speakers will be louder than a single driver cabinet.
     
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  18. punkrot

    punkrot

    Sep 8, 2020
    Hiroshima, Japan
    I am essentially unendorsable.
    The bass sounds fine out of other amps. The cabs were a Hartke half-stack something-or-other and a creepy mystery cab which looks like a much maligned Ampeg fridge that fell out of a portal to Hades, but it's hard to tell. The cabs belonged to two different studios. The one studio closed because of rona-nomics, so no way to know what the Hartke was. The mystery cab is in the punk-run underground studio we're currently using. But the other bands use it and it sounds fine.

    Oh, I also tried it at a low volume out of my guitar cab which is a Randal 2x12 1x15.

    The uber-rumble happened in all instances.
     
    Jim C likes this.
  19. BogeyBass

    BogeyBass Inactive

    Sep 14, 2010
    usual case a bass amp that needs updating would have less bass or seem spongy. or the output tubes are running hot.

    for a tube amp rebuild its the usual suspects, checking socket connections or replacing sockets,
    main power supply caps, and if the dc blocking caps after the phase inverter are little leaky, bias will sit high.
    this one still has a rec tube, so if fuses start popping or if it eats rec tubes often. usually power supply caps need replacing.

    far as 2 much bass, i understand its 2 parallel channels. you just cut bass or keep it low.

    Ive used 100 watt tube amps with a buttload of speakers to keep up with a band.
    Basically a 8x10 is all i've ever used.
    Depending on how many speakers your using, i dont think a 50 watt amp is really going to keep up with a loud band.
    unless you were pushing a 810 or 4x15.
     
    Iristone likes this.
  20. sunbeast

    sunbeast Supporting Member

    Jul 19, 2006
    Denver, CO
    I knew I had read this before about the B25 having weird impedance needs, so I had to look it up. According to this thread https://www.thegearpage.net/board/index.php?threads/how-to-run-my-ampeg-b25b.608895/ the B25 was built to handle down to 8ohm operation, but only when utilizing dual 16ohm cabs that were originally sold with it. I believe your amp would have been the same. The 8ohm transformer tap was only accessed by switching that occurs when both speaker outputs are used at the same time. Some people have mentioned using a “dummy plug” into the extension output in order to engage this switching (not a dummy cable though!!). Possibly a modification was already done to your amp to separate the 8 ohm tap to a separate jack, but worth looking in to!
     
    bobyoung53, Wasnex and Jim C like this.
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