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Help, I need a little SWR advice

Discussion in 'Amps and Cabs [BG]' started by DR Burkowitz, Jul 10, 2002.


  1. Hey There Boys & Girls & Gifted Animals:

    I have a rig problem, and I need some advice from my fellow TB'rs

    The RIG:
    SWR Golliath II (x2)
    SWR SM-400s (very early model no cooling fan)
    DBX 211 compressor
    Boss Chorus (rack mount)

    Bass:
    Conklin Sidewinder 7 tuned Low B to High F
    Bartolini P/U's & Bartolini 5.4 preamp

    The Problem:
    Unwanted Distortion particularly from lower notes

    Background:
    I've been running essentially the same rig for near 7 years now the most recent addition 1.5 years ago was the new Conklin Bass, prior to that I was using my Tobias Signature 6. Anyway The last 2 months or so I've noticed that shortly into using the rig on a given day I begin to generate a terrible distortion out of the cabs, particularly on lower notes (anything on the B, and about half of the E string), I also noted that the general quality of my tone was going to hell. Anyway after some help from my guitar player (I know, I know, don't trust your guitar player) we had determined that it was probably the horns in the cabinets (you'll have to forgive me I am no where near as gear tech orientated as I wish I was) so I called my local store of choice and ordered a pair of new horns. Got them today, put them in, and I have the same problem. Everything up to 2 months ago was sounding and working beautiful - the only other thing that changed around that time was that I finally replaced the original tube, on the advice of a local music store. The tube in the amp itself is just your standard 12-ax7, I replaced it as specified in the owners manual.

    So kids what am I missing, and why did my tone go to hell. I'm at a loss, and my local music store is of little help. Please help any and all advice would be very appreciated.

    Best Wishes,
    DR Burkowitz
     
  2. ndjx

    ndjx

    Oct 26, 2001
    MN
    Its just a guess maybe the speaker cables are old?
     
  3. If I followed your story correctly... it sounds like the tube may be bad or wrong. Have you tried putting back in the "old" one? New cables is a good idea, and maybe a new battery in the bass?
     
  4. narud

    narud Supporting Member

    Mar 15, 2001
    santa maria,california
    have you tried you basses and head through some different cabs?
     
  5. ihixulu

    ihixulu Supporting Member

    Mar 31, 2000
    getting warmer
    1) the battery in the bass might be old as already had been suggested,

    -or-

    2) not all tubes are created equal. maybe you have a dud? what brand did you use?

    -or-

    3) it's time to get the bias checked/adjusted on the power sections in the amp, a very minor procedure.
     
  6. bassmanjones

    bassmanjones

    Feb 23, 2002
    Boston, MA
    Wouldn't a bad tube have an effect on everything played though? He says he only has a problem with the low notes...my guess is something may be up with the speakers. They might just be old and if not cared for or allowed to dry out there's the possibility that some or all could start to go bad.
     
  7. Jon Burnet

    Jon Burnet

    Jan 21, 2001
    Memphis, TN
    i have noticed that with my 400 the low notes clip the tube alot easier because they take more wattage to push. i would say go buy a grove tube and see if it helps.if you have never changed the tube my vote would be bad tube bad.
     
  8. I usually trouble shoot by substituting the big components first, then narrow it down.

    The fact that it was distorting with BOTH cabs makes me believe it's the amp (or bass). Could be the new tube, could be other components. Two G2s are a lot for a single SM400 to push, it's possible that you've burned up something besides the preamp tube.

    Here's what I would do:
    try different bass (still distorting?)
    try different instrument and speaker cable (still distorting?)
    try the amp with other cabs (still distorting?)
    try another preamp tube (still distorting?)
    send amp to repair shop
     
  9. boobinga

    boobinga

    Feb 9, 2001
    Pacific NW
    DR...Lots of good advice here. I'll be interested to know how you end up solving this. By the way, if it ends up an amp problem I've heard that SWR has a pretty good turn around service if you have them service your amp direct. Good luck!
     
  10. I had the same thing happen in my old '94 Henry 8x8 with my SM 400S.

    Took me a long time to figure it out.

    Turned out to be Voice Coil Rub from the speakers.

    Had to look into a recone.

    Now tones back like new.

    Take your amp and your 5 string to the Local Music Retailer and plug your amp into a new cabinet and check it.

    Betcha' your Goliath II's are tired and need a recone.
     
  11. WOW :eek:

    Thanks for all of the advice guys.

    OK, tried new battery: same problem

    new cables: same problem

    Different bass: same problem

    I'm heading out to the store now to pick up a new tube, and try differnt cabs. I'll keep you posted.

    Thanks again for the all of the input :D

    Best Wishes,
    DR Burkowitz
     
  12. chadds

    chadds

    Mar 18, 2000
    Make sure your bridged/stereo switch isn't in the bridged mode with with the speakers plugged in the stereo jacks. I did this once and got an electronic farting noise{hey new band name}on low notes.
    I also concur that the Sm-400 is better suited to running one of your cabinets. In bridged mode it puts out a clean 400 watts at 8 ohms. The way you are using it each cabinet is getting 175 watts. The SM-400 puts out 175 watts per side @8ohms and 220 watts @ 40hms. Try the SM bridged into one cabinet without the compressor, crank the preamp to where the led flashes, back off a hair and crank the master as much as you need. Try this with tone controls flat and you may have discovered a new amp! This will roar You might not need the other 4-10. Then, I'm spending your money, you can buy another sm-400 used or an SM-900 which will do both cabinets stereo at 8 ohms.
    Thanks I love these amps
     
  13. Don't use a run-of-the-mill 12AX7 tube in your amp.
    I own a SWR SM 400-S and use a 5751 preamp tube.

    I'm not an audiophile, just a bass player. So the main thing for me (beyond mechanical reliability, which any 3-spacer 5751 will serve up in spades) is tightness in the bottom octave. Detail in that range may seem a strange subject, so let me liken the difference between these tubes and all others to the difference between MP3 and CD. The first time I taste-tested an MP3 file against a CD, I listened to an exposed low tuba passage. In the MP3, the pitch was reproduced faithfully, but that was all. On the CD, I could fairly hear each individual juicy flapping of the tubist's lips. Now there is no way that EQ or speakers or any other device can add what's not there. It can add emphasis to a certain frequency, sure, but not detail. Of course, as a Precision Bass player, I'm a fanatic about "grunt." It's the defining characteristic of the P-bass sound, and one of the reasons that audiences feel so good about the P-sound is (first among other things) the very vocal quality imparted to the bass by "grunt."

    As I say, I'm not an audiophile, but there are two themes that recur in Joe S's FAQ that translate into terms useful to the bassist. The first is that of "palpability," and the second is of spaciousness of the soundstage. Because a note from an electric bass is composed of so many discrete elements, each of which must be reproduced with integrity, I think these two measuring sticks relate equally to the production of "grunt." However, the bass grunt test cuts more finely than these. While Joe notes its relative imprecision in hi-fi equipment (compared to the magic tubes), one of the tubes that made Joe's "short list," the Tung-Sol, entirely lacks the three-dimensionality I can hear in the four magic tubes. Of course, the "grunt" I'm so crazy about is probably not present on most recordings, so it may not be a crucial issue in hi-fi tubes, but if it is there, I think it would take these magic tubes to allow you to hear it.

    Thanks again to Joe S for his eye-opening FAQ, and thanks to Steve Oda for patiently helping me understand many related things including tube break-in and guitar usage of 5751s (now I understand that bass is an entirely different proposition from guitar; that last octave is so demanding that many fine guitar tubes are unsuitable for bass).

    At the top of the recommendations list in "Joe's Tube Lore" is the Sylvania 5751. It is a triple-mica, black plated beast that is supposedly the creme de la creme of 5751's. I netted one from an eBay auction along with another recommended tube, the Tung-Sol 5751.

    Was Joe correct? Absolutely. The Sylvania is the best 5751 I own. It is marked JHS 5751WA with yellow lettering. This tube is similar but superior to the Raytheon, adding a final touch of realism to the audio stream. Find it and know the joy.

    In a SWR:

    Nonetheless, judicious use of the Aural Enhancer circuitry (subtler than cranking EQ, but very effective and far less power-hungry) can make the amp's sound stand out a bit more in a very nice way (EQ, by the way, is very flexible with semi-parametric bass, mid, and treble). The clean, detailed sound of the amp is characterized by a wonderful vibrancy and "liveness" thanks to its one-tube preamp. Substitution of a great 5751 tube (any 50s-era black-plate 3-mica JAN Sylvania or GE will do) for the standard 12AX7 opens the amp up into a spacious, deliciously growly 3-dimensional sound that shows the Blue's unusual but responsive speaker arrangement off to its fullest.

    The SWR preamp has a wonderful direct interface built right in, and whether you go direct or line, your bass goes through the tube first. One is all you get and one is all you need. The caveat is this: you're totally at the mercy of the sound of that one tube. So you're going to have to take the time to find the right tube. Although you have probably experienced the generality that tubes sound warm (because they generate even-order harmonics) and that solid-state devices sound cold (because they generate odd-order harmonics), while I would take a good tube sound over a good solid-state sound, I'd take even an average solid-state sound over a bad tube sound--the debates about tubes vs. solid-state devices per se make no sense to me.

    I listened very critically to a decent 12AX7 and as raucous and loose-sounding as it was, I was sure I could do better (no amount of EQ-tweaking helped; in fact it made things worse). Then I ran across Joe S's three-part FAQ about substituting the 5751 for the 12AX7 (see http://www.audioasylum.com/audio/faq/joes-tubes.html#12AX7 for the first part and keep paging down for the rest). I lucked into a good one and tried it (a 1959 three-mica, black-plate, green-print Sylvania JAN 5751). Pure magic. The bottom tightened up to a nearly unbelievable extent. The mids were vibrant yet not peaky at all. The highs were smooth and sweet. The gain is noticeably lower, but the quietness of the tube more than makes up for that loss (since a good S/N ratio is what the 12AX7's extra gain aims at in the first place, even if it misses).
     
  14. jerry

    jerry Doesn't know BDO Gold Supporting Member

    Dec 13, 1999
    Hawaii
    I would try and borrow a more powerful head.... a seven string is going to eat up a lot of wattage in the low end....the SM400 is a great head....but it doesn't have a lot of headroom!
     
  15. You can add a power amp to the great SWR preamp.
     
  16. iammr2

    iammr2

    Jun 10, 2002
    Tejas
    I run an SM400 and ran into that same issue. What was happening that I had turned the bass tone knob up and dialed in the parametric to 31hz and boosted that slider. I was going for lots of really deep bass. The speaker cabinet at the time was tuned to 41hz, so I was boosting the sound below the cabinets range. Floated that big 15 incher with ease. Pulled the bass slider down and turned down the bass a little and the problem disappeared. Since you're using a 7-string, is it possible that you were going for that low B thump and exceeded the speaker cabinets' design parameters? Thought maybe you might be making the same mistake I did.