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Pre-amp interfacing with SWR Bass 350

Discussion in 'Amps and Cabs [BG]' started by BWB, Oct 9, 2001.


  1. BWB

    BWB

    Aug 30, 2000
    Knoxville TN
    Well - here's an interesting question. I just
    acquired a used SWR Bass 350 head. While the
    tone of the amp is good - it's not 'my' tones; the
    tones I created with my ADA MB-1 programmable
    preamp.

    The SWR Bass 350 has no PA input to bypass the
    internal preamp. Meaning, my only option is
    (apparently) to run the output of the MB-1 preamp
    into the preamp stage of the Bass 350 and then
    out through the chain....etc.

    This does work, but I find that the preamp on the
    Bass 350 clips with the gain past about 11 o'clock
    and the PA section does the same at 11-12 o'clock.
    This is to be expected, given the set up. The
    question is (you electronically inclined folks)
    that, assuming I am happy with the sound I am
    getting now without the Bass 350 amp or preamp
    going into clip, is a resistive pad in line with the
    connection between the MB-1 and the Bass 350
    input the way to go to damp down the input
    signal to the preamp section of the Bass 350?

    I am stumped to come up with another solution
    short of modifying the amp and adding a switch
    and jack to disable the Bass 350 preamp and use
    the MB-1 direct to the 350 PA section. This could
    be done, but I'd rather leave the amp stock as
    I am not convinced it's a keeper. Thoughts?
     
  2. Chasarms

    Chasarms Casual Observer

    May 24, 2001
    Bettendorf, IA USA
    have you tried plugging the preamp into the effects return? This bypasses the preamp stage. I have used my bass pod pro with several rigs using this method with great success. Just plug into the effects return and into the preamp with your bass.

    Chas
     
  3. brianrost

    brianrost Gold Supporting Member

    Apr 26, 2000
    Boston, Taxachusetts
    What Chasarms says.

    Plug into the effects return and set the blend knob fully clockwise. This bypasses everything but the master volume control of the 350.
     
  4. BWB

    BWB

    Aug 30, 2000
    Knoxville TN
    If this works, am I correct in assuming that if I
    back off the effects blend knob on the 350 that
    I can further 'color' the tone by adjusting the
    tone controls on the PA section? As opposed
    to running it fully clockwise to only get the
    sound of the MB-1 preamp output?

    Unfortunately due to life (translation: I have a
    20 month old daughter and a wife in graduate
    school who has an exam Wednesday) I won't
    be able to try this until Wednesday night.

    I didn't get a manual with the used 350, so I've
    been winging it. Thanks.
     
  5. I think that you can download the manual from the SWR website. Go here:

    www.swreng.com
     
  6. No - this is not correct. If you back off the blend knob, you can plug something into the input of the SWR and it will be heard also. It will blend the two pre-amps but since you are plugged into the external pre-amp, the SWR pre-amp controls will have no effect. If you want to use a singal splitter or switch, you can send your guitar signal to either or both preamps and combine or select which preamp you would like to use.
     
  7. More...

    I downloaded the manual.

    You should be able to hook your preamp into the active input and adjust the gain control so that you are not clipping the pre-amp. The gain control is really a pad. Use the Master Volume to control the volume. According to the manual, that active input will take a pretty hot signal. If you do this, of course, the preamp controls on the SWR will affect the sound.

    I'm not recommending one way over the other. The way that sounds best is the way to go. Both ways should work.

    Running through both pre-amps will give more noise in the signal, but it may not be noticable. Try both ways, See what you like.
     
  8. BWB

    BWB

    Aug 30, 2000
    Knoxville TN
    Thanks for everyone's input on this. I have a gig
    this Saturday night and am going to put in some
    time with the freshly downloaded manual.

    I played a gig last Saturday night with the MB-1
    just run into the passive input of the Bass 350
    and it sounded acceptably good to play the
    gig as we keep the stage volume low - but on
    a couple of tunes I'd play harder and the thing
    would clip - I could hear it clipping without even
    looking at the lights and was alternating
    adjusting the output of the MB-1 and the
    preamp gain and master vol controls on the 350.
    While being aware that this wasn't the solution
    and I was going to have to think of something
    before this coming weekend.

    Wednesday night is rehearsal night, so I'll get a
    couple of hours to fool with the thing before I
    have to get on stage with it on Saturday.

    Scott
    :)
     
  9. BWB

    BWB

    Aug 30, 2000
    Knoxville TN
    Looking at the SWR Bass 350 manual, I note that
    the cosmetics of the amp shown on the front cover
    of the manual differ greatly from mine. The one
    on the cover is black with silver front trim and
    handles. Mine is black, with silver and purple
    silkscreening and regular old bolt-on black rack
    handles. An earlier version of the 350, I assume?
    Anyone know?

    Also, I don't see fan venting on the top rear left
    cover - mine has that in addition to the left
    side venting.

    Scott
     
  10. BWB

    BWB

    Aug 30, 2000
    Knoxville TN
    Wednesday night was rehearsal night - so I tried all of this out.

    I can indeed run the output of the MB-1 into the
    effects receive jack and run only the master volume
    control on the Bass 350. However, I'm not getting very
    much headroom. This could be that the output
    settings on my MB-1 programs are low
    but in general I have them cranked. I tried
    running the output of the MB-1 to the active
    input rather than the passive input and the
    signal seems to be less hot (as expected) and
    is working better for limiting clipping than the
    passive input was at a similar volume.

    I think the next thing to try is an above
    suggestion of splitting the input of the bass
    between the Bass 350's preamp and the MB-1 and
    then using the effects blend knob to mix the
    two of them. As I do like having my tones from
    the MB-1, but being able to color them to suit
    different rooms with the amp is vital. Maybe
    in a week or two when I've got some time.

    Scott
     
  11. By headroom, do you mean that you were not able to get loud enough by turning the master volume all the way up or do you mean that you began to get distortion at some lower level?

    Was the blend knob fully clockwise when this happened?
     
  12. BWB

    BWB

    Aug 30, 2000
    Knoxville TN
    Yes - the blend knob was fully clockwise.

    No, distortion was not noted. With the master
    volume at 3 or 4 o'clock that amp was not too
    loud - you could talk in a normal tone of voice
    and be heard above the amplifier. Just wasn't
    enough volume.

    Running the MB-1 through either the passive
    or active jacks was way plenty of volume. Much
    more than I need, frankly.

    What makes you ask?

    Scott
     
  13. Headroom is usually described as having enough power so the your peak amplitude does not cause distortion. Your external pre-amp may or may not have as stong a signal as the builtin pre-amp but you can compensate for this by turning up the master volume. As long as you can turn up the master volume enough to get full power from the amp, you should be OK. You probably want to run the master volume a little high so that you won't have to drive any pre-amp stages to distortion. If you can't drive the amp to full power with the master volume at 10, then the signal from the pre-amp is not enough to drive the effects return efficiently. Use the active input for sure.

    If you run through the active input, run the gain a little low so that tonal adjustments and small volume adjustments do not cause the 350's clip light to light. Otherwise you will end up adjusting the gain control constantly.

    An aside:

    A master volume that is adjustable from 1 to 10 does not mean that the amp is running at 50% when it is set to 5. This all depends on the strength of the input signal. Most amps will drive full power set on about 4 or so (maybe even less - it all depends). Anything beyond that (with a given input signal) drives the amp to distortion. The reason the master volume goes to 10 is to handle those weaker signals.