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Help! Alembic F-1X -> amp = distortion!

Discussion in 'Amps and Cabs [BG]' started by secretdonkey, Dec 30, 2004.

  1. secretdonkey


    Oct 9, 2002
    Austin, TX
    Here's the deal... I just picked up an Alembic F-1X preamp and love the thing. Pending the arrival of a Crest CA9 I bought on Ebay, I had simply been plugging the F-1X into the effects return of my SWR SM900 amp, which sounded plenty good.

    When I hooked it up to the CA9, I found that I was getting some fearsome distortion on certain transient peaks. I initially thought that the problem was in one side of the amplifer, but after I was able to make both sides of the amp do this, I began to suspect that the amp might not be the problem.

    I had the F-1X's volume on 6... which worked fine with the SWR... anyway, I turned back to the volume to 4 and have had no further problems with the distortion through either side of the CA9.

    So... is it reasonable that I might have to be careful to never turn the Alembic up past 4 (and risk destroying my two Whappo Jr.s if I do?) or does this just not seem right?

    Thanks for any input.

  2. Lyle Caldwell

    Lyle Caldwell

    Sep 7, 2004
    The CA-9 has a much more sensitive input than other power amps. You can plug your bass directly into the CA-9 and play at a respectable volume.

    So just don't turn the Alembic's output up and all will be well.
  3. secretdonkey


    Oct 9, 2002
    Austin, TX
    Using the #2 input (6db pad) seems to buy me a couple of notches on the volume control... it will still distort at around 8, but 6 is fine.
  4. r379


    Jul 28, 2004
    Dallas, Texas
    If you think you are having a problem with your F1-X I would contact Alembic. I recently bought one used and had a problem with it. I called them and, knowing I had bought it used, they still helped me fix it. Great bunch of folks.
  5. IvanMike

    IvanMike Player Characters fear me... Supporting Member

    Nov 10, 2002
    Middletown CT, USA
    problem solved
    for kicks you can find out the input impedance of the ca-9 and the input impedance of the effects return of the sm-900
  6. redneck2wild


    Nov 27, 2002
    Memphis, TN
    What settings are you using on the Alembic F-1X preamp?
    Are you boosting the lows? If so, when you cut the lows does the distortion stop?
    What type of Bass are you using? Is it active?
  7. secretdonkey


    Oct 9, 2002
    Austin, TX
    I'm using 1-10-1 with bright on. With an MTD 535 - signal isn't unusually hot. I can plug into the #2 padded input and gain a couple of notches before the distorting... but it still happens.
  8. secretdonkey


    Oct 9, 2002
    Austin, TX
    From the CA9 spec sheet:

    These numbers mean nothing to me, but I wouldn't be surprised if they might point towards the solution. Anyone know if the "standard" setting is more or less sensitive than options 1 and 2?
  9. zombywoof5050


    Dec 20, 2001
    When talking input sensitivity, lower numbers means higher sensitivity.
    That standard setting on your amp is more sensitive than options 1 & 2. The value is equal to the amount of voltage required to drive the poweramp to full output, so a lower number means a higher sensitivity.

    If the Alembic preamp is in fact sending a hot enough signal to overdrive the poweramp, then you might want to switch the poweramp to the option 1 or 2 setting. This will allow you to crank the Alembic a bit more for some added 'tube warmth' if desired.

    The Alembic will distort (by overdriving the tube) on very high volume settings and those settings will be lower on basses with a higher output level (that's what the attenuated input#2 is for), and some tubes will overdrive quicker than others.
    If you find that it's the Alembic making the distortion, then you could try some other brands of tubes until you find one that doesn't distort as much on higher volume settings.
  10. Dr. PhunkyPants

    Dr. PhunkyPants Guest

    Aug 11, 2002
    don't mod the amp, just back off on the input gain knobs on the CA-9. Set them at 12:00 at most and see where you are. Remember, gratuitous lows--especially lows like an Alembic pre can spit out can be enough to overdrive ANY power amp, even a venerable CA-9. And one other thing--I wouldn't mod the CA-9, since some preamps (like my SWR IOD) have modest outputs that only .775 amps can really do justice to. Mod the power amp and you'll limit your options in the future.
  11. zombywoof5050


    Dec 20, 2001
    I agree, don't mod the poweramp, just turn down the gain controls on it (I didn't know that you had to do an internal mod on your amp, or I would have said this the first time).
    With the input sensitivity on it's highest setting, you'll know that you can always get the most out of the amp with whatever preamp you use.

    When I got my Carver poweramp, it came with it's input sensitivity preset at 1.75V (or somewhere thereabouts). I changed it to 0.775V to ensure that I could always get the most out of any preamp that I hooked it up to. I just have to make sure that I don't overdrive the input to the poweramp, and I can do that with the input gain knobs on the poweramp by turning them down if the output from the preamp is too high.
  12. zombywoof5050


    Dec 20, 2001
    Actually, it's more a function of the input 'sensitivity' rather than the input 'impedence'. You probably knew that and mistakenly said 'impedence', but I still wanted to clarify.
  13. IvanMike

    IvanMike Player Characters fear me... Supporting Member

    Nov 10, 2002
    Middletown CT, USA
    you are correct sir

    i didnt even think to ask where you had the input gains on the ca9 set! Running a bass rig tends to be different than running a pa. usually on pa's you set the input sensitivity all the way up and adjust at the board. With bass rigs, i like to get a good sound from the preamp volume control and then bring up the input gains to an appropriate volume. On my stewart that could be anywhere from less than 9 o'clock to about 12 o'clock. BTW, i found the preamp out on my alembic much hotter tha the effects send or line out of my swr, and the one from my demeter hotter still.