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Preamp driving power amp specs

Discussion in 'Amps [BG]' started by TravTrav, Feb 18, 2014.


  1. TravTrav

    TravTrav

    Joined:
    Jun 6, 2010
    Location:
    WA
    What specs should I look at to know what preamp will drive my power amp?
     
  2. mjmeche

    mjmeche Supporting Member

    Joined:
    Jul 14, 2007
    output voltage some amps take .775V some 1.2 and other 1.4 need to make sure you can drive the amp. My current situation I have a WTDI and don't know whether to get Crest Audio Prolite 2, Peavey IPR2 or Crown Drivecore. Also want to bridge @ 4 ohms
     
  3. Passinwind

    Passinwind Charlie Escher Supporting Member

    Joined:
    Dec 3, 2003
    Location:
    Columbia River Gorge, WA.
    Output level(s) of your bass(es), played by you
    Gain of the preamp at settings that sound good to you
    Max output of the preamp at suitable power amp impedance load
    Input sensitivity and input impedance of the power amp
     
  4. chadds

    chadds

    Joined:
    Mar 18, 2000

    That says it.
    :)
     
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  6. nick98338

    nick98338

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    Mar 9, 2012
    Location:
    Graham, Washington, USA
    I also have a WTDI. I don't know the nominal output. I can say that it is not 1.4 volts unless you have the gain and master knobs up pretty high. At levels that I use the output does not properly drive an amp that wants 1.4 volts.
     
  7. mjmeche

    mjmeche Supporting Member

    Joined:
    Jul 14, 2007
    I have pretty much decided on a Crest Prolite 2 DSP .775Vrms. That is pretty much what i said output voltage from preamp.
     
  8. TravTrav

    TravTrav

    Joined:
    Jun 6, 2010
    Location:
    WA
    How would I know the preamps output is suitable for my power amps impedance load? Like, could you throw me some numbers/an example.
     
  9. nick98338

    nick98338

    Joined:
    Mar 9, 2012
    Location:
    Graham, Washington, USA
    Aguilar Tone Hammer - They don't say. Eden WTDI - They won't tell ya. It is... ah... uncommon for the equipment manufacturers to openly publish such specifications. Even if they tried, the numbers would be difficult to make standard.
     
  10. DigitalMan

    DigitalMan

    Joined:
    Nov 30, 2011
    Matching a preamp to an existing power amp is about as backwards as I can imagine doing it. The preamp is the voice. Power amp be darned. Find the preamp you like then figure out how to make it work. Trade the power amp, buy an inexpensive line mixer, etc...
     
  11. SactoBass

    SactoBass There are some who call me.......Sactobass

    Joined:
    Jul 8, 2009
    Location:
    Sacramento California
    TravTrav:

    Read the specs of the preamp and find "output voltage".

    Read the specs of the power amp and find "input sensitivity".

    Those are the main two parameters to look at.

    I have an Alembic F-1X tube preamp. The output voltage is 1 volt.

    I have a Fender MB1200 power amp. The input sensitivity is 1 volt.

    That means my preamp has the capability (the "horsepower" if you will) to drive the power amp to its fully rated output power.

    If my Fender power amp had an input sensitivity of .775V, then I could easily drive my power amp using my 1 volt output preamp and have horsepower to spare in my preamp. If my power amp had an input sensitivity of 1.4V, then my 1 volt output preamp would not have enough horsepower to drive my power amp to its fully rated output power.

    Hopefully that info helps!
     
  12. TravTrav

    TravTrav

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    Jun 6, 2010
    Location:
    WA
    Perfect! Thanks so much, sacto.
     
  13. SactoBass

    SactoBass There are some who call me.......Sactobass

    Joined:
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    Sacramento California
    You are very welcome, good sir!
     
  14. TravTrav

    TravTrav

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    WA
    Oddly enough, a lot of manufacturers don't seem to list output voltage in their manuals for preamps. Seeing output level instead, and that's in decibels.
     
  15. nick98338

    nick98338

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    Mar 9, 2012
    Location:
    Graham, Washington, USA
    .775 volts = 0dB - a few power amps' input sensitivity
    1.0 volts = +2.2dB
    1.2 volts = +3.8 db - many power amps' input sensitivity
    1.4 volts = +5.14db - some power amps' input sensitivity
     
  16. TravTrav

    TravTrav

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    WA
  17. Passinwind

    Passinwind Charlie Escher Supporting Member

    Joined:
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    Location:
    Columbia River Gorge, WA.
    The Alembic F2B is the classic worst case that I know of. It has a high output impedance and although Alembic says 10K or higher works OK for a load, in my experience a bit higher tends to work better, or at least did with the one I owned. As long as the load is 10X or more the output impedance of the preamp, no worries; below that it's one of those "just depends" deals.

    Knowing just the max output voltage of the preamp is not always a perfect indicator of how it sounds at that level, or how much EQ boost, drive, how hot a pickup, etc., it takes to get there. For example, the early BMax version was plenty hot for driving any amp I tried it with, but keeping it dead clean and doing that was a bit tricky in some cases. I've heard that they later toned it down some on front end gain though, which worked a lot better for me when I did that mod myself. And of course, in many cases you may never need to fully drive a big power amp anyway.
     
  18. TravTrav

    TravTrav

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    Jun 6, 2010
    Location:
    WA
    Oh, man. I see why so many people just use amps that are designated bass heads. Good info, though. Thank you.
     
  19. Passinwind

    Passinwind Charlie Escher Supporting Member

    Joined:
    Dec 3, 2003
    Location:
    Columbia River Gorge, WA.
    It's not always that dire by any means, but I would highly recommend trying stuff first or buying used at prices that allow painless flipping.
     
  20. zon6c-f

    zon6c-f

    Joined:
    Jun 9, 2007
    Location:
    Metro Atlanta, Ga.
    As I know so very little technical information/ application..I have employed blind luck with great success.

    In my quest for 'tone-supreme', I purchased a Furman PQ-3 [ 3-band fully parametic EQ and pre-amp....either use the preamp or the EQ individually].

    I used my Furman front-end..into my trusty 1971 Kustom 200-B head. which vastly improved tone and volume..made an otherwise anemic amp sound awesome. Once at a jam, I was actually asked to turn down by an humbled guitarist.

    Of course I would love to run my pre amp into raw power amp, with the Furman as tone/ volume control. My only regard for the amp specs would be watts RMS and distortion %.

    Ignorance is bliss..proving that sometimes we over think things too much.

    I M O ..Probably whatever amp you can afford will be well suited to whatever pre amp you use.
     
  21. chadds

    chadds

    Joined:
    Mar 18, 2000
    When it doesn't work it's very unsatisfactory. You've got this rack with a serious looking pre and pwr amp into some cabs and the 1x15 combo from the opening act blows it away.:)

    There is a point when if the pre isn't putting out the right voltage that there just is no more volume from the amp. This may be right when the drummer starts playing.:)

    Crank that amp and you're amplifying nothing. The tone is weak, you can hear it but all the punch is missing. Or it is full in some frequencies and appears to disappear in others.

    My comments come from gigging pre amps and pwr amps live in duos, trios, and large band settings. The same rig that sounded like it would work from my home practice would be woefully inadequate live. I'd shake my head and wonder why my 1000w was so weak. Drummer is frowning, honeys aren't dancing.

    This isn't rocket surgery. :) One just has to obey the laws of physics or electrical engineering in this case.
    "It should work" or "it's called a bass pre" or "it's +4" or on TB "it works for me" won't save the gig if you've ignored the facts.

    Bringing the big boom is our job. The band will rock with other players and frequencies missing. If we sound flaccid the whole presentation suffers.
     

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