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Difference between PA amp and bass amp

Discussion in 'Amps and Cabs [BG]' started by jadviga, Mar 1, 2005.


  1. Hi,

    I'm new to the bass amp world and I would like to ask if there are any design differences between PA amps (I know they are usually stereo but they can be bridged) and bass amps. I'm taking about power amplification of the signal which is coming from standalone preamp.

    I'm asking this question because I have samson PA amp which I currently don't use and I'm thinking of using it for bass amplification (together with trace-elliot premap).

    Thanks in advance for your answers,

    Tomaz
     
  2. AlembicPlayer

    AlembicPlayer Im not wearing shorts

    Aug 15, 2004
    Pacific Northwet, USA
    the short answer is...yes, you can use that amp for a bass system.
    I have used QSC, Mackie, Yamaha, Crown and various other stereo power amps for both PA and bass systems. A good clean reliable power amp matched with efficient speakers properly matched with the impedance load of the amp is what you're after.
     
  3. Lowtonejoe

    Lowtonejoe Supporting Member

    Jul 3, 2004
    Richland, WA
    Like AlembicPlayer said, you are good to go. The only problem you might have hooking it up properly (you may need to make a cable or adapter).

    Uh...check the output. Is it in watts or volts? If it is in volts we may need to cigitate on this for a while.

    What is the model of the amp?

    :)

    Joe.
     
  4. billfitzmaurice

    billfitzmaurice Commercial User

    Sep 15, 2004
    New Hampshire
    Owner, Bill Fitzmaurice Loudspeaker Design
    All amps have voltage output. You're probably thinking of constant voltage distribution systems, which are used in zone coverage systems but not PA.

    The main difference between high quailty PA amps and a bass amp power section is just that, quality. PA amps are generally built to fidelity standards that are much higher than musical instrument amps. The exception here would be amps such as those from Bogen which are meant for high speech intelligibility in industrial applications but are anything but high fidelity.
     
  5. The amp specification is:
    250 watts per channel into 4 ohms, 150 watts into 8 ohms (stereo) and 500 watts into 8 ohms (bridged mono)

    My idea was to go for 8 ohm speakers since the amp can be bridged . I think this should work fine ....

    But still it is not clear to me if there are any design differences regarding the fact that the bass amp "knows in advance " what will be the type of input signal (with respect to frequency range ...) ?
     
  6. haujobb

    haujobb

    Dec 16, 2004
    Wallaceburg
    It will work fine, I'm currently using a Samson F-800 and I've been very happy with it.
     
  7. Bob Rogers

    Bob Rogers Left is Right

    Feb 26, 2005
    Blacksburg, Virginia
    The difference is that PA amps are designed to have a flat frequency response across the entire audio spectrum. Their goal is to add no color to the sound at all. Tone colors (should) come from the bass, effects, and preamp in a bass amp configuration using a PA power amp.

    If someone designs a power amp exclusively for bass (usually in conjunction with a preamp) they can (a) make compromises with some parts of the audio spectrum and (b) design the amp as part of the tone equation. This can lower the overall cost and improve the tone of the overall system.

    The advantage of the PA amp approach is that once you have shaped your tone at the line (post preamp) level all flat devices should react in the same way. Your tone through a direct recording, a PA, a PA/amp cabinet combo, a set of headphones should all be the same. Of couse, in the real world you have to make tweaks, but they should be smaller than the big adjustments that you have going from a bass amp to any of those devices.
     
  8. Thanks bob .... that was the answer I was looking for.

    Since I am a technical guy :) I'm still curious what are the tricks. maybe do you know any implementation details ?

    tnx
     
  9. Lowtonejoe

    Lowtonejoe Supporting Member

    Jul 3, 2004
    Richland, WA
    Yes, I realize that.

    PA = Public Address. If you are not careful the power amp you buy off of ebay may be one of these instead of something used for sound reinforcement.

    And QSC and Crown and...

    Too true.

    :)

    Joe.
     
  10. billfitzmaurice

    billfitzmaurice Commercial User

    Sep 15, 2004
    New Hampshire
    Owner, Bill Fitzmaurice Loudspeaker Design
    I 'd hardly put QSC or Crown in the same class as Bogen. Both are first rate high quality products.

    It's true that 'Sound Reinforcement' is a better description of the amps we're talking about, as opposed to 'Attention KMart Shoppers' variety PA. The moniker PA was adopted decades ago by the pro-sound and musician community and is more or less interchangeable with sound reinforcement in common parlance today. That's because in the '50s and early '60s crappy PA is what was used as that's all there was, and while the quality of the gear improved the name of the original stuff used stuck.
     
  11. Bob Rogers

    Bob Rogers Left is Right

    Feb 26, 2005
    Blacksburg, Virginia
    I really don't know many details. Of course in tube amps you get a different quality distortion from the power amp than the preamp, so you can design for that. (If you are trying to compensate for that in a pre through a flat amp, you have your work cut out. Some claim it can't be done, the they're wrong aren't they ;) ) But on a more mundane level, instead of designing two flat amp you can put the humps in one at the same point as the valleys of the other. This doesn't have to be scientific but you can imagine giving two tasks to an engineer. (1) Build a preamp that sounds good through every flat response - keep the cost down. (2) Build a preamp and a power amp that sound good together - keep the cost down. (2) is much easier than (1).
     
  12. Lowtonejoe

    Lowtonejoe Supporting Member

    Jul 3, 2004
    Richland, WA
    No man, I think you missed my point. The 'Attention K-mart Shoppers' type of amp are made by many manufacturers including those I mentioned.

    Do an e-bay search on power amps and see how many (of those) you get.

    When I first started to learn about this stuff I almost made that mistake. Luckily I picked up on it and now my rack rig has a QSC PLX2402 in it and sounds awesome!

    :D

    Joe.
     
  13. Thanks again for the answers ....

    I just wanted to clarify what are the possible drawbacks (or advantages) of using the pa amp instead of the bass amp.

    tnx again to all who replied to my question
     
  14. remo

    remo

    Jan 15, 2005
    would you guys say its fair to say you sacrifice fidelity as amp power increases?
     
  15. Lowtonejoe

    Lowtonejoe Supporting Member

    Jul 3, 2004
    Richland, WA
    Just a few off the top of my head.

    Drawbacks:
    1. A rack is generally bigger than a head.
    2.

    that's all I can think of.

    Advantages:
    1. Much more power available than with just a head.
    2. Modular design means to change your tone you can just replace a preamp while saving some money by keeping your power amp.
    3. Price per watt is significantly lower.
    4. It looks really cool. :cool:

    :)

    Joe.
     
  16. Lowtonejoe

    Lowtonejoe Supporting Member

    Jul 3, 2004
    Richland, WA
    Absolutely not.

    :)

    Joe.