What do I look for in a power amp???

Discussion in 'Amps and Cabs [BG]' started by Gintaras, Oct 29, 2005.

  1. Gintaras

    Gintaras Supporting Member

    Dec 11, 2004
    Kent Island, Md.
    this is a new area for me and looking for some suggestions. I am a midlife newbie looking to upgrade my amp. Hartke B90 does not cut it at the local jams with 2 or 3 guitarists. I keep hearing about the Sansamp RBI and BBE Bmax preamps. Thinking about picking one up but know little about which is the proper power amp. I did see one bassist at a show who was using QSC's but and he sounded great.

    Are power amps basically generic in use? When a power amp is called a DJ amp, is it really for that purpose?

    I really wanted to get a stereo amp so that I could use one of 1 or 2-4 ohm cabinets depending on the situation. Please comment if that makes sense or NOT...

    Thanks..Gus :help:
  2. Look for power, price, weight. Other than that, they're relatively generic. Some stereo amps bridge, turning them into one big mono amp perfect for mono application like bass. Make sure the stereo channels are rated to go down to 2 ohms so that the bridge mode min load would be 4 ohms, that way you can use 2 8 ohm cabs together (making 4 ohm load).

  3. Gintaras

    Gintaras Supporting Member

    Dec 11, 2004
    Kent Island, Md.
    That was a great explanation in 3 sentences!!! I did not know that bridging the stereo channels was the same as hooking up 2 cabinets. Thanks for the clarification and giving me enough info to start looking. :hyper:
  4. LiquidMidnight


    Dec 25, 2000
    Power amps can be used to drive guitar/bass rigs and PA gear, so obviously, you can use them in DJ applications. But I would stay away from the power amps on ebay which are advertised as "DJ Amps", because they are cheap junk.

    Some reputable power amp companies are

    And I've yet to hear any compliants about the Beheringer amps.
  5. I'm using the new 1400 watt behringer, and the only complaint I have is it's ridiculously heavy.
  6. jokerjkny


    Jan 19, 2002
    NY / NJ / PA
    what about slew rate, and dampening factor, etc. etc. etc?

    i think Ivanmike did a little FAQ on this, no?
  7. Another option to running in bridged mode is to run individual cabs from individual amp channels. Let's say you're running a 4 ohm cab and you want to add another 4 or 8 ohm cab. Well, with most bass amps, you're out of luck unless it's stable into 2 ohms. With the power amp, you could run one cab from each channel. The power amp doesn't care that it's seeing different loads or anything because the channels are separate. Also a good way to biamp, or to adjust volume/tone differences between two dissimilar cabinets that don't sound well run together.

  8. In the early days of transistor amps (the 1960's) some solid-state amps sounded pretty good, others sounded awful. Various amp parameters were developed in an attempt to explain why some amps sounded better than others...these parameters included slew rate, damping factor and others. But still, some good-sounding amps scored poorly on these simple measurements, while some amps scored well but sounded lousy.

    Unfortunately, at the time, we didn't have high-speed digital oscilloscopes to capture data or computer models that could really explain what was going on--poor circuit design, higher-order odd harmonics, transistors that were inconsistent in quality, etc. Gradually the designs were sorted out, the poor designs fell by the wayside, component quality improved, and now programs like PSPICE can accurately predict how a circuit will behave.

    Today's amps are generally pretty darn good (with the exception of some of the cheapest DJ or junk-shop crap). The brands mentioned earlier are all very good quality and will do quite well, so we don't really need to isolate a single parameter like slew rate.

    Power, price, weight, yep that's what I look for.
  9. jokerjkny


    Jan 19, 2002
    NY / NJ / PA
    good thoughts, nash bridges...

    but then why does the Crest CA6 seem to get sooo much press around here despite weighing close to 50 lbs., and peeps still drag it around to gig after gig?
  10. I don't know if the Crest gets that much more press than the other brands. Crown and Crest have been around a long time, they held up pretty good when there were some unreliable amps around.

    My last amp purchase was a QSC RMX1850HD, for around $500 shipped IIRC. It's been reliable, sounds great, and is very flexible, though it's relatively heavy.
  11. fdeck

    fdeck Supporting Member Commercial User

    Mar 20, 2004
    Madison WI
    HPF Technology LLC
    Like steveksux and jokerjkny said, designing a power amp to sound good has ceased to be rocket science. The frontiers are in the human factors, including size, weight, and price. Not to be overlooked are also factors that relate to how you plan on using the amp. For instance, many large power amps require you to plan for specific ventilation and mechanical installation requirements. Others (Class D) are more forgiving because they generate less heat and weigh less.

    An interesting note is that it becomes a bit of a guessing game to figure out what each manufacturer means by their power ratings, when there are amplifiers on the market that would trip a standard circuit breaker, and probably incinerate themselves, if operated continuously at their rated power. Over on the rec.audio.pro forum, a guy once posted internal pictures of a 1400-Watt power amp that looked like it had a roughly 500-Watt power transformer.

    You get more of an assurance that an amp will work for your use if you buy from a more reputable maker, because those guys -- the QSC's etc. -- have the most experience with their products in the widest range of real-world conditions.
  12. tombowlus

    tombowlus If it sounds good, it is good Gold Supporting Member

    Apr 3, 2003
    North central Ohio
    Editor-in-Chief, Bass Gear Magazine
    What to look for in a power amp?

    Three symbols (two letters and a number): C - A - 9.

  13. You mentioned 2 4 ohm cabs, you'd have to run the stereo amp in stereo, not bridged, one speaker for each channel. None will operate in bridged mode for a 2 ohm load (2 4 ohm cabs connected together.

    Or you can run both cabs in stereo to balance their output, or to biamp as someone above mentioned.

    A big mono amp can often run a 2 ohm load, both 4 ohm cabs together also.

    You get max power out bridging a stereo amp into a 4 ohm load, that's the advantage going that way.

  14. FunkyLemz


    Oct 17, 2005
    Los Angeles, CA
    Ive been told by a reputable source for bass players
    Slew greater than 50
    Damping greater than 500
    Class A - AB