Author Topic: How much power do I need for my power amp? (Read 247 times)

haddimudd · « **on:** October 06, 2004, 05:02:42 AM »

I have the common F-1X/SF-2 preamp situation for my Alembic bass (and all the others) and now I am in need for a befitting power amp. I got rid of all my old gear (amps, speakers) and trying to get a fresh start.

I laid my eyes on the PLX series by QSC and now I am wondering how strong a power amp really needs to be nowadays.

In the past my strongest amp head was a Trace Elliot AH250 with 250 watts. I never felt I would need much more, so in what situation would I need more than that? What is a good overhead to cover future situations?

I was guessing that in live situations (of which I hadn't too many in my life yet) the bass is more often than less run through the PA, so I would think I don't need an overly powerful amp myself, am I right?

Also, what would be a good speaker combination with my F-1X and the ability for bi-amping if I am after a sound like Stanley Clarke for slapping (not to mention Mark King) and a Pastorius sound for my 6-string fretless? 1x15 or 1x18 for the lows and 2x12 or 4x10 for the highs? Any better ideas?

The setup should work primarily for band room and medium gig situations, not the Hollywood Bowl in the first place .

Thanks a lot!

willie · « **Reply #1 on:** October 06, 2004, 05:40:32 AM »

You can never have too much power aaarrhh aaarrhh aaarrhh. I have 3500 watts and thats right I NEED MORE POWER. Ha Ha. Seriously if you want to bi-amp I would recomend a Stereo PA style power amp with 500 watts per channel. Most 4x10 & 1x15 cabinets can handle that and your amp should have more power than your cabinets can handle so you never push the amp into clipping which puts DC current through the voice coils of the drivers which causes them to heat up and fail. I use 2 Crown amps that are rated at 1500 Watts when in bridged mono (1 amp for lows to 1x15's 1 amp for highs to 4x10's) or 700 watts per channel in stereo when I use 1 4x10 & 1x15 cabinets bi-amped. Get a good idea of which cabinets you'll be using then pick an amp that puts out at least that much or more.
Willie

David Houck · « **Reply #2 on:** October 06, 2004, 06:27:54 AM »

I use the PLX 2402. My cabs are all 4 ohm, and the 2402 seems perfect to run one 4 ohm cab off each channel (700 watts per channel into 4 ohms). Also, I've been running full range rather than bi-amping. It seems to me that in running full range, I am making more efficient use of my speakers; in other words, I'm getting more sound out of each cab. And I'm very happy with the sound I'm getting from the rig. (I should note that all my cabs have 10 speakers). The 2402 has worked well for me for stage sound in small venues in a band with guitar players that are too loud.

Everyone's needs and preferences will be different. While 700 watts per channel into two 4 ohm cabs seems to be working well for me, there are others in the group who have rigs with much less power that work well for them. And of course there are others with rigs that require more power.

haddimudd · « **Reply #3 on:** October 06, 2004, 06:51:28 AM »

That's pretty much what I thought. I maybe getting about 500 watts per cabinet/channel in my case then.

Also I was curious what is it about some cabs being 8 ohms and others 4? Isn't 4 ohms (or less)more desirable in any case? Why would I want to get more ohms anyway?

David Houck · « **Reply #4 on:** October 06, 2004, 08:27:12 AM »

Here is my understanding of the issue. If you are running 4 cabinets, two off each channel, then if they are 8 ohm cabs, the load on each amp channel (assuming parallel connection) will be 4 ohms. If those same 4 cabs were 4 ohm cabs, then the load on each amp channel would be 2 ohms. Many amps cannot handle a 2 ohm load safely for an extended period of time; thus 2 ohm loads are, as a general rule, avoided. (There are of course amps that can handle a 2 ohm load with no problem; it's a general rule not a hard and fast rule). A four ohm load makes more efficient use of your amp's power capabilities than an eight ohm load. In the case of the 2402, each channel provides 700 watts into 4 ohms, but only 425 watts into 8 ohms. (The PLX 1602 is 500 watts into 4 ohms or 300 watts into 8 ohms). Thus, if you only use one cab off each channel, then four ohm cabs will be preferable to eight ohm cabs; but if you are typically running 2 cabs off each channel then the 8 ohm cabs might be a better choice.

bassman10096 · « **Reply #5 on:** October 06, 2004, 10:24:25 AM »

One of the nice things about the PLX's (I have a 2402 as well) is that they are rated for 2 ohm loads in stereo. For instance, I have run various combinations of 4 ohm cabs in parallel (increasing the load to 2 ohms) on one channel of the 2402, whic puts out 1200w @4ohms. I run my 18 ELF sub at 8 ohms off the other channel and all seems to be working fine. The only caveat QSC places is that 4 ohms is the lowest the PLX can handle in bridged mono.
The PLXs seem to one of rather few power amps explicitely rated for 2 ohms, however. I would never take a chance with an amp the manufacturer was not willing to rate for a low-ohm load.
By the way, though they cost more than some, I've been thrilled with my PLX. Great sound performance and very light weight (low 20 lbs!). I'd buy another in a heartbeat.
Bill TBO

(Message edited by bassman10096 on October 06, 2004)

jeff · « **Reply #6 on:** October 06, 2004, 10:39:00 AM »

So far this discussion has centered around the wattage of solid state amps, but for those of us who have had the pleasure of playing thru a good tube amp, we all know that a tube amp of the same power rating as a solid state amp sounds WAY louder. A tube amp rated at 300 watts will blow away a solid state amp rated at twice the power into the same speaker load.

The tone of the tube amps, in my very humble opinion, is also far superior in the midrange and treble frequencies which is of great importance with an instrument that has the range of an Alembic. With deep bass, however, nothing can beat the rock solid bottom of a high quality solid state amp like a Crown or QSC, and many others.

Disadvantages with a tube amp? They tend to be very heavy, expensive and maintenance can be involved (e.g. tube replacement) in longer term use, which is why many players opt for solid state gear.

Want the best of both worlds? Do what I do - biamp. Crown on the bottom, Aguilar or Ampeg (or McIntosh) on the top. The result with an Alembic is KILLER tone! That's my three cents.

rraymond · « **Reply #7 on:** October 06, 2004, 12:12:31 PM »

I'll add my 1.5 cents to this; I'm a QSC PLX2402 owner and fan, too. I drive it with an Ampeg SVP-Pro - I still like my Ampeg gear.

dannobasso · « **Reply #8 on:** October 06, 2004, 12:29:55 PM »

I have PLX 1602 2402 and 3402's. I like the light weight and they have good enough power for my situations. Live I use the 3402, practice the 1602. I'm a power fiend and can clip the best of amps. So I must learn restraint. The cabs are 4 5.3 and 8 ohms. The Elf system is 8ohm and 400w continuous. But the lows are so low that they rattle the room without the big wattage. My next show will be epi310 nd epi 115 with the 3402 F1X-SF2 set up. If you don't mind schlepping weight transformer amps are great and they tend to (to my ear) add some color to the tone. i JUST LIKE 20LBS! I also own Carver and Crest amps and a Samson for a practice PA. I would buy PLX again as well.
Danno

dadabass2001 · « **Reply #9 on:** October 06, 2004, 12:48:05 PM »

Hi guys,
Nobody has mentioned the RMX series of QSC amps yet. I own a RMX 1450 that I couple with an F-1X. It's 480 watts/channel into 4ohms, can run down to 2ohms in stereo (4ohm minimum for bridged mono and 1400 watts) and sounds great. I play in small to medium clubs mostly with an Acme Low B-2, but I used it biamped twice this summer with a 1-15 cab for lows and a 2-10 with horn for highs and that was a treat also! I believe the RMX series is a little less expensive than the PLX.
Mike

dela217 · « **Reply #10 on:** October 06, 2004, 01:54:27 PM »

I use the RMX 1450 too. I think they are ok, but most folks want the lighter weight one. I think the PLX uses a different technology/transformer for lighter weight. I have had no problems with not having enough power with my RMX 1450. Most of the time I have it set up for mono use into 4 ohms though.

palembic · « **Reply #11 on:** October 06, 2004, 02:15:02 PM »

Just an Idea Hartmut: use the F1-X (with the SF-2 in the effect-loop) in Bi-amp. Choose good speakers for mid and high and good speaker for low. Than choose -appropriate for the speaker- for each speaker a good power amp bridged. The highpass out of the F1-X goes to the High/mid combination, the lowpass out of the F1-X goes to the low combination.
I'll bet you'll have clean power!!!

Paul the bad one

haddimudd · « **Reply #12 on:** October 07, 2004, 12:48:45 AM »

So speakers come first, then comes the power amp, got you!

I know of the QSC RMX and I think they are a great budget alternative if you don't mind the extra weight. I will try to go for the minimum weight I can get (knowing everything together will end up dang heavy anyways) so the PLX will be my first choice. On the other hand I don't know my budget yet, so maybe plan B comes into place at some point with the RMX being the alternative.

Danno, is schlepping an official english word? It's hillarious because it is so extremely German at the same time.

David Houck · « **Reply #13 on:** October 07, 2004, 05:40:41 AM »

Hartmut; if weight is a primary consideration, go with two racks instead of putting all the components in one.

gare · « **Reply #14 on:** October 07, 2004, 06:30:30 AM »

Dave makes a very good point..break things down into small packages. I use a 400+,which has a few pounds to it..thats one case, everything else goes in another. I'd rather make a second trip than deal with a wrenched back or popped tendon.

Gary