Probably stating the obvious but wouldn’t any amp rated for 500W at 4 ohms deliver 250W at 8 ohms?
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I have seen a lot of 500w @4ohm amps being rated for 300w @8ohm lately.
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And I have seen 350W @4ohm be rated for 250w @8ohms.
I think the Ampeg PF 350w head is like that.
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Yeah, it is not listed in the specs, but on the back it says it.
Ampeg PF-350 Portaflex 350W Bass Amp Head
I am finding, in my searching, that you really do need to be careful, and check each specific amp manual, and even read the back of the amp (like in this case if it doesn’t say in the specs). In most cases, the math works out, but you need to be sure before making purchases.
In my case, my Cab is 400w at 8ohms, and I am looking for around 200w to 250w, but I have room for error if I ended up getting a 500w at 4ohm head, thinking it was 250w, and ended up being 350w, I would still be safe and not blow the speakers, but if I did not, it would be one for that bonehead move thread 
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Pretty sure that portaflex uses the same power module as the Darkglass 500W amps. Someone (Dave?) posted about that a while back. So it might actually be a 500W amp they are under-rating for some reason. Or Darkglass is being optimistic 
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Very well could be, probably is, so it shows that you really need to know what the amp is before relying on math based on what the amp is rated for at 4 ohms.
Have you thought about just getting the TC Electronics BQ500.
will give you the 250w at 8ohms and left flat would almost be the same thing as a power amp, allowing you to do whatever you want with a pre-amp.
I know the allure to getting a power amp alone and using your pre-amp to color the sound, but that, for the price ($249) offers the power with very little to zero tone shaping. Still might be the way I go, not sure yet.
I found this great Carvin solid state amp with tube pre-amp, and it would work perfect in every way for me, but I can’t verify weather the DI can be run before the pre-amp or not. It does not have a PRE/POST switch by the XLR output on back, but has a TUBE Bypass switch. This probably does what I want, but I am not 100%, and I want to make sure I can go DI to my DAI before any effects or pre-amp. If I can’t verify that, I will probably end up getting the TC Electronic BQ500
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Yep. I was just being specific about what I was looking for. Most of the old used power amps have specs that are all over the place compared to what we see on bass gear.
Like these…
SoundTech PL350M ($70)
A single channel with 350 watts @ 2 ohms.
If I connect it to an 8 ohm cabinet I would end up with only 87 watts.
American Audio VLP300 ($60)
Two channels
Each channel with 150 watts @ 4 ohms or 100 watts @ 8 ohms.
It has a bridge mode to tie the two channels together so I could get 300 watts @ 4 ohms. This would give me 150 watts @ 8 ohms.
Gem Sound XP-550 ($90)
Two channels
Each channel with 500 watts @ 4 ohms.
Or each channel with 300 watts @ 8 ohms.
Or bridged to have a single channel with 600 watts @ 8 ohms
I was really looking for any gotchas that might happen with these power amps. Don’t do this, watch out for that, kind of stuff.
@T_dub I’ve considered those before. Same price as the SA-500W but with the added DI. Seems like a better deal as long as the preamp doesn’t color anything. I’ve ruled it out at this point since the price puts it out of reach for me.
$90 for the Gem versus $250 for the BQ500.
I think I would like to hear from owners of the cheap TC heads about if it adds any tone color or not. I never got to find out with mine. I have heard reviews where it sounded totally transparent, but on TC’s site they have one that sounds like it is adding a little.
If it is just a transparent EQ it would be a cool head for Eric’s idea here but less interesting for people looking for an amp that adds some character, for example.
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@eric.kiser Those little TC heads are the least expensive I’ve found on the new market from a solid brand. I’ve wondered the same about what coloration they have. Ideally, I don’t want another filter stage at all even if it’s set flat. I’ve thought about buying something like this and physically bypassing the tone controls.
There’s also a home theater company that makes piggyback power modules for subwoofers. I think they are just putting an ice in a box.
The Darkglass 500 is liberally interpreting specs compared to their competition with the same power stage.
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Yeah, I am finding all sorts of amps that are rated much higher at 8 ohms then 1/2 of what they are rated at 4ohms.
Many 350w @ 4ohms = 250w @ 8ohms
500w @ 4ohms = 300w @ 8ohms
250w 2 4ohms = 180 @ 8ohms.
Are they under rating the 4ohm value, or are they stating somewhere between peak and rms @ 8ohms?
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Who knows what they are doing. Think of it like a product manager … There’s no way I can sell a 175 Watt amp against the competition. There’s not even a noticeable level difference until we double the power. That power measurement is for some test signal that isn’t like playing bass. When they play bass, they probably can get that much power.
Or maybe the 8 ohm spec is good and the amp design can’t quite produce double the output at 4.
I ignore all those numbers. Is the amp 100, 200, 400, 800, 1600 range. Anything less is splitting hairs.
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This one brand new will do 600 Watts at 8-Ohms (because you can bridge the two channels together into one) for $269.
The tradeoff will be that it has fans that are likely much noisier than the tiny one in a bass amp. The good news is that the fans are speed regulated according to actual temperature. They think rack mount stuff is most likely in another room or in a rack off-stage.
In your request you already gave permission for it to be rack-mount, which makes it heavy, big and noisy. That’s why the designed-for-bass amps are more expensive than rack mount.
It’s possible to put it in the closet or something. Just pay attention to how hot it’s getting and that something easily flammable isn’t touching it. This particular amp makes the same heat as an old style 40 Watt light bulb just sitting there until you start playing, then it gets hotter.
The reviews are good and it’s from our trustworthy friends at Crown . . .
https://www.sweetwater.com/store/detail/XLI800--crown-xli-800-power-amplifier/reviews
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So, the inputs are stereo or mono XLR, how would you get two inputs for stereo?
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How about 100 Watts? These people are putting an ice-power amp in a box for $220. Quiet, small, light, top quality circuit maker.
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It has all the connectors. They give you a switch to choose if one input goes to both channels, the outputs are bridged or stereo.
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Thanks, i couldn’t read that and my screen wouldn’t blow it up big enough.
What about the ice box amp you just posted.
how do you make connections, in and out with that.
Sorry for the questions, I am just trying to understand how this all works.
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It has an RCA (“Cinch” in Europe) input connector. Adapter cable needed. I wouldn’t suggest using something like that unless you need it cheap, home use only and you don’t mind if it isn’t plug and play. It’s designed for home stereo levels, so driving it with DI may be a bit hot and driving it with a pedal output may be a bit low depending on the pedal. It may require some funny looking knob settings, like the makeup gain on a compressor or EQ set unusually high . . . or low. No problem; it’s just not plug and play for the beginner.
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This looks like it might do the trick for @eric.kiser.
Can you confirm @DaveT?
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It has the spec numbers. How good of an amp this is or if it will keep working I have no idea. It’s not one I’ve used.
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