Power ratings

[BottomEndian]

Right. Something's been puzzling me. For the last few years, I've been using a Peavey Max 700 head, which runs 475W into 4 ohms. When I compare the Peavey's power amp stage against my recently acquired Tapco Juice J800 power amp (that's 800W bridged into 4 ohms) with all other things being equal (same cab, same stuff running into the power amp inputs), the Peavey's noticeably louder at full volume.

So, my question is this: is the power rating for SS power amps (designed for PA applications) calculated differently from the power rating for the power stage of SS bass amps? I know a watt is a watt, but is this a matter of headroom? We all know that valve amps are rated for their "clean" output, but that you can get much more out of them with a little bit of "nice-sounding", musical distortion from the valves. Is there a similar but lesser thing with SS bass amps? And presumably a power amp designed for PA applications will be designed to be completely clean all the way to the top of the volume knob, so there's no headroom available to push into that slight distortion.

(Don't get me wrong -- 800W into my Barefaced Vintage is more than enough... it's just not as loud as 475W from the Peavey.)

[alexclaber]

The Peavey may have higher distortion levels which will make it sound louder. It may also have less flat frequency response, with more mids and less bottom, again making it sound louder. However your Tapco power amp should still go louder, just need to EQ it for the same sound and keep turning it up and up.

I do know that some of the old Peavey heads actually used the same power supply and possibly the same power amp module as their PA power amps (hence the weight because the power supply was enough for two channels but one wasn't there!)

Alex

[alexclaber]

As you're using a VXL to drive the power amp my guess is that you have a lack of gain so you're not reaching full power.

Alex

[BottomEndian]

[quote name='alexclaber' post='548631' date='Jul 23 2009, 10:16 AM']As you're using a VXL to drive the power amp my guess is that you have a lack of gain so you're not reaching full power.[/quote]
But as I say, with all things being equal. In other words, when I've been testing the Peavey against the Tapco, I've been running the VXL directly into the Peavey's power amp input.

Oh, hold on. The Tapco is, of course, designed to ideally accept a balanced connection (but I'm running a TS jack into it at the moment), while the Peavey's power amp input is happy with standard TS jacks. So that means there's a potential 14 dB increase at my fingertips if I run a TRS input into the Tapco (if I correctly remember the difference between balanced and unbalanced signals)? That could compensate enormously.

The VXL's about to be replaced in the chain with a Bass PODxt with a TRS output, so we'll see what happens. Sonic death, I suspect.

[quote name='alexclaber' post='548630' date='Jul 23 2009, 10:15 AM']The Peavey may have higher distortion levels which will make it sound louder. It may also have less flat frequency response, with more mids and less bottom, again making it sound louder. However your Tapco power amp should still go louder, just need to EQ it for the same sound and keep turning it up and up.[/quote]
That might explain a lot too. So there's no apparent disparity between the ratings of bass amps and power amps like there is between valve and SS? (And yes, I say again: I know a watt is a watt, but there's all that lovely distorted headroom with valves.)

[quote name='alexclaber' post='548630' date='Jul 23 2009, 10:15 AM']I do know that some of the old Peavey heads actually used the same power supply and possibly the same power amp module as their PA power amps (hence the weight because the power supply was enough for two channels but one wasn't there!)[/quote]
That explains a lot as well. Especially my spinal pain. When you're 5'6", lifting a 25kg head onto a two-cab stack is... troubling.

[BottomEndian]

[quote name='BottomEndian' post='548646' date='Jul 23 2009, 10:31 AM']So that means there's a potential 14 dB increase at my fingertips if I run a TRS input into the Tapco (if I correctly remember the difference between balanced and unbalanced signals)?[/quote]
Actually, I've just had a think and that's not right, is it? There is a level difference, but not 14 dB. Isn't it just that there's a 14 dB difference in the s/n ratio?

Aaargh. It's been too long since my HND. Can't remember this stuff.

EDIT: A quick Google shows I'm way off the mark here too. Hmmm.

Edited July 23, 2009 by BottomEndian

[alexclaber]

[quote name='BottomEndian' post='548646' date='Jul 23 2009, 10:31 AM']But as I say, with all things being equal. In other words, when I've been testing the Peavey against the Tapco, I've been running the VXL directly into the Peavey's power amp input.

Oh, hold on. The Tapco is, of course, designed to ideally accept a balanced connection (but I'm running a TS jack into it at the moment), while the Peavey's power amp input is happy with standard TS jacks. So that means there's a potential 14 dB increase at my fingertips if I run a TRS input into the Tapco (if I correctly remember the difference between balanced and unbalanced signals)? That could compensate enormously.[/quote]

6dB increase if they're summing balanced inputs but some balanced inputs don't sum and have a floating side IIRC. The (very commonly) overlooked issue is that different power amps have different amounts of gain. If you look at the QSC PLX range all their amps have the same gain of 32dB (40x), but this means that their most powerful model (3400W) will have the same output as their least powerful (1200W) model with the same preamp output. However the Crest CA series have gains from 45x to 115x, so the more powerful the amp the louder it is with the same preamp (at equal settings) driving it.

[quote name='BottomEndian' post='548646' date='Jul 23 2009, 10:31 AM']The VXL's about to be replaced in the chain with a Bass PODxt with a TRS output, so we'll see what happens. Sonic death, I suspect.[/quote]

Death indeed. Doom?

[quote name='BottomEndian' post='548646' date='Jul 23 2009, 10:31 AM']That might explain a lot too. So there's no apparent disparity between the ratings of bass amps and power amps like there is between valve and SS? (And yes, I say again: I know a watt is a watt, but there's all that lovely distorted headroom with valves.)[/quote]

There is disparity because bass amp heads are rarely rated to such stringent specs as PA power amps. The few that are (like the DB750) are considered incredibly loud for their rating because they really can produce their rated power at essentially zero distortion (and if you push them harder they'll get louder still, just dirtier).

Alex

[Mr. Foxen]

[quote name='alexclaber' post='548680' date='Jul 23 2009, 11:06 AM']Death indeed. Doom?[/quote]

Line6 is not Doom.

[BottomEndian]

[quote name='Mr. Foxen' post='548717' date='Jul 23 2009, 11:24 AM']Line6 is not Doom.[/quote]
No, but it's a spinal compromise.

Hold on: Spinal Compromise = Doom band name.