Watts?

[lowell]

I found a thread on here already discussing solid state vs tube watts. So there is technically speaking, no difference between the two. Watts is watts. Without opening that whole can of worms and having a redundant post I have a couple q's. I recently fixed an SVT Pro 7. It is a great sounding amp (class D). However, it certainly did not sound like it was 1000 watts when I plugged my guitar into it. I was using a 4ohm speaker too. Why would this be? Fyi I typically find bass amps like GKs and Hartke to also seem like they are NOT as loud as their stated wattage.

So I ask this question because I'd like to build a hybrid bass amp. Tube pre, ss PA. My bassist is saying he needs 300watts at 4ohms for the gigs we do. (we're a loud blues/rock/r+b band). He is obviously saying this based on the fact that his Hartke head is 500 watts and works well on our gigs. If I were using LM3886 PAs (ha ha!) I would need 6 of 'em driving 6 separate 4ohms speakers!!! Maybe this is incorrect and someone will enlighten me on commercial ss bass amps' wattage ratings. This seems like a ridiculous project so if need be I will build a discrete 300watt PA.

[Alex R]

People say, tube compression creates a sense of loudness.

Just sayin'!

[lowell]

Haha! It's all good. I think that this must be right because I just finished my hybrid and it's only 1 LM3886... it's loud as hell!!! Fyi my preamp produces some great creamy distortion and compression.

[teemuk]

What is 1000 watts supposed to sound like anyway? The only definitive characteristics I can think of would be headroom but then again, those SVT PRO hybrid amps deliberately distort the power amp signal with a tube so...

I think even the aforementioned thread mentioned that:

Output power =/= Loudness

The speaker system is practically the defining factor on how loud an amp is. Given equally sensitive speakers, a 1000W amp is just a fraction louder than a 100W amp, and since the first one has more headroom and less distortion it sounds cleaner, which actually may create an image of it being quieter than the 100W amp, which might produce significant amount of distortion (additional harmonics) as well as compression. The real capabilities of the tremendous power are revealed when you need to cut through with a loud bass signal that still retains all the clarity. Or when you want those "string pop" things of modern bass playing to have some dynamics and "snappy-ness" to them, instead of sending the amp to overdrive realm.

[txstrat]

As what would you describe watts? Used energy? Wasted energy? Or energy which is necessary to move a speaker? All of which would only be half the truth I think, cause all the energy used by any device can't get to the end of the line. Effectiveness is the magical word here.
A while ago I bought an active stage monitor with a digital power amp of 150 watts (RMS). Brought it to the rehearsal room and could barely hear my voice over it, even though it was full open.
Gave it back and bought the same monitor with an analog power amp of 200 watts (RMS). Aahh, what a difference. And I don't think the 50 watts is responsible for the difference in loudness or headroom. Maybe analog devices are more effective than digital ones. And maybe tube devices are more effective than solid state?
I don't know. Just my thoughts. Hope I haven't opened pandoras box again.

[kg]

the perception of loudness always comes down to headroom: hit the supply rail with an OTL design (ie, 99.9% of transistor amps) and you hit a brick wall.

put another way, i think it is the action of the output transformer that makes a huge part of the ss vs tube amp characteristic.

[teemuk]

Uh, a transformer coupled tube amps also hits a brick wall when overdriven to the limits of their power supply... like this:


I don't know where the misconception comes that tube amps would for some mythical reason be free of limits determined by the power supply.

[jmaf]

I found a thread on here already discussing solid state vs tube watts. So there is technically speaking, no difference between the two. Watts is watts. Without opening that whole can of worms and having a redundant post I have a couple q's. I recently fixed an SVT Pro 7. It is a great sounding amp (class D). However, it certainly did not sound like it was 1000 watts when I plugged my guitar into it. I was using a 4ohm speaker too. Why would this be? Fyi I typically find bass amps like GKs and Hartke to also seem like they are NOT as loud as their stated wattage.

So I ask this question because I'd like to build a hybrid bass amp. Tube pre, ss PA. My bassist is saying he needs 300watts at 4ohms for the gigs we do. (we're a loud blues/rock/r+b band). He is obviously saying this based on the fact that his Hartke head is 500 watts and works well on our gigs. If I were using LM3886 PAs (ha ha!) I would need 6 of 'em driving 6 separate 4ohms speakers!!! Maybe this is incorrect and someone will enlighten me on commercial ss bass amps' wattage ratings. This seems like a ridiculous project so if need be I will build a discrete 300watt PA.

The way I see it musicians have always been using the wrong unit of measure for loudness. If you trace an analogy with other fields, you'll quickly notice where using Watts is just wrong. A Scania truck has more watts than a Ferrari, but if you're looking for speed, the Ferrari is fastest, if you're looking to carry a load of coal up a road the Scania makes it possible.

Musicians use Watts like it means loudness. Watts is what the electrical device is dissipating inside itself to produce the work you want.... That IMO is the source of the confusion, of course Watts mean the same thing for transistors and tubes and anything else in nature, it's the exact same watts you burn on a gym bike. But using Watts for a measure of loudness is where it gets messy, because it depends on everything from the tubes, to the efficiency, to the ears, to the room, the tone, the instrument, everything....

In the craze of the 70's (I think) Fender started using "Musical Power" for their "watts". What was that? 1.41 * rms current * 1.41 * rms voltage - which gives us about twice the RMS power. Was it wrong? No....it was Fender's way of competing back then. And it's the most honest form of PMPO out there, if you go have a look at computer speakers you'll laugh your pants off at some of the power ratings.

Watts is just wrong for loudness. Comparing watts on a class D amp of 2011 with the original SVT is comparing apples to oranges IMO.

[txstrat]

Watts is what the electrical device is dissipating inside itself to produce the work you want....

Didn't know how to put it. Now my latest post makes sense to myself. Thanks jmaf.

[jmaf]

Didn't know how to put it. Now my latest post makes sense to myself. Thanks jmaf.

Your post made perfect sense before

[teemuk]

http://www.tcelectronic.com/media/Ac...ent_020209.pdf

If you can read past the self-assertion and glorifying their product with the expense of others' the explanation of crest factor, perceived loudness being more dependent on average than peak levels, and the effect of clipping distortion to those variables will make perfect sense in explaining loudness differences of different systems.

The only things I don't agree with are the statements implying that clipping distortion of solid-state amps is rarely desireable and that tube amps clip softly. I could buy the first statement if great number of today's SS instrument amps would not feature "tubey" soft clipping limiters. But they do. I could buy the second statement if tube amps clipped softly. But not all of them do.

Next, go see/listen a youtube demo of what that described soft clipping tube emulation feature actually does to the overall tone of that amp and you start to get a great picture why there is indeed a need for both low headroom clipping systems that may sound loud, and high headroom systems that may not sound as loud but keep the tone intact and clean, some might even say "sterile". There is a great difference in tone.
Personally, I like to have an opinion to vary between those modes but I also realize that there are plenty of people who prefer only a single one of those options (whether their preference is clean or dirt), and they may even hate the other one.

I know this is not really a tube vs. solid-state discussion - and honestly there is no need why to make it such - but the loudness issue just usually happens to fall down to clean versus distortion, and usually those are presented by examples of valve (distortion) and solid-state (clean) because that's what we tend to be accustomed to.

[kg]

Uh, a transformer coupled tube amps also hits a brick wall when overdriven to the limits of their power supply... like this:


I don't know where the misconception comes that tube amps would for some mythical reason be free of limits determined by the power supply.

so you're saying that PI is transformer coupled to the output stage?

[teemuk]

No. I'm saying that power supply's limits make tube amplifiers clip, just like those very same limits make solid-state amps clip. And the clipping is not in all cases nice, soft and smooth, on a contrary. As is demonstarted by the oscilloscope capture that shows a Trainwreck clone overdriven to power amp distortion. I could post several more of such scope captures, from Fenders, Marshalls, Mesa/Boogies etc. all portraying about similar hard clipping characteristics.

Yes, generic transformer coupled tube amps similarly hit a "brick wall" when clipping. They can't magically exceed the limits dictated by their power supply.

[jrfrond]

Class D power amps are what I call "fake power". They work well with sustained signal, but they lose the battle with repeated high-power transients. Yes, they are light, cheap and convenient, but are no match for a brute-force power amp.

Concerning LM3886's: these power amp IC's from National Semi's "Overture" series are quite remarkable, and make a nice, easy to design power amp. Though they deliver 68WRMS max, they can be "stacked" or operated in "bridge" mode for increased wattage. Thye've become an industry standard in many guitar amps and active speakers, including the Tech 21 Trademark 60. It's a reliable IC with excellent thermal and overcurrent protection built in. I'd highly recommend trying these for an experimental build. The data sheet provides all of the info you need.

[teemuk]

Robust chip, yes, but I wouldn't build a bass amp using them.

They are great for, say, ~60W or ~2x60W amps but once you start needing more power - as in bass amps - you need to start bridging or [gulp] paralleling them and that's where those chips no longer are easy, realiable or even so cheap to implement.

There is a National application note discussing such design but with all those precision matched components and DC servos implemented to the design it's kinda getting into realm of making solutions to problems that wouldn't exist if you'd just choose a different type of design, abandoning the LM3886 completely.

If you want a cheap and simple route for bass amp, I'd try finding some kit-based MOSFET design in the 300W range instead.