Curious about Mesa Rectifiers and the like....

[Killjingle]

A big concern was always if u underpower a speaker u could heat up the voice coil. Obviously with a 150 watt tube head (Triple Rectifier) headroom is not a problem, but continously playing at lower than optimum volume is this still a concern? I see Ken wants to pick one up just so he can be loud enough if he ever wants it, but I know I rarely get to even get to 4 on my Single and my bros Double Rectifier prob never gets past 3. These things are very capable of getting stupid loud.

Thoughts?

[bassist_25]

Well the connundrum is that you need to be pushing so much gain through a tube amp (and a SS amp, IME) to get it to sound good. That's the problem with mega-watt tube amps. You could always use a power break, I suppose. If you're using FOH support, it's always a problem because you don't want to be over-powering the mains just to get a nice tone. If I were buying a Mesa head, I'd probably just go with a Dual Rec. If I wanted all of the cool channels and what-not that come with the Triple, I'd probably just upgrade the Dual to a Road King. Maybe i'm not the best person to say, "Go with a smaller amp," because I have 1.6K watts of power hanging in my rack (and there was a time I use to make fun of the power-freak guys like this), but it's solid-state, which is a different ballgame, and bass requires lots of power to reproduce the fundementals of notes.

The class of power seems to be tied into how much percieved volume an amp has. I'm not an engineer, so I don't know the differences between classes. Perhaps Lonewolf or someone could explain that.

[lonewolf]

The voice coil will blow with:

too much "nonharmonic" amplifier clipping -- usually caused by trying to get more gain out of a weak power amp. You can run 30 watts as much as you like as long as its a CLEAN 30 watts....drive that amp into clipping (DC to the speaker) and you will probably get POOF!

moving the voice coil past its excursion limit -- this generally happens when you overpower the speaker with a solid low tone. This is why its not as good an idea to go 2X the rms speaker rating with instrument amps as is commonly done when matching power amps with PA speakers.

CONTINUATION:

The biggest difference between tube power amps and solid state power amps is that its harder to push the tube power amps into clipping than solid state and so they can be pushed to higher spls before shutting down or clipping.

In addition, switchmode power amps generally have a peak rail voltage that is only 1.414 times the rated rms rail voitage whereas a typical linear power amp has a 2x peak. That's a lot of additional instantaneous headroom for the heavyweight linear amps.

[Ron]

The class of power seems to be tied into how much percieved volume an amp has. I'm not an engineer, so I don't know the differences between classes. Perhaps Lonewolf or someone could explain that.

Paul, by "class" do you mean class A, B, A-B?

[bassist_25]

The class of power seems to be tied into how much percieved volume an amp has. I'm not an engineer, so I don't know the differences between classes. Perhaps Lonewolf or someone could explain that.

Paul, by "class" do you mean class A, B, A-B?

Yep.

[Killjingle]

I followed to a point...

I guess in lamens terms?

[MeYatch]

in layman's terms underpowing a speaker doesn't do any damage. powerng a speaker with a clipped signal will do damage. This is more likely to happen with an underpowered signal, which is probably where the myth comes from.

people smarter than me have told me you can blow a voice coil with a clipped signal even if the speaker is rated much much higher than the power its receiving.

as lonewolf said you can also blow a speaker with clean power if your putting much more power into it than the speaker can handle.

[Killjingle]

gotcha

[Ron]

The class of power seems to be tied into how much percieved volume an amp has. I'm not an engineer, so I don't know the differences between classes. Perhaps Lonewolf or someone could explain that.

Paul, by "class" do you mean class A, B, A-B?

Yep.

The class of an amp simply has to do with the way the power supply and output transistors/tubes are configured.

Class A: the transistors/tubes are fully switched on by a large DC bias and the AC signal rides on top of that DC bias. The best sound quality but very inefficient for the weight. They also get really HOT. Needs a very large power supply. The power handling capacity of the transistors/tubes must be top notch, so they are expensive all around.

Class B: the transistors/tubes are in a push/pull configuration, with one set handling the positive part of the wave and one set handling the negative part. This causes switching noise at the zero-crossing point, where one set turns off and the other set turns on. Rarely used because of the advent of class A-B configurations.

Class A-B: Same push/pull configuration as a class B amp, but the transistors/tubes are given a small DC bias to keep them turned on at all times. This prevents switching distortion at the zero-crossing point. I would guess that over 90% of the amplifiers on the market use this configuration, since it maintains a good balance between sound quality, efficiency and price.

Class C: Much like a class B design, but designed mainly for high efficiency. Rarely used in audio applications because of nasty switching distortion. Usually used for radio frequency amplification.

Class D: Usually this describes the pulse width modulated power supplies used to power automotive audio amps. Since only a small wattage can be derived from the 12V source from most car batteries, the class D amp bumps the 12V up to higher voltage positive and negative rails. This usually then feeds the more common A-B designed audio stages.

Class E-F: Other high efficiency designs like class C. Practically unusable for audio.

Class G-H: Basically class A-B amps that vary the power supply as needed to achieve higher efficiency. When run in low power modes, the power supply also lowers it's voltage output. Class G uses multiple fixed supply rails where class H monitors the input signal and adjusts the supply rails on the fly.

Whew.

[SpellboundByMetal]

you saved me a question, ron!!!!!

[Ron]

Chad, a tube amp is also much easier on speakers than a solid state amp.

When a tube amp clips, the clipped wave form is rounded at the top. Since it is rounded, there is still some cone movement during the clipping phase and this helps keep the voice coil somewhat cool.

When a solid state amp is clipped the waveform is squared off at the top, meaning that there is a constant DC voltage on the speaker for a short period of time. During this time the voice coil of the speaker isn't moving and heats up like a car cigarette lighter.

As far as ultimate power handling, I've seen demos at trade shows where high dollar speaker drivers were plugged into a 110VAC wall outlet and they survived.

[bassist_25]

Here's an interesting question: Is a watt a watt? What I mean is one watt of solid state power considered equal to one watt of tube power? I've heard many guys argue over this, but I've never got into the debate because I'm pretty ignorant about the subject. I know that a 200 watt tube amp will sound louder than a 300 watt solid state amp. Why is that? Is it just because the tube amp can be driven safely into clipping whereas the solid state amp requires lots of clean headroom?

[MeYatch]

Here's an interesting question: Is a watt a watt? What I mean is one watt of solid state power considered equal to one watt of tube power? I've heard many guys argue over this, but I've never got into the debate because I'm pretty ignorant about the subject. I know that a 200 watt tube amp will sound louder than a 300 watt solid state amp. Why is that? Is it just because the tube amp can be driven safely into clipping whereas the solid state amp requires lots of clean headroom?

its my understanding that tube amps also tend to accentuate the midrange more, also making them appear louder.

[Ron]

Here's an interesting question: Is a watt a watt? What I mean is one watt of solid state power considered equal to one watt of tube power? I've heard many guys argue over this, but I've never got into the debate because I'm pretty ignorant about the subject. I know that a 200 watt tube amp will sound louder than a 300 watt solid state amp. Why is that? Is it just because the tube amp can be driven safely into clipping whereas the solid state amp requires lots of clean headroom?

Yep. Since the tube amp generates mostly even-order harmonics when clipped, the clipping is "softer" sounding and harder to perceive. The odd order harmonics generated when a solid-state amp clips are pronounced and nasty sounding.

As long as a volt is a volt, an ohm is an ohm and an ampere is an ampere, a watt will always be a watt.