Amp that puts out more power than it consumes?

[DeepEnd]

I was browsing on CraigsList and found an amp that looked interesting, specifically a Vox VT80+. I checked it out on the Vox web site and noticed something odd: It's rated for 120 Watts into 4 Ohms but it only consumes 54 Watts. I could understand 254 Watts or even 154 Watts but that just doesn't make sense. The Fender I have now is rated for 65 Watts into 8 Ohms and consumes 180. Are they maybe citing power consumption in the absence of a signal (i.e., it takes 54 Watts to power that single 12AX7 and the various digital effects)?

[WRGKMC]

The amplifier's output power must always be less than then the amps AC power requirement specification. An amplifier cannot deliver more (or even as much ) power that it takes from the wall socket. Having more output then input is as impossible as perpetual motion

 

The specs show...

 

Power amp output VT80+: maximum 120 W RMS @ 4 ohm

 

Power supply requirements: AC, local voltage

 

Power consumption VT80+: 54 W

 

The power consumption wattage is misleading. They test power consumption with the amp idle, not when its producing its maximum operating wattage consumption when the amp is being run at max volume.

 

This amp likely has a power supply designed to draw more current from the outlet as needed from the wall outlet. (many SS amps and PA heads are deigned this way because the power transistors draw differently then power tubes do) Specifications only list the AC power consumption with the amp just turned on and volume off.

 

Many products you buy may list, minimum and maximum wattages, and energy saver modes as well. Guitar amps aren't one of them.

 

Keep in mind, an amps operating AC wattage is the hourly rate of electricity consumption, not an instantaneous wattage like an amps output can be.

 

The testing I've done on products has always been at idle for obvious reasons. You have no way of standardizing how hard you would push an amp over a period of time so the maximum power consumption can vary all over the place. 1000 Hz sine wave is a standard for testing output wattage. It could be used to test the power consumption at the same time but it simply wouldn't be a realistic test for operating consumption.

 

An instrument that produces all kinds of frequencies and draw all kinds of different wattages. Once a manufacturer prints something like a maximum wattage number they have to live by that number. If someone could draw more wattage playing a bass then guitar for example. This would leave a manufacturer open to law suits for false information so they aren't going to post a maximum operating wattage even if they had it.

 

Your AC unit or microwave on the other hand has a steady high wattage consumption when different motor speeds are chosen so those specs can be published. Amps like this don't have a steady consumption do you only get a minimum posted.

 

 

An amplifier output is not a steady wattage either. An amp doesn't output 120W steadily, and it outputs practically nothing with the volume turned off. Caps can come into play as voltage storage devices. Besides filtering they store voltage which can be drawn upon to create peaks but they aren't a continuous supply. They need time to recharge after they have provided those wattage peaks. (milliseconds) However, No matter how large and efficient they are they cannot provide perpetual motion.

[DeepEnd]

Fixed:

. . . The power consumption wattage is misleading. They test power consumption with the amp idle, not when its producing its maximum operating wattage consumption when the amp is being run at max volume.

 

This amp likely has a power supply designed to draw more current from the outlet as needed from the wall outlet. (many SS amps and PA heads are deigned this way because the power transistors draw differently then power tubes do) Specifications only list the AC power consumption with the amp just turned on and volume off. . . .

 

. . . Caps can come into play as voltage storage devices. Besides filtering they store voltage which can be drawn upon to create peaks but they aren't a continuous supply. They need time to recharge after they have provided those wattage peaks. (milliseconds) However, No matter how large and efficient they are they cannot provide perpetual motion.

There, was that so hard? Everything I needed to know in a few short paragraphs instead of your usual wall of text. Anyway, thanks for your answer. It's pretty much what I suspected (and mentioned in my original post). I'm guessing my Fender was tested under different conditions, which would explain why it's rated to consume 180 Watts.

[WRGKMC]

If you don't like my posts, no one is forcing you to read them.

 

As far as the differences Its simply the circuits and components the manufacturers choose to use. Fender amps Typically use older SS designs and components that require a steady current supply all the time whether they are amplifying or not. This makes sense because they migrated from Tube technology to SS and wanted to maintain the same kind of fender tones.

 

It can also help prevent catastrophic failures. When the power supply takes an active role in changing its power requirements, the power supply and power amp can be more susceptible to extended failure, ie. if a power transistor blows because you load the speakers too much, the failure may not be isolated to that section of the amp and may migrate to the power supply as well.

 

This is where quality components and protective measures come into play. Fender uses bargain basement parts that have been around a long time and work well enough. For them its about profitability and market share. Having the power supply isolated from the rest of the circuit gives them a longer lifespan.

 

Yamaha tends to lean towards newer technologies and they are very good at quality control and using quality parts. They do their homework when designing amps and borrow tested designs from many different manufacturers. You could say their strong point is taking risks to deliver new technologies.

 

The thing is Yamaha isn't trying to clone older tube tone designs like Fender does and can simply design an efficient amp that sounds good. The only issues you do run into is getting them repaired if and when they do fail. I for example can troubleshoot most Fender amps using a simple meter and signal tracer without a schematic because they are ultra simple and parts are readily available. Yamaha can have proprietary parts and weird circuit designs. I's probably need a schematic to figure out the extent of the damage.