# How much does it cost to run an amplifier

My SO has noticed a sudden, and very large, spike in his electricity bill. His roommate has a band that practices at their house about 2-3 hours a week. Could this explain the hike in electricity. The bands electrical equipment consists of:
1 microphone attatched to 2 - 15 in. speakers( JBL brand)
1 Line 6 Spider Guitar Amplifier
1 Marshall Guitar Cabinet ( I don’t know the model)
1 Bass guitar cabinet (with 6 12" speakers).

Any help would be appreciated and specific sources would be very helpful in presenting the case to his roommate.

Thank You

It might have something to do with it, but I doubt it. Did the spike occur after his band started practicing?

-A microphone attached to speakers doesn’t draw any power… what kind of amp is powering those speakers? It’s probably a couple hundred watts. The one I use for my band is 400 watts and is more than enough for practice.

-You say there’s two guitar amps, and they are usually 100 watts (A guitar cabinet also doesn’t draw any power, you need to know the power of the amp that drives it). I’ve been trying to find info on this, but I’ve heard that 100W tube amps can draw up to 400 watts of power.

-A bass guitar cabinet with 6 12" speakers needs A LOT of power if its loud. Let’s assume 400 watts.
So, adding up all these wattages gives you 1600 watts of power being drawn. If they practice 3 hours a week, that’s 4800 watts a week, times 4 weeks in a month. That’s 19.2 kilowatts per month. If your electric is 10 cents/Kwh, your bill would go up by less than two dollars. And that’s being liberal.

Don’t be sure that’s not the reason for your spike until someone checks my math

That would depend on the wattage of the various piecs of equipment, and what you mean bye a “very large spike”. Let’s assume that all the equipment together draws 2000 watts. Running it, say 3 hours a week = 2000 x 3 x 4 = 4.4(weeks per month avg.) = 24000 Wh = 2.4 kWh each month. Lets’s further assume your electricity costs \$0.20 per kWh. That would mean an increase of 2.4 x \$0.20 = \$0.48. That’s not a very big spike. Even if the equipment drew 10 times the amount i assumed, that would still be just \$4.80 per month additional, so I don’t think that’s it.

Ooops…decimal point error. “That would mean an increase of 2.4 x \$0.20 = \$0.48.” should obviously read “24 x \$0.20 = \$4.80”

:smack:

On the other hand, if the band is a new thing, you might want to make sure that the equipment’s turned off when not using it. That could draw enough to give a big spike.

It’s probably something similar even if it’s not that – something that didn’t used to run all the time that is now, like a broken appliance or intermittent fault in wiring. Check the actual usage amounts from before and after, too. There might have been a change in billing.

This will sound a tad simplistic, but…

Did his electric company raise his rate? Maybe there’s an extra service charge or convienence charge or other nonsense like that.

I thought most amplifier powerstages didn’t draw much juice when they’re not given any (much) signal from the pre-amps? Obviously they’ll draw some, but in the interests of fighting ignorance, anyone know roughly how much (say percentage-wise compared with flat out)?

It’s very small compared to the draw of the amplifier at full power. What the quiescent power draw is depends largely ont he amplifier design. Tube amps draw considerably more than solid-state amps. While i have no figures to quote, I’d say that a typical high-power solid-state audio amp only draws on the order of a few watts in the quiescent state.

Not all amps draw the same power when in idle or standby mode as when at maximum volume. There are a lot of factors but there is usually a design tradeoff between efficiency and low distortion. Can’t give you more specifics as it’s been many, many years since I was into analog electronics.

Do some simple measurements. Borrow an amp meter with a clamp if you can or just do some checks at the electric meter coming into the house. Measure usage over a period of time with the equipment off then measure it again with equipment on.

Unfortunately, those clamp-on ammeters require you to be able get it around just one of the conductors. If you simply clamp it around the power cord, you’ll get no reading, no matter how much current is being drawn. They do make plug-in power monitors that can tell you that sort of thing, along with other factors, such as AC frequency and power factor.

I have some personal experience in this. If you forget to turn your bass amp off for nearly a month, your wife will tear you a new one due to said bill. (I think it was about 20ish bucks more, but there could have been other reasons) Watch the spinny thing on the electric meter when they are jamming sometime. It creates it’s own breeze, hell, it’s own weather patterns, when 3 amps are turn on at the same time.

Hijack here…sorry.
Lets say you have a 100 watt amp and speakers that can handle, say 125 watts. Will any damage (or anything really) occur to the amp if you run at full power at all times? I’m talking about stereo equipment, not instrument stuff, if that makes a difference.

Running the amp at full power won’t hurt it unless the speaker’s impedance curve goes below the minimum impedance of the amplifier for too long. Then the amp will go into thermal protect mode and turn itself off.
Also, if you’re running the amp at “full power” and your input signal level isn’t properly matched, you do have a much greater chance of the amplifier clipping the waveform of the signal and blowing the speaker.

Thanks much. I’ll let you guys get back to the original topic now.

[/hijack] or whatever the hell it is

If you have a 100W amp and you have the thing full at full power you WILL clip, I don’t care how much money you spent on it, and you will probably damage your speakers if they are only rated at 125W because that is most definitely Peak Power.

If the output stage of the amplifier is “Class A”, then it will draw half of the maximum power with no input signal. Class A isn’t often seen in general consumer hifi equipment, but is common in valve amps, in top-end hifi equipment and in stage equipment.

So if the stuff is accidentally left on, it’s still drawing heaps of power.

Desmostylus: thanks! I was in the habit of often leaving my home studio (including a couple of guitar amps and a large power amp) on for quite long periods. No longer…