# SMPS and power amps

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#### intel48

Couple of questions, I am a hobbist, so please answer if you can simply.
An example of commercial power amp specs...Stereo amp rated at 2100 w RMS/chan, (amp does deliver this output power), 3000 w peak/ch....power consumption, at the mains 240Vac is 630 Watts.

Ques 1. Power consumption is 630 watt @ 240 V ac....doing the maths, power consumption would be approx 240vac x 3.15 A = 630 W (VA), this would be correct?

Ques 2. If I have 2 x amplifier modules rated at 1000 W RMS, 1800 w Peak, +/-100 VDC supply, using same formula, 240vac x 4.16 A = approx 1000 w,
in reality purchasing an after market SMPS power supply, what would I really need, as an example this SMPS specs are as follows, 500 w , 240VAC input, output +/- 65 VDC.......using these specs, is that the actual power it can deliver, or would it be the power consumption, as in the eg: at the very top, where 630W was used.

Or does the manufacturer, stating the power supply specs, but can be used in a power supply for a similar amp to the very top one, what I mean is, power consumption 500 w , using the same ratio of power supply, and 2 x amps (2100w/ch, and 630 total power consumption)......500w power consumption, could power 2 x amp modules rated at approx 1600 w/ ch

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#### trobbins

Qu.1 the current would only be 3.15Arms if the power factor was 1. 630W means that some meter has measured the real component of mains supply power delivery to the power supply when it is connected to the amp, and the amp is operating under a 'defined condition'.

Unless the amp has a very nice switchmode supply the PF can be much much lower than 1.

Qu.2 if the amp module requires 1000W rms at +/-100Vdc, then that is what the power supply has to 'at least' deliver. There is no correlation with what the power supply draws from the AC mains until you know the power supply and its specifications.

#### Mark Tillotson

The mains power consumption may be the quiescent consumption, or some sort of best guess average for normal use. Usually power consumption and mains current are both given, in which case the current rating is for selecting the correct fuse and cable ratings.

#### Osvaldo de Banfield

Power input to a SMPS is always bigger than the (sum of) the power output, because there are internal power consumption (MOSFET's drivers, logic, PFC if any, fan, traffo, etc.). Sometimes there is a specified instant power consumption at starting, called "inrush" what is the current demanded to build up internal voltages, charging capacitors, etc.

Be sure that the SMPS's switching frequency and the amp one are not harmonicaly related, because some extraneous effects may appear.

#### wg_ski

The above mentioned amplifier actually draws about 32 amps (at 240V, twice that on a 120V version) when it is delivering the stated 2100 watts per channel. It will only do that for a few tenths of a second at a time, but will do so repetitively. Unfortunately if you do so on a regulsr basis you will literally wear the thing out. Run it into thermal limit enough times and your iNuke will be ready for the landfill. The 630 VA rating applies for putting out 1/8 power with pink noise. Used this way it is “reasonably” reliable.

The problem with using SMPS’s for audio is that it needs to deliver those high power levels for at least short periods of time. The actual current required is the full load voltage divided by the minimum load impedance, for at least 25 milliseconds (half a sine, at 20 Hz). This is much more than the average current draw, even with a steady state load (by a factor of about 3). Off the shelf generic supplies might not have that headroom, unless you use one very oversized and very expensive.

#### intel48

Thankyou, that has cleared up a lot, so, they are rating power consumption at mains at 630 VA, which is 1/8 power, so full power would be 5040VA, that makes sense, because it will only run at full rms power, when connected to 32amp 3 phase outlet, and def pushes what its rated at, which is approx 2050-2100 / ch RMS

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