# Peak current, crest ratio and power factor of hi-fi equipment

**URL:** <https://forum.psaudio.com/t/peak-current-crest-ratio-and-power-factor-of-hi-fi-equipment/27399>\
**Category:** Power Components\
**Created:** [February 4, 2022, 11:21am UTC](https://forum.psaudio.com/t/peak-current-crest-ratio-and-power-factor-of-hi-fi-equipment/27399 "2022-02-04T11:21:43Z")\
**Posts on this page:** 1\
**Page:** 1

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**Author:** ![hadf345](https://sea1.discourse-cdn.com/flex015/user_avatar/forum.psaudio.com/hadf345/32/129138_2.png) [@hadf345](https://forum.psaudio.com/u/hadf345)\
**Post date:** [February 4, 2022, 11:21am UTC](https://forum.psaudio.com/t/peak-current-crest-ratio-and-power-factor-of-hi-fi-equipment/27399/1 "2022-02-04T11:21:43Z")

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Peak current, crest ratio and power factor of power amplifiers, preamplifiers, cassette decks, turntables etc. is a way to understand how those devices can distort the AC mains supply and is hence relevant for their own sound quality. I would be interested in some numbers about this, especially vintage hi-fi equipment with no processors or switched-mode power supplies. @Paul stated here that 0.7 is a normal power factor, but did not mention how he knows that.

> [@PowerPlant vs. Double Conversion UPS](https://forum.psaudio.com/t/powerplant-vs-double-conversion-ups/7079/4):
>
> Ted’s right. Moreover they use a class D output stage and cannot handle power factors of less than 1 without even more distortion. If you try and power anything with a PF of 0.7 (common for amps and preamps) you’ll get a nasty divot out of the peak of the sine wave under any heavy current use. These are fine as intended, as battery backups, but not to replace a real regenerator like a Power Plant.

I read a switched-mode power supply typically has a PF of 0.6 or 0.7 and that the peak current is within 2.5 times the average current. But I guess linear transformers used in vintage hi-fi equipment could then also be within the 2.5:1 ratio. Crest ratio is important to discuss, because it’s the whole reason why a PS Audio regenerator might sound better than the mains supply yet there is hardly any discussion of what the peak current is on devices.

The Eaton 9PX UPS can handle peak current that is 3 times higher than the average current, and this is what prompted the topic. A crest ratio of 3:1 is about 6 dB. Music often has a crest ratio of 18 dB. That is about 6 times more than the 3 dB that is in a pure AC sine wave, so the peak current drawn by the power supply could easily be more than 3 times the average and it sometimes is.

Any help is appreciated, but keep in mind that it is very dangerous to measure the peak current of devices with an oscilloscope for example, because the mains supply can leak AC to the chassis and electrocute you. In short, if you don’t know what you’re doing don’t mess with it (verification of your own knowledge is always critical, because you don’t know what you don’t know).