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RE: Better to not share a preamp in the same outlet or strip as the amp?

From my personal experience I have the preamp and power plugged into the same 20 amp dedicated circuit wall duplex receptacle. Both pieces of equipment are analog.
( 120V 20 amp dedicated branch circuit, with #10-2 with ground NM-B cable, Romex is a Trade name of NM cable).

The thing that must be considered is the size of the branch circuit wiring used, and the length of the branch circuit wire from the electrical panel to the wall receptacle outlet. You do not want the AC mains voltage fluctuating, bouncing around, caused by the dynamic load placed on the power supply of the amp, when driving the amp playing a dynamic musical source through the amp. One reason many use #10awg wire for the branch circuit wiring for a 20 amp circuit. For a short branch circuit run #12 may be fine. Though it may depend on the size of the power amp and how hard it is driven.

As for any digital equipment, I personally have found it is best to feed it from another dedicated circuit. The idea, theory, is to decouple the digital equipment power supply/s from the analog equipment power supply/s.
I suggest you search the archives, here on AA on the subject, of Al Sekela and rcrump just to name two.

//

EDIT:

Impact of fluctuating AC mains voltage on a power amp's power supply.


atmasphere,

5,153 posts 06-03-2014 10:46am

With power cords its all about voltage drop across the cord. Some of that is at 60Hz, and some of that is much much higher- well above 30KHz-100KHz depending on the power supply in the unit with which it is being used.

I've seen a 2 1/2 volt drop rob an amplifier of about 30% of its output power. The cord was rated for 10 amps, and the draw was about 6 amps. This measurement was done with a simple 3 1/2 digit Digital Voltmeter.

The more insidious problem is high frequency bandwidth. The power supplies of most amplifiers have a power transformer, a set of rectifiers, and a set of filter capacitors. The rectifiers only conduct when the power transformer output is higher than that of the filter caps. So:

When the caps are fully charged the amp is able to play. As it does so, the caps are discharged until the AC line voltage waveform gets high enough again that the rectifiers in the power supply are able to conduct. Depending on the state of charge of the filter capacitors, this might only be for a few microseconds or it might be a few milliseconds. Either way, the charge is a spike which has very steep sides- and requires some bandwidth to make it happen.

If the power cord has poor high frequency response, it will current limit on these spikes. This can result is subtle modulations in the power supply or even a sagging power supply voltage.

Romex wiring found in many buildings actually works quite well. So it really becomes all about that last few feet and also how well the power cord is terminated- molded cords generally are not terminated very well. If the ends of your power cord get warm after a while, you know you have a problem!

This can be measured, its quantifiable and also audible as many audiophiles know. Anyone who tells you differently probably has not bothered to do any measurements- please refer them to this post.

The same holds true for VD, Voltage Drop, on branch circuit wiring.



Edits: 01/15/17

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  Atma-Sphere Music Systems, Inc.  


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