confused about 20 amp power cables

Food for thought.

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Dynamic Headroom.

@almarg Said:            02-08-2010 at 08:00am

It refers to the ability of an amplifier to deliver a greater amount of power on brief musical peaks than the amount of power it is rated to deliver continuously.

That can be good in the sense that the peak power levels required by a lot of music can be vastly higher than the average levels that are required. Classical symphonic music is one of the most extreme examples of that.

However, high dynamic headroom can also be an indication that the amplifier's power supply and/or its thermal design are "weak," because it indicates that the amplifier cannot sustain its maximum power capability for very long.

Regards,
-- Al

https://forum.audiogon.com/discussions/dynamic-headroom

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kijanki  Said:           06-07-2022 at 07:27pm 

2x200W amp might take from mains close to 1kW during peaks. The problem is that peak supply current won’t be expected 8A, but rather close to 40A. It is because current is drawn only for very short time (millisecond pulse) at the peak of full wave rectified sinewave. It applies to most of LPS. Power delivered with such short pulses not only creates larger voltage drops in house wiring, but also heat-up amp’s power transformer, that has to be oversized (higher copper losses and higher core losses for eddy currents and hysteresis).

https://electronics.stackexchange.com/questions/329443/current-through-the-smoothing-capacitor-in-bridge-rectifier

It's not just the ampere rating size of the AC power fuse used in a power amp that determines the wire size needed for branch circuit wiring and the size of the wire used in a power cord.

The power supply of a power amplifier likes/needs a steady state AC mains voltage.

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Thanks @jea48 --

I read the recent thread you participated in (AC Power in misc-audio), lots of good info in that thread.  I may end up putting in a Furman P-2400 at some point.

@mintakax Said

I read the recent thread you participated in (AC Power in misc-audio), lots of good info in that thread. I may end up putting in a Furman P-2400 at some point.

I don’t know enough about P-2400 to recommend it one way or the other. Especially if you would be plugging the T+A PA 3100 HV integrated amp into it.

The T+A PA 3100 HV integrated amp has a very robust power supply.

"1000VA toroidal transformer with 120,000µF of filter capacitance."

Jmho the amp should be plugged directly into the 20A dedicated branch circuit wall outlet.

Available power at the wall outlet for this,

for very short time (millisecond pulse) at the peak of full wave rectified sinewave.

03-18-2025 at 01:02pm

is pretty much unrestricted. A 20A circuit will easily pass very short time (millisecond pulse) s many times the 20 amp breaker’s handle rating. (Same for the 10A slow blow fuse in the PA 3100 amp.

Limiting factor? VD, (Voltage Drop) on the AC mains caused by the load of the power supply on the branch circuit wiring. Therein the connected load of the amplifier playing high dynamic music at a high volume level. (Not a steady continuous load... This load, "very short time (millisecond pulse) at the peak of full wave rectified sinewave."

What determines VD on the branch circuit wiring? Connected load in amperes, length of the branch circuit wiring X two, and wire gauge size. (Remember the 20A breaker will pass short pules of current well over its’ handle rating, all day long.)

Question.

What AWG wire size did the electrician install for the 20A dedicated branch circuit? #12AWG? #10AWG?

Guesstimate length of the wiring from the electrical panel to the wall receptacle outlet? Try to include up, down, over and around lengths to the total length of the branch circuit wiring.

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https://www.stereophile.com/content/ta-pa3100-hv-integrated-amplifier-measurements

T+A specifies the PA 3100 HV’s maximum continuous power as 300W into 8 ohms (24.8dBW) and 500W into 4 ohms (24.0dBW). With both channels driven and using our definition of clipping, which is when the output’s percentage of THD+noise reaches 1%, fig.4 indicates that the amplifier clipped at 318Wpc into 8 ohms (25.0dBW). The T+A amplifier also exceeded its specified power into 4 ohms, clipping at 525Wpc (24.2dBW), again with both channels driven (fig.5).

(I don’t hold the AC wall voltage constant for these tests. With the amplifier idling, it was 121.6V; with the amplifier clipping into 4 ohms, the AC supply voltage had dropped to 117.9V.)

Just a guess measurement were taken with an RMS multimeter.

What was the base line for the AC VD measurements? What did the current, in amperes, measure on the branch circuit wiring?

What determines VD on the branch circuit wiring? Connected load in amperes, length of the branch circuit wiring X two, and wire gauge size.

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Thanks!  I believe the wire was 12AWG and the run is roughly 60ft.  Most of the advice I've received has been to plug the amp into the 20A wall outlet.

Edit:

It would be nice if a reviewer took the time to measure the AC line current at power output clipping.

From the owner’s manual specs:

Output Power* (Peak)
8 ohm 380 W
4 ohm700 W

Peak is not max continuous output power.

Just for a rough AC mains current draw calculation using 4 ohm 700W.

700W / 120V = 5.8A + unknown loses.

700W / 120V = 5.8A + unknown loses would be for one channel.

Both channels driven peak watts would be 1400W / 120 = 11.67A + loses.

Problem is my above calculations are flawed and do not express what is actually happening on the AC mains branch circuit wiring.

It doesn’t account for this.

2x200W amp might take from mains close to 1kW during peaks. The problem is that peak supply current won’t be expected 8A, but rather close to 40A. It is because current is drawn only for very short time (millisecond pulse) at the peak of full wave rectified sinewave.

I’m not sure what type of current measuring test equipment would be used to measure for dynamic short spurts of current draw on the AC mains branch circuit wiring caused by high dynamic music passages for music being played. A regular Clamp Amp meter will not catch, register, the current draw event fast enough, imo. Unless several peaks were close together. ??? Not even sure then. Maybe an Oscilloscope?

@kijanki might be able to answer the question. And, more than likely, rephrase it better, what I’m trying to say.

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