Power cable

Discussion in 'Audio Hardware' started by Orbe, Oct 5, 2020.

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  1. DrZhivago

    DrZhivago Hedonist

    Location:
    Brisbane Australia
    I can hear the difference between different interconnects (RCA) and speaker cables. Swapped almost all stock power cables on my gear for after-market ones, but could never conclusively discern any difference between them.

    Regards
     
    timind likes this.
  2. Ingenieur

    Ingenieur Just a dog looking for a home...

    Location:
    Back in PA
    One more step. The energy a Cap holds
    Assume a DC rail of 89 VDC and 40,000 uF
    E = 1/2 C V^2 = 128 Joules
    A Watt = Joule / Sec
    So the caps can supply 128 W for 1 sec
    (Ignoring R, etc., which won't change on the output side with a power cable swap, other than the aforementioned tc).
    So in 1/2 Sec ~ 256 Watts
    1/4 ~ 512 Watts
    0.1 sec ~ 1,300 Watt and so on

    So if you have a bass note of 100 Hz (0.01 Sec) or 10 mSec that takes 100 W that is 0.01 x 100 = 10 Joule, the caps can recharge that 8% 92 to ~100%) of the caps capacity in 1.5 tc or 0.018 Sec.
    18 mSec vs the 10 mSec it takes to discharge.
    If the cap is discharged to 50% to get to 58% takes only 0.15 tc or 1.8 mSec to recharge vs 10 mSec.

    The cable is inconsequential in this response
    imo
     
  3. Ingenieur

    Ingenieur Just a dog looking for a home...

    Location:
    Back in PA
    The technical explanation.
    If you draw 80 A at 120 V that is 9,600 kva
    The CAPS provide the instantaneous power.
    If 500 W (assume a purely resistive load) the caps supply it, and the receptacle power will replenish it.
    500 W at 120 is only 4.2 A

    If you use 500 W for 0.1 sec that is only 50 joules, caps are over sized for this reason.

    V drop is moot
    The xfmr steps voltage down to 80 or less, so a drop has less impact. Not to mention the most the speaker may see is 50 v or so
    P = (50^2) / 8 Ohm = 300 W

    now let's look at the V drop for 50' (100' loop) of 12AWG. ~ 80 A x 1.7 Ohm/1000' x 100' ~ 14 v! Panel board to receptacle

    To get to the Caps you must go thru the xfmr
    It has limiting Z a 500 Va may have 1.5 Ohm or more. Plus it's L limits inrush current.
    My point, between line, recept., xfmr, etc. you likely have 2-3 Ohm, so shorting the xfmr sec you may draw 40 A.

    imo size the cable for 15 A (14awg iirc) you'll be fine for up to 500 W.
    It may be an NEC code violation to use larger in a 15 A receptacle. Maybe 12 in a 20
     
  4. Rick58

    Rick58 Forum Resident

    Location:
    Eagle, ID, USA
    Not gonna bother trying to explain or justify things, but I heard a positive difference with Shunyata Venom 3 power cord on my Parasound P 7 preamp. Got a Venom 14 for my new A 21 amp. Looking forward to hooking things up and eventually making some comparisons between stock and that cord.

    May get another for CD player eventually.
     
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  5. Rick58

    Rick58 Forum Resident

    Location:
    Eagle, ID, USA
    The Venom 14 has 14 ga conductors which are rated to the 15A current max draw of the A 21 but my other/older Venom 3 uses 12 ga conductors (but still only 15A rated connectors). I figure there is an advantage of using the 12 ga wire cord for the A 21 and use the newer 14 ga one on the P 7 preamp. Prob will use the newer 14 ga on the new A 21 for a while anyway, then swap around.
     
  6. jea48

    jea48 Forum Resident

    Location:
    Midwest, USA
    From an Audiogon thread

    [​IMG]
    atmasphere

    8,723 posts
    06-03-2014 10:46am
    Please do Ralph!
    Alright...

    "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."

    audiphile power cords | Audiogon Discussion Forum

    Power amps like, need, the AC mains voltage steady. Pushing an amp playing music with high dynamics you don't want the AC mains voltage fluctuating due to VD (Voltage drop).

    .
     
  7. Rick58

    Rick58 Forum Resident

    Location:
    Eagle, ID, USA
    I’ll let others debate or whatever but If the ends of your power cord get warm after a while, you know you have a problem!

    I’ll say. Same with the wire itself. I don’t think with the Shunyata cords I’ll have any such issues.
     
  8. Ingenieur

    Ingenieur Just a dog looking for a home...

    Location:
    Back in PA
    Another angle:
    1000 W amp driven to 500 W
    8 Ohm resistor
    sine wave input
    I = sqrt(500/8) = 8 A
    V = sqrt(1000 x 8) = 63 V
    P = 8 x 63 = 500 W

    If we put a continuous signal into the amp what will the line current be?
    500/120 = 4.2 A (assume 100% eff) constant

    Power in W = Joules/Sec or joules
    = Sec x power
    A 100 Hz wave is 0.01 sec long uses
    0.01 x 500 = 5 Joule
    If freq = 10,000 Hz ~ 0.00001 Sec
    0.00001 x 500 = 0.05 Joule
    The power caps on this monster may be 500 J at 80 v
    the time constant may be 0.20 sec or less

    Using the 100 Hz example we use 5/250 = 2% of the charge per o.01 Sec wave
    The caps can recharge 65% in 1 tc or 0.2 sec
    The constant signal uses 0.2/0.01 x 2% = 40% of the caps charge but during that time it can be recharged 65%. The DC voltage also drops, this is the balancing act the designer juggles. The cable is part of his design and not the limiting factor imho.

    In other words the caps are almost always charged greater than 90% because nominal average power may be 10-20% of the amps rating so the caps can easily keep up so you never have a huge inrush current.
     
    Agitater likes this.
  9. head_unit

    head_unit Senior Member

    Location:
    Los Angeles CA USA
    OR, we are all in someone else's head o_O
    I feel coming on a conflation between cable swaps and those physics experiments where the results change if there is a conscious observer...
     
  10. head_unit

    head_unit Senior Member

    Location:
    Los Angeles CA USA
    To quote King Crimson: "De-fek-tive" :p
     
    Ingenieur likes this.
  11. Ingenieur

    Ingenieur Just a dog looking for a home...

    Location:
    Back in PA
    You will have far more voltage drop thru the utility transformer, service drop, branch ckt to the receptacle than 6' of cord. Period.
    The NEC has no v drop code, but recommends 5% from service xfmr to load receptacle.

    If you draw 80 A the V drop on a long 12 AWG 20 A ckt may be 12%+ or 15 vac. The cord if 14 AWG and 6' will be 12/1000 x 2.7 x 80 = 2.6 vac
    But you will never see 80 A

    if a 3 V drop cost 30% of an amps rated power you have other issues.
    They can supply up to -10% or 108 vac

    the rectified voltage = 2 x Sqrt2 x Vrms/(2 x Pi)
    0.9 x Vrms
    That is where the caps will float
    Vrms is the xfmr sec not the recept.

    page 8 table 3.2
    https://www.entergy-louisiana.com/u...on_standards/2008/power_quality_standards.pdf
     
    Gibsonian and Agitater like this.
  12. jeffmackwood

    jeffmackwood Forum Resident

    Location:
    Ottawa
    If you would like to explore that subject matter further, I highly recommend Lee Smolin's book: Einstein's Unfinished Revolution: The Search for What Lies Beyond the Quantum (2019). While I have not yet bought into Smolin's own theory (that he puts forth in the latter part of the book) his very thorough analysis of just about any even partially-credible theory put forward to date is fascinating. I admit to having to re-read many sections in order to fully grasp what was being said. At the very least it's a great exercise in brain elasticity! :)

    Jeff
     
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  13. chipcalzada

    chipcalzada Forum Resident

    Location:
    The Philippines
    @Orbe I've had good results with trying different power cables on my Cayin amp as well. I don't know if its the power supply design of Cayin but its quite responsive to changes in power cords, there were noticeable differences between different brands that I tried (Audioquest, Nordost, XLO and Furutech). This is my subjective opinion and I made no measurements whatsoever.
     
    Rick58 and Orbe like this.
  14. rpd

    rpd Senior Member

    Location:
    Nashville
    Oh my goodness
     
  15. rpd

    rpd Senior Member

    Location:
    Nashville
    I’d love to see you guys put $10,000 up in your ability to hear this stuff. I bet we’d get a whole lot of different “opinions”....
     
  16. jea48

    jea48 Forum Resident

    Location:
    Midwest, USA
    Constant continuous load? That wouldn't be a real world example for a power amp.

    Show what's happening to the AC mains current draw and AC line voltage when a power amp is being pushed hard playing music with high dynamics. The power amp is not drawing current at a steady constant rate.

    Example, playing Deep Purple, 'Machine Head' album pushing a power amp hard can you calculate the AC mains current draw by the power amp's power transformer and the DC power supply as the DC caps in the power supply are recharging?

    Power amps like, need, the AC mains voltage steady. Pushing an amp playing music with high dynamics you don't want the AC mains voltage fluctuating due to VD (Voltage drop).

    .
     
  17. rpd

    rpd Senior Member

    Location:
    Nashville
    What’s going on between the power plant and the fancy mains???
     
    Tom Hakala likes this.
  18. Orbe

    Orbe Forum Resident Thread Starter

    Location:
    Guernsey uk
    This is not a very expensive cable it’s cost works out at just over 6% of what I paid for the amp. I can not explain the difference in sound but to me it is worth every penny.
     
  19. Tullman

    Tullman Senior Member

    Location:
    Boston MA
    He blinded me with science.
     
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  20. Tullman

    Tullman Senior Member

    Location:
    Boston MA
    You’d be surprised, some people know what to listen for. Gambling is a different matter.
     
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  21. Ingenieur

    Ingenieur Just a dog looking for a home...

    Location:
    Back in PA
    If you want to go BIG get one of these.
    Power issues almost eliminated
    Page 36
    2000 va, run a dedicated 10 AWG ckt to your gear. Filters noise, 3% THD, voltage regulation +/- 3%.

    while your at it have two 8' ground rods driven 8' foot apart and 8' from the existing and bond them all with 4 AWG bare copper buried 8" or so.

    https://stevenengineering.com/tech_support/PDFs/39MAIN.pdf
     
  22. Ingenieur

    Ingenieur Just a dog looking for a home...

    Location:
    Back in PA
    In my example it is.
    In real world it will modulate with the signal.
    But if the music requires 500 W
    You may draw (50% overall eff plus pf) 1000
    Or 8 A, not 80
    If the music requires 100 W, draw 200 or 1.7 A

    it only draws what is required limited by the impedance

    my MA6300 has a 5 A slow blo
    It will blow in 0.2 at 20 A, 0.01 at 80
    The branch CB May trip at 80 A in 0.1

    again, the drop from the utility, panel, branch will by MUCH more than the power cord, 10 or 20 times

    a good portion of transient power is reactive supplied by the caps (and most returned by the speaker coils)

    look at a speaker Z graph, it has Z magnitude and phase angle and is usually only resistive at a few Hz
     
    Last edited: Oct 6, 2020
  23. Archguy

    Archguy Forum Resident

    Location:
    Richmond VA
    What issues were not eliminated?

    Everyone should do some genuine blind A/B/X testing now and then. We did a bunch at my place before the covid struck. Very illuminating. Amps and preamps sounded wildly different from one another, while certain signal cables (ceteris parabus) ended up mutually indistinguishable. People thought they could tell the differences but they could not do so reliably. But it's hard to manage all the variables and come up with something trustworthy. Note: we did not compare power cables. Additional note: I like premium cables of all kinds.

    It's been said before, at any rate: 'different' is easy, 'better' another matter entirely.
     
  24. head_unit

    head_unit Senior Member

    Location:
    Los Angeles CA USA
    Yes, though it is hard to do truly blind. And many folks who believe they hear differences are vehemently reluctant to put that to the test. As I said in another thread, it is belief = RELIGION at the core of it (whether or not there is or is not anything physical going on which maybe we don't know how to measure yet).

    I bought a friend a pretty new Onkyo off Craigslist for $30 (!!) as a Hannukah present to replace an old Yamaha which was getting scratchy. We both agreed it had a fuller bass sound. Then again we did this
    Denon vs Parts Express, round 1
    and the results were surprising to say the least.

    Personally I am quite comfortable letting the engineer part of my brain say there won't be huge differences, buying good but inexpensive stuff like Blue Jeans, and not worrying about it further and instead spending the money on other things.

    I do want someday to get a good demo at a dealer and see for myself.
     
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  25. Ingenieur

    Ingenieur Just a dog looking for a home...

    Location:
    Back in PA
    The chart below show typical cap values for various power outputs.
    100 W ~ 40,000 uF
    Granted, a cap has a large inrush, but once charged it depletes little while playing, in addition the xfmr limits inrush (as it does sec short circuits).
    The rated output of my amp is ~25 V
    So let's say the DC rail is 30 to allow for v drop.
    A 40,000 uF cap can store 36 Joule
    A Watt ~ Joule/Sec or Joule = Watt c Sec
    Assume a peak of 140 W (the max my amp can do) and it lasts 0.1 sec, that is only 14 J
    The cap is 36, but much of that will be returned by speaker L and WILL NOT BE supplied by the utility, ie, receptacle, depending on frequency. But even so 36>14. So caps will recharge at the signal zero crossing.

    if the total R (cord, amp internals, etc.) is 1 Ohm, time constant is 0.04 sec, meaning in 0.1 sec it can recharge 92% of capacity, but it only drained 14/36 or 40%

    people can spend their $ as they choose, obviously, but all I am trying to do is inform
     
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