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ground-loop problems

Discussion in 'Electronic Repair' started by William Sommerwerck, Jun 9, 2009.

  1. I'd like to thank everyone who took the time to respond to my question. I
    was particularly appreciative of those that told me about noise & grounding
    problems I've never even heard of.

    I'm not quite ready to put everything on one circuit. So I'm going to call
    both Parasound and Pioneer to see what insights, if any, they have to offer.

    Again, thank you-all for your help.

    PS: As for balanced cables being an OTT solution for home installations... I
    have five power amps, four of which sit next to the speakers they drive.
    Given the distances, and the fact that the amps draw significant current,
    and some are on different circuits, it would not be a good idea to use
    unbalanced cables.
     
  2. I'm not quite ready to put everything on one circuit. So I'm going to
    Should be -- but isn't. Each device has its own ground. Each ground may have
    a slightly different AC potential. This is the cause of "ground loops" when
    you connct the devices.

    All the equipment in my system is transformer-powered. That, in and of
    itself, does not prevent ground loops.

    You're fortunate to have no problems with 80' runs. Professionals use
    balanced lines for a good -- it avoids problems.
     
  3. You're fortunate to have no problems with 80' runs. Professionals use
    I've never experimented with single-ended and balanced installation, using
    the same equipment, so I can't speak from experience. However, balanced
    inputs and outputs have become common in "good" equipment, partly because
    they add little to the cost, * and partly because -- especially in A/V
    systems -- they make things easy for the manufacturer and dealer.

    In a system where the amplifiers don't sit right next to control unit (qv,
    my system), the designer & installer don't have to worry about hum and
    interference. The customer isn't going to be happy if the dealer has to do
    extensive troubleshooting to get rid of noise, or (worse) if the house has
    to be rewired to reduce the inter-component ground potential.

    I remember, ca 1978, installing a relatively simple Crown system in an
    equipment rack. We had all kinds of grounding problems. Some of this was
    probably due to the Crown equipment itself (surprising, because the same
    products were used professional), but we wound up have to completely isolate
    the units from the rack. This involved wrapping the screws in vinyl tubes,
    and using faucet washers to lift the ears away from the rack. Our first
    attempt used black washers, which contain carbon and are conductive. These
    were quickly replaced with non-conductive red washers.

    * Nor are there any additional electronics.
     
  4.  
  5. <lots of interesting stuff snipped>

    The issue -- in my mind -- is the distinction between "mains" (AC) ground
    and audio ground. They're not the same -- at least, not in the U S of A.
    This is why it's possible, on devices with three-wire power cables, to
    sometimes reduce the hum by lifting the ground on one and "rotating" the
    plug. Indeed, the Parasound power amps have a "ground lift" switch on the
    back.

    I've spoken with Magnolia and Pioneer, and neither had the "Aha!" response I
    was hoping for. I'll call Parasound today and ask them.
     
  6. The issue -- in my mind -- is the distinction between "mains" (AC) ground
    here.

    Not that I know of. Only power tools (and similar products) are
    double-insulated.

    This is common experience, not something I've made up. I'm sure other people
    in this group can report similar stories.

    Could we agree to drop this discussion for the time being, until we can find
    a /real/ expert on grounding?
     
  7. Could we agree to drop this discussion for the time being,
    Well... <ahem> Balanced inputs and outputs have been common on the "better"
    audio equipment for around 20 years. They're particularly desirable if
    you're a nut about fully balanced circuitry. And you pay for them whether or
    not you want them.

    Balanced ins and outs became really popular with the introduction of the A/V
    system controller, precisely because they eliminate, a priori, grounding and
    hum problems, without adding a lot of money to the system's cost.

    I previously owned Brand K electronics, which were fully balanced, and I
    never had hum problems. I could crank the volume all the way up, well past
    normal listening levels, and the system was dead-quiet (other than through
    the phono input). Why would I want to use unbalanced lines?

    Balanced cables cost only a little more than unbalanced cables. Unlike RCA
    plugs (which should have been banned decades ago), they rarely pop loose,
    and you can plug and unplug them without getting a "big blast o' hum". *

    * The better RCA cables have "long" collars, so the ground is made before
    the hot side when plugging in, and vice-versa when pulling the cable.
     
  8. This is precisely the kind of discussion I did not want this question to
    devolve into.

    I don't understand why you think an audio system with components separated
    by 20' or more, and connected to different power lines, can be wired with
    unbalanced interconnects, on the naive assumption that there will never be
    any problems with hum or noise.

    For what it's worth, all my prior systems had the power amps sitting next to
    the preamps. The components were connected with unbalanced cabling, and I
    never had problems with hum, noise, etc. Nor did it ever cross my mind that
    any of these systems would be "better" with balanced wiring.

    My Parasound components -- and the Apogee electronic crossovers -- have both
    balanced and unbalanced inputs and outputs, and can be freely connected as
    desired. Other than the fact that balanced cables cost slightly more than
    unbalanced -- why would anyone in their right mind use unbalanced cables?
    Balanced cabling is in every way "superior".

    I'm friends with the manager of the Bellevue Magnolia. I'll ask him what
    their installation department's opinion on this matter is, and /why/ they
    hold that opinion (whatever it might be).
     
  9. For what it's worth, all my prior systems had the power amps sitting
    This is not correct. Changing the circuit from an unbalanced input or output
    to a balanced input or output does not add a gain stage.

    The power amps were designed by John Curl, one of the "inventors" of
    full-complementary push-pull amplification. I will ask him what topology the
    Parasound A21 uses.

    The tuner does, but I use the unbalanced outputs. We were talking about
    power amplifier connections, anyway.

    This is common. It is not generally considered poor design.
     
  10. If your equipment is designed for balanced operation it's quite
    BIG WHOOPS! I wrote that in a rush.

    Balanced inputs are commonly converted to unbalanced by grounding one
    side -- to the SIGNAL ground (that is, zero volts in an amplifier with a
    balanced power supply), NOT the mains ground.
     
  11. Don't forget about capacitive coupling between the windings in the
    mains transformer. Depending on transformer geometry, the coupling might
    be stronger to one mains lead than to the other. So it is advantageous
    to make the stronger coupled one ground.

    Regards,
    Michael Karcher
     
  12. Well they can't be 'better' since you're introducing extra electronics
    bang... bang... bang... bang... [sound of William Sommerwerck banging his
    head against a concrete wall] bang... bang... bang... bang...
     
  13.  
  14. Balanced inputs are commonly converted to unbalanced by grounding
    [More loud and anguished head-banging from yrs. truly.]

    I "know people". I'm going to find someone who's a legitimate expert on
    audio grounding, and try to get some sort of definitive answer.
     
  15.  
  16. David Lesher

    David Lesher Guest


    The Apollo 11 landing was almost aborted by such an issue.

    The LM guidance computer was fielding all kinds of high priority data
    from the landing radar and control inputs. It was also, unbeknownst to the
    crew, also looking at the rendezvous radar as well. [This so an immediate
    Abort to Orbit could be accomplished; if the landing was abandoned.]

    If the 2nd radar saw nothing, great, no data. BUT as it happens, it ran
    off a different phase of the LM power system, and the little big of noise
    between it and the landing radar was enough to be noticed. As a result,
    the computer started spitting out 1201 alarms, which was palnned for &
    acceptable, but disconcerting to everyone involved.

    <http://history.nasa.gov/alsj/a11/a11.1201-pa.html>
     
  17. GregS

    GregS Guest

    No, but you can have 180 degree in phase situatuion
    between the split 240 transformer, and have 240 volts potential going
    to the audio setup. I always like to use only
    one leg of the transformer split out on the pole or one breaker. In my opinion
    there is a chance of more problems using both sides of the transformer
    allthough some audio installations use a split transformer to
    reduce posible noise. So its all in how you look at it.

    greg
     
  18. GregS

    GregS Guest

    Really, if you feed two equipment from a separate
    breaker, one on one side of the 240 volt transformer
    and one on the other, with the transformer center tapped
    and becoming neutral, the two sides of the voltage
    cancel. Or at least the possible electrostatic
    charge is neutralized to zero. But that
    would onlt seem to work if both pieces of equipment
    had identical power supplies in every respect.

    greg
     
  19. David Lesher

    David Lesher Guest

    The UK has very different wiring than the US.

    Here, a standard circuit is 120v/20A or 2400 watts [at unity PF...]

    In the UK; ring wiring supplies 240v/30A, or 7200 watts. Plugs
    have internal fuses based on the device.

    (The US may well have a 240V/20A outlet for an air conditioner;
    where it's 120-N-120.)
     
  20. So what is the UK philosophy in this regard?
     
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