Tweakers' Asylum

• The main benefit of dedicated circuits is isolation. - Al Sekela 14:43:16 08/11/07 (2)
  In Reply to: RE: Another "decicated line" post - need a nudge to get going posted by CheapEric on August 10, 2007 at 06:24:52

  Audio equipment power supplies generate electrical noise on the AC power circuit, and any other equipment on the same circuit is exposed to this noise. Separate dedicated circuits reduce the coupling of noise among the components.
  
  With plenty of panel space, it should be easy for your electrician to run several circuits for not much more than the cost of a single circuit. In your setup, I would have separate circuits installed for the receiver, the CD player, the video gear, and the subwoofer (four circuits total). Adding more circuits for future expansion (such as preamp and monoblocks) is cheaper at the time and more expensive later.
  
  Hubbell does not have a good reputation for audio outlets. I would install Oyaide outlets on each circuit, in separate plastic boxes. Put a line conditioner on the video circuit, and choose one that will allow you to kill all the power to the video gear for serious audio listening. Line conditioners for the audio components are optional. I would use parallel filters that damp the lines, such as Quiet Lines, Alan Maher's products, or DIY Hammond chokes or R-C networks. A series filter on the sub's AC may benefit the main system if the sub uses a switching power supply.
  
  Be sure the video signal input is isolated. The separate earth connection for cable or satellite TV can be a source of annoying hum, and represents another entrance path for RF noise even if the ground loop is silent.
  
  

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  • A question or two about the filters you suggest, Al... - CheapEric 07:00:21 08/13/07 (1)
    In Reply to: RE: The main benefit of dedicated circuits is isolation. posted by Al Sekela on August 11, 2007 at 14:43:16

    Thanks, first, for your input Al.
    
    Something I noticed during last weekend was that whenever I turned the VCR on, and am not using the VCR tuner - i.e. using the TV to change channels, not the VCR - the picture from my bunny ears when down the crapper in a big way. The distance that my antenna is from the VCR is greater than all my other source components, so they are all in the VCR's sphere of influence. I'll start keeping the VCR unplugged until I need it: I don't need the clock anyway : ).
    
    I suppose the DVD player can be on the same circuit as the VCR, since there too both components won't be used at the same time.
    
    The filters, though, are what intrigue me. I must have missed many of the recipe posts, and then when I "search" there's been so much commenting on them that it's an exercise in futility finding the recipes. I'm aware of the Alan Maher products, will look up Quiet Lines, but the R-C networks and Hammond chokes I've read about are still a mystery to me. I'd hate to have everyone repeat themselves about those two subjects but if anyone is willing to go through the trouble of posting links or emailing me directly, I would greatly appreciate it.
    
    My video input signal is from the forementionned aerial that is in the basement nearby my equipment (that's isolated, right?). We might be getting digital cable soon, or we may improve on the aerial by getting a roof mounted array of some kind. Your idea of "too many circuits now" instead of adding more later makes sense there, since we'd add a decoder box for cable.
    
    As for the sub's power supply, I have no idea. I'll check the owner's manual. Again, "series filter"? Google's getting a workout later! : )
    
    As far as the Oyaide's are concerned, yeah, I agree. I would just rather upgrade a component for the same price... as I said - average equipment.
    
    Thanks, Al. Once again demonstrating why you're an asset to the AA.
    
    

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    • AC Filter basics. - Al Sekela 17:23:35 08/13/07 (0)
      In Reply to: RE: A question or two about the filters you suggest, Al... posted by CheapEric on August 13, 2007 at 07:00:21

      First, your experience with the VCR is similar to mine. We have a Sony VCR that we almost never use. When it is on, though, AM radio reception in the house becomes difficult. I'm not sure how much of the noise is placed on the AC, and how much is broadcast.
      
      Digital equipment generates RF noise, and when it is powered by AC, it puts some of that noise onto the AC line. This problem is so widespread that there are several manufacturers of packaged EMI/RFI filters that are designed into equipment. Corcom is one of them, and here is a quote from their FAQ:
      
      "The designers and manufacturers of digital equipment must concern themselves with RFI for two reasons: (1) Their equipment must operate properly in the application environment, often in the presence of significant levels of RFI, and (2) Their equipment must not emit RFI that interferes with RF communications often vital to health and safety. The necessity for reliable RF communications has given rise to legal regulations ensuring RFI control for electronic equipment. "
      
      Corcom and other filter manufacturers make a variety of packaged filters that reduce the level of high frequency noise on the AC line that gets into the equipment, and that comes out of the equipment. There are similar filters built in to many consumer surge protection power strips (look on the back for some text regarding "EMI/RFI").
      
      These have one or more stages of filtering that includes shunt capacitors and series inductors. In our audio discussions, shunt filters are called "parallel" filters because they go across the AC line-to-neutral (and may involve line- and neutral-to-ground). The current to the load is not impeded by any series element. "Series" filters do have elements through which the load current has to flow. The packaged filters include both types to obtain better noise reduction.
      
      Capacitors have impedance that goes down as the frequency increases. When placed in parallel with the AC line, they shunt high frequency noise while doing little to the 60 Hz AC. Inductors have impedance that goes up as the frequency increases. When placed in series with the AC line, they block high frequency noise while doing little to the 60 Hz AC.
      
      The simplest filter would be a single capacitor across the AC line. While this would reduce the amount of high frequency noise that gets into the load or comes out of the load, the reduction is only partial, and the low impedance at higher frequencies causes noise to be reflected.
      
      Adding a resistor in series with the capacitor seems counter-intuitive, since it increases the total filter impedance at all frequencies. However, the resistor dissipates energy from noise that would be reflected by a simple capacitor. This is the principle behind Quiet Lines devices. These devices work well in cases where the house wiring interacts with the filter capacitor to form a resonant circuit, or where the noise frequencies go high enough to allow noise wavelengths to fit within the house wiring.
      
      Series inductors have some inherent resistance in the wire from which they are made. This may diminish performance of some audio power amps, so the usual advice is to avoid filters with series elements in conjunction with power amps.
      
      All inductors have a self-resonance frequency, above which they act like capacitors. A large-value inductor such as the Hammond 193L choke, has a self-resonance around 5 KHz. The inductance, 5 Henrys, is large enough that the choke draws little current at 60 Hz. Thus, it makes a good parallel capacitor filter for higher frequencies when plugged in to the AC line. It is better than most real capacitors because the nature of the coil and core make it robust against power line spikes. Real capacitors have to be rated for continuous AC exposure to be safe. They have to be self-healing and not develop a resistive leak after a spike. This limits the capacitor types available to the X- and Y-rated types.
      
      There are two areas where filters are useful in audio. First is at the audio system, where parallel filters such as the Hammond filter or the Richard Gray Power Station (custom inductor built for the purpose), or other proprietary filters for audio applications, reduce existing AC line noise on the wiring. Second is at non-audio appliances that generate much of the noise on the AC wiring. In these cases, filters such as those in the surge protector strips or the better-quality packaged filters such as Corcom, are good. The resistance of the series elements does not harm the appliance performance, and improves the noise isolation.
      
      Placing R-C filters or Quiet Lines at unused outlets throughout the house may also be useful. How much they help at any given outlet depends on the proximity of the outlet to a noise peak within the house wiring. There are usually enough places that this can give audible benefit.
      

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