Tweakers' Asylum

RE: Test for dirty ground?

71.222.169.194

kenster

In Reply to: RE: Test for dirty ground? posted by Jayme on September 17, 2007 at 12:15:09

To really get a handle on your AC quality, U need an O-scope or U could borrow a noise sniffer from The Cable Co. which will audibly tell U how much garbage is on your line.

Without AC regeneration, or a line stabilizer, U are at the mercy of your local power Co. for AC stability but when it comes to noise, there are a myriad of products that deal with line/GND noise.
Some research/recommendations would be in order here.

Cheers,

~kenster

http://www.audioprism.com/noisesniffer.html (Open in New Window)

Follow Ups:

Yes, our AC mains are 'dirty" indeed. - cheap-Jack 13:39:59 09/17/07 (3)
Hi.

I tested it with a wideband powerline & EMI noise analyser which reads out the the levels of the dirty stuff riding the AC mains.

From its built-in loudspeaker, I also hear radio broadcasts coming out from the wall outlets in a few different domestic locations powered via different hydro companies !!!

Go figure how dirty are our powerlines!

c-J
- Filter Low Frequencies? - Jayme 15:32:16 09/17/07 (2)
  I believe I might have a Low Freq oscillation (1 to 5Hz) of at most 2V riding on my Line.
  
  Would a high-pass filter (series cap with shunt resistor or shunt choke) work to eliminate it? Would I put such a network before or after the mains transformer? Or is that just crazy thinking?
  - How you measure such LF oscillation on the powerline ? - cheap-Jack 08:18:15 09/18/07 (1)
    Hi.
    
    Frankly it's news to me when you replied my post in the Tube/DIY forum
    that LF oscillations (i.e. "motor-boating") still occur even when all the tubes (including the retifier tube) of your amp are pulled out !!!
    
    How can this happen? Where comes the LF energy to move the speaker cone?
    
    Any powerline craps must go through the amp first before going to the loudspeaker. But you said there is no amp as the power amp is not working (with all tube pulled out)?
    
    It doesn't make sense to me. Bud.
    
    I'd address to the powerline filter issue later once the mysterious motor boating on the speaker cone is resolved.
    
    c-J
    - RE: How you measure such LF oscillation on the powerline ? - Jayme 17:49:01 09/18/07 (0)
      I meant just the preamp signal tubes are pulled. The rectifier is of course still in, as are all the tubes in the amp itself.
      
      Check the schematic in that same thread. There are "safety" resistors which tie the B+ to the output just in front of the output coupling capacitor. When the output tubes are pulled, the PSU noise is directly coupled to that output cap, and the LF oscillation looks like LF signal.
      
      And, I am measuring the AC at the wall with a couple multimeters, both a digital and analog DMM. I can watch the needle wiggle, and the digital meter seems to track up and down in a periodic manner with about a 1 second period.

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