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Phono Cart Impedance Question

I have a little bit of hiss through my 6 ohm, 0.28mV cart but only at a volume pushing the upper end of my listening volume...and it's only audible before I drop the needle, and even then not from the listening position.  I realize I therefore likely have a "non problem"!  

But I still have a generic question on to the sensitivity of producing hiss as it relates to cartridge impedance alone.  If one kept all other cart specs identical (including output of course) would you expect hiss to go up or down at the same volume and system gain if I used an 8 ohm or 12 ohm cart instead?  It seems like the hiss would likely go up just like moving to a higher impedance speaker under the same gain setup but perhaps I'm looking at this incorrectly? I realize moving to a slightly output cart could very well reduce the hiss.

Thoughts?   Sorry if this is a ridiculously obvious question and answer.

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Showing 1 response by intactaudio

intactaudio
293 posts
 
If I had to guess, the broadband hiss is from a noisy tube gain stage and since it changes with volume setting tubes would be a good place to look. Check to see if the noise is the same type / level in both channels and if there are differences swap the tubes left to right and see if the noise follows the tubes. Writing down some basic notes during this process helps a lot.

The noise types you typically get from a cartridge / SUT combo are:

  • low frequency line hum (50/100, 60/120) from EMI which can usually be modified by SUT / cable placement.
  • more of a buzzing sound that points to ground connections and use of an unshielded cable from the SUT to the phono input.
My test to see if any type of noise is an issue is to listen to an album side at what you would consider a loud level and then lift the needle and check to see if the noise is audible from the listening position. In general i find the line frequency stuff to be rather benign, the buzz to be unacceptable and the hiss tends to kill dynamics.

dave


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