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.

128x128three_easy_payments
@uberwaltz   Sorry for the confusion here.  I meant that I have the lower output configuration of the VTPH-2A which is set at 64dB for MC (vs the 69dB configuration).  It's only 43dB in MM mode which is of course how I use it when running through the SUT.  I use the SUT with a gain setting to match the 64dB gain that I would get running through MC mode of the VTPH-2A.
how much gain do you have on your line stage?

My line stage/preamp is a DEQX HDP-5, which provides almost no gain. Actually less than 1 db with the internal jumper settings I use, and it would even provide negative gain if those jumpers were set differently. It is designed that way in order to allow headroom for the various digital signal processing functions it provides.

Also, my power amp (a Pass XA-25) has a lower than average gain of 20 db. However my speakers (Daedalus Ulysses) are very efficient, at 97.5 db/1 watt/1 meter.

On the DEQX volume is set by means of up and down buttons, rather than by a rotary control. When I listen to LP’s I typically have it set at around 60% to 70% of full scale.

I agree with your suspicion that the culprit in your case is most likely a tube that is a bit noisy.

Best regards,
-- Al

Thanks three easy!
Now I see how i misread it.
I fixated on the 64db part ... Lol.
I did not know the Herron came in two flavours of 64 and 69db.
Do you have any other tubes to try?

@almarg 

I'd like to hear your XA25 through those high efficiency speakers.  I'm running a XA30.8 through 90db speakers and suspect we are going after a bit of the same sonic profile.  Mostly acoustic jazz from the 50s/60s emanating from my speakers.
@uberwaltz   I don't have any extra tubes to try at the moment.  It takes 5 tubes - a combo of (2) 12AX7 with (3) 12AT7 or you can use (4) 12AX7 and just one 12AT7 to get the extra 5dB of gain.  Keith uses all EH tubes for this model so at least they are pretty cheap.