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.


Yes, I was referring to the internal resistance of the cart itself.  I'm running the cart through a SUT set at 30 ohms.  The " white noise"-like hiss is mainly through the tweeter and only becomes audible as volume is increased near the peak of my listening range.  It doesn't change much if I adjust the gain over a 22dB range nor does it change with different loadings.  When I bypass the SUT and use the MC input on my phono stage I still get the same hiss.  I used to have a HOMC (2.0mV) cart and it didn't produce any hiss at all through the same phono stage.  I'm wondering if a ~0.5mV cart would pretty much eliminate the issue.  It just seems to be related to the gain needed on the 0.28mV cart in my system.

Good suggestion.  I disconnected the leads from the cart and I still get the same white noise type hiss.  I have a Herron VTPH-2A.  I'm wondering if it could be a bad tube issue.  I think I'll send Keith a note and see what he thinks.

Other ideas?
I have a zyx with just 0.24mv output.
I can hear no more background noise with that than a 0.4mv Scheu or a 2mv mm cart So I would not have thought it was the cart output vs gain in itself.

Sounds like something in the phono from your last test.

Agreed on the phono stage.  I sent Keith a note and I'll see what he thinks. 

I have a Herron VTPH-2 (not the -A version), in the low gain configuration that is most commonly used (64 db gain for LOMCs). I use it with a 0.5 mv cartridge, an Audio Technica AT-ART9. I find it to be incredibly quiet.

0.5 mv is only about 5 db greater than 0.28 mv. So assuming those specs are accurate and are defined on a consistent basis, if I were to go to a 0.28 mv cartridge I would be setting the volume control on my preamp 5 db higher than I presently set it. Based on experiments I have done I can say with total confidence that were I to do so there would be zero perceivable hiss, even if I were to listen with my Stax electrostatic headphones firing directly into my ears.

So either:

(a) the VTPH-2A is a bit more noisy than my VTPH-2 (which I doubt), or
(b) something in your VTPH-2A is not performing optimally, or
(c) noise is being introduced somewhere in the signal path between the output of the phono stage and the volume control in your preamp or integrated amp. Perhaps by the circuitry at the front end of the preamp or integrated amp, or perhaps as a result of a ground loop between the phono stage and the preamp or integrated amp.

Also, on a typical single-turn rotary volume control a 5 db change probably corresponds to something like 35 to 45 degrees of rotation, assuming the control is not being used at relatively low settings (where volume changes occur more rapidly as a function of rotation). So regarding ...

I’m wondering if a ~0.5mV cart would pretty much eliminate the issue.
... If your preamp or integrated amp has a single-turn rotary volume control just turn it down from the settings you usually use by around 35 to 45 degrees (or less if you typically use the control below say the 10 o’clock position), and that will give you an idea of how much the hiss would be reduced if you were to go to a 0.5 mv cartridge. Again, assuming the specs are accurate.

Finally, regarding ...

I disconnected the leads from the cart and I still get the same white noise type hiss.

This is not really a fair test of the noise performance of the phono stage. A fair test would require either shorting the input of the phono stage, or at least terminating the input with a low impedance. (That may be particularly relevant in the case of the Herron phono stages because of the ultra-high input impedance of their LOMC inputs, if loading plugs are not used). See the following writeup, although it involves completely different equipment:

Best regards,
-- Al