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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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almarg's avatar
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almarg
9,670 posts
 
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

uberwaltz's avatar
uberwaltz
13,381 posts
 
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?

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three_easy_payments OP
2,097 posts
 
@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.
three_easy_payments's avatar
three_easy_payments OP
2,097 posts
 
@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.
chakster's avatar
chakster
6,144 posts
 
Tubes can be noisy and microphonic, they can also be expired, they do not last forever. As for the 12AT7 i would recommend NOS Sylvania Gold Brand with Gold Pins - this is amazing tube with moderate price for a NOS. A tube phono stage owner must have a bunch of backup tubes, an issue like this is one of the reason i would never use a tube phono stage myself. But when i’ve been using a tube amp i quickly realized than some nice NOS tubes (like those Telefunken, Sylvania, Matsushita) are always better than any new tubes, the difference is sound is huge. So it’s always an open question, endless tube rolling.
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