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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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three_easy_payments's avatar
three_easy_payments OP
2,097 posts
 
@almarg

Thanks for weighing in. I too use the 64dB gain setup on the VTPH-2A. I suspect this is a noisy tube issue. I don’t think it’s a ground loop and there is certainly no 60hz hum. Just white noise at high volume. If I move the single volume knob on my line stage down by 35-45 degrees I’m pretty close to dead silent (no noise unless ear is almost on the speaker). I get no white noise using other components on my line stage and I even tried swapping the inputs around. I think we can rule out a line stage issue. Also I agree that it is doubtful that the 2A is noisier than the 2! I’m curious what Keith says but if I were a betting man I’d guess that I’m going to try swapping out some tubes. 

Btw - how much gain do you have on your line stage?  Mine is 10dB.
uberwaltz's avatar
uberwaltz
13,381 posts
 
Hold on a minute?
You said you are running through a SUT?
If so surely you should have the lowest gain engaged?
I too run a SUT for my MC carts through my Chinook but have gain set at 45db., 47k and 50pf.
I would opine 64db going through a SUT first is too much and quite possibly the cause of the hiss.
You are likely adding at least another 20db, possibly 24db at 30 ohm.

Sorry just reread where you state is same hiss even when you bypass the SUT.
But still running the SUT you would want the lowest gain available I would imagine in the Herron.
three_easy_payments's avatar
three_easy_payments OP
2,097 posts
 
@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.
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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