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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typo...should have said " I realize moving to a slightly HIGHER output cart could very well reduce the hiss."....since I could probably use less gain to obtain same volume.
By the terms "8 ohm" and "12 ohm", I presume you refer to the internal resistance of the cartridge itself.  Yes?  If so, what is the value of the load resistor in your phono stage.  If the value is anything above 100 ohms, the answer likely would be "no difference".  But it also depends upon what is causing the hiss.  There are a few different sources of noise that might be described as a hiss.  So your question is not very specific.
The hiss from your cart is small compared to phonostage.  One easy way to tell is to listen to hiss with and without cart - I guarantee one will be much greater... 
Also, loading resistor is not important, as it gets shunted by cart during normal operation.  A 47k load is just as quiet as a 100 ohm load once a 10 ohm cart is attached... 
@lewm 

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.
@hagtech 

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.
@uberwaltz 

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

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:

https://www.sounddevices.com/microphone-preamp-noise/

Best regards,
-- Al

@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.
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.
@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.
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.
Both my phono-pres have 4 amplification stages. Basis Exclusive
max. is 71 dB, Klyne 3,5 ; 67 dB. The ''sense'' of 4 amplification 
stages is to use the lowest possible for a given cart because the
''higher amplification the higher distortions'' (hi Raul). 
Herron, according to uberwaltz , produces ''2 flavours'' instead
( 64 and 69 dB).  ''Hiss'' may be other expression for distortion?

Three, go here   http://www.tubeaudiostore.com/tubes.html.
Some tubes are much better than others. Roger sifts through hundreds of tubes and categorizes them as regular, low noise and super low noise.
I changed the three 6922's in my ARC phono amp for Roger's Super Low Noise tubes and my noise level dropped at least 6 dB. Very impressive. The tubes are now 6 years old and still going strong. 

Mike


@mijostyn   Thanks for the link on tubeaudiostore.  I've never ordered tubes from him but those Super Low Noise tubes sound compelling.  Although super low noise certainly comes at a price!
Thx for that link Mike
I am on the lookout for some more tubes for my Chinook but very wary of eBay sellers and some of their claims.
Will give Roger a trial.
Yes, they are pricey but every last one I have gotten from him has been super quiet, 6 so far. They test each tube individually on a tester I think Roger actually design. Clio works for him. Earth to Clio! Want to chime in?
I did not realise it was "that" Roger ... Lol.
Just had email reply as did not see 6922 sln tubes online but he has them at $90 each.
Times 4.
Ln are $70 a pop.
Wth, it's only money.
You have to pay to play
Yup, that Roger. Hope you like them. They made a big difference in the noise level of my ARC and lower noise means better sound in some respects. They work so well I have not felt the urge to change phono amps ever since I started using Roger Modjeski's (hope I spelled that right) tubes. Go for the SLN tubes. It would cost you a lot more to get a quieter phono amp!
Enjoy,
Mike
Just to note that running the phono stage with no cartridge connected is very likely to produce volume control dependent levels of hiss. Most of our phono stages will behave that way.
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


@intactaudio 

Thanks for your thoughts.  My own troubleshooting suggests the same culprit - noisy tube in the gain stage.  Upon setup I had addressed other issues you identified including placement of the SUT (which was sensitive to proximity to toroidal transformers) and by using a very well shielded cable between the SUT and the phono.  I tried several cables and I'm getting the best performance from an AQ Colorado with its active noise suppression.  It beat out some shielded Cardas cables I had.

I'm left now with no buzz or hum.  I also don't think the SUT is contributing to the "white noise"/tube rush.  It's exactly the same even when I remove the SUT from the chain and run the cart leads directly to the MC inputs on the phono.  Noise appears to be equal in level on both channels.

I'm just waiting to hear back from Keith before proceeding further.
I realized I had a spare pair of Mullard 12AX7's from a preamp I sold, so I started experimenting a bit this evening.  The long and short of it is that I've ruled a bad/noisy tube as the issue.  I swapped the Mullards into the 1st gain stage - exact same white noise at very high volume when stylus hasn't touched the vinyl; again, the noise goes away once it touches and this volume level is really louder than I'd ever listen.  I then replaced the original tubes into the 1st gain stage and used the Mullards in the 2nd gain stage (which actually increases the gain by 5dB as they're replacing a pair of 12AT7's).  Same exact white noise under same volume conditions, albeit a bit louder just because of the gain.  I then used one of the removed 12AT7's from the 2nd gain stage and swapped the output stage 12AT7.  Again, same result.  I then replaced all tubes back into original configuration - the sonics are actually best that way, unsurprisingly.

So I now suspect this is an RFI issue with the cart/cable relationship.  I see there are no shortage of threads on this forum about RFI and phono.  Again, this really isn't a huge problem and perhaps I should stop obsessing over white noise hiss that only is audible when the volume is cranked with a LOMC cart before the stylus ever touches the vinyl.
I doubt RFI three. All the original tubes in my ARC were noisy. The SLN tubes if I remember correctly are 1 in 100! But it could be just inherent noise in your phono section. It does not seem that bad according to your description. The best thing to do might be nothing rather than spend money chasing your tail. My own rough test for phono noise is if I can hear it between songs over the background noise of the blank groove I'll go after it. If not it won't matter.
@mijostyn  I'm thinking you're right and I do feel like I'm chasing my tail for no good reason.  I think this is likely normal noise in the phono section and perhaps I could lower it slightly buying a set of Roger's super low noise tubes but I'm wondering if the juice is worth the squeeze.  Noise isn't audible from listening position and goes away entirely when needle hits the record.  I suspect anyone with a LOMC and a tube pre will hear some white noise hiss if they crank up the volume before the needle hits the vinyl.
Op.
If you are talking levels that are only vaguely audible with ear pressed hard against speaker then I would say I might have the very slightest hiss at about 80% volume.
This is so slight though but I could even be imagining it.
Seated, needle in groove, anything at sane volume level..... Deathly Hallows quiet.

This is with a Chinook tube phono.
Running through a Denon au320 sut prior to it.

I would relax and sit back and enjoy.
Maybe think about the sln tubes at $90 each......
@uberwaltz  Agreed.

What do you guys think...if I wanted to perhaps try just a couple of the SLN tubes to see if they start to lower noise where would be the best place to start?  As follows:

1st gain stage (pair)
2nd gain stage (pair)
output stage (single)

It would be nice to just dip my toe in the water to check for improvement w/o making a financial commitment for all 5 SLN tubes at $95/ea.  Where would the biggest improvement most likely be heard?
Whatever you decide, keep in mind that all tubes change noise characteristics as they age, and the curve for increasing noise as tubes go from SLN to not so SLN is not predictable from tube to tube. So SLN tubes are a crap shoot wherein the game is rigged against you. No aspersions on RAM tubes are intended; it just is what it is.
If you really want to learn more about tubes you’d better read Tube Assylum forum, some folks like are crazy about tubes and tried almost everything and they are not sellers. I spent a year on this forum just reading and making notes. If you’re in America then vintage Sylvania Gold Brand (Gold Pins) 12at7WA is superb even compared to my Telefunken ecc801s.

The best tubes are NOS Military Grade, they last much longer, they are stable, low microphonic and very quiet. None of the new 12AT7 or 12AX7 can beat them. Tube rolling is fun, but very expensive.

Look for NOS tubes, save for NOS tubes.

I don’t know much about 12AX7, used Soviet tubes in my Luxman amp for a short time, but 12AT7 was in my WLM Minueta amp for many years and i’ve been looking for cheaper alternative of Telefunken ecc801 (very expensive), i found Sylvania 12at7WA and Matsushita 12at7WA (gold pins) amazingly good.
I have the vtph-2a and with needle off, volume cranked, ear a foot away from speaker, I certainly hear white noise. When I drop the needle nothing except some very loud tunes and some extra clicks and pops. At volumes I typically listen at, nothing with my ear next to the speaker. With a tube phono pre and tube integrated, I'd expect some noise when the gain cranked and needle is up. I think you are gtg..  My tube rolling experiences with the Herron is - I prefer Keith's tubes every time! 
... if I wanted to perhaps try just a couple of the SLN tubes to see if they start to lower noise where would be the best place to start? As follows:

1st gain stage (pair)
2nd gain stage (pair)
output stage (single)

While I'm not familiar with the internal design of the VTPH-2 or 2A, and I've never taken the cover off of my VTPH-2 (having seen a number of past comments which like Jmolsberg's comment above have described finding tube rolling to not provide much if any benefit to Keith's phono stages), my guess is that if you want to give it a try the first gain stage would be where to start. Especially if that is where the 12AX7s are used.  (I don't know if the 12AX7s are used in the first stage or the second stage).  

Since signal level is presumably lowest in that first stage any noise generated by that stage will degrade signal-to-noise ratio more than it would be degraded by a similar amount of noise generated further downstream. Also, it may be relevant that the 12AX7 has a higher intrinsic gain than the 12AT7. 

Good luck. Regards,
-- Al
You mentioned it may be a tube issue have you tried tapping the tube pins on countertop lightly or tap glass bottle with pencil eraser. I have same issue sometimes with my broken in or newly purchased NOS tubes. Some metal flakes can be on internals of tubes and can make a light hiss or even a horrible noises. I've always been amazed by just tapping a tube can make it dead quiet again.

@lewm
@almarg
@chakster
@jmolsberg I appreciate all of your really helpful feedback/input.

Three, if you are going to do it put them in the first gain stage.

Mike
Back in the early 1980's, I had a preamp with three M/C cartridge impedance settings.  My neighbor, the factory sales rep, change one resistor to give me a 10 ohm setting.  It got rid of the hiss.
dan, possibly you got that result, because a 10-ohm load resistance would result in a very severe high frequency roll off in the audible range, using almost any cartridge except maybe a very LOMC with a 2-ohm or lower internal resistance.  You threw out the baby with the bathwater, as the saying goes.  "Hiss" is probably at about 2kHz or higher frequencies, usually.
In case anyone is curious, Keith confirmed what I was hearing was likely normal.  He indicated :

"There will be some white noise if you turn the level up beyond where you would normally listen as the VTPH-2A has a lot of gain and you would not want to play music at those levels.If you notice a significant difference between the two channels left and right then you may have a noisy tube (most likely a 12AX7)." 
Thx for the update.
Sort of confirms what a few were thinking.
Good luck and enjoy your music!
@uberwaltz Yep!

Although I will say I've learned a lot over the past few days interacting with both Keith and Roger on this topic.  I'd be really curious to A/B a 6922-based phono stage in my system someday and see it how it performs.  Maybe something like the Manley.  But honestly, the music coming out of my Herron is joyful and a true bargain at its price point.  My money is being allocated towards vinyl over gear for the next 12 months at least ;-)
I am pretty happy with my Chinook.
It was a toss up between this and the Herron.
Had got as far as talking to Keith on the phone about the Herron.

However a storming deal turned up on a Chinook so........