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Why the volume drop for this .5mv cartridge

This is somewhat related to the "Do I need a SUT" thread, but I didn't want to muddy that.

I've got two cartridges: an Ortofon 2M Black; a Grado Statement Master 1.  The first is MM with 5mv output, the second is MI with .5mv output.

My phono pre is a Rogue Audio Triton, with 40db, 55db, 60db, and 65db gain settings.  That feeds a Schiit Ragnarok which feeds some KEF LS50s.  The Ragnarok appears to have a linear volume control.

I have the phono pre's gain set for 40db with the Ortofon, and the ideal listening volume is with the Ragnarok's volume control set to "12:00".  With the Grado, I have the gain set for 65db and to match the output volume of the Ortofon for the same material, I've got to set the Ragnarok's volume just short of "3:00".

Robert Harley's "Taking the Guesswork out of Phonostage Gain" offers an algorithm that puts the ideal gain (for 1v output) for the Ortofon at 46db and for the Grado, 66db.

The  "KAB PHONO PREAMP PARAMETER COMPUTER" puts the gain for the Ortofon and Grado at 36 and 56, respectfully.

It seems like Harley's offering better matches what's going on in my system, as 55db is just too low for the Grado and my amp.

To my naive mind, I would think that if I have the phono pre's gains matched to the output of the cartridges, I should have the same output volume to the Ragnarok, and thus the same volume level settings from the amp.  Capacitance and resistance loading is the same for both (50pf and 47k).

Am I missing something?  This is relevant as I prefer the Grado, but I'm just about out of headroom with that amp.  I'm wondering what's wrong - my Grado, my phono pre, the Ragnarok, or my thinking.  Or some combination thereof.

I don't recall that the output volume difference was this great on the Sphinx that the Ragnarok replaced, but I may not be remembering correctly (probably 18 months ago).  The Rag's input impedance is 10k, and is set to the highest output gain (26db).




128x128tlainhart
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tlainhart's avatar
tlainhart OP
5 posts
 
@folkfreak @almarg (Al) - thanks for the education. 

I get it now - I didn't realize that there wasn't any real preamp gain.  I assumed (without knowing anything) that since the Ragnarok had preamp outs, that there was something of signficance there, gain-wise.

Looking at Schiit's other preamps, I see that their Sega has "1" for gain output, and the Freja has "14db" for their tube stage.  Rogue Audio's preamps seem to have between 10 and 14 db for line-level gain.

Thanks again -- Todd

almarg's avatar
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almarg
9,670 posts
 
Tlainhart, re 5 cm/sec, note in my post from 7-4-2012 which I linked to earlier that 5 cm/sec can mean two different things, which differ by 3 db.

Re 26 db of gain being too low, note that I said 26 db is "very low for an integrated amp." The Vidar is a power amp, and as Folkfreak indicated earlier 26 db is a typical gain for a power amp. Also note that the 28 db figure for the Parasound Halo integrated applies to its power amp section. A separate figure of 10 db is presented for the gain of its preamp section, so its total gain is 38 db. As you’ll realize that is 12 db more than the gain of your Ragnarok.

Generally speaking gains provided by integrated amps tend to fall in the area of 36 to 40 db or so, which approximately corresponds to the sum of the gains that would typically be provided by the combination of an active preamp and a power amp.

Using a phono stage whose gain is appropriate for a particular cartridge in combination with a low gain integrated amp and a low sensitivity speaker can be expected to result in the volume control having to be used in the upper part of its range, as you’ve found with the Grado. As Folkfreak indicated, what is surprising is that the same issue doesn’t arise with the Ortofon. But as long as you never find yourself wanting to turn the volume control higher than its max setting, and you are happy with the sonics (as you appeared to indicate), as some of the others have said there’s no need to take any further action.

Regards,
-- Al

folkfreak's avatar
folkfreak
1,349 posts
 
@tlainhart 1V is the rated input to drive the Ragnarok to full output - note how in the specs here they are all referenced to 1V input. As I noted you are in effect using a passive pre into the 26dB power amp stage so getting no real preamp gain
http://www.schiit.com/products/ragnarok
tlainhart's avatar
tlainhart OP
5 posts
 
Thanks all.  I'm happy keeping the amp with the range I described - just trying to understand the difference between the phono pre out for the different cartridges, which I assumed would be normalized with the appropriate gain setting.

@folkfreak - I'm not understanding your comment that the Ragnarok's pre wants to see 1v incoming.  I would expect the phono-pre to do that, with the gain adjusted per Harley's calculations.

I'm understanding from your post that there's enough variance in real cartridge output from spec that it may be that 65db really isn't enough for the Grado - e.g. perhaps the Grado is putting out .3 or .4.

@almarg - I've read the thread you referenced - thanks for that.  I believe that my Grado is putting out .5mv @ 5cm/sec.  While I can't find the "5cm/sec" clarification for my model, the latest model is using that qualifier, so I'll assume the same for mine.

You lost me on "4" though.  Although the Ragnarok is capable of putting out 100w, 26db of gain might be too low?  I looked at Schiit's Vidar power amp, which puts 200w into 4 ohms, and that's listed as putting out 27db.  Parasound's Halo Integrated says 28db for 240w into 4 ohms.


yogiboy's avatar
yogiboy
5,701 posts
 
As long as you get sufficient volume at the 3:00 setting you should not worry about it.  IMO, you are better off with the volume control when it is in the upper range than the lower range of the amp!
almarg's avatar
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almarg
9,670 posts
 
Excellent comments by Folkfreak, with which I agree entirely. Some further comments:

1)There are two ways in which cartridge output ratings can be defined, and unfortunately manufacturers usually do not indicate which one their spec is based on. See my post dated 7-4-2012 in this thread. The result can be a 3 db specification difference even for cartridges which in fact provide identical output voltages. And in addition, as Folkfreak indicated I wouldn’t count on such specs being particularly accurate either.

2)The reason for the differing gain recommendations you mentioned is that the KAB calculator indicates the gain required to boost a cartridge’s rated output to only 325 mv, while as you indicated Harley’s recommendation is based on boosting the cartridge’s rated output to 1 volt. 1 volt is 10 db more than 325 mv, which corresponds precisely to the difference between the two recommendations.

3)Both Stereophile and Soundstage measured the sensitivity of the LS50 as being about 84.5 db at 1 meter, for an input of 2.83 volts. In much of the mid-bass region, where lots of energy is typically required, the impedance of the speaker is not much more than 4 ohms. 2.83 volts into 4 ohms is 2 watts, which is 3 db more than 1 watt, so in that region the efficiency of the speaker is not much more than 81.5 db/1 watt/1 meter. In other words, very low.

4)Given also that the amp’s 4 ohm power rating of 100 watts corresponds exactly to the upper limit of KEF’s recommended range of amplifier power, it seems clear that the root cause of the issue, to the extent that it is an issue, is the Ragnarok’s overall gain of 26 db, which is very low for an integrated amp.

Regards,
-- Al

dill
2,531 posts
 
The "so called" ideal preamp gain range is from 10:00 to 2:00, You are under 3:00 so just a bit over. I wouldn't worry about it.
folkfreak's avatar
folkfreak
1,349 posts
 
A 10x difference in output voltage should correspond to 20dB difference in gain (hence the results you get from both gain calculators say to add 20dB between the two)

It may be that the differences you are seeing are simply down to tolerances between the two cartridges -- output specs are pretty approximate so if the Ortofon is a little high and the Grado a little low ...

Your bigger issue is that you don't have enough gain to drive the integrated amp. Fact is 26dB is standard power amp gain so in effect you are getting nothing from the pre-amp stage. In other words the Ragnarok really wants to see that 1V -- I'm surprised the Ortofon performs as well as it does especially as the KEFs are not exactly sensitive speakers

Short of a change to a different pre/power combo or a SUT at the front end I'm not sure I have any answers
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