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Phono Preamp Gain

Hi all,

I am in the process of getting a new cartridge and I want to make sure the output voltage is a good fit for my system. First off here's what I'm working with:

VPI Prime
Schiit Mani (30dB, 42dB, 48dB, 59dB gain options)
Prima Luna Dialogue Premium Integrated (239mV input sensitivity using KT88 tubes) (S/N ratio 81)
JBL L100

My question is what do I use for Vout in this equation to calculate the correct gain to choose on the Schiit Mani phono preamp??


20log(Vout/Vin)


Using the input sensitivity of the integrated and the output voltage of the  Soundsmith Otello ES Moving Iron Cartridge I get 

20log(.239V/.00212V) = 41dB gain

Is this correct?
My main issue is I dont know if my assumption to use .239V is correct.

Cheers



nmo25
bdp24's avatar
bdp24
9,815 posts
 
In the specs for the Mani on the Schitt website, the 30dB gain setting is called "Decca Mode’. Decca/Londons produce a 5mV signal. Make of that what you will.
mulveling's avatar
mulveling
1,913 posts
 
Well 40 dB on 5 mV is only 0.5 V. While 30 dB on 5 mV results in an absolutely anemic (for line level) 0.158 V. You pipe that into a preamp next to an input holding a hot digital source of 2V - 4V (e.g many balanced DACs), and you’re going to have to be careful to remember to turn the preamp volume way WAY down when you switch from vinyl to digital. I would never even attempt such a setup.
nmo25 OP
2 posts
 
I appreciate the discussion and I am trying to wrap my head around this. 

So to find the correct phono stage gain gain ‘on paper’ for a cartridge with 2.12mV output would I assume the phono would output a voltage of ~1V line level?

Vout =1V
Vin =.00212V

Phono stage gain would technically be 53.5dB ?


mulveling's avatar
mulveling
1,913 posts
 
Really, anywhere in the range of 0.5 V to 1.0 V output from your phono stage (calculated by specs; peak levels can be much higher) is typically fine. I tend to like it in the hot side towards 1V in practice, but you run the risk of cutting into overload margins of the phono stage (varies by model) that way.
bdp24's avatar
bdp24
9,815 posts
 

My Herron mm phono amp provides 42dB of gain, which works fine (to use understatement ;-) with my 5mV output London cartridges. I don’t know how Schitt came up with 30dB for Deccas, but remember, 5mV is the cartridge’s nominal output, not it’s maximum. Transient peaks may produce even higher output, right?

Another phono amp incorporating a setting specifically for Decca/Londons is the Andros by Zesto Audio, whose impedance switch includes 15K ohms (the cartridge likes to be loaded down, to electronically damp it’s high frequency resonance). Zesto designer/owner George Counnas told me he put that in the Andros specifically because of all his friends and industry colleagues who use Decca/Londons, a cult favorite!

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