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Confused about gain: phono + pre, or just phono?

I'm trying to figure out how "low I can go" on my phonostage. I understand that the ideal numbers aren't necessarily "written in stone" in that the cart will still work even if the number isn't exactly hit. I'm looking to try to understand the ideals.

So, when trying to sort out what your phonostage will support, I've seen the formula that takes your cart's output in mV, divides that into 1, takes the log of that, and multiplies it by 20. The result is the targeted minimum that your phonostage should provide. Said another way:

Targeted phono gain (in dB) = 20 * [log * 1/(your cart's output)]

My question: is that resultant just what your phono stage should support, or what your phono+pre supports?

For example, say you have a .25mV cart.

1/.00025 = 4000
Log10 of 4000 = 3.6
20x = 72

So, you need 72dB.

But what if your phono does 60dB and your pre does 12dB? Are you good to go, or do you need 72dB from the phono by itself?
socrates7

Showing 2 responses by dcarol

dcarol
62 posts
 
Yes 0.25mV will work into 62dB but noise comes into it at these levels. 0.25mV should ideally be used with 65dB as the lower you go in gain the more hiss you'll introduce. Imagine using 0.25mV into a 40dB (MM) then increase the gain to 65dB. As you increase the gain the signal-to-noise ratio changes 'balance' so you end up with more signal than noise.

I have a few turntables with a few phonostages. The Denon DL304 @ 0.18mV is a real problem for a lot of stages. Some of my audiophile friends 'think' that noise/hiss is par-of-the-course when using 0.18mV - 0.4mV with a ANY phonostage.
A friend uses his DL-304 with a Naim Prefix and all you hear between tracks is HISSSSSSSSS!

I chose to use the Whest stages years back because apart from the audio quality, the background hiss/noise was the lowest I had come across using a DL304. In fact with their smallest whestTWO which I have in my home/office I have plenty of gain and absolutely NO NOISE or HISSSSS. A sign of a great design.

I also use a Dynavector XX2 MK2 (0.25mV), new Ortofon A90 (0.27mV) and Shelter 901 (0.6mV I think. using various stages.

dcarol
62 posts
 
The phonostage gain with reference to the cartridge has nothing to do with the following preamplifier.

What your phonostage needs to do is amplify the signal from the cartridge correctly under 'ideal transfer' characteristics which should give you low noise and low hiss as is my and Hdm's case.

Whatever the output level is from your phonostage afterwards is whatever it is. The most important thing here is gain matching the cartridge to phonostage and NOT phonostage to preamplifier.

Most preamplifiers can handle an input signal upto 8V and more if they are 'discrete technology' types. A phonostage without variable gain output would output approx 560mV-660mV with your standard 0.25mV cartridge (depending on cartridge output variances).

I would just set your phonostage for 65dB is you have a 0.25mV cartridge and get on with listening to music.

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