2. analog
  3. 1286221855

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 6 responses by socrates7

socrates7 OP
77 posts
 
"I would just set your phonostage for 65dB is you have a 0.25mV cartridge and get on with listening to music."

I would have done just that, but this thread was more "since I don't have one, carts with what parameters should I be looking at".
socrates7 OP
77 posts
 
Interesting -- two responses, and contradictory. ;-)

I've heard about the 500mV target. But I see the KAB calculator is targeting 375mV.

I understand that a .25mV cart "will work" with a 62dB (375mV target) gain phono pre -- but will a 72dB phono stage (500mV target) be "better" in some way (and why)? Or will I be cranking the dial on a 62dB phono in ways that would be suboptimal?
socrates7 OP
77 posts
 
KAB sells pre-amps and phono pre-amps -- is their calculator then based on their own as-designed input sensitivity of 325mV (not 375mV, I mistyped above)? The question then is, is the 325mV "standard" or do some target a 500mV input sensitivity (or something else)?
socrates7 OP
77 posts
 
I've sent a note to KAB trying to understand their formula.

So, according to the website, too much gain results in increased levels of noise being passed up into the system. Seems to be the case that they'd recommend under-powering, at least a bit, so that getting to the volume you want, you'd be turning the knob on the pre-amp, which means that any noise being injected would be a function of the pre (or the rest of the system) and not compounded with the noise of the phono.

Does that even make sense?
socrates7 OP
77 posts
 
Ok, I got it.

I guess the "magic number" then is the input sensitivity on the pre-amp. Which assumes that the manufacturer actually knows it. LOL.

FWIW, Robert Harley's post on this (here: http://www.avguide.com/blog/taking-the-guesswork-out-phonostage-gain) seems to indicate that it's 1v you should be targeting, not .5v nor .325v.

So, what is the deal with that number? And how do I found out what I have? Is "input sensitivity" called something else?
socrates7 OP
77 posts
 
Mihaitaa -- very helpful, thanks. FWIW, I think you're right. Or rather, that (my understanding of) Harley is way off.
More to discover