www.kabusa.com
Click on phono preamps at the top of the page and then scroll to the bottom of that page for the "phono preamp parameter calculator".
That gives you the ideal gain number for the phono preamp. Unless you are running a passive preamp, my advice to you would be to focus entirely on what you need at the phono stage, which is what the KAB calculator does.
FWIW, I have found it to be pretty much dead on and having either too much or too little gain can be problematic and result in less than optimal sound quality. As you see from the KAB site, optimal gain for .25 mV is around 62 db. 72 db would, IMO, be quite high and in many cases result in overload and compromised sound quality. |
I might be wrong, but usually the preamps have 500mV input sensitivity, which will mean 66dB of gain required for the phono stage to bring 0.25mV to 500mV.
Going 62 dB instead will load the pre with 315mV at the input instead of 500mV.
Of course, the pre will pick up the task of amplifying to whatever the input level of the power amp is.
I dare to say that going with less than 66dB of gain at the phono stage level will work, only 66 dB will do better, signal to noise ratio wise. |
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? |
My answer was only looking at the mere numbers and factoring in the main principle that, considering the noise floor of any amplification stage, loading it in its optimal zone will improve the S/N signal to noise ratio.
Thus there is no fundamental contradiction, so to speak, KAB targets a lower preamp input voltage, hence recommends less gain.
It could very well be that KAB reached the conclusion that the sweet spot of preamps input is less than 500mV? Don't know, I tackled this from the numbers angle only.
Many preamps indicate that they handle overloads very well, over the specified 500mV and harvest better S/N ratio in the process. |
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)? |
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? |
My point is that if you "underload" the preamp (load it to 325mV max instead of 500mV max, IF 500mV is its sensitivity) you will get less S/N ratio out of the preamp (less input signal with the same noise floor of the preamp = smaller S/N ratio).
You say that KAB tailors the calculation for their OWN preamps, with 325mV input sensitivity.
This makes perfect sense and only proves my theory that if your preamp has 500mV input sensitivity, thus you should use an outboard phone stage with 66dB gain to raise the output voltage of your cart.
Thus apply the mere definition of dB to get the needed gain to raise your cart output voltage to the sensitivity level of the preamp you'll be using. That's all I'm saying.
There are two variables to use in the formula, the output of the cartridge AND the input sensitivity of the targeted preamp that will receive the output of the outboard phono stage. |
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? |
Usually 1V is the starting input sensitivity of power amps. The ones with loads of power will have higher numbers in here or else you won't get to turn your preamp's volume knob too much before being blasted out of your seat.
So I guess that it goes this way.
1. you have the cartridge and know from its technical specs what its output voltage is.
2. You have/intend to buy a preamp and you know from its technical specs what the line input sensitivity is. Usually 500mV (but I might be wrong here). This is not the sensitivity of the preamps' phono stage which you'll bypass if it already has one. You want to buy an outboard phono stage, right? Because either your preamp doesn't have one or the one it has doesn't satisfy you.
3. Now you use optimal_outboard_phono_stage_gain = 20*log(Vpreamp/Vcart) where Vpreamp is the line level input sensitivity of the preamp and Vcart is the output of the cartridge.
4. Of course it's not going to be the end of the world if you're a bit off, that's why I said "optimal_outboard_phono_stage_gain".
5. Take a look here: http://en.wikipedia.org/wiki/Line_level
Might see them MAX for consumer electronics at 0.447V |
Mihaitaa -- very helpful, thanks. FWIW, I think you're right. Or rather, that (my understanding of) Harley is way off. |
Not only will a .25 mV cartridge work with 62 db of gain, it has worked optimally in my experience with 2 different cartridges and two different phono stages, neither of which were KAB phono preamps, for me over the past 5-6 years.
My previous cartridge was an Ortofon MC 20 Super with an output of .25 mV and it worked perfectly with 62 db of gain into a 100 ohm load using a modified DB Systems phono preamp (modified to give 62 db of gain) into a line input on an Audiolab 8000A.
I've also used (and am currently using) Denon 103R's which are rated at .25 mV into that phono stage as well as an Aqvox phono stage into the Audiolab mentioned above as well as a Jungson JA 88C integrated.
Both of the 103R's I've used in the past 4 years have come with individual spec sheets indicating slightly higher output than normal specification. One with about .29 mV and the other had .30 mV.
My Aqvox has variable gain on the balanced inputs between 60 and 75 db and I've run both of the above Denon 103R's at the lowest gain setting. In other words 60 db. Going higher is as simple as turning the gain pots on the front of the unit and I've done it.
Those cartridges work best in my system with 60 db of gain, not any more.
Too much gain (and not enough gain, for that matter) is not a good thing. |
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.
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I've had no noise with the DB Systems stage (which is a very inexpensive phono preamp) and the Aqvox but reviews of both have noted that these are extremely "quiet" phono stages. Both are pretty much "CD quiet" both while the music is playing and between tracks. As you point out, it is a matter of the quality of the design.
Of course, it is always a question of YMMV and I think there is a legitimate caveat with respect to pairing tube phono stages and low output cartridges; in general, that can be a combination that leads to a fair bit of noise once you get into and past the high 50's with gain.
I guess I've just been fortunate to own quality phono stages at different price points but, as I said, IME the KAB calculator is just about dead on. Could be I've just been lucky. |
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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"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". |
From experience, I would say 60 db of gain is adequate for most application for a cartridge rated at .25mV output. I run a .30 mV cartridge into a phonostage with 60 db of gain and there is absolutely no noise issue at all. I do have to crank the linestage fairly wide open (13 db of gain) to feed my Stax headphone amp which apparently has very low gain, but with speakers, gain is not an issue.
With a low output cartridge, whether noise becomes an issue can be dependent on HOW gain is achieved. With solid state, noise is usually not an issue (the one area where solid state is clearly superior). With tubes, getting such high gain using active gainstages can result in high noise level. That is why a lot of people use step up transformers in front of the first active gainstage (transformers do not add noise) in tube phonostages. My tube phonostage has such a step up transformer built into it. |
Enyone want to enjoy the amazing DL304 the most, should try it with Einstein little big phono ,
although price different doesn't make sense
as a package, it is one of the best combo's you can get around 4000$, dead silence, liquid, smooth and dynamic and highly musical. |
