The immediate problems of phono reproduction are not necessarily low noise performance, but how the overall circuit handles the input from the phono cartridge. As most know, there is a significant amount of high frequency output that comes from a phono cartridge, especially a MC type. This must be handled with care, or you will slew rate limit, or change the subjective character of the phono reproduce signal to something more compromised than you might think. Much of our effort up until now is finding the optimized way to handle a phono cartridge, with all its 'faults' and get the best sound quality possible. Dynamic headroom is a first consideration, for example.
Understanding low noise design, in general, can be very useful. Perhaps not as useful as it once was, with analog tape recorders and phono stages, but good to know. However, it is NOT just a spec. where the lowest number gives you better sound. I have heard examples where reaching for the LOWEST measured noise, will give sonic compromises with an existing design. Now, can you have both good sound and very low noise? Yes, but it usually costs more, because it is more complex to implement (more parts, more current). Perhaps, it would be interesting to show where designers have gone wrong in the past, just for simplicity, or a lower noise spec.
Ed,
There is a very fundamental misconception on your part, in that wide band noise doesn't really bury a signal. You can hear signals deep into the noise.
As a matter of fact, it may even be the opposite of what you argue, in that noise can push an unperceptible signal over the threshold of perceptibility.
Masking happens between a dominent tone and near lying frequencies at a lower level, and the effect gets less the more the two frequencies are removed from each other.
I think the curve ball got pitched past you as well. See my previous hint.
One more hint: dB is a function of a ratio.
If I may venture a guess, that would be finding the right bias for a differential input. If you make it low, noise figuires will look good, but it won't be much of a sound. If you crank it up, the noise figure will suffer by a couple of dB (VERY important for the Great Spec Game), but it will likely come on song (as if anyone cares).
As you say, you can have both, but then it costs more, and the Bean Counters won't have it.
Semantics gents ,
Ed claims no need to chase and lower thd once into the noise floor , agree or disagree ..?
Ed claims no need to chase and lower thd once into the noise floor , agree or disagree ..?
10 * log of the ratio between two powers. That's a function.
OK, so semantics aside, notice the fundamental assumption swept under the rug?
OK, so semantics aside, notice the fundamental assumption swept under the rug?
Optimum dc current in a bipolar input stage will give you lowest noise figure for a SPECIFIC impedance. There can also be a 'best fit' range with an inductive input.
Jfets like all the current they can get.
Jfets like all the current they can get.
Is that the same as 'electronic cooling' where you have an active shunt that makes the resistor noise appear much lower than one would expect from the resistance value?
jan
I have read about some psycho-acoustic tests that did just that! Have one tone masking another, then bring up the noise and Presto! the masked tone can be heard again.
Now to find that reference....
I DID post it some time ago here sometime. Wish people would read my posts and remember them 🙁
Jan
Yes Jan, that is much of the basis for MP3 Coding. I started by pointing out JC is doing something new and now it is a rehash of 80 year old work. So maybe we should stick to only the 40 year old stuff SY is getting really confused.
Those interested in learning more can look up masking and critical bands.
Those interested in learning more can look up masking and critical bands.
Vac I don't think you've been reading correctly. I mentioned Fletcher found it took 65db of wideband noise to mask his target tone. He and others later refined this. The issue under discussion was in the trade off between distortion and noise how do you weight things. My simple version puts distortion 60 dB below noise.
ES,
It would be much easier and nicer if you weren't playing twenty questions and just came out with what you were alluding to in the very beginning. Unless of course you don't want to reveal what it is you say that John is working on? I think things go off the rails when people are guessing what the original subject matter was supposed to be directed at and everyone starts to guess and second guess what the conversation was supposed to be about. It reminds me of a teacher asking open questions trying to get people thinking instead of teaching a specific point that the lecture was intended to be about. I have noticed you seem to like to allude to things instead of being direct. Perhaps that is just how you like to discuss things but it becomes hard to follow what becomes a back and forth guessing game. No disrespect meant here.
It would be much easier and nicer if you weren't playing twenty questions and just came out with what you were alluding to in the very beginning. Unless of course you don't want to reveal what it is you say that John is working on? I think things go off the rails when people are guessing what the original subject matter was supposed to be directed at and everyone starts to guess and second guess what the conversation was supposed to be about. It reminds me of a teacher asking open questions trying to get people thinking instead of teaching a specific point that the lecture was intended to be about. I have noticed you seem to like to allude to things instead of being direct. Perhaps that is just how you like to discuss things but it becomes hard to follow what becomes a back and forth guessing game. No disrespect meant here.
Keep spinning it, Ed, eventually someone is going to figure out the fundamental error.
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