 
|
Audio Asylum Thread Printer Get a view of an entire thread on one page |
For Sale Ads |
|
|
Audio Asylum Thread Printer Get a view of an entire thread on one page |
For Sale Ads |
In Reply to: Is phono cartridge a " balance " device ? If so, why is 99.999% phono preamplifer single ended ? posted by adnut on January 04, 2001 at 11:51:55:
***Some phono guru told me that phono cartridge is basically a " balance " device.It is not. It is neither balanced nor single-ended. It is correctly called "floating" source that can be used either way. Much like a battery. The connection to the circuit defines wether it is now a balanced circuit or whatever.
But all this is really not important, or at least far less important than in the case of say, a preamp interfacing with a power amp. Why? Because the catridge has no ground reference, while the preamp and power amp do. Connecting two chassis always creates some issues that floating sources simply don't have.
The funny part is that floating sources can be connected to single-ended inputs and still behave like trully differential ones. I would much rather use the term differential, because it is better defined than the "balanced" - that has many definitions. We have built single-ended circuits with 140dB dynamic range that behaved completely as you would expect from differential circuits. The trick was - they were floating. Much like the input circuit in your DVM doesn't need to be trully "balanced" or "differential" (and they usually are not) in order to not have your typical single ended nastiness.
All this simply means that one should not get stuck in some terminology black hole, but rather do what is right. One particular case - tube inputs in phono stages. There, given the floating nature of the cartridge, it is more advisable to connect it to a single-ended input, gaining 6dB better noise performance (for the same resouces) that is extremely valuable in tube phono stages working with MC cartridges.
Again, each case is different and every designer sees it in a different light, and two products from the same designers might be different. All thank to the floating nature of this source.
Follow Ups:
Very interesting information. Thank you for taking the time to explain...Aurel.
hi victor,i am confused by your explaination below regarding "differential" phono stages. i have an aesthetix io phono stage which i run with "balanced" phono cable and interconnects. your statement below says that a 6db gain in noise performance is derived from a single-ended input; am i missing something? my understanding is that a "balanced/differential" input would yeild a 6db gain in noise reduction.
> > > One particular case - tube inputs in phono stages. There, given the floating nature of the cartridge, it is more advisable to connect it to a single-ended input, gaining 6dB better noise performance (for the same resouces) that is extremely valuable in tube phono stages working with MC cartridges. < < <
i have learned much from your posts. please set me straight.
mikel
***i am confused by your explaination below regarding "differential" phono stages. i have an aesthetix io phono stage which i run with "balanced" phono cable and interconnects. your statement below says that a 6db gain in noise performance is derived from a single-ended input; am i missing something? my understanding is that a "balanced/differential" input would yeild a 6db gain in noise reduction.A typical confusion. Often people say that balanced line has twice the signal, sort of implying that there is an inherent 6dB S/N advantage, but this is simply not so. S/N has to do with with the max signal, and the noise level of the input circuit. So yes, if you CAN boost your signal, then you DO gain S/N, but his doesn't apply here, because the cartridge comes with fixed output - it is whatever it is designed to produce, say - .2mV full scale. No matter how you connect it, you still get that .2mV max signal.
Given that the source voltage is fixed, you now need to reduce the circuit noise in order to improve your S/N - that's the only way. Unless you are willing to buy a new cart that gives you perhaps 1mV output.
Now, let's pretend we have a single tube, a dual triode, allocated for the first stage duty. Now you have the design decision to make.
First, you can configure it as a differential amplifier, a long tailed pair, for instance.
What happens in that case, is that each triode has the internal input noise source that is now connected in series with each input. You have two uncorrelated noise sources in series with your .2mV, and they add up so there is 3dB more noise than there would be in case of a SINGLE triode.
Another possibility, as long as you have the same dual triode to play with, is to connect the two triodes in parallel. Now you only have a single noise source in series with your signal, plus this noise source is now reduced by 3dB - that's how two uncorrelated noise sources add up if connected in paralles.
Net result: two triodes connected in parallel will produce 6dB less noise than the same tube conected as a differential input stage. Provided, again, that your source amplitude is fixed and can not be increased.
Of course, this is just one design consideration, there are many others, so your final answer might be different, but noise-wise this is how it works.
hi victor,to the degree my non-techie mind can grasp i "think" i understand it now. your explaination is 180 degrees different from my previous belief. i guess i thought that "balanced" circuts gave you a "magic" 6db of additional noise performance but i guess not.
one additional question; with my aesthetix io/koetsu rosewood platinum signature combo i am able to use the 64 db setting with the balanced phono cable vs. the 72db setting with single ended phono cable to get the same gain coming out of the io. dynamics and noise seem to be better with the balanced/64db combination. can this perception be correct? is there an additional gain stage in the circut that is boosting the signal in the balanced circut?
i apologise since i am asking about a design you may not be familiar with.
thanks again for your explaination.
happy listening!
mikel
***i apologise since i am asking about a design you may not be familiar with.You are right, I only have quite superficial familiarity with that product - and it seems to be very interesting one. So I simply don't know those details. But try contacting Jim White - he is a really nice guy, and I am sure he will be glad to answer your questions. What you are describing sounds a bit confusing to me.
Best of luck.
This post is made possible by the generous support of people like you and our sponsors:
Top of Page ]
[ Contact Us ]
[ Support/Wish List ]
[ Copyright © 2024, Audio Asylum, all rights reserved ]
