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Some phono guru told me that phono cartridge is basically a " balance " device. If that is the case, why is 99.999% phono preamplifers available are single ended ? Am I missing something ? Do I lose 50% of the information if I use a regular single ended phono preamplifier. Thanks in advance.
Follow Ups:
A balanced device means that there is a +ve signal and -ve signal which is equal and opposite ***relative to a zero reference***.If the coils in a cartridge had a "center tap" tied to ground, then it would be a balanced device. I don't think there has ever been a cartridge designed with center-tapped coils. Feeding a single-ended stage with such a device would short half of its "balanced" output to ground.
The coils in cartridges provide a "floating" or "differential" output, so if you fed a single-ended stage, the potential across the coil relative to ground will be the signal, regardless of which end of the coil (polarity) is tied to ground.
If anyone has wondered abt what the difference in a single ended and balanced microphone is all you have to do is take one apart. A balanced dynamic mike in my experince has a transformer output with the center tap grounded. Sure the phono cart is very similar electrically and if its coil windings could be center tapped to provide a ground connection that would be a may to shield the system. In my way of thinking the reason its used unbalanced is that above --one needs a convenient ground to minimize hum pickup with such a lo output device. Maybe we need the windings center tapped. Do it someone. Regards Max
***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.
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.
adnut,Fact is, David Manley writes about this in his VTL Book written MANY yeara ago. Dunno about you, but when i use my balanced step-up transformer the noise does indeed seem to be lowered while what noise there is, is "pushed" to the outside right/left away from the center images.
Enjoy the music,
Steven R. Rochlin
Steven R. Rochlin wrote:Dunno about you, but when i use my balanced step-up transformer the noise does indeed seem to be lowered...
Yes. Transformers excel in that regard. First they offer exceedingly high common mode noise rejection (on the order of 145dB at 60 Hz for the Jensen MC step ups) and they're passive so they don't have bias currents flowing in them as with active devices that produce a constant level of thermal noise (hiss) regardless of signal level.
se
The balanced signal from the phono cartridge is converted to un-balanced then it is amplified with SE circuits.Robert Morin
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