Balanced in phono stages preamp?

I had an Aesthetix IO and it had a balanced input but as I recall it is not a balanced preamp, it converts to single ended in the input stage and then uses a differential amplifier to recreate a balanced signal.

Many CD players pull this trick by adding a chip at the output, which not only is a phony way to do it but also will likely degrade the sound a bit compared to the SE outputs on the same piece of gear

I agree, but would like to point out that since the data on the CD is single ended, any CD player with a balanced output has to "create" the inverted signal in some manner. Some use more DACs, some use inverters after the DAC, but in every case there is no such thing as a balanced CD player from front to back since the data on the disc isn't balanced.

Jeff_jones, you are correct. The signal encoded on the vinyl disc is also single ended.

Balanced is hype. Long (and I mean really long) signal runs can benefit from balanced but not typical home setups.

ALL sources are single ended.

All speakers are single ended.

Your ears are single ended.

All sound is single ended. There are no balanced instruments or sounds.

it is neither SE or balanced- it simply is

You lost me there. I'll have to think about that one, but I would argue that the record groove as well as sound itself is single ended. I don't think something is balanced unless you have a pair of signals of opposite polarities.

Since nothing in the home stereo meets this requirement unless we create the opposite signal, it is single ended. I'll have to ponder the situation of a cartridge hooked up to the inputs of a diff amp as noise rejection at this low level makes sense. I may try that myself, but I see no compelling reason to go balanced after that.

Raul, good to hear from you. What is this "our design" you speak of?

I agree there are some theoretical advantages to differential designs; however we both know that many balanced devices are not differential. I believe Atmasphere's are but many (most?) are not.

By hype I mean the advantages are outweighed by the complexity of the circuits, and the ability to reject common mode noise is simply not needed in the home environment. The only exception I can see where it might come in handy is the very early stages in a phono stage. Otherwise, why take an inherently single ended source, convert it to balanced, and handle it that way only to recombine the 2 polarities at the speaker? Most of those who are trying to sell balanced equipment take advantage of the fact that the average consumer doesn't understand the circuits. They tout the advantage of noise rejection (which isn’t needed) and love to point out that pro audio uses it (which isn’t relevant.)

As you may know I feel simplicity is the key to good sound. Balanced circuits don’t fit in with this philosophy. My amplifier has 3 SETs directly coupled. My phono stage has a step up followed by 2 stages of amplification with the RIAA in between. With high efficiency speakers this is all you need.

Have you ever wondered why the phono is the only hookup in your system that requires an extra wire for grounding (else it hums)? This is the result of trying to operate a balanced source in single-ended mode.

That is simply not true. It is not required. A cartridge connected to a single ended input sometimes will hum with the ground connected and sometimes without. Sometimes the ground connection makes no difference. After playing records for almost 40 years I have proven this to be true.

While it may be true that balanced equipment might have been used in the recording process, the groove in the disc is not balanced. Balanced has 2 signals of opposite polarity per channel so a stereo signal would require 4 separate signals. There is no medium (tape, vinyl, digital, etc.) that provides these balanced signals so all sources are single ended. Why even imply that vinyl is balanced?

OK, now my brain hurts. Here's an interesting read.

http://www.ultracad.com/articles/differentialrules.pdf

It would seem to support Ralph's assertion that a cartridge is balanced IF you accept that differential signals are the same as balanced. If you go with Hagtech's definition that a 3rd ground leg is required to meet the definition of balanced then a cartridge is not.

However, I can't find any definitions or discussions (other than this one) that require this ground. The ones I have found discuss currents in the 2 legs as equal but in opposite directions, which a cartridge would fufill. It also seems to me that if you want to get a ground refernce involved, as soon as you hook up the leads to a differential amplifier that they could be referenced to that circuit's ground.

Then again, I suppose Ralph's assertion that what really matters is the circuit and how it sounds and it doesn't matter what you call it might be the best approach.

if I provide two independent floating bias supplies for the input of the preamp, I don't have to have the grid resistors go to a common point.

Perhaps I have no imagination but I don't see how that can work. Everything still has to have a common reference point. The bias is applied from grid to cathode, and the cathodes have to have the same reference in a diff amp, so the supplies would have the same reference and not be floating. Correct? It sure would be nice if you could post a picture on this forum.

That still doesn't explain how you can establish bias with 2 floating supplies like you claimed earlier. I say you can't.

I’ll say it again. The cathodes are tied to a common point; there must be a DC path from grid to cathode to establish bias so the grids must also be referenced to this point. The supplies can’t float.

As soon as you hook up these differential signals they are referenced to the common connection via the grid-cathode bias circuit.

I need to see a schematic of how you can accomplish what you claim before I believe it.

Don't get me wrong, I am intrigued by the idea of feeding my cartridge into a diff amp and have that on my list of things to try. I just don't think what you described is possible.

Interesting. So the voltage on the grids is slightly different and the coil of the cartridge is hooked across the grids? Doesn't this put some DC current through the coil?