Balanced in phono stages preamp?

So in this particular case, the differential circuit *does* care about ground.

Well, no it doesn't. In our preamp we have two resistors because we have to have a 47K input impedance and because the tubes require a grid leak resistance- for biasing. We could have set the unit up with a pair of 1M resistors and put the 47K across the input, from pin 2 to pin 3. It would have worked as well, but it would have been more parts.

When we load the cartridge, the load is applied with a single resistor from pin 2 to pin 3 of the XLR. The ground functions only as shield with no signal currents.

>>We could have set the unit up with a pair of 1M resistors<<

Exactly! For the circuit to work you *must* have a common mode connection to ground (the 3rd terminal). Or some other reference voltage similar to a ground. I don't understand why you keep trying to deny this. Just because you make the connection inside the box doesn't mean it is non-existent.

If you can get your preamp to operate in balanced mode without these 47k or 1M resistors connected to ground, then send them to me and I will eat them.

jh

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Hi jh, It sounds like we're not talking about the thing. How about if I create a bias voltage for the input section that is set at something other than ground? I could set it a -1 volt for example. You really want to eat those resistors??

Forgive me, I tire of this thread. What started as an intelligent debate has devolved into childish wordplay. I must be annoying everyone as I keep repeating myself (a sign of insanity) like a broken record. I'm like a homeless bum pushing a shopping cart mumbling to myself. Seriously, didn't I just say:

"...or some other reference voltage similar to ground..."?

And before that:

"...the receiver is providing the common mode reference..."?

Maybe my posts are moderated and nobody else can see them. If so, I apologize. I had thought the see-saw analogy and the fact that the input stage is providing the common mode reference (pivot point) for the cart would make sense.

Why did I bother? It's very simple. I like the truth. I don't like the way marketing can obscure and twist reality. You see, there are a few phono stages out there with XLR inputs that have pin 3 tied to ground. Hence, they actually run single-ended. Clearly that is not the case for atmasphere or bat. Just a few I won't name. The problem, as I see it, is that perpetuating this myth that a cartridge in and of itself is a balanced transmitter gives these folks a pass. Customers end up believing. Hey, it had an XLR input, right?

The tragic irony here, is that the guy doing the most to benefit the disengenuous is someone who makes the effort to do it right.

jh