How to accomodate a balanced only phono stage ?

(I was just about to click "submit" on the following, when I saw Dave's (Dgarretson's) post above. Thanks Dave).

I should have added at the end of my previous post that there is a second reason why it is preferable to use a properly designed adapter cable, rather than an rca-to-xlr adapter.

Most or all commercially available rca-to-xlr adapters connect xlr pins 3 and 1 together (i.e., they ground the "cold" or inverted signal polarity). The resulting difference in the impedance of pin 2 (relative to ground) and pin 3 (relative to ground) will pretty much negate the common mode noise rejection capability of the balanced input.

Regards,
-- Al

A standard RCA/XLR converter plug may not work, as these typically short XLR pin 3 to ground.... As suggested by Lewm, if in an RCA configuration cartridge negative phase and shield to RCA barrel share a common wire, then grounding the shield to pin 1 or chassis will have the effect of shorting out and eliminating one half of the balanced signal.

Actually, that is not correct. The phono stage will see the same signal amplitude whether or not pin 3 is grounded. There will be the same difference in voltage between pins 2 and 3, as generated by the cartridge, either way. The cartridge will not "care" whether those lines are referenced to the phono stage's ground, or are floating.

The difference will be, as I said in my post immediately above, that the impedances of the two signal lines relative to ground will be unequal if pin 3 is grounded. That will severely degrade rejection of common mode noise, but will not affect the amplitude of the signal that is processed through the phono stage.

Essentially, it would convert the balanced input stage into a single-ended input stage, but with no change in signal amplitude.

And again, to be precise, it is one polarity, or one of the two signals in a balanced pair of signals, that is shorted to ground, not one half of a signal. Each of the two signals comprises a complete waveform containing all of the signal information, and the waveforms on the two signal lines are identical except for being inverted relative to each other.

Best regards,
-- Al

Elizabeth, Keep your shirt on. Nothing I wrote was incorrect. And it may help the OP, if the OP is concerned with the details of this hobby. And most of us here are already nuts enough to be that way. On the other hand, your comment that cartridges do not have three-wire outputs may reflect a lack of understanding on your part. As others wrote, nearly all cartridges are inherently balanced devices, and the two sides of the coil deliver a balanced signal. What you are grounding in an SE phono stage is what would otherwise be the negative phase of the signal PLUS the shield on the cable, ALL going to chassis ground at the phono stage, typically.

I should have added that IF one does use an RCA cable to carry a balanced signal, then one must lift the chassis ground connection on the RCA jacks, for sure. Else, like Dave said, you will lose the negative half of the signal to ground. This equivalent to a 6db loss in signal strength.

I should have added that IF one does use an RCA cable to carry a balanced signal, then one must lift the chassis ground connection on the RCA jacks, for sure. Else, like Dave said, you will lose the negative half of the signal to ground. This equivalent to a 6db loss in signal strength.

Hi Lew,

That's not true in the case of a phono cartridge, as I indicated above. There would be a 6db loss in signal strength in the case of an actively driven balanced pair of signals, such as between powered components (that are not transformer coupled), but that is a different situation altogether.

And again, I suggest that you not refer to "losing the negative half of the signal." That would imply that half of the waveform, and the corresponding signal information, is lost, which as you probably realize is not what happens.

Best regards,
-- Al

Al, Interesting point you make re not losing signal strength. That runs counter to my actual experience when I accidentally grounded one half of the signal in a full balanced set-up. But now that you say it (and now that I realize I knew it, and you are correct), I can think of another reason why I definitely lost at least 6db of signal strength until I un-grounded the 2nd of the two signal-carrying conductors. (Note I have avoided using the terms "positive" or "negative", which are merely conventions and could also be confusing.)

As to my statement regarding the "negative half of the signal", I know very well what is happening. I had just been criticized for being too pedantic, so I decided not to elaborate on that statement for fear of confusing someone. Perhaps my over-simplification could also be confusing, so thanks for mentioning it.