Servo-balanced vs "normal-balanced", anyone?

Hi all,

Just wondering if anyone could help me out on this one:

I've got an RME 9632 card with the standard RCA i/o connectors (servo-balanced, if I understand the manual correctly). There is XLR i/o available as an upgrade, but I don't have it at the moment.

I also just picked up a EH 12ay7 mic pre, which is known to have a problem with hum if you don't use it in a balanced environment.

If I (for example) connect it directly from the balanced XLR out to the 9632 (using an XLR to RCA cable) it hums super-loud.

My question would be: since the RME's RCA ins are servo-balanced (apparently), is it possible to get it to "play nice" with the 12ay7 so I won't get (excessive) hum?

I would have thought that the fact that it's servo-balanced means that you can run the tip and ring together and it would act as if it was balanced. So I wonder if maybe the wrong pins are being put together within the cable? Does that sound plausible to any of you?

I've Googled and done a search on this board and I can't seem to find anything that makes it clear what the relationship between "real" balanced and servo-balanced is.

Any help greatly appreciated,
Matthew

Your sound card RCA connectors are unbalanced*. Try connecting your cable like this:

XLR PIN1 -> nowhere, leave open
XLR PIN2 -> RCA hot/tip
XLR PIN3 -> RCA cold/ring

Assuming you had PIN1 connected when you tried it?

Martin

* The HDSP 9632 ships in a basic version including two RCA/phono breakout cables (headphone: TRS jack). Therefore all analog I/Os and the SPDIF I/O are unbalanced.

As you said, the 12AY7 pre needs a true balanced input as it has a lot of common-mode noise on its output.

As Martin states, RCA/Phono connectors are inherently unbalanced. You could try buying a 1:1 rep. coil transformer to overcome this problem by properly de-balancing the output of the preamp, or find a balanced input to use.

Ah, ok. So to compare "actual" balanced (3-pin) with "servo-balanced" is really apples and oranges, then.

I guess I'll check out my pin situation and if that doesn't work, look into picking up the balanced option.

Thanks for clearing that up, guys. :thumb: