Making a Balanced Audio Connection

[clearchris]

I have been wanting to add a balanced line out to my SAE P102 preamp for years. During the rehab of the unit, I found the following in the manual for the SAE P101 preamp (P102 is unobtainable). I believe it means (though it does not directly say this) that I can create a balanced line out by using both MAIN OUT 1 and 2. MAIN OUT 1 is two rca jacks, one red one white. Same with MAIN OUT 2.

The manual basically says that MAIN OUT 2 is "out of phase (inverted)" with respect to MAIN OUT 1.

It sounds like I can take the MAIN OUT 1 "right" jack tip as "hot" in my balanced connection, take the MAIN OUT 2 "right" jack tip as "cold", join both grounds, and that's the three wires for my balanced XLR connection. Same for both "left" channels. Or is there something more to this? The rest of my rack (crossover and amps) are all balanced connections.

Here's the whole excerpt from the manual:



I'm hoping this infernal humming coming from my system. The preamp sounded so good on my bench, and now it's so clear, the hum when I put it in my rack is super annoying.

Thanks!

[budm]

Re: Making a Balanced Audio Connection

The hum may be due to Ground loop issue.

[budm]

Re: Making a Balanced Audio Connection

P101: Yes you can create Balance output using Main out 1 CH A (called it +) and Main out 2 CHA (called it -) as Balanced output for Ch A, same is applied to CH B.
But does P102 has the same output configuration?

[clearchris]

Re: Making a Balanced Audio Connection

P101: Yes you can create Balance output using Main out 1 CH A (called it +) and Main out 2 CHA (called it -) as Balanced output for Ch A, same is applied to CH B.
But does P102 has the same output configuration?

They are pretty similar units. The would be absolutely terrible people if they used the same nomenclature between adjacent product versions and changed the features. I suppose it's time to buy that cheap and cheesy oscilloscope and verify before I blow up the preamp.

About the grounding, I have an older house that doesn't have 3 prong plugs. So my stereo rack has one of those adapters with the screw, and I dutifully screwed it into the outlet, but I know there's just two conductor plastic coated cable behind the outlet, so there's no real grounding. I don't have cable tv, so there's no ground there. I do have an ethernet line running from my rack to the wiring closet, but I'm going to take out the hub (for testing) and directly connect to the flatscreen. The flatscreen is connected to the preamp via fiber optic cable and a converter box.

It's really annoying, I can't hear the hum now, it comes and goes apparently. Swapping cables, etc, sometimes works, sometimes doesn't. It's quite a pain to track down.

Just noticed my amps have a "ground lift" switch, I'll try that too.

[budm]

Re: Making a Balanced Audio Connection

The ground lift switch on the Amp is to let you isolate the Amp circuit ground from safety ground.
To track the hum problem is start with just connecting power amp amp speakers first then start adding additional component one at a time and listen for the hum.

[clearchris]

Re: Making a Balanced Audio Connection

Well, if that's the case, there's no hum when I take my crossover out. To do that, I have to use unbalanced cables from the preamp to the amp. So it's not an exact test, and why I figured I'd see if I could build a balanced cable from the preamp to the crossover, I could also use that same cable to go direct to the amps. It actually sounded really good with no crossover, but no subwoofer.

If it is the crossover, I can't really isolate that can I?

[clearchris]

Re: Making a Balanced Audio Connection

Budm: You were right again. I checked the schematic, and I'm 80% sure there's no difference between the two outputs on the P102. I'll have to double check the next time I open it up, but I'm not expecting to be pleasantly surprised. Ah well, back to the drawing board.

[clearchris]

Re: Making a Balanced Audio Connection

I picked up an aphex 124a unbalanced to balanced converter and the buzzing is gone and the system sounds much better. I was going to build a converter, but I picked up the 124a for around $30 and I couldn't compete with that.