bal/unbal patchbay question.

[Steenamaroo]

Hi folks.
I have, what should be, a simple question for you all.


I have two preamps here - different brands, both balanced TRS outputs.
I used TRS cables into a TS patchbay after the outputs today by mistake and realised the error very quickly, but....

One of the preamps carried on as normal with a little bit of audible buzz on the output.
The other had it's signal high passed to the hilt. This could be remedied by grounding the ring.

So to summarise, both balanced output preamps were sending signal on tip and sleeve with their rings left open (leave it!).
Had I used a TS cable by mistake, I probably would have had cause to notice as the rings would have been grounded.


Any ideas why one would have a healthy output regardless and the other would not?

It's not a big deal. I'm just curious to know.
If it helps, I know the high-passed sounding one has output transformers. The other does not.

Many thanks in advance.

 

[ashcat_lt]

If it helps, I know the high-passed sounding one has output transformers. The other does not.

I do believe that this is your answer, and according to this link it's because "the only connection to ground to complete the circuit is through capacitive leakage."

 

[Steenamaroo]

Ah, perfect. Thanks for that link.

So it's simply just how it is. A balanced transformer output needs to be used as such, or needs to have one side grounded to allow for a full unbalanced signal?

Sweet. Much appreciated.

You can imagine my surprised when I set up for some guitar recording and everything sounded like it was coming out of laptop speakers.

 

[ecc83]

Ah, perfect. Thanks for that link.

So it's simply just how it is. A balanced transformer output needs to be used as such, or needs to have one side grounded to allow for a full unbalanced signal?

Sweet. Much appreciated.

You can imagine my surprised when I set up for some guitar recording and everything sounded like it was coming out of laptop speakers.

ER? BIT of a minefield this!
A FLOATING balanced transformer output would connect to tip and ring. The sleeve connection playing no part in the proceedings and would normally be connected to earth or "chassis" (might even be an earth lift switch on some gear).

Thus you would get the full signal voltage on both a TRS and TS jack, the latter shorting the ring to ground of course.

Some very old balanced out gear had a centre tap on the transformer connected to earth and in this case a TS plug would short half the winding and give you 1/2 the voltage but in actual practice the drive amp might protest and the output be even lower and/or distorted. It is USUALLY permissible to lift the centre tap but NOT on valve gear!

Top "pro" gear will have two amplifiers per pin driving an anti-polarity signal and shorting one of those to ground might cause problems,
unlikely however these days and with top line equipment. (then there are "servo" systems that deliver the same signal voltage whatever TF you do to them!) .

Lastly we have the "impedance" balanced output. Sometimes frowned upon as being a poor relation but it has its merits. The noise immunity of balanced INPUTS depends upon a very closely matched, low DRIVE impedance on both legs and this is easy to achieve with close tolerance resistors. The Z bal circuit is also inherently short proofed and it is also impossible to get the polarity wrong!

Dave.

 

[Steenamaroo]

ER? BIT of a minefield this!
A FLOATING balanced transformer output would connect to tip and ring. The sleeve connection playing no part in the proceedings and would normally be connected to earth or "chassis" (might even be an earth lift switch on some gear).

Thus you would get the full signal voltage on both a TRS and TS jack, the latter shorting the ring to ground of course.

I guess that's the key point.
If I had used a TS cable then the ring would have been shorted to ground.
I used a TRS cable and a TS patch bay which had no connection for the ring. It was left open.

FWIW it was a pair of auditronics 110a preamps with these jensen transformer output cards.