Help with Cables!

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Aoresteen

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Help with Cables! Balanced output to unbalanced input

I need to connect the outputs of my mic pre-amp to the inputs of my Delta 1010LT card.

Inputs 3-8 on the Delta 1010LT are unbalanced RCA jacks.

Outputs of the Nady PRA-8 eight channel preamp are 1/4" TRS balanced.

Each cable will be 30 inches long.

The tip of the 1/4" TRS connects to the center of the RCA jack.

Should I tie the ring to the sleeve and connect it to the outter contact of the RCA jack or should I just connect the ring to the outter RCA contact?

Or do I float the ring and just connect the sleeve?

Thus far I've only sent unbalanced audio signals to the RCA jacks on my Delta 1010LT (worked very well) but now I have to send mic signals to them for the drums (dang drummers!).

I called Nady but they are stumped and asked me to send them an email they could pass onto 'higher'.

Thanks!
 
Last edited:
This may be a dumb question, but why not just use 1/4" TRS to RCA adapters?
 
Dastrick,

All the RCA to TRS adapers I've found are wired as stereo (2 channel). The sleeve is a common ground, tip is L and the ring is R. Here is a typical TRS to RCA adapter from eBay:

rcaTRS.jpg


A BALANCED TRS is wired differently: Sleeve is the shield, ring is the negative phase, tip is the positive phase. It carries a MONO signal.

TRS connector - Wikipedia, the free encyclopedia

So the issue is how to wire the TRS to carry a MONO signal.
 
I found some more info.

"Helpful How-To's": How to Properly Connect Balanced Outputs to Unbalanced Inputs, and Vice-Versa | Benchmark Interaction

It seems that there are 3 types of balanced output topology: 'impedance balanced', 'transformer balanced', and 'active balanced'.

I sent Nady another email asking what type topology the Nady PRA-8 uses.

1. If the Nady PRA-8 is impedance balanced, the cable should be wired as:

TRS tip to RCA center
TRS sleeve to RCA outer (grd)
TRS ring floated or connected to shield


2. If the Nady PRA-8 is transformer balanced, the cable should be wired as:

TRS tip to RCA center
TRS sleeve to RCA outer (grd)
TRS ring connected to TRS sleeve


3. If the Nady PRA-8 is active balanced, the cable should be wired as:

TRS tip to RCA center
TRS sleeve to RCA outter (grd)
TRS ring NOT connected (floated)


This type of information SHOULD be in the Nady PRA-8 user manual but it isn't.
 
You have 8 mono (balanced)outputs on the Nady. You have 6 mono inputs(3 L-R stereo-unbalanced), and 2 mic/line(balanced) ins on the Delta.
Convert two of the outputs on the Nady to use the line-ins on the Delta(as unbalanced). You have to change the six to unbalanced for the RCA's anyway.

You can't change the RCA's to balanced no matter what you do. Just make all your inputs the same.


Honestly... unless you're getting your power from a generator, it won't matter.
 
Curiosity was killing me. I pulled the Nady PRA-8 out of my rack and popped the hood. As I suspected it is NOT transformer balanced - the cost of 8 output transformers would raise the price of the PRA-8 significantly (it's a $100 at Musician's Friend).

The outputs are balanced using a JRC 4558D op-amp which is the same as a TI 4558.

nadypra8output.jpg


Detail:

nadypra8outputdetatil.jpg


Since it is using an op-amp I think it is an active balanced output which means I should float the ring.

Any thoughts on this?

Thanks!
 
michaelst said:
You have 8 mono (balanced)outputs on the Nady. You have 6 mono inputs(3 L-R stereo-unbalanced), and 2 mic/line(balanced) ins on the Delta.
Convert two of the outputs on the Nady to use the line-ins on the Delta(as unbalanced). You have to change the six to unbalanced for the RCA's anyway.

You can't change the RCA's to balanced no matter what you do. Just make all your inputs the same.


Honestly... unless you're getting your power from a generator, it won't matter.
Click to expand...

Thanks michaelst, but I'm confused. How do I change two of the outputs on the Nady to unbalanced?
 
michaelst said:
You don't have to worry about the balanced/unbalanced thing.

and here's what you need: F TRS to M XLR Adapter

You'll also need M TRS to M RCA for each Nady output.

Like this: 1/4" to M RCA
Click to expand...

Thanks!

I have 6 male TRS plugs and 3 six foot RCA M to RCA M cables that I will cut in half and solder on the TRS plugs. I just need to figure out which pins connect to each other. I've made my own cables since 1972 and these shouldn't be that hard.
 
UPDATE: I finally connected with an engineer at Nady. We talked and I was impressed with his knowledge. Bottom line is that I should float the ring. So it's a simple patch cord:

TRS Tip to RCA center

TRS sleeve to RCA ground.

TRS ring not connected.


So I have to use a TRS plug and NOT connect the ring. If I use a TS mono plug it will short the ring to ground which I do not want.

Simple!
 
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