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Having trouble with unbalanced output balanced inputs
Old 30th January 2013
  #1
Here for the gear
 
🎧 5 years
Having trouble with unbalanced output balanced inputs

Hello, looking for some help understanding an issue I am having.

My setup:
I have a Roland SPD-30 Octapad (Electronic drums/sounds) connected to a Korg Kaoss Pad Quad (dynamic effects processor). Going into a USB dual pre/audio interface - which has 2 powered speakers connected.

The Rolands Left and Right output is 1/4" (displays TS cable being used in the manual)
The Koass Pads input and output are RCA.

I am using a 1/4" TRS to RCA - coming from the Left/Mono output of the drum pad into the RCA input of the Kaoss Pad.

I have the same type of cable (1/4" TRS to RCA) going from the RCA output of the Kaoss Pad into 1 channel on the usb dual pre/audio interface (the inputs are balanced xlr or 1/4" combo inputs). I have 2 powered monitors connected to the interface.
This seems to all be working properly.

Here is my issue:
The Korg Kaoss Pad (Effects processor) also has a Mic line in (1/4” phone jack)

When I use a microphone through the kaoss pad it comes through the monitors cracking and low (mic is good/cable is good). But when I change the cable connecting the Kaoss Pad/mic to the audio interface form a RCA to 1/4" TRS -switch to- a RCA to 1/4" TS the cracking is gone and the level is good.

So my obvious fix is use the cable thats works. But I want to understand the reason:

So I cannot have an unbalaced RCA output going to a Balanced 1/4" input using a RCA to TRS cable?

If so, is the unbalanced 1/4" output's of the drum pad going to unbalanced RCA inputs of the effects pad (using a TRS to RCA cable) also bad? and effecting it without me noticing?

I appreciate anyone who takes the time to help me out here!
Old 30th January 2013
  #2
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NeoHippy's Avatar
 
🎧 5 years
actually it shoudlnt matter if you use TRS-RCA or TS-RCA....and vise versa.

If you use TRS on the interface input...it will take the not used ring signal and phase reverse it and mix it with the tip signal. Which shouldnt be a problem, cause no signal should be be on the ring.

Dont know why it makes a difference in your case.

cheers
Old 31st January 2013
  #3
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Lotus 7's Avatar
Quote:
Originally Posted by jaymac902 ➡️
...When I use a microphone through the kaoss pad it comes through the monitors cracking and low (mic is good/cable is good). But when I change the cable connecting the Kaoss Pad/mic to the audio interface form a RCA to 1/4" TRS -switch to- a RCA to 1/4" TS the cracking is gone and the level is good.
Your RCA to TRS cable probably has the ring on the TRS plug floating (open). Connecting an unbalanced signal to a balanced (differential) input without grounding the (-) side of the input will result in noise and a low signal, if any. A balanced input must either be driven by a balanced output, or the low side must be referenced to ground. When you use a RCA to TS cable, the ring connection on the input jack is grounded by the extended shell of the TS plug.

If you add a jumper from the ring to the shield in your RCA -->TRS cable plug , it will work as well as your RCA-->TS cable.

A RCA to TRS cable should never have the tip (+) connected to the ring (-). Doing so will cancel the signal when connected to a balanced input since it's then identical on both the (+) and (-) inputs The whole point of balanced inputs is to cancel common-mode signals. If such a cable is connected to a TS input jack the signal will be shorted to ground since the ring connection will now also be the (S) connection.
Old 31st January 2013 | Show parent
  #4
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Lotus 7's Avatar
Quote:
Originally Posted by NeoHippy ➡️
...If you use TRS on the interface input...it will take the not used ring signal and phase reverse it and mix it with the tip signal. Which shouldnt be a problem, cause no signal should be be on the ring.
"phase reverse it and mix it with tip" How does a cable or the input do that?

The ring ((-) input polarity) is either grounded (has no signal at all and is referenced to the ground side of the unbalanced input) which will work, OR it's floating and through capacitive coupling in the cable and connector will pick-up noise and possible be capacitively coupled enough to ground to allow some weak high-frequency leakage and noise through. A differential input with one side open will not create any "phase reversal" or any mixing with the signal on the tip.

The two "sides' of a differential (balanced) input are not normally referenced to ground, although some may have high-value bleeder resistors present to charge coupling caps. An unbalanced signal can be properly "read" by a balanced input if one side of the input IS referenced to ground (the common side of the unbalanced output source) through a low impedance. That means grounding the ring on a TRS input jack when driving it from a unbalanced source OR using a TS plug at the balanced input.
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