Proper wiring for unbalanced synth output to balanced ADC input?

[nms]

Anyone?

[johnnyc]

There are 2 ways you could do this:

Method 1 (with unbalanced cable):
TS tip to XLR pin 2
TS sleeve (cable shield) to XLR pin 3
XLR pin 1 not connected
I use this method for doing coax BNC to XLR for testing gear as the input signal

Method 2 (with balanced cable)
TS tip (cable +) to XLR pin 2
(cable -) to XLR pin 3
(cable shield) to XLR pin 1 (so basically wire the XLR the normal way)
Connect both (cable -) and (cable shield) at TS end to sleeve
Look here page 21 http://www.symetrix.co/wp-content/up...2/88192_ug.pdf

The important thing is pin 2 and pin 3 of the XLR need to be signal connections, pin 1 and grounding/shielding can vary depending on the needs.

Also balanced out to unbalanced in is different so don't use this method.

[lontas]

First, when dealing with TS outputs, don't think of it as "ground"--think of it as "audio return path". Ground is a relative concept. In well-designed gear, the audio return path is designed to be very quiet in reference to the audio signal--if it weren't, your synth would make horrible buzzing no matter where you connected it.

My understanding is this: Connect the tip to Pin 2, connect the sleeve to both Pin 3 and the shield. Leave the shield unconnected at the A/D input. The idea behind this scheme is that the balancing circuitry on the receiving end cancels any noise the cable picks up along the way, while the shield shunts RFI away from the input.

Connecting the shield to the receiving end only makes the shield become an antenna for RFI garbage. Maybe that's why you were getting buzzing. You don't want that at the input, you want the RFI to get shunted back into the output where it can't get amplified. HOWEVER, your synth will need to have a good connection to earth ground in order for this to work--otherwise, the RFI has nowhere to go and will eventually make its way back around towards the A/D input.

Finally, make sure the synth and A/D are both plugged into the same electrical circuit. Good luck. I'm no electrical engineer, so please correct me if I've gotten anything wrong.

[johnnyc]

What lontas is suggesting is another valid option to try. The problem is different manufacturers handle pin 1 differently, so it's often best to follow their specific advice, very bizarre in your case that the manufacturer's advice doesn't seem to work very well.

[Warren Beck]

Simple - matching transformer.

Un-balanced - transformer - balanced patch-bay/converter/mixer/etc.

[nms]

Originally Posted by lontas

First, when dealing with TS outputs, don't think of it as "ground"--think of it as "audio return path". Ground is a relative concept. In well-designed gear, the audio return path is designed to be very quiet in reference to the audio signal--if it weren't, your synth would make horrible buzzing no matter where you connected it.

My understanding is this: Connect the tip to Pin 2, connect the sleeve to both Pin 3 and the shield. Leave the shield unconnected at the A/D input. The idea behind this scheme is that the balancing circuitry on the receiving end cancels any noise the cable picks up along the way, while the shield shunts RFI away from the input.

Connecting the shield to the receiving end only makes the shield become an antenna for RFI garbage. Maybe that's why you were getting buzzing. You don't want that at the input, you want the RFI to get shunted back into the output where it can't get amplified. HOWEVER, your synth will need to have a good connection to earth ground in order for this to work--otherwise, the RFI has nowhere to go and will eventually make its way back around towards the A/D input.

This made perfect sense to me. I tried wiring the cable in 3 different ways and this worked best. I recorded 8 bars of silence from the synth over each cable configuration then compared them.

The reason for the massive hum was the missing ground prong on the power cable. It snapped off a year ago when moving but I never noticed a difference so I neglected replacing the cable. When using a TRS to TRS cable with ground connected at both ends the hum was negligable. In the current configuration the connection is considerably quieter though.


I suppose my next move would be to get a transformer. This would adress the impedance difference I gather. I was checking out WELCOME TO JENSEN TRANSFORMERS, INC. for a stereo transformer box. DI boxes typically convert the signal to mic level though which won't work for me as I only have one good preamp. I imagine one of these would work for the impedance matching and isolation while still giving me a balanced line level output?