SE to Balanced Line Converters

[xrk971]

I am looking for a commercial single ended to balanced line out converter or preamp stage. Pre-made units boxed and ready to go don’t seem to be readily available. It seems like a basic thing but not sure why something for say $40 from Behringer or similar doesn’t immediately come up on a search. However, a $10 Sparkfun THAT1646 breakout board with TRS jack did come up. If anyone has suggestions for a commercially made ready to use one, please share here:

Sparkfun THAT1646 breakout board:
https://www.digikey.com/products/en?mpart=BOB-14003&v=1568

Needs a +/-voltage PSU and a panel jack.

I have made simple 2 transistor converters using a CFP in SE Class A and that works well but looking for an ultra low distortion IC implementation here.

 

[gofar99]

Hi, If a transformer solution will do for you....try Edcor USA. They make such critters.

 

[russc]

Mesa Boogie Clearlink Send Output Buffer and Line Driver | MESA/Boogie(R)

 

[MAAC0]

CLEANBox Pro – Dual Channel Level Converter – ART Pro Audio
Rolls MB15b ProMatch Balanced/Unbalanced Converter 3.5mm/RCA/XLR

 

[xrk971]

MAAC0,
Thanks for that tip - this was exactly what I was looking for. Don’t know why a google search could not turn up something like this. $55 is a great price too. Only thing is the -88dB noise floor. Most of my stuff is -125dB noise floor - but it will do until I make a custom one.

Manual even has a schematic:

Gofar99, thanks for the tip but I want to avoid transformers for the extra 3rd harmonic they can add.

Russo,
Thanks for the tip on the Mesa Boogie clearlink - but I think the Rolls unit is closer to what I was looking for.

 

[Speedskater]

To repeat from other threads:
The XLR pin #1 pins connect to the chassis at the connector, not to the circuit 'ground'.

 

[dtaylo3]

Also this one: ART DTI Dual Transformer/Isolator

 

[xrk971]

As much as I don't like transformers for doing this, the ART DTI unit looks very handy. Just having a box with all those connectors pre-made and ready to go is a feat in itself. The isolation from hum/ground loops is another bonus.

Thanks, dtaylo3

 

[turk 182]

To repeat from other threads:
The XLR pin #1 pins connect to the chassis at the connector, not to the circuit 'ground'.

not to mention that if this is to be considered standard practice, that in order to maintain true galvanic isolation that no circuit ground should be connected to chassis.

 

[Speedskater]

not to mention that if this is to be considered standard practice, that in order to maintain true galvanic isolation that no circuit ground should be connected to chassis.

That's the exact opposite of 'good engineering practice'.
If you want galvanic isolation use an audio input or output transformer, but still connect the circuit ground to the chassis.

 

[xrk971]

Circuit analog ground should be connected to chassis/earth safety ground via ground loop breaker 10ohm resistor and anti-parallel diodes or an NTC for safety and hum/RFI reduction.

My Sparkfun THAT1646 breakout boards arrived today. Will probably use a handy 5v to +/-24 DC-DC followed by +/-15v 7815/7915 regulators.

 

[MAAC0]

Noise floor depends on quality, so better op-amps perhaps help.

 

[xrk971]

I made a +/-15v power supply from a +/-24v DC-DC converter and LM7815/7915 voltage regulators to power the Sparkfun THAT1646 SE to Balanced drivers. Connected it to my TPA3255 Reference Class D amp with balanced inputs. Now I can use SE headphone outputs to drive the TPA3255 rather than always having to rely on the balanced output section of the Focsusrite. These Sparkfun breakout boards are very convenient and sound great.

 

[astromo]

Handy piece of hardware you've turned up xrk. I'm filing that one away as a mental note for future. Thanks for the tip.

MAAC0,
Thanks for that tip - this was exactly what I was looking for. Don’t know why a google search could not turn up something like this. $55 is a great price too. Only thing is the -88dB noise floor. Most of my stuff is -125dB noise floor - but it will do until I make a custom one.

Interested to see what you come up with as a follow on.

 

[xrk971]

Jhofland designed this for me. A SE/Bal to Bal converter with selectable gain of 0dB, 6dB, 20dB using OPA1656 and LME94724. Works great. This is prototype and production version will have SE output as well. So SE/Bal to SE and Bal converter with 0dB, 12dB, 20dB gain.

TPA3255 Reference Design Class D Amp GB

 

[astromo]

Cool. I'll keep my eye on where this ends up.

What's your thinking behind the selectable gain?

Is that to give an SE input signal a boost, so that a user can level things up if they switch across from a Balanced input?

Or just for general flexibility?

If the former, I suppose a selection switch could be rigged up without too much difficulty?

 

[audiobomber]

Old thread but seems there's still interest. Here's another ready-made option, Nobsound NS-05P passive preamp, converts XLR to RCA or vice versa and provides level control.

https://www.amazon.com/Nobsound-Ful...eywords=Nobsound+NS-05P&qid=1592927693&sr=8-2

 

[astromo]

Interesting piece of investigative work into the NS-05P from atomicbob over at SBAF:
Goldpoint SA2X - Nobsound NS-05P passive attenuator comparison technical measurements | Super Best Audio Friends

Post #10 summarises the performance differences (low attenuation appears to result in frequency roll off above 3 kHz).

Post #12 fingers the 50k pot in the NS-05P to be the culprit with a comment that a 10k pot would improve matters.

There's also review of the importance of cable selection.

 

[00940]

I might be wrong but... isn't this kind of input bootstrapping patented by THAT ?

 

[MAAC0]

A simple NE5532 or other better op-amp inverted unity stage put between out and pin 2 will also do the job or even a cheated resistor / cap balanced out. Many options to choose.