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Balanced to double unbalanced converter


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Hi there,

I was looking for a solution to convert my balanced line level signal to 2 times unbalanced line level.

I read this article and made a project largely based on this: https://www.electronics-lab.com/project/balanced-audio-unbalance-converter/

But ...
There are 3 issues with it:
- I have a hum on all outputs at 50Hz and on harmonics at 100Hz, 150Hz and 250Hz. This originates clearly from the power supply (mains 230V 50Hz) and is only clearly hearable when no music is played. Since I want to use this on a in-ear system on stage or in studio recording, this will be very annoying. I have no idea how to solve this.
- 1 of 2 unbalanced output signals is heavily distorted (not too loud, just corrupt, even less loud) - I made this for 4 balanced inputs on 1 power supply.
- the sound quality of the good output is not good either compared to the original: I miss some lows and some freshness in the high frequenties. I was able to see that on a multiband EQ visualiser on my X32 mixer (lows are more or less -5dB). I can equalize this but I shouldn't do that. And I have to do that on every balanced output separately.

Attached you find the schematics of the 2 PCB's I made:
- PCB power supply +15 -15 V=
- PCB balanced to unbalanced for 2 input channels (please ignore both the loose TS and TRS jacks at the output side).
Input is done via a XLR/Jack combo connector, output is done via a TRS jack (stereo) the has the same signal on TIP and RING (thus mono over 2 channels). This output signal goes directly into an headphone amplifier with a stereo TRS jack input.

Advantage for this setup: compensation of the 6 dB signal loss when converting from balanced via ie. a DI (transformer 1:1) PLUS 6dB gain because off doubling that signal to 2 channels (left and right). Thus compensating 12dB on the output of the mixer console is a lot. The headphone amplifier could not compensate this neither.
An alternative solution exists by using a DI in reverse. 4 channels = 4 DI's plus 4 Y-jack cables and still loss of 6 dB although I'm not 100% sure if that is true for all DI's. I didn't check this for 100%.

Any way ... this project would leave me with an output that I could dial in via the volume pots and I could make use of standard XLR and Jack TRS cables. On top of that I could build 1 device for 4 channels. Ideal for my situation.

Anu idea's?

Schematic_Voeding+15V 115V_2021-11-10.pdf Schematic_Balanced to unbalaced_2021-11-10.pdf

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It is very difficult to help someone with home made circuits as there so many things that can go wrong.
Like bad components, poor solder joints, miss read schematics, etc.

The transformer you are using has two secondary windings of 6 volts rms (8.4 volts peak) each, what are you getting for voltage out of your power supply? I gather you  need 15v dc.

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