Need help understanding 9018K2M Balanced output

[Trixtan]

[SOLVED] Need help understanding 9018K2M Balanced output

Hello,

I bought a diynhk ES9018K2M kit to build a DAC. I want to create my own IV Stage with tube amplification, so I didn't solder the provided opamp and output capacitors. I take the signal from the DAC and DACB output pins directly, and bring it to my output stage.
Yesterday I tried to measure with the oscilloscope the output of both channels playing a pure sinusoid (the probes connected to the pins directly), and the result surprised me a bit. In both channels, the positive and negative signals are correctly out of phase, like I would expect from a balanced output, but the negative is half the amplitude of the positive. I think they should be the same amplitude, right? I checked the volume registers, and they both have the same value. Can you give me a hint about what can be wrong? Thanks

 

[JonSnell Electronic]

Schematic?

 

[Ken Newton]

While I'm not familiar with your DAC chip, but assuming it is a current output type, I should think the most likely cause is a lower impedance load on the DAC chip's negative output pin than is on the positive. As is asked above, please post a schematic of the DAC chip and I/V circuit.

 

[Trixtan]

Thank you for your replies. I didn't have the schematics of the DAC board, but I was able to find it out from the PCB (later I found it also in internet). You can find it in attachment.
I was also able to understand the problem I had. Basically, by simply not installing the opamp, and being OUT unconnected, R5 and C1 are connected to ground, and R6 and C2 are open circuit. This way no current flows from DAC- to ground, but circa 1,9 mA flow from DAC- to ground causing a voltage drop on R5. This is why the voltages are different on DAC+ and DAC- (DAC- being twice so high). I will just isolate the DAC pins by cutting the tracks.
Thank you for the hint