nkefaloyannis
Member
Hi all, I built a 24x2 summing mixer with a passive odd/even input with resistors 5,1kΩ as Re, and a NEUMANN V475-2A mixbuss board before the stereo output. The situation is like this. When I connect the built to my audio interface, if I feed the mixer with -18dBFS 1kHz sine test tone to any of the inputs, I get unity level (-18dBFS) back to the DAW when a variable stereo pot (20kB) that I connected as Rg reads 6,2kΩ. I understand that this is correct and as expected, but, if I raise the level by 1 dB (either from the input or the output of the V475 [Rg])I can hear and see that the tone starts to distort. It seems that the headroom of the V475-2A maxes out at -18dBFS. I have also noticed that the pot raises the level of the output until it reaches 15kΩ, but it is not a clear sine after 7kΩ (1-2 dB) over unity gain, unless I compensate for that level raise, from the input. I connected the pins of the xlr out of the summing mixer to an oscilloscope and I saw that the level of the + and – pin has a ½ level difference. If I sweep the input test tone there is no difference from 20Hz up to about 100Hz but for the rest of the spectrum the – pin is about half the amplitude all the way up to 20kHz. When I feed a stereo signal to the mixer and back to the DAW the waveform is asymmetrical ( I took a screenshot from the DAW) if the level are higher than -18dBFS. In this example levels are -0.5dBFS I/O. I changed all the electrolytics including the ones in the power rails, but nothing changed. I changed the NE5534AN twice with new op-amps, nothing changed. I measure the power supply, voltage and current and is up to specs. If anyone from the community with electronics skills and knowledge on this board - because I don’t have any-, could give me a hint as where I could possibly look for, his/her help would be much appreciated.
Regards,
Nikos Kefaloyannis
Regards,
Nikos Kefaloyannis
