ZED max balanced input level for stereo channels (distortion problem)

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1

Hello,
with my newly acquired ZED-14 I am getting a distorted sound when using the stereo channals with a balanced source, going into the jack-sockets. Using the same source with the mono channels all is fine. The manual states a maximum input level of +30dBu for the mono channel jack sockets. For the stereo channel jack sockets it only says “0dBu nominal”.
Lowering the input level with the stereo level control makes the signal quiter but the distortion remains. This is the same for all 4 stereo channels. Using the stereo return RCA-inputs (ch. 7/8, 9/10) with an unbalanced source there is no distortion. The balanced source I used is an Alesis ML-9600 harddisk recorder, almost fully driven (-1dB).

So, can anybody tell me the maximum input level for the balanced jacks of the stereo channels?

thanks & best regards
Peter

2

addendum: The peak LED (“PK!”) is not lit when the signal is distorted, so I guess the very first input circuit is overdriven. Maybe there are limiter diodes before the level pot(?).

3

addendum 2: Just cross checked with Marantz PMD321 CD-Player. Leaving all pots and faders on the ZED in the same position and using the same cables, the signal on the VU is slightly higher than with the Alesis and the PK! LED lights up occasionally - but the sounds is clearly less distorted than with the Alesis HD-recorder. So it is a source problem (although with the mono channels the Alesis works fine!) - I guess there is some ultra low or ultra high frequency component which saturates the input circuit or causes IMD.
So still my question aims for the maximum allowed input level of the stereo channels.

Thanks in advance,
Peter