Why do I lose low end when using jack inputs 1&2, and it comes back if I press Hi-Z.
When using SuperAnalogue channels with unbalanced line signals, it is important that you use the correct type of cable and connector.
Balanced connections allow the use of long cables while reducing susceptibility to external noise caused by electromagnetic interference. A balanced cable contains two identical wires, one carrying the signal in phase with the source, and the other carrying the signal out-of-phase with the source. These two wires are twisted together and then wrapped with a third conductor (foil or braid) that acts as a shield In order to be effective, these cables must use three-conductor connectors on both ends which are usually XLR or jack connectors.
By using a balanced cable from an unbalanced source you are effectively adding the signal on the in-phase wire to the same signal on the out-of-phase wire.
Therefore, by the time the signal reaches the balanced TRS input of SiX, the signal is out of phase with itself, and the most obvious characteristic of this is that you will lose all the low frequencies.
Pressing the Hi-Z switch effectively makes the TRS input of the SiX unbalanced (TS) so whilst the problem disappears, it does mean that the preamp may not be best matched to the source in terms of it’s impedance.
If you’re using a guitar or a synthesizer, the output it’s almost certainly unbalanced. Therefore you should use unbalanced cables with unbalanced 1/4" TS connectors. These can be identified with a single black ring approximately 7mm from the tip of the connector.
However, if you are connecting from an audio interface (such as an SSL2 or 2+) the outputs are almost certainly balanced and you should therefore use balanced cables and connectors. These are often referred to as stereo or TRS and can be identified with two black rings approximately 7mm and 15mm respectively from the tip of the connector.
Besides these examples, there are several combinations of balanced and unbalanced source / cable / connection configurations which will cause the same issue so it is recommended that you always use the correct type of cable and connector.