@dionakra Could you explain better what you mean?
I wrote to Soulution and received a kind answer from Cyrill Hammer.
He told me that:
“Yes, this is normal behavior, but please let me explain.
The 721 is DC coupled design. This means that DC which shows up at the inputs of the 721 could pass through preamplifier and would present at its output. This would be no problem for the preamplifier at all, but it could harm components downstream, especially loudspeakers. Therefore, we have added a protection system to the 721 which prevents your system from critical DC offset levels. The 721 does permanently monitor the DC-offset at its inputs and as soon as there is more than 10mV DC offset the DC-protection goes on. There are some tracks on some CDs which in fact produce DC offset. This will trigger the protection. There is nothing to worry about your unit and your system is perfectly OK.
Your previous preamp the Spectral DMC30SS Series 2 is most likely an AC coupled design and does not need kind of additional protection.”
It makes perfect sense to me, because I noticed that behavior only in some points of some songs. These days I’m listening to several CDs and I’ve never seen the DC-offset protection switched on again, therefore this behavior is limited to some rare cases and with specific songs/CDs.
Speaking of balanced connection between CD player and preamp and the fact that the protection switches on more often, Cyrill told me that:
“The balanced connection will present twice as DC offset to the input stage than the unbalanced connection. Therefore, the DC-protection gets activated more often. The CD-player does of course produce a small amount of DC-offset by itself. However, as the DC-protection does not get activated when there is no music playing, the CD-player’s own DC-offset level is for sure below the threshold level for the protection circuit in the 721.”
I still use unbalanced connection and the activation of the protection is very limited. This, in conjunction with Cyrill Hammer’s explanations and reassurances, makes me feel peaceful. In any case next week I’ll make a new test with a different CD player, just to see if (using the same CDs/songs that caused the activation of the 721 protection) I’ll notice an identical behavior.
