2. amps-preamps
  3. 137574-117123

Soulution preamp DC-offset protection

Good morning,
I've just bought a used but mint Soulution 721 preamp. It has replaced a Spectral DMC30SS Series 2. Apart from the sonic differences between the two, I'd like to know more about the DC-offset protection that the Soulution preamps have. Soulution claims that the input signal is permanently monitored for DC-components and at a level > 15 mV a high-class coupling capacitor is switched into the signal path. If DC-offset has decreased, the coupling capacitor is removed automatically after 15 seconds. During the first listening hours, I noticed that this capacitor switched on at least 5/6 times (a capacitor symbol appears in the display and after 15 seconds, when it's removed you hear a mechanical "click" sound). I'm wondering if this is normal or maybe it's a symptom that requires further investigation. I read that the DC-offset could came from the recordings itself and, actually, if I play the same CD and the same song, the DC-offset protection circuit of the Soulution switches on every time in the same point. Maybe it just something I did not realize before because the Spectral preamp showed me nothing of all this. It could be something like "if you don't see... you don't worry". Can someone help me to understand if I have to be worried or not? Thanks a lot!!
katfnc

Showing 1 response by erik_squires

erik_squires
5,268 posts
 
Gang,

This is a unique, but by no means the only, DC offset solution.

Many solid state electronic makers employ some sort of servo circuit with very long time constants to actively correct incoming or outgoing DC bias.

I say SS makers, because 99% of tube preamps have a DC blocking cap at the output, and a lot of inexpensive gear has DC blocking caps at the input.

In addition to DC blocking, discrete analog circuits may have some sort of auto-bias sensing circuit. While playing music I could imagine this starts to look like DC on the outputs during some circumstances. Is the CD player using discrete output stages? If so, I’d look there. :)

Best,

E
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