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McCormack DNA 0.5 Deluxe thumps turning on/off

Hi guys.

I have an McCormack DNA 0.5 that thumps when turning on/off. I recently bought it used and love the sound and all but I cant seem to look past the thumps, i´ve had amps that have done this before but this amp play in total different league. I know the deal about turning the power amp on last when starting and then last when done listening.

I have also plugged it in without any speaker or line cables connected and put a multimeter at the binding post and it picks up a DC current, same for both channels. Note, this happens only when turning on/off and overall performance other than this is excellent.

I also noted that if I have, say my cdp playing and the volume up a little bit you can hear the relay clicking and also a for a fraction of a second there is music playing. I have yet to come to a conclusion on what the problem is and have contacted Steve himself about it, but as an unpatient man I want things done in short notice.

So I would be happy if someone could help me or at least figure out what the problem might be.

Thank you
Fredrik
gruggn
phd
1,320 posts
 
This is perfectly normal since there is no sound degrading relay in the signal path that would mute the sound upon powering it up.
gruggn OP
8 posts
 
So maybe the protection circuit is only "active" if the DC goes high enough? Well that makes sens in a way, that is probably why it is called an "advanced protection circuit".

I guess I shouldn´t worry, after all, it sounds like heaven through my speakers.

Thanks again,

Fredrik
hifigeek1
770 posts
 
I believe there is a mute relay on turn on/off which might not be working. The relay could be locked in the on position. I know there is a protection circuit in that amp. I have an old CB for a 1.0 in my office. I will look at it on Monday.
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