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
Sounds like it needs to have some worn capacitors changed.
Okay, but how can I check if they are the culprit?
Why turn it off at all? As long as you are not dealing with tubes or poweramps, just leave it on. Thats what I do and I know many manufactures will recommend the same thing. I'm not saying that you have no problem, that I don't know, but it might make things easier for you to live with until you figure out whats going on.
I´ve now talked to the people at SMCAUDIO and they said that I should measure the DC offset at the speaker terminals and if after turn on it goes down to zero there was nothing wrong.
Because of electrical bills and the risk of fire, if something is wrong I don´t want to be at work when it collapse. So to the question(s), what if there is a high enough DC offset to be worried about, what may be the cause, and what causes the thumps? If there is a protection crcuit wouldn´t it stop the DC from reaching the speakers? I thought of the idea of installing a relay but I want to fix the problem at the source.
Can it be the relay in the protection circuit that is failing? Sorry if Im hassling but i really want it to work.
Have you tried contacting Steve McCormack? He is usually very helpful, give him a call.
I have a DNA-0.5 and a DNA-0.5 Deluxe and my friend has a DNA-0.5 Deluxe and they all "thump" when you turn it on. It is my understanding that this is related to the power supply caps charging up, but perhaps Steve McCormack can post and give more insight.

When you turn on your amp, does the front LED turn from yellow to green after about 15 seconds? If not, that would indicate a problem with the amp.

BTW, I usually keep the amp powered-up as it sounds better after being on for 24 hours.
Okay and this as never damaged any of your loudspeakers? As I said before I've had amps that have done but maybe I am paranoid. Ah well I will measure the DC offset and see if something's wrong.

Thanks for the replies
Gruggn,

No, the "thump" has never damaged my loudspeakers. I also have an Audio Refinement integrated amplifier that gives a loud "Pop" when you turn it on.

I don't know what loudness or duration of the "thump" would indicate a problem with the amp.
Jebe1,

Well that is certainly reassuring, I always thought it would damage my speakers but time will tell and until I get that multimeter in my hands I wont know.
Okay and this as never damaged any of your loudspeakers? As I said before I've had amps that have done but maybe I am paranoid. Ah well I will measure the DC offset and see if something's wrong.

Thanks for the replies
This is perfectly normal since there is no sound degrading relay in the signal path that would mute the sound upon powering it up.
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
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.