short hum at startup of recapped NAD 3120

[Fborden]

Hi all,

I am pleased with the recapping I recently did of a NAD 3120. Compared to the previous Quad 33 preamp I think it sounds a bit more open and defined. There is a small problem though. When I startup it will produce a short hum like sound in both speakers even at minimal volume level. The hum is only there for a sub second period of time.

My Question obviously is what can cause this hum?

Thanks,
Frank

 

[bradfro]

I would consider installing the triac solution.

http://audiokarma.org/forums/index....orth-5-and-an-hour-or-so-of-your-time.504673/

I know some of the NAD 3020's I've had will make this short buzz or hum when the power switch is pressed.

 

[Fborden]

Hi Bradfro, thanks for the suggestion. I will certainly look at this. I have some additional information on the type of hum my amp is producing can you tell if the triac solution is still valid.
If I switch on my NAD it will give a slight thump noise and after this it is quite for some seconds and then there is the hum I refer to. The hum is as said quite short but I think it should appear. Can you tell me if that is behaviour see in other NADs as well and if not what can cause i.

 

[leesonic]

The 3020 and 3120 (and others) don't have any protection circuitry in the form of a relay. There are muting FETs at the output of the preamp, and the power amp is protected with fuses and thermal cutouts. They all have some kind of buzz when you turn them on. I usually install my own protection circuit when I restore these.

Lee.

 

[leesonic]

http://audiokarma.org/forums/index....-board-installed-no-more-welcome-buzz.718439/

http://audiokarma.org/forums/index....project-with-cnc-machined-front-panel.810480/

 

[merlynski]

I would consider installing the soft startup triac solution.

http://audiokarma.org/forums/index....orth-5-and-an-hour-or-so-of-your-time.504673/

I know some of the NAD 3020's I've had will make this short buzz or hum when the power switch is pressed.

FWIW, the triac mod is not a soft start function, it takes the switching current load off of an unobtainium switch.

 

[newzealand]

hi there
i did a recap a while back and found a similar effect after the job was done,this was one of my first recaps ,
i found just the smallest bit of solder joining two points that were not meant to be, a clean up it was fixed,
you are most likely very good at recaps but i think a good look with a jewelers eye piece may be helpful,

i have worked on that model nad and know that the pcb is very crowded so this is why i say this ,
good luck and i hope you enjoy fixing it as its all fun in this hobby
mike

 

[bradfro]

FWIW, the triac mod is not a soft start function, it takes the switching current load off of an unobtainium switch.

I fixed my post, thanks

 

[losthorizon]

It's fascinating to read these posts as I have a 3020a that I use in a bedroom and it plays through a pair of Wharfedale 225s, I am pleased with the sound and have just purchased a 3120 that I will recap.