NAD 3020A Amp "thumps" the speakers at turn on

[Mark-V]

Hi folks.
A long shot but probably common to many brands... 
This amp has developed a problem of thumping my speakers at turn on.  I usually make sure to have an earphone plugin the  socket  when I turn it on to prevent speaker damage but any ideas of what the problem could be? Old caps maybe? I have had it for something like 30 plus years so I guess there could be some caps on the way out...
Other than that it still performs and works as good as the day I bought it.
Mark

 

[ln76d]

Electrolytics caps in PSU

 

[JohnRoberts]

Yes probably degraded electrolytic caps. PS is first place to look but could be elsewhere. Most premium amps engineer quiet start up so ID that part of the circuit to check.

Thumps are unlikely to damage speakers unless louder than music peaks, but wrong so should be fixed.

JR

 

[CJ]

most of the transistor amps that come in here have a pop to some degree,

sometimes these Quench-Arc snubbers work wonders when placed across the pwr sw>

http://www.cde.com/resources/catalogs/Q-QRL.pdf

 

[JohnRoberts]

Thumps would generally be DC settling after turn on...  Many amp designs involve a matched start up to roughly balance out DC settling issues.  A significant PS imbalance or caps almost anywhere in the feedback could be suspect.

JR

 

[mhoyle]

I recently bought a minty NAD3120 which has the thump on turn on which evidently is common. Tried the trick with putting in a  1/4 inch to minijack adapter in the headphone jack which works great - it physically  switches out the speaker o/ps. You don't need to plug in a pair of headphones, just the adapter. Easier than trying to find the capacitor(s)  that's leaking.

 

[RuudNL]

No idea if the 3020B is much different from the 3020A?
But here is the schematic of the 3020B.
My first idea would be to check C901 and C902.

 

[DerEber]

Try to connect the pre-out on the back side to the "normal" not the "lab" input. It has an built in hpf..... at least in the 7030.
Anyway it might be time to change the caps.

best,
Stephan

 

[gyraf]

I've had a similar problem once, think it was fixed by replacing C615/616 (1000uF)

But it's a good idea to just shotgun and replace all electrolytics while you've got it open

Jakob E.

 

[Mark-V]

Hey everybody, just been reading your replies…
1st - sincere apologies for never responding. I am mortified at my lack of courtesy. Was around that time that my laptop hard drive decided to die on me so lost a couple of months data due to not adhering to my own strict backup regime!

Around that time I also built some new Bluetooth speakers and the NAD has been sitting unused. However was thinking about hooking Bluetooth to it and using it again with the good old AR speakers and remembered about that “thump” and this forum…..
Sigh - old age must be creeping in.

I have not opened the amp yet but it could probably do with a good blowout of dust etc so will check those caps as well. Yeah, I have one of those mini jack adapters that I plug in when I turn it on but it would be nice to try and fix it as well. The “thump” is really loud.

Anyway - thanks once again for all your replies and apologies for my lack of courtesy.

Mark