I have an NAD 3125 power amp. Approximately 15 seconds after it is powered on, there is a whooshing noise and then the audio comes on and plays normally. There is no conventional speaker relay that clicks (at least I can't find one). I imagine there is some sort of power up muting circuit but the whooshing sound doesn't seem normal. I cannot find a schematic for this model and was wondering if this symptom sounded familiar to anyone.
Thanks for your reply.
-- David Farber Los Osos, CA
"David Farber"
** Fraid that is an integrated amp.** Not very unusual - one likely cause is poor contacts on control pots and switches.
As the coupling caps in the amp charge after switch on, brief DC voltages are applied to many pots and switches - if the contact is corroded ( ie tarnished) some noise will be generated.
Some cleaning fluid should be applied to all the parts where this can happen and the control or switch operated vigorously for a few seconds afterwards.
IME the kinds of fluid that evaporate quickly are useless and the oil and solvent based one like WD40 are by far the best for this.
... Phil
I have seen this before. It is the audio "un-muting" circuit I'm pretty sure.
I can probably scan the schematic and send it to you, I'm pretty sure I have a hard copy somewhere.
email me direct and I'll reply with the schem.
mark snipped-for-privacy@labolgcbs.net and reverse "labolgcbs" to read "sbcglobal" .
mz
I really didn't find any bad transistors or caps. So I removed the left and right channel muting transistors and the whooshing noise disappeared. Not sure why the transistors needed to be there in the first place. When powered up now, there is just has a very slight thumping noise through the speakers which was present before the transistors were removed. In case you're wondering, the transistors are Q102 and Q202.
-- David Farber Los Osos, CA
David - I have the same issue with my NAD 3125. I have the schematic but am a bit of a novice. Any advice or clue as to locate the Q102 & Q202 muting transisters?
David - I have the same issue with my NAD 3125. I have the schematic but am a bit of a novice. Any advice or clue as to locate the Q102 & Q202 muting transisters?
They are likely to be Mosfets, 2SJ XXX or 2SK XXX?
I don't usually repair hi-fi, but the most common ones on pro audio equipment are J111 - J113.
I find it is very easy to spot the abbreviated "J11x" marking, being very different to the usual transistor ID marks.
Cheers,
Gareth.
ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.