NAD C320 warmup

[velvetwaves]

Hi,
I bought a used NAD C320 amp (Mid-90's model). The seller had informed me of a known problem, that it takes approx 5 mins to warm up, before it can play anything. It does take that long on the first start in morning, however if I switch it off after approx one hour of play, it doesen't need any warmup when switched on again after 15 mins.

Furthermore, while playing perfectly for one hour , the volume suddenly increases, intermittently, only on the treble end (though I don't hear any clipping type of sound). After 5 mins of topsy-turvy treble volume, it settles to its original tone again and keeps playing perfectly.

a. I want to know if the above facts are a known issue with NAD C320,
b. and what could be the component that is creating it (is it power supply related capacitors or something else?)

Thanks in advance,
VW

 

[avionic]

Sounds like ..
1. Dirty controls/switches
2. oxidized/pitted relay contacts
3. Cold,cracked solder connections can't be ruled out..nor circuit board hairline cracks on copper traces.
4. DC offset may be a little on the high side.

 

[EchoWars]

What do you mean "takes 5 minutes to warm up'? After 5 minutes a scantily-dressed model marches into the room holding a large placard stating 'You may now operate your amplifier'? Please elaborate.

What source are you listening to when you hear this sudden increase in treble? (IOW, does this occur regardless of the source material? Phono, CD, Tuner, etc...)

 

[MOPAR3]

After 5 minutes a scantily-dressed model marches into the room holding a large placard stating 'You may now operate your amplifier'?

I wish that would happen here!!

 

[velvetwaves]

Thanks

Thanks avionic...

Sounds like ..
1. Dirty controls/switches
.....

 

[velvetwaves]

Hi EchoWars,
Sorry for being vague... now the elaboration:
Step-1: I switch on the power button > the power LED glows in "Orange" colour.
Step-2: I switch on the CD button to choose source > The CD LED glows in "Lemon yellow" instantly, however the power LED changes to "Red". I can't hear anything if I play CD thru my DVD player.
Step-3: After 2 minutes* the power LED changed to "Lemon yellow" and I can hear music now.
*(A week earlier, it took 5 mins to arrive at step-3, after it was delivered to me from a distant city. The amp was not played for probably 2 months till then)

What do you mean "takes 5 minutes to warm up'? After 5 minutes a scantily-dressed model marches into the room holding a large placard stating 'You may now operate your amplifier'? .....

:lmao::lmao::lmao: can any amp make this happen? I am ready to sell my house to upgrade to that one

What source are you listening to when you hear this sudden increase in treble? (IOW, does this occur regardless of the source material? Phono, CD, Tuner, etc...)

I am using EL Cheapo DVD player to play CD's presently. No other source.
BTW the "sudden increase in treble end" is moderate, as if the volume knob went from 9'o clock position to 10'o clock.

Hope the above clears the picture...

Regds,
VW

 

[EchoWars]

Hi EchoWars,
Sorry for being vague... now the elaboration:
Step-1: I switch on the power button > the power LED glows in "Orange" colour.
Step-2: I switch on the CD button to choose source > The CD LED glows in "Lemon yellow" instantly, however the power LED changes to "Red". I can't hear anything if I play CD thru my DVD player.
Step-3: After 2 minutes* the power LED changed to "Lemon yellow" and I can hear music now.
*(A week earlier, it took 5 mins to arrive at step-3, after it was delivered to me from a distant city. The amp was not played for probably 2 months till then)

Then we have a relay in the signal path...between the amplifier output and the speakers. You should hear a 'tick' of some sort when this relay closes. If the DC offset looks good, then the relay driver transistor or perhaps the supporting electrolytic caps need replacing.

I am using EL Cheapo DVD player to play CD's presently. No other source.
BTW the "sudden increase in treble end" is moderate, as if the volume knob went from 9'o clock position to 10'o clock.

Hope the above clears the picture...

Regds,
VW

Sounds like an intermittent cap somewhere (probably ceramic or polystyrene), and can be a real challenge to track down. Not impossible, just a PITA.

 

[velvetwaves]

Thanks a lot Echowars,
I do hear the "tick" sound when the Power LED colour changes. Will check things as suggested...

Then we have a relay in the signal path...between the amplifier output and the speakers. You should hear a 'tick' of some sort when this relay closes. If the DC offset looks good, then the relay driver transistor or perhaps the supporting electrolytic caps need replacing.Sounds like an intermittent cap somewhere (probably ceramic or polystyrene), and can be a real challenge to track down. Not impossible, just a PITA.