Nikko Alpha 450 buzz until warmed up

[CrazeeD]

Hello All, I have a Nikko Alpha 450 power amp that buzzes until warmed up (10 min or so), after that its quiet and sounds great. It's not a crazy loud buzz but it's certainly enough to annoy. A little backstory, I have recently replaced 1 filter cap as it had leaked and wasn't even making contact with the board. I didn't replace the other 3 filter caps because they all tested within spec and have low esr. Bias has been adjusted per manual and seems to dial in as expected. Buzz also happens with inputs shorted. Any advice would be appreciated, Thanks!!

 

[ivandezande]

Both channels?
Power supply. Replace all caps, transistors, zeners.

Also if you replaced one, replace them all.

 

[CrazeeD]

Yep both channels. So power supply is the most likely culprit you think? I was suspicious of it myself but since other caps tested good I was doubting myself.

 

[Robisme]

Also replace the round rectifier. At least check it or sub in 4 diodes to see if the hum goes away.

Had a similar issue with a Marantz and it was the rectifier for the small supply.

I wouldn't suspect main caps if the hum is in both channels. Isn't this a dual mono amp? I could be wrong.

Rob

 

[CrazeeD]

Also replace the round rectifier. At least check it or sub in 4 diodes to see if the hum goes away.

Had a similar issue with a Marantz and it was the rectifier for the small supply.

I wouldn't suspect main caps if the hum is in both channels. Isn't this a dual mono amp? I could be wrong.

Rob

The power supply has 2 separate boards but it looks like they work together to power both channels. Looks like I'm digging in deeper.

 

[ivandezande]

The power supply has 2 separate boards but it looks like they work together to power both channels. Looks like I'm digging in deeper.

You need to do the left and right regulator boards.
The left rectifies and filters, the other turkey regulates. But both need new caps, transistors, and zeners.

 

[CrazeeD]

You need to do the left and right regulator boards.
The left rectifies and filters, the other turkey regulates. But both need new caps, transistors, and zeners.

I've certainly heard of re-capping being common on these old units but is it also common to swap out transistors and zener diodes?

 

[ivandezande]

I've certainly heard of re-capping being common on these old units but is it also common to swap out transistors and zener diodes?

Yes.

 

[CrazeeD]

Yes.

Sounds like I have work to do, thanks!