Hello everyone,
My Nak preamp has a hum that doesn't goes up with volume control. Frequency seems to be at 60Hz, plus to this I can hear something like "radio talking" also doesn't go with volume. Hum is present with no devices connected to inputs.
Sound anyway clean, no distortion.
I've checked power supply, everything seem to be OK +/- 0.2V from Service manual values.
Looks like ground problem, can't find it.
Out of ideas.
Thanks in advance!
M
My Nak preamp has a hum that doesn't goes up with volume control. Frequency seems to be at 60Hz, plus to this I can hear something like "radio talking" also doesn't go with volume. Hum is present with no devices connected to inputs.
Sound anyway clean, no distortion.
I've checked power supply, everything seem to be OK +/- 0.2V from Service manual values.
Looks like ground problem, can't find it.
Out of ideas.
Thanks in advance!
M
Same problem with mine. Adjusted values per service manual. Sounds great except for the hum. Thanks!
Many causes for hums, first step is determine if it's 50/60Hz mains or 100/120Hz rectified hum. Both channels affected? Increases with volume. MUTE normally causes a -20dB attenuation, is the hum present with mute ON, it will be very quiet if present. Do you have anything like an oscilloscope? Would help troubleshooting...
You folks who have problems, would you please mind stating what country's version you are having issues with? Bizarrely, this model differs in whether it is IEC Class I or Class II by region:
Canada, Japan, and Germany get versions with a 2-pin power plug (Class II).
The US, Europe (rest), Australia & UK and Saudi Arabia and other got a 3-pin IEC receptacle with PE screwed scraight to back panel (Class I). That means no non-floating sources and power amps for you guys if you want to avoid problems.
WTF?
That same back panel also seems to serve as a central star ground, given that none of the RCA jacks seem to be isolated (please verify)... the outputs should be though, given that an RF bypass cap to chassis is indicated there. If so, the shielded cable taking phono output to input switching would be completing an internal ground loop if the schematic is to be believed. Or would you leave the MM and MC input jacks of all things isolated and prone to RF ingress?
This model apparently dates from 1987-89 and is chock-full of high-strung circuitry. It just appears that whoever designed it was utterly clueless when it comes to ground loops. This is bewildering to say the least. WTF? 😕
Maybe the mechanical design was done by someone else, and they weren't aware that the thing required isolated jacks or something. I mean, they certainly look like they couldn't be. Then again, neither do those on the Pioneer VSX-409, and yet the schematic indicates otherwise.
Canada, Japan, and Germany get versions with a 2-pin power plug (Class II).
The US, Europe (rest), Australia & UK and Saudi Arabia and other got a 3-pin IEC receptacle with PE screwed scraight to back panel (Class I). That means no non-floating sources and power amps for you guys if you want to avoid problems.
WTF?
That same back panel also seems to serve as a central star ground, given that none of the RCA jacks seem to be isolated (please verify)... the outputs should be though, given that an RF bypass cap to chassis is indicated there. If so, the shielded cable taking phono output to input switching would be completing an internal ground loop if the schematic is to be believed. Or would you leave the MM and MC input jacks of all things isolated and prone to RF ingress?
This model apparently dates from 1987-89 and is chock-full of high-strung circuitry. It just appears that whoever designed it was utterly clueless when it comes to ground loops. This is bewildering to say the least. WTF? 😕
Maybe the mechanical design was done by someone else, and they weren't aware that the thing required isolated jacks or something. I mean, they certainly look like they couldn't be. Then again, neither do those on the Pioneer VSX-409, and yet the schematic indicates otherwise.
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