Phase Linear 400 issue help!

[NavLinear]

sounds about right

Since the hum is on both channels it would be good to verify that the power supply is not the source of your hum - does your meter read frequency? An oscilloscope would be my first choice but a digital multi-meter capable of reading frequency could help determine/eliminate potential problems areas.

 

[enoyes12]

looked it up and apparently it does

 

[enoyes12]

i have to find the manual for it

 

[NavLinear]

i have to find the manual for it

What make and model do you have?

What I'd measure first is the rail voltage - should be between +80 to + 84 VDC on one rail and -80 to -84 VDC on the other. Both legs should be within a volt of each other. Switch the meter to AC and measure the ripple voltage - should be less than a couple of volts but I'm not sure what the actual spec is.

Verify that the power transformer bolts are tight. If one of these are loose there is a potential for one of the plates to vibrate and transmit this vibration frequency to the output signal.

Verify that all wires and bus bar at the reservoir capacitors are snug.

 

[Northwinds]

Thanks, and you can thank the guys at Audio Karma. they sent me here

That would be me

I know you said you don't want to put money in this but man, do the White Oak upgrades and you won't want to own anything else (except maybe another two or three.... or ten LMAO). These are more addictive then Nav's avatars

 

[laatsch55]

Nav, you need to do this more often, very methodical of you. I have a tendency to bounce around a bit which probably confuses the less knowledgeable (like me).. Very consise directions too. Nice Dennis...

 

[Gepetto]

Old, dried out and ineffective C6 capacitors can seriously degrade the PSRR (power supply rejection ratio = hum from power supply into the amp) of the amp so you should give that a look. That will also show up as poor low frequency response. The other key capacitor for PSRR is C3.

 

[laatsch55]

So, if C3 was a blackgate that could also affect the sound?

 

[enoyes12]

meter is a Velleman DVM890F. ill check the rails in a little bit. I wish I had a scope as well but I wouldn't know how to use it.

 

[Gepetto]

So, if C3 was a blackgate that could also affect the sound?

It is NOT in the audio sound path Lee. It does affect the filtering of the PSU and therefore the background hum and noise. Only C6 and C11 are in the audio pathway (and C11 is not truly in the audio pathway but it comes close).

Remember in the original PL0171/PL400C/PL14 era control boards, PL had only capacitive filtering of the power inputs to the control board sensitive circuits. Later PL20 and PL36 added crude shunt regulators to improve this but it was still substandard (and it burned traces off the board to boot).

 

[laatsch55]

Love your Sig Bud, Jefferson was RIGHT!

 

[laatsch55]

It is NOT in the audio sound path Lee. It does affect the filtering of the PSU and therefore the background hum and noise. Only C6 and C11 are in the audio pathway (and C11 is not truly in the audio pathway but it comes close).

Remember in the original PL0171/PL400C/PL14 era control boards, PL had only capacitive filtering of the power inputs to the control board sensitive circuits. Later PL20 and PL36 added crude shunt regulators to improve this but it was still substandard (and it burned traces off the board to boot).

10-4 Sir.

 

[enoyes12]

I replaced the electrolytics yesterday. Are there any others I should replace?

 

[laatsch55]

Post a pic of your work top and bottom of the board so we can see what kinda shape that buggers in. From the rest pretty cherry 400.

 

[laatsch55]

There are some things hat can be done to a PL 14 board that will give you aglimpse of what a White Oak driver board can do for you...

 

[enoyes12]

 

[Gepetto]

View attachment 12163

Do you know what the mold like stuff is that is growing on the backside of this board?

 

[enoyes12]

It's not mold there's some kind of print on the board itself. you can see the pattern repeat across the board

 

[laatsch55]

Could be "The Valley Fever " spores....

 

[Gepetto]

It's not mold there's some kind of print on the board itself. you can see the pattern repeat across the board

Not the white dots evident in the photo, that is some kind of growth. Those are random. The green coating is the solder mask.

I would take Isopropyl alcohol and a short brush and clean the mold spores off the board.